This document was started in response to Hurricane Katrina hitting the Gulf Coast (including New Orleans) in 2005. It hopefully is of use for a longer period of time than just the recovery from the damage caused by Katrina.
That New Orleans would suffer a levee breach and flood a significant chunk of the city was always a possibility. That this occurred immediately after a large, strong category 3 hurricane moved through the area (and nearly centered on New Orleans) is extremely unfortunate. Just handling the immediate and long-term problems caused by a category 3 hurricane is difficult enough. To compound problems by adding the urban flooding, made this a terrible catastrophe. The size of Hurricane Katrina made this a much more difficult storm to handle, compared to other category 3 storms.
Katrina was a big storm. Tropical storm force winds were seen over a roughly triangular area of approximately 430 miles wide by 500 miles deep (about 100,000 square miles). Hurricane force winds were seen in a roughly triangular area of approximately 215 miles wide by 330 miles deep in the center of that (about 35,000 square miles). Wikipedia has a nice image of the area of these winds (originally from NOAA). Actually, the article on Katrina at Wikipedia is quite good in general. Apparently Katrina may be reclassified as a category 5 hurricane at 2nd landfall based on air pressure and storm surge data. Katrina generated at least 25 tornados in the region.
The use of the city of New Orleans and its importance has changed a lot since it was originally started in 1718 (although there probably has been a settlement there far before that). Ironically, that location was chosen because it was one of the few pieces of high ground in that part of Louisiana (the French Quarter). Having so much lower ground so close by is the problem.
There is no way that the people who originally started New Orleans had any idea it would grow to a metropolitan region of 1.5 million people, and how important a port it would become. Or, that in the process of taming the Mississippi River from flooding, that the city would sink and that downstream salt marshes which help to protect it from storms would die off. It is entirely possible that there are other locations not too far away, that might better suit the things that New Orleans had become prior to Katrina.
Rebuilding the city in a new location loses or throws away all the infrastructure that is already in place. But it does not throw away the most important stuff, the knowledge of what is needed, what works, how to maintain it, etc. It also gives the city the opportunity to throw away mistakes. Personally, I think that New Orleans should get rebuilt somewhere else. But it isn't in my area of knowledge to know where. I also think that something needs to be done to stop the further loss of salt marshes of the Mississippi River delta region, and possibly to reverse that process. Again, this is not a field of knowledge that I have expertice in. But, I think people who do have that required knowledge should decide before rebuilding starts, that rebuilding in the current location is the best solution.
While I may have an engineering background, my specialty is not in anything normally associated with house construction. My background is in materials science and engineering, which is the study of what to make things out of, how to protect these things from corrosion/erosion/oxidation/etc., and studying why the materials might fail in service.
Some people are good at theory, some are good at practical things, a few are good at both. I happen to fall into the latter category, at least with respect to science and engineering type stuff. Home renovation and carpentry have been long time interests, and doing home renovation gives me access to a lot of materials that I probably wouldn't see in an industrial setting. Different kinds of woods (spruce, fir, hemlock, oak, poplar, cedar), wood substitutes (polyethylene - sawdust composites, strawboard, wood fiber - polymer composites), gypsum/wallboard, mortar, lightweight concrete, marble, plastic laminate, adhesives, epoxies. Various research projects have also exposed me to straw bale building construction, straw board, rammed earth construction, structural insulating panels, and cogeneration.
This document should not be considered an engineering document. It is more of a book report, with questions I would like to see answered scattered throughout. Hopefully it can help people decide what they want to do in rebuilding.
There are many kinds of housing which could be used to replace houses which were destroyed, or need to be demolished as a result of a storm. Building the number of houses necessary is somewhat like a housing boom gone crazy, so having flexibility in materials and labour is probably a good thing. A lot of the people made homeless by the storm are not highly skilled and have no job. So, having work that they can do is probably a good thing.
I see no value in putting up a cheap house which will not survive the next storm that visits the area. I see little value in putting up a good house which rots because of the hot-humid climate. (Or, water is the enemy of house survival in the long term or in a storm.) There is little value in putting up a lot of good houses that all look the same, especially if they are close to each other (or even touching each other). Houses that don't function for the people living in them are of little value as well. Humans are not all the same, and where they live shouldn't be either. Leave the assembly lines to the automobile companies.
With that as a prelude, I think a good choice in replacement, low-income housing is:
I have recently learned that a lot of people in the Gulf region feel much differently than I do. They feel that houses are in fact disposable, and shouldn't be expected to last appreciably longer than 5 years. How do you provide good, safe housing, when people think it is disposable?
People are starting to replace housing in the New Orleans area, even before FEMA has decided what the flood level is to be set at. It looks like some houses may need to be 10, 15, or even 20 feet above ground level, to meet FEMA guidelines. How the heck do you build a nice house, when it is on 20 foot stilts?
The damage caused by cyclones (hurricanes, tornados, etc.) falls into three categories: wind damage, flooding damage and storm surge damage. Storm surge only occurs in the "vicinity" of a large body of water, like the ocean, large lake or large river.
Wind damage can be direct (such as tearing off a roof) or indirect (such as throwing debris as projectiles). Flooding damage breaks down into damage caused by water flowing downhill and damage caused by submersion. Water flows can incorporate debris, which then are used as projectiles. Storm surge is the (extra) "tide" that is generated by the wind pushing on the water (mostly in right, front quadrant).
Initial data on what kinds of housing is tolerant of hurricanes, cyclones, etc. is to observe what has evolved on its own in climates prone to storms. This is often augmented with statistical analysis of damage after a storm passes through the area. Newer ideas arising from physical tests and computer simulations are becoming apparent.
