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Healthy Home Basics - Foundations, Decks, and Garages

By HHI Staff

From The Healthy House Answer Book: Answers to the 133 most commonly asked questions. Questions 22-29.


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22. What is the healthiest type of foundation?


There are four basic foundation types: concrete slab, crawl space, basement, and pier. In general, pier foundations are the easiest to build in a healthy manner because they lift a house up off the ground. When a house is well separated from the soil, it’s more difficult for radon, subterranean termites, and ground moisture to get into the living space. Pier foundations are often used on hillside lots or in hot/humid climates.


Actually, any foundation can be healthy—if constructed and maintained carefully. You need to be concerned with moisture (both liquid water and relative humidity) which can lead to mold or rot, radon (a cause of lung cancer), subterranean-termite control (toxic chemicals should be avoided whenever possible), energy savings (to minimize heating/cooling expenses, and reduce the potential for condensation), and selecting materials that are inherently healthy.


23. Don’t concrete slab foundations tend to be damp and moldy?


No, not if they’re constructed correctly. We’ve built healthy concrete slabs several times and like them because they can easily be surfaced with a covering of low-tox ceramic tile. If you’re on a very tight budget, a colored concrete slab decorated with natural-fiber area rugs can be an attractive choice. And, it can still be covered with tile later, when you have some extra cash.


Actually, we’ve found that very few sensitive people react to concrete. This is especially true if no chemicals (usually called admixtures) are used in the basic concrete mix. You should also avoid chemical curing compounds—misting water on a slab will keep it moist so it will cure slowly and naturally.


24. I want to use concrete foundation walls for a basement or crawl space. Is there a healthy form-release agent and dampproofing material?


Contractors usually coat wood or metal foundation forms with a petroleum-based oil so they won’t stick to the concrete. However, the oil often contaminates the concrete enough to bother sensitive people. Although it costs a little more, some people have had success by simply using a vegetable cooking oil instead. But if the forms are already saturated with petroleum-based oil from past jobs, a better solution is to first line them with polyethylene plastic sheeting. That way, after they've been filled with concrete, which has then cured, and the forms removed, the plastic can be easily peeled off.


Dampproofing coatings are often black, odorous, tar-like compounds. Because they’re on the outside of the foundation wall, they aren’t directly exposed to the living space, so they usually don’t often affect the indoor air quality. But in rare instances, they can, so sensitive people often substitute a dampproofing made with Portland-cement—just to be safe. Thoroseal is one popular brand, but there are others.


25. We’re considering a new house with either a crawl space or basement. Which is healthier?


That’s a little like comparing apples and oranges. In new construction, both must address the issues of radon, moisture, materials, and termites—but they usually do so in different ways. If care is taken in design and construction, either can be a good choice.


A basement is healthiest—if it’s considered living space. It should be conditioned, ventilated, filtered, and not be shut off from the rest of the house. This will help keep the basement air fresh. While there are certainly basements that are built incorrectly, the rules for constructing basements properly are fairly straightforward and understood by many builders. The rules for building crawl spaces, on the other hand, can be in conflict with each other—depending on the season.


Crawl spaces usually have vents around their perimeters. When the vents are closed, a crawl space is somewhat like indoor space. For example, it’s warmer than the outdoors in the winter, so water pipes won’t freeze. But when the vents are open, there’s more of an exchange of air with the outdoors, so it’s more like outdoor space than indoor space. In reality, most crawl spaces are neither indoor nor outdoor spaces, they behave differently in summer than in winter, and they often have moisture problems. There are two solutions. Some experts advocate either building a crawl space like a short, tightly constructed, insulated basement without vents (this may be in violation of some building codes) and treating it like living space year round. Others suggest leaving all the vents open and treating it like outdoor space all year. (Be sure to insulate those water pipes!).


If you have an existing basement or crawl space that’s contaminated with moisture, mold, radon, or termite chemicals, you’ll first need to do some remedial work by using the healthy-house design principles of eliminate, separate, and ventilate. It’s imperative that you carefully analyze why the basement or crawl space is contaminated before you try to fix it. Otherwise, you can spend a great deal of money and not solve the problem. Because some situations are difficult to diagnose, you may want to consult an expert for some advice. We’ve found that companies that do pre-purchase home inspections are often very helpful.


26. Do you think it’s worth the expense of installing a radon mitigation system in a new house?


Radon mitigation means taking measures to minimize radon levels indoors. That’s a good idea because radon causes cancer, so it’s a pollutant that should be treated with respect. But, the only way to tell if the radon level is too high is to actually measure the concentration of radon in the indoor air—and you can’t do that