The most survivable floor plan is a convex hull of at most, 3:1 aspect ratio. Since people tend to like 90 degree corners, this means the floor plan is rectangular. The most survivable roof plan is a hip roof with no dormers or gable ends. Gables and dormers provide flat surfaces which the wind can act against in a destructive manner. These flat surfaces are not as strong as the walls of the building. The roof overhang should be minimal.
Typically, the structure of most concern is the roof. If the roof is not fastened well enough, it can be lifted off. If the roof overhang is "excessive", the roof may be damaged or removed. Gable ends and dormers allow the wind to exert large forces on the roof, damaging it. If the walls are not fastened to the foundation, the "house" can move off the foundation.
Most hip (or hip with gable ends) roofs I've seen have wood trusses set onto the walls, some kind of wood sheathing is applied to the outer ends of the trusses to enclose the roof, and some kind of roofing goes over the sheathing. In the case of severe winds such as hurricanes, straps to hold the trusses down are used, in addition to nails or screws or .... The sheathing is typically nailed to the trusses. The exterior may see a coat of special paint, construction (tar) paper, waterproof membrane or other treatment in whole or in part, before the roofing material is applied.
I've never really been a fan of nailing, it's mostly friction that holds things together. I would rather see 100% application of construction adhesive to the trusses under the sheathing, and the sheathing screwed down completely, or screwed on the edges and nailed in the field at the recommended spacing.
I like asphalt shingles. Apparently you can get storm and/or impact rated shingles, those would be the kind to use in this case. People tend to install these storm/impact shingles the same way ordinary shingles are installed. This doesn't work. You must do it properly. I actually like the idea of having a metal (probably galvanised steel) strip which is screwed into the trusses through the sheathing, but nobody seems to carry things to that extreme. Nails with bigger washers at the recommended nailing pattern might be an alternative. But, we want LOTS of clamping force to hold those shingles onto the roof. No matter what you use, the fastener has to be perpendicular to the roof. If it is not, the shingle will tear out the clamping area with little trouble. But, if a shingle does tear off, it isn't quite the dangerous projectile that other kinds of roofing are.
Windows and doors are another point of concern. If a window or door is broken, the force of the storm can be directed at the roof, and cause it to fail. The first part of the door to examine in terms of strength, is the jam/frame. The "body" of the door or window should be rated for impact as well as strength. In the case of flooding, the quality of the weatherstripping probably helps a great deal.
In a serious storm, the envelope of the house should remain intact (obviously). The walls need to be properly fastened to the foundation. The roof must be held down with specially designed fasteners. Windows need to be closed and should not break if hit with debris. Doors need to remain closed and sealed.
Impact resistant windows are the best type of window to use. Impact resistant films applied to ordinary glass are not as good, if for no other reason that they are not fastened to the frame of the window. Shutters can be designed to be strong and should be made to fit the window. Shutters should be better than fastening plywood over a window. Shutters are probably not as effective as impact resistant glass. Plywood coverings are not as effective as impact resistant glass. I believe the standard test is to "throw" an 8 foot 2x4 at 38 miles per hour at the window opening. No half inch thick common construction material stands up to this test, not: plywood, oriented strand board, etc. Either shutters or plywood coverings should be used in lew of impact resistant glass. Remember to bear in mind, that your windows will not stand up to "full impact" with shutters or plywood.
Impact resistant glass has a couple of other benefits: it is of some help in building security (break and enter, etc.), and it is slightly quieter.
In the case of flooding, there are also other mechanisms/paths whereby water can enter. One way valves on drains can help prevent sewage from backing up into the house. But if the house is surrounded by high water for an extended period of time, water will likely invade the house through multiple paths. Cracks in the foundation or floor, and the wall/foundation joint would be a couple of examples.
While it is possible to build storm resistant, wood frame walls, the more common storm resistant wall is masonary. In commercial construction, this wall is probably the cement block wall. Lots of places around the world where storms are common, also see cement block walls for residential construction. But, a modern alternative exists. The Insulated Concrete Form (ICF) wall has been shown to have sufficient strength. It is already insulated, and has inset furring for attaching finishing (interior or exterior). Being a concrete wall, it shouldn't be surprising to know that it should contain reinforcing steel (rebar). In the absence of specifications on steel reinforcement in your area, you probably should follow what is being done in Dade County, Florida. A possible alternative to rebar, is to use some kind of fiber re-inforcement. The best fiber re-inforcement I am aware of is a mix of steel and polypropylene fibers called Novomesh 700. One big advantage of fibers over rebar, is that if it becomes necessary to drill a hole through the wall, it is much easier if the wall is fiber re-inforced than if it contains steel rebar.
Concrete tends to be stronger if it has less water. Or rather, there is an optimal amount of water to add to the concrete when mixing it up. Adding more water than this tends to cause a greater loss in strength than being slightly low on the amount of water present. It is very common for water to get added at delivery, to make the concrete more workable. This additional water should be viewed as a bad thing as far as strength goes.
There are lots of additives for concrete. One of the better ones IMHO is fly ash. Fly ash is a product of generating electricity by burning coal. It happens that fly ash (somewhat processed) is a very good additive for concrete. It allows for less water to be used, produces a stronger concrete, and is more workable: the downsides are that it develops its strength more slowly than "normal" concrete, and that it must be damp/wet cured longer than "normal" concrete. With ICF construction, the forms are watertight, and never removed. So, the only area which needs concern during the 7+ day cure is the open top of the form.
If you are charged with building a gazillion houses, the extra time it takes for the concrete to cure properly, and to develop enough strength for further work; is not an issue at worst, and can be a benefit.
So, instead of the power company throwing fly ash in the garbage, we add it to the concrete. And we get stronger concrete in return. Sounds like a good deal to me. Anything else we should be looking for at the dump? Yes! Blast furnace slag (from steelmaking) can often be another wonderful additive to concrete. There may be others.
Most properties, other than 28 day strength, are better with fly ash containing concretes. Some of the properties seem to be a little sensitive to how the concrete is cured. In a lot of concrete construction, the forms are stripped off as soon as the the concrete is strong enough, and if curing is a concern they have to treat these new surfaces that are exposed to the air (they need to consider the "free" surface at the top from the beginning). In the case of ICF wall construction in housing, the forms are impervious to water and are never removed. So, the surface of most concern is the top surface. Such a small area should be relatively easy to keep damp/wet. Many cement/concrete mixes limit fly ash additions to about 30% because of the slower strength development and the sensitivity of some properties to curing.
Some longer term work has been done with High Volume Flyash Concrete, typically in the 50-65% fly ash range. If blast furnace slag is also an additive, the fraction that is portland cement can be minor. And this is a good thing from an environmental point of view, since every tonne of portland cement involves approximately one tonne of carbon dioxide emissions.
Wood frame houses which will stand up to Category 4 and 5 hurricanes can be built, but they require skilled tradespeople, better materials and extra resources. In "ordinary" times finding skilled tradespeople and better materials shouldn't be a problem. When recovering from a disaster, I would expect the supply of both skilled tradespeople and better materials to be unreliable: you might find them, you might not.
ICF walls can be used in situations where most of the labour available is not highly skilled, if there is adequate supervision (as little as a single person per house). Which is a bonus when you want to use unskilled labour in house construction. One reason for using unskilled labour, is to get the future home owner involved in the construction, and also to get future home owners in the neighbourhood involved as well. Other sources of unskilled labour are volunteers just looking to help building new housing for people who need housing. Another reason to consider building methods which can employ unskilled labour, is that in a recovery effort, there is a huge demand for labour in general. There might not be enough skilled labour available to do all the work which needs to be done.
The introduction of cross-linked polyethylene (PEX) tubing into the plumbing industry has also introduced a place where unskilled labour should be able to help. A skilled person is still needed for determining the path to use for any given line, and introducing any holes needed for that line. It is probably best if a skilled person cuts the lines to length, and finishes connections. But a semi-skilled person might be able to help with some of that.
Like plumbing with PEX, electrical wire can be run by less skilled people, once the route is made available by a skilled person. Cutting to length is probably more able to be done by a less skilled worked than in the plumbing case.
One would hope that good concrete is available, but I've read a few articles about the Houston, Texas area which scare me. Apparently, it is quite easy to get weak concrete within the city of Houston, and outside city limits it is the usual situation. Too much water, not enough coarse aggregate, weak aggregate, dirt in the mix; all of these apparently happen regularly. In the case of Houston, there are no local sources of coarse aggregate, it all has to get trucked in. I can see a similar sort of problem occuring elsewhere in the Gulf Coast region.
In one writeup of a particular ICF wallsystem, there was a section on fire rating the wall. I don't think it is necessary to fire rate (or increase the fire rating) these residential walls, but part of that writeup specified 0.6 pounds of 0.5 inch polypropylene fibers be added to each cubic yard of concrete. This fiber reinforcement is there to increase the cracking resistance during setup and the damage tolerance and survivability of a wall once set. If plastic fiber reinforcement is used, the slump of the concrete is expected to decrease. Adding a superplastizer is a normal thing to do to increase the slump. I would think that would be a very good thing to do with all ICF walls in general. Adding both fly ash and fibre reinforcement may or may not require other additions to adjust the slump.
There are lots of different ICF wall systems on the market place. Different materials, different designs, .... You generally have to pick one and stick with it, they are usually not designed to work with each other. Some of these form systems use a polymer based on soy (vegetable oil), which is usually considered a "green" technology. Among the polystyrene based forms, some are extruded and others are expanded. The expanded polystyrene is considered the more "green" technology. Some forms are made in whole or in part from recycled polystyrene. And there are probably other types of forms as well.
Storm damage usually knocks out electrical service. This eliminates the use of refridgeration for food. It probably also knocks out dehumidification and air conditioning, which use electric fans for circulating air and refridgerant. The area where hurricanes occur is often classified as a hot-humid climate, and the storm season is during the hottest and most humid time of the year. Heat stress to humans is a definite problem.
Storm damage can knock out or damage fuel systems, like natural gas delivery. It can also affects fresh water and sewage systems.
Regardless of the floorplan, one statistic which should interest people is how much value of a household is within X feet of the ground. Or rather, how much value is within X feet of the floor on the base level. I didn't note the number (which probably depends on how many stories the house has, but this number ignored that), but more than half the value of a house typically sits between the floor and 3 or 4 feet up. Flooding always effects from the ground up. One of the best things people can do to protect their valuables, is get them further up from the ground. In the context of building houses, use a crawl space instead of slab on grade construction. A 2.5 foot crawl space, raises the ground floor by about 3 feet. Just on the basis of flood insurance, this has to be a good thing to do.
If you want to live someplace where FEMA has specified a high flood level, your "crawl space" could be higher than a typical ceiling, or possibly taller than a house. Some work has been done on using cement walls in a tropical setting which stand up to waves. These walls aren't continuous (some water is expected to flow through the contained space). This sort of wall construction might work to put a storage area under one of these houses that is required to have its ground floor above flood level. These spaces weren't designed to be conditioned air spaces however.
I guess if you don't think about crawlspaces, they are cheap and easy to build. Put a short wall on the footings, put in joists for the ground floor, and go from there. Well, with that much thought, it probably wouldn't surprise you that this approach doesn't work in a humid climate. They just accumulate water, insects that like water in houses (like termites), and fungii (rot).
If you build slab on grade, you end up running most services in the ceiling/attic. Leaks happen in plumbing. If all your plumbing runs above the living space, the chances are that leaks are going to effect your living space. Which is annoying, but what is much worse is what happens if some kind of utility delivery (electrical, water, sewage, ...) problem happens between where the service enters your house, and where the utility enters the "footprint" of the house? Guess what, someone may end up needing to dig up your living room, bedroom or bathroom floor in order to fix this utility delivery. And if there is any flooding, even very minor flooding, you leave yourself open to significant damage to your house and its contents.
In a humid climate, a conditioned crawl space is perhaps a better option than slab on grade, with the insulation on the perimeter. Most models of this kind of crawl space have either internal or external insulation, but if the house is going to be built with ICF walls it is just as easy to extend these walls down to the footings with the result that the crawl space is insulated on both the interior and exterior.
During construction, care should be taken to ensure the crawl space stays dry. A sealed waterproof membrane needs to be placed on top of the soil. I actually like the idea of putting a thin (approximately 2 inch thick) layer on concrete on top of that waterproof membrane (called a "rat slab"?). If radon is a problem (it isn't expected to be in the Gulf Region), a ventilation pipe from below the waterproof membrane needs to be started to exit the conditioned space in an approved manner (always above roof?). Can a person build on top of an existing slab on grade, by putting in a foundation around the slab, and using the slab as this "rat slab"?
With a slab on grade type of construction, typically the floor must be formed with control joints in it. If not, mother nature may arrange for a network of cracks to develop with time. During flooding or periods when the water table is high, this can be a path for entry of water into the house. I like the idea of radiant floor heating, and wonder if putting this type of heating in would remove the need for control joints since the temperature of the slab would remain almost constant (little or no thermal expansion). Would this also work with the "rat floor"? I wouldn't think this "floor" should be heated to the temperature wanted for the conditioned space, but rather to some temperature midway between the conditioned space temperature and the ground temperature (above dew point). In a flood plain, FEMA (may?) mandate the use of flood vents. I believe this is to negate the upward force on the bottom of the house if the water level outside the house is higher than the water level inside the house. How does this process work with conditioned crawl spaces?
If the lot size allows for it, a utility shed of similar construction could be added. While a shed might be considered a luxury not in keeping with low income housing, it does allow a place for power generation. I am not thinking of a standby generator, instead I am thinking of a cogeneration plant providing electricity and "work" (heating, cooling, shaft work, etc.) at all times. And putting something like a cogen plant in a shed, justifies making the shed robust.
It is very common for big storms to knock out electrical distribution. Having local power generation capability can help in minimizing this. If the local generator is powered by natural gas, and the pipeline gets effected, there can still be troubles. Most other power sources seem to involve a fuel tank of some kind, and so that is the limit on generating local electricity. If the area sees sustained flooding, again this local electrical power generation isn't likely to be working.
Some prime movers can be a little noisy, so putting them in a seperate shed allows for more noise-proofing. In terms of wiring of electrical and hoses for various fluids, whether it is one shed per house, per pair of houses or per quad (4) of houses doesn't really matter. It is easy to have (nearly) equal length runs to all houses connected. Connecting to more than 1 house might allow for better economics.
These sheds might also have space for the storage of garden/outdoors implements. These sheds may not be tall enough to act as effective wind breaks for houses, but they may be effective barriers to waves and flowing water. If so they need to be constructed similarly to the house with footings, the shed walls anchored to the footings, the shed root anchored to the walls, etc.
Should the rebuilding effort consider adding other outdoors elements which might also be effective barriers to water and/or wind? Does it make sense to put up durable fences? Maybe I've been watching too much television, but it seems like outdoor barbeques might also be useful. I've also seen plans for relatively large, outdoor masonary pizza ovens. Just looking for ideas to slow/stop flowing water.
And we can always make use of trees of various species (preferably native?). High winds of any kind are capable of damaging trees, and a side effect of that can result in damage to houses. Probably the worst damage results when the trunk breaks on a taller tree which is close enough to the house that more than just the uppermost part of the canopy can impact the house.
I think a person needs to look at landscaping and forest issues in general. A lot of the time, if you look at the houses which are damaged by high wind causing a tree to break and fall on the house, the trees in the vicinity are close enough that they would also present a significant fire hazard in the event of a forest fire.
If you are putting trees around your house, the distance between trees should be similar to what should occur in a forest under equilibrium with fire. Typically this is quite a large spacing. Some species of trees need to be closer together than others, as they form a communal wind break instead of a number of individual windbreaks. The height that you allow a tree to obtain, has to be related to how close it is to the house. If the tree is farther away, you can afford for it to get taller. If the top 10 feet of a mature tree is not very robust (capable of penetrating roof) and that tree is most likely to break 10 feet above the top of the house wall in a high wind, we can afford to let that tree get something like 20 feet taller than its distance from the house. In that statement we have 2 fuzzy values: just how much of the top of a tree is "not dangerous" if it falls on a house, and where is a tree likely to break in a storm. The angle it falls at also comes into play, as we are considering the closest distance between house and tree. The safe thing would be to restrict the tree height to equal the distance it is from the house. I suspect that many people would prefer to allow trees to get taller than that.
Putting up various outdoor elements during house construction, or soon after, allows for their placement in such a manner as to be of maximal usefulness in protecting houses and neighbourhoods in future storms. However, their placement probably needs some theoretical input.
It may be that there are well developed theoretical treatments of building design with an emphasis on high velocity air and water sources of damage. I have run across phenomenological work, but this is only a rough guide to what to do and what to avoid.
We may want to add elements to houses that are close to edges, or that protrude from flat faces of a house. How does the probability of damage change when we do this? How much extra strength do we need to design in, to make up for this? How does the wind or water flow past one house effect the survival of "downstream" houses? How does fluid speed effect this? If we design a group of houses for improved survival in a category 5 hurricane, it would be bad to find out that we decreased survival probabilities in lesser storms (which are more likely).
Cogeneration (Cogen) has one common alternative name of Combined, Heat and Power (CHP). Combined, Heat, Power and Cooling is an extension to CHP. A related term is Distributed Energy or District Energy.
If a person wants to generate electricity by burning a fuel, the combustion temperature is usually very high and the exhaust temperature is moderate. The machine which takes energy out of the combustion process usually has a rotating shaft on it, which is coupled to an electrical generator to make electricity. In many cases, the energy in the exhaust is ignored (wasted). The idea of cogeneration is that we try to make more complete use of the energy available: we build a set of machines which provide heat and/or cooling, and electricity and/or shaft work. If we do this intelligently, we can make more efficient use of the fuel(s) used to drive the process. Normally we think of improvements as being incremental, a small change in efficiency. In the case of cogeneration, this is true in some cases as well. But some cogeneration implementations have resulted in large efficiency gains as well.
Cogeneration isn't a new technology, it has been used in industry since the late 1800's. It's use in a residential setting is fairly new. The small size of residential cogeneration limits what technologies are viable.
A lot of electricity is generated from heat. This heat can come from burning a fuel, from nuclear fission or fusion, from solar, from geothermal, etc. In the thermal generation of electricity, some of the energy is converted into electricity and the rest escapes as waste (low grade) heat. Some methods get over 50% efficiency, most good conversion systems run between 33% and 50% efficiency. This is the same as saying we are throwing away an amount of energy somewhere between the same amount of electricity we generate (50%) and twice the electricity we generate (33%). Even if the electricity is generated at 67% efficiency, the amount of energy wasted is half of what was generated. What cogeneration is all about, is doing something with that wasted heat.
Now the electrical generating plant that made the electricity can try to capture that waste heat and do something useful with it. But, unless they are close to some other business or community which can use the heat, there is usually nothing that can be done.
However, if we decide that we are going to burn a fuel (or maybe use solar, geothermal, ...) close to where the energy is needed, we can use more of that energy if we are smart about things. It's difficult to be as efficient as the best boilers/furnaces are in generating heat, but for that small difference in efficiency we can hope to generate a significant amount of power (electrical power or shaft rotation power). And some of that heat can be turned into cooling if need be.
If we are putting a cogeneration plant in, you should also keep in mind what kinds of power/heat/cooling you need. If part of your demands involve pumping, it may be better to use the shaft output of the cogen plant for driving the pump, than to generate electricity to generate shaft power with an electric motor.
There are all kinds of heat sources and "prime movers" used in cogeneration plants. You can use solar, geothermal or most fuels: natural gas, propane, methane, biogas, landfill gas, gasoline, diesel, biodiesel, ... as heat sources. Prime movers are the machines which use the heat to generate work (or electricity). Our common spark ignition (Otto cycle) and Diesel engines are well known. Gas Turbines (jet aircraft engines), steam engines and Stirling engines are other examples. The steam engine and the Stirling engine are external combustion engines, while the remainder are internal combustion.
Otto (the ordinary, spark ignition engine) and Diesel cycle engines can be a little noisy. However, they are available in smaller sizes than gas turbines or steam engines. Stirling engines are not as commercially available as other kinds of engines, but can be designed to be much smaller than either an Otto or Diesel cycle. The free piston variation of the Stirling has no output shaft, it uses a linear alternator to turn the cyclic motion of the Stirling engine into external "work".
Picking a prime mover is determined in part by how much shaft work/electrical power we need, and in part by how much heat we need. For small applications that need commercially available parts, Otto cycle is used in the smallest applications and Diesel can be used for larger ones. For medium or larger applications, the gas turbine is the modern alternative with probably the steam engine/turbine applicable in some cases as well.
The Stirling, especially the "free piston" version, hasn't really caught on commercially. This is not to say there isn't experience with the Stirling. NASA has used the Stirling a number of times, in sizes as small as 10 W! The Swedish are making conventional submarines as quiet as a nuclear submarine, with Stirling engines. And there are many other niche applications where Stirlings are being used. Personally, I think the Stirling is THE engine to use for "residential" applications (houses or apartments) due to its very low noise level and low maintenance requirement. And being an external combustion engine, it should have better multi-fuel capability than any internal combustion engine.
In the case of multi-fuel capability, in most cases it is a situation of a trained professional spending a great deal of time converting some prime mover from one fuel to another fuel. In the case of an emergency, and this time of a trained pro isn't available, the multi-fuel capability isn't useful. Some prime movers can actually use different fuels in service by just changing a setting. This is more useful in an emergency, when the primary fuel is not available. The downside of having switchable fuels by changing a setting, is usually the presence of a fuel tank of some kind. Which introduces a fire danger. If the fuel is biogas, the "fuel tank" is releasing combustible material from a non-combustible feedstock continuously, and isn't as much a fire hazard.
Most of you are familiar with the radiator on the back of refrigerators, it gets warm/hot when the refrigerator is operating. Many Recreational Vehicles (RV) have propane powered refrigerators. Well, in a similar vein it is possible to generate a supply of cool/cold refrigerant, if you have a heat supply. Things like household air conditioners and dehumidifiers have been built to work with a supply of cooled refrigerant supplied by some external circuit, but household refrigerators with this capability are rare. I can find marine applications (kitchens on boats), and there are probably commercial units.
A person could add heating and cooling capacity by using shaft horsepower to drive a pump, pumping refrigerant through a ground loop system. This can provide winter heating and summer cooling when used with a heat pump in the house. But, if you pick up your heating and cooling needs this way, what do you use the cogen heat output for? Likewise, you can probably find a way to introduce solar inputs into the cogen equation, but the same question results: what do you do with all the heat?
I've seen articles whereby excess electrical capacity from a site as small as a single house can get sold "back to the grid". I've also seen house construction where a standby generator can be connected to a house, but it is only a fraction of the building demands that can be run. The possibility of "islands" of energised wires in a region that is nominally without power is something which concerns electrical repair people. This is one reason why the wiring for houses which have generators is so complicated.
Most high-end houses don't have their own generators, let alone something like a cogeneration plant. Why do I think this is a good thing for use in low income housing?
Low income housing is mostly about housing which is not large and not fancy. It shouldn't be about CHEAP houses which fall apart or are easily damaged. If more survivable houses are installed, protecting the investment by installing dehumidification equipment makes sense. Dehumidifying air reduces problems associated with mold growth, condensation, rot, etc. This is the primary reason to put dehumidification into a well built, low income house. In the case of larger disasters when power lines are down for extended periods of time, having distrbuted electrical generation from liquid or gaseous fuels makes a lot of sense.
Coming out of a disaster like a big hurricane, the electric utility may have lots of downed lines and decreased capacity. It might be advantageous to either have distributed energy available, or the utility might be more open to seeing it installed.
Normally, the question of loss of utilities (electricity, water, gas, sewer, etc.) wouldn't be of concern to a rebuilding effort. The extended nature of the outages from Katrina has made this problem a little more noticable. This section talks about issues related to utilities in a local or distributed context.
A lot of jurisdictions are concerned with how much electrical power their jurisdiction uses compared to how much it can generate. It may be that some jurisdictions in the Gulf Coast area are looking for opportunities to install cogeneration.
If electrical power is knocked out and damage isn't widespread, most people can expect to have electrical power restored in a few days (assuming their house can still take power). Widespread damage and strong storms can push the outage to a week or more. Having some of the electrical usage of a house on an independent supply of power might be useful, especially if delivery of food into the affected zone is difficult.
Just about everywhere someone looks (at a county level or greater), low income housing is needed. But what is low income housing? What are its requirements? What are its goals?
Some jurisdictions appreciate that these buildings need to be well built, as the residents may not be able to afford the maintenance a house might normally get. In the case of low income housing which is rented out, tennants may damage the building in excess of what lack of maintenance may do.
Okay, so we (or at least I) want to build houses for low income people in storm affected areas that are more expensive than a lowest cost house would be. We may be building these houses on lots where a low income house was before, or perhaps we have a fixed amount of land onto which we are going to "squueze" in the largest number of houses possible. In any event, we are building houses that are not large. There is just enough house to fit the requirements. Some sizes I've come across:
Low income housing apparently cannot be just a simple box on a slab, from the inside or the outside. The recommendations for hurricane resistance are to use a plain rectangular box with a pure hip roof and minimal roof overhang. The hurricane recommendation is at odds with the low income (or probably just humanistic) recommendation. The only individuality to the hurricane house is the size and placement of doors and windows, and the external sheathing/paint scheme.
Typically, the roof overhangs the walls by a couple of feet. So, we should be able to place projections on the order of a couple of feet deep on the walls. These projections probably need to be limited to at most 1/4 of the wall length (these numbers are guesses). A house needs a certain number of closets, and closet dimensions typically fit within these parameters.
Another possibility, is to push rooms part way out of the rectangular floor plan. If a room is 10x10 and is in a corner, maybe push it 3 feet out, so that only 7x7 is still within the rectangular floor plan. If that is possible, it is a pretty good deal, pushing parts of walls out 3 feet, and doubling the room size. Does a 3 foot room pushout effect house survival appreciably? In the absence of roof overhang, how does one incorporate these pushouts into the roof system?
I don't know if there is a charcteristic length applicable within which the survival probability of the structure isn't altered significantly. But knowing how much variation from a rectangular box is allowed would make it easier to come up with more interesting house exteriors. There is only so much you can do with a rectangular box. :-)
One of the reasons for having roof overhang, is to allow for roof ventilation; air comes in at the soffit (roof overhang) and exits at the top (usually along a ridge). For low flow rates, this is supposed to happen quite easily. In a storm, one would probably prefer it didn't happen at all. Some new building design work I've seen for humid climates has no roof ventilation. The roof is still insulated, and the attic space is part of the conditioned envelope of the building. Waterproofing of the roof is needed, on the outside of the roof sheathing. This type of design probably doesn't require roof overhang either.
Roof overhang is also there for shedding rain away from a resident trying to open a door, for shielding the sun's rays, protecting the house foundation from moisture, etc. If the need for roof ventilation can be removed, it is possible that overhangs for deflecting rain or shade can be made less permanent. In the event of a storm, this overhang is removed and doesn't endanger the house integrity. Another possibility is to limit overhang to only those parts of the house which require shading from the sun, or are entrances.
One downside to making the floorplan more "interesting", is that decisions on interior wall placements need to be done before the concrete walls are poured. If we are hoping to have future owners participate in the construction similar to Habitat for Humanity, we need them involved much earlier in the process.
If manufacturing space is available elsewhere, perhaps volunteer and "owner" teams could start building the interior wood walls beforehand? Then a person uses a crane to place the walls inside the house before the roof trusses are set on the walls. Once the floorplan is settled, the interior walls are pretty much defined. No real reason to wait until the walls are poured and set before building them. And it does remove local weather from the equation to a large degree.
The analyses of structural damage are all done "in isolation", the recommendations being made do not refer to the surroundings. For example: if the house in question, or a neighbouring house, has a tile roof and the tiles break off and become projectiles during a storm, it doesn't effect the probability of "this" house being damaged.
A building which is significantly damaged by storm alters the pattern the wind which follows close to the ground, and possibly becomes a source of debris which can cause damage to this house or others. So, the better built wood frame homes and most (?) masonary homes are going to serve as "wind breaks", for houses (and shade trees) in the neighbourhood.
In an "ordinary" storm, the wind is more or less coming from a constant direction, whereas with these cyclonic storms (hurricanes, tornados, etc.) the wind direction can run through 90, 180 or even 360 degrees during the course of the storm. While houses that are significantly damaged by these storms are in some sense a hazard to the more resistant homes, these "stronger" homes are a form of protection to the "lesser" homes. If an entire residential development can not (or will not) be constructed of stronger homes, is there some optimal placement of stronger houses amongst the lesser houses? If we have cogen "sheds" in the development as well, they can also act as wind/storm breaks. I would expect that certain roof slope angles might work better in helping the stronger houses act as wind/storm breaks for the lesser houses.
Like many things, this concept is probably known by many names. Co-housing is one such name. I don't think it is a likely concept to work in a disaster recovery situation, but who knows?
Co-housing developments are small communities within larger communities. Being small, a lot of activities for which transportation normally might be needed, can be accomplished with a short walk. The community agrees to share many resources, allowing each unit to be smaller. Decisions tend to be made by concensus. It seems these co-operative housing developments consist of up to 35 units.
One advantage to co-housing, is that a larger cogeneration plant might be considered, which could improve economics as far as co-generation goes.
Regardless of the financial status of the people affected, there are a lot of people who have had their homes damaged or destroyed. And it is not just the people who live at or near the poverty level, that cannot afford to rebuild ANY kind of structure to live in. There is a tremendous number of houses and other living structures that need to be built in the region!
Wood frame houses tend to be very popular. Nothing wrong with a wood house in general, but there are lots of places to save money in construction that produces a "cheap" house. You use lumber that isn't as good, you can minimize the size and number of fasteners, you can minimize the amount of insulation, you don't seal a vapour barrier as well as it could be, you put in a furnace which is too small, etc. Being a wood structure, if water can accumulate in the structure (rain, condensation, flooding, etc.), rot can be a problem. In a place where hurricanes, tornados, storm surge, flooding, termites, etc. don't come along, the house should last 30, 50, 80+ years. But it wouldn't very likely be very cheap to operate, and so some low income family is going to be spending a big part of their small income, just to maintain and live in a "cheap" house. And the next storm that comes along, the house gets damaged or demolished, and we start the story all over again. Doesn't seem fair, and is a waste of resources.
The above paragraph isn't meant to say that all wood frame houses are bad. There are some very well built wood frame houses in all sorts of difficult climates.
I like what Habitat for Humanity does, they get people who are interested in owning a house to contribute "sweat equity", a bunch of people to volunteer unskilled labour, a few skilled people to help/supervise, and find materials at reduced or no cost, and build homes. The future owners are likely to be keeping an eye on things, as are other future owners putting in sweat equity on other people's homes before working on their own. And most volunteers aren't there to skimp on corners (they might accidentally, but will likely stop once they are informed of it). For the price paid, you probably end up with a pretty good home.
There are a LOT of people who are homeless out of this, and I suspect most of them are also out of work. They likely have little or no resources or savings. I think being able to contribute sweat equity towards a new home would be a good thing. Something similar to the spirit of what Habitat for Humanity does. A side benefit is that they have a good chance of picking up another skill.
In hot-humid areas (like the Gulf coast region) you may want to have a sealed attic (an attic that is not ventilated, but is actually part of the conditioned house envelope). This is in some senses controversial, since it is contrary to a lot of building codes. A sealed attic does require waterproofing between the roof sheathing and the shingles/tiles/.... The waterproof membrane approach to this can be quite expensive materials-wise, while the paint approach requires a lot of skill to avoid pinholes.
With ICF walls, the large thermal mass of the concrete is symmetrically buried within insulation. Since the temperature and/or humidity of the interior of the house is what we are trying to control, it would be better if the thermal mass wasn't quite so well insulated from the interior.
While these ICF walls have the forms more or less firmly attached to the concrete after it sets, in the event of a storm I can't help but think that the integrity of the exterior foam could be compromised. If strong winds tear away the exterior covering, is the building wrap strong enough to protect the foam from hurricane force winds? I haven't seen this issue treated in any online literature yet. But, this is a "minor", cosmetic issue in the event of a serious storm.
Low cost housing is going to mean smaller homes, probably with little or significantly reduced architectural interest. They might be boring to look at, except after a storm when all the neighbouring homes are reduced to toothpicks. The best designs for hurricane resistant, low cost homes using ICF technology are rectangular, with a length to width ratio less than 3 (a ratio of 1 is square). Does setting the house at some angle with respect to the front sidewalk/street make a house more interesting?
It is expected that going to a quality, impact resistant window design is less expensive than using quality "ordinary" windows with shutters. Now, if an impact resistant window was "trimmed out" so that it could easily take the plywood sheets that are often applied to windows prior to storms, I think you have a pretty good combination. A bonus with impact resistant windows, is that they are more difficult to break all the time. Perhaps the house is empty in the time leading up to the storm, or an errant baseball, or .... The laminated glass in impact resistant windows usually blocks a lot of UV and sound. Whether the absorption of UV means that the window itself ages and will need replacement sooner, I don't know. As near as I can tell, none of the film applications have been approved for use in Dade County, which gets its share of hurricanes. But, whether you use shutters, plywood or impact resistant windows (or some combination), the object is to prevent the windows from breaking in a storm, which can then allow the wind to lift the roof off. All of this window treatment may be in excess of what low cost housing normally provides, and hence would probably need to be donated in some way. Don't forget any skylights that might be present.
For a small enough house, if you build it with poured concrete walls and attach a hip roof on top with hurricane straps, the interior walls are (probably) not load bearing and can be placed (more or less) anywhere convenient. In addition, there is less requirement on their being "correctly assembled". Or, as I see it, that once the walls and roof are up, the interior framing, drywall, and a host of other things are probably open for being done by less skilled people, like potential home owners. This is not saying that things like plumbing and electrical are part of this, they still need to be under the control of a licensed tradesperson. But, having flexability in interior wall placement can help to offset the "boringness" of a small rectangular house with no gables or dormers to prospective home owners.
Using resources wisely, or even optimally, is a good place to start with green construction. If you are cutting pieces to length/size, planning the cuts to minimize waste is a good thing to do. There are also some places/locations in a house where a joint of some kind is more acceptable than other places. Recycling wood (and other material) scraps from construction sites instead of disposing of them is another aspect of green construction.
Certain construction materials make better use of raw materials than do others. Oriented strand board and various engineered wood products (for example, laminated beams) can make better use of wood fibre than the larger logs required for plywood and structural 2x6, 2x8, 2x10, etc.
There are lots of places in residential construction, where concrete can be used in stead of wood. So, in a sense, concrete is a green material. However, the production of concrete involves the use of lots of energy. Which isn't something we are expecting in a green material. Concrete can be reused afterwards (after the house containing it is demolished) in various places. It is possible to replace some of the (portland) cement in concrete with fly ash. The fly ash is a waste product, and so finding a use for it is a green thing. Blast furnace slag, silica fume, and some other materials are also finding use in concrete.
There are lots of things which can be done in the interest of energy efficiency. Using lightly coloured roofing materials will decrease how much sunlight is absorbed, and turned into heat. Planting shade trees can also help with this.
When purchasing appliances for use in these new, low income houses; energy efficient appliances should be chosen. If there are low income houses "in the region" which survived the storm, it might be a good thing to update their appliances at the same time. The developer is likely making a volume purchase of appliances, and getting a better price than a single unit purchase.
If good concrete can be acquired to build all the houses to be replaced by this method, that is wonderful. But, if a person asks for 2500 psi concrete (or similar), and what you get has dirt, fine aggregate, weak aggregate or excessive water and hence is a weak or very weak concrete, I don't think requiring fly ash additions or polypropylene fibers is going to save things. The house may be well insulated and functional in normal weather, but just like an average wood frame house it is going to be damaged by the next big storm. And a lot of money will be wasted.
I have seen the opinion that concrete tiles are better for roofs in a hot-humid climate. And by default, those tiles would be light in colour, and hence not absorb so much solar energy. My argument against them is that IF they break, they become quite damaging debris. An asphalt shingle if wripped off doesn't have the damage potential of a concrete tile.
Using (part of) a rebuilding effort from a storm is an easy way to incorporate a lot of distributed energy production in the form of small cogeneration plants. If it is agreed that the Stirling is the best cogeneration plant in those circumstances, this could give the demand to get Stirlings on the commercial market. But, it in the near term I don't think we could install that many Stirlings, and would probably have to work with small Otto cycle cogen plants with a number of "handbuilt" Stirlings for "evaluation purposes". Another technology in this instance which might be tried out is the quasi-turbine, which apparently can mimic a Stirling (or other) cycle.
As far as building houses goes, if a person was to try and get future owners involved in construction similar to what Habitat for Humanity does, I think you need to automate the house design and specification process. These houses are all basically rectangular boxes with an aspect ratios between 1 and 3, with small perturbations. There are a number of perl modules which are CAD oriented in CPAN. With the right interface, I think a prospective owner could direct the perl modules to a suitable floorplan, and the supporting routines could generate a list of materials for that floorplan. If a single source of ICF was chosen, this could probably include cutting and stacking instructions.
Access to some covered warehouse/construction space, roof and wall components could be built in a controlled environment. Wall components should be simple enough to be built by volunteer and future owners under supervision. Minimizing the length of time from defining the foundation until the roof being up is necessary to keep water out of the crawlspace before the house is finished and to minimize water damage in construction.
As of mid-October, the rebuilding effort has been going on for a little while. All the pictures I've seen show people hammering away on the ordinary wood frame houses that seem to be the norm. I sure hope that a big storm doesn't come along sooner rather than later, and turn those houses into toothpicks. I do not know exactly how these houses are being constructed, it is possible to build a wood frame house which will stand up to large storms. It is more likely, that they are not built that strong. So then the question is, how long will it be before another big storm comes along? If it is a long time, then you probably can't fault the choice made. There is no correct answer to what kind of house to build.
The next hurricane season is about 1.5 months away, and there is still lots of rebuilding to do (according to CNN). FEMA hasn't even decided on where the new flood level will be, which holds back all kinds of work.
According to Mapquest, it's a 2500 mile trip from where I live to the affected area. The local hardware stores are having problems getting concrete, and are "blaming" it on the needs of the Gulf Coast region. I'm not sure if the local cement plant is shipping concrete to the area, but it is probably shipping concrete to places in that general direction who are seeing their normal supplies going closer to the Gulf Coast.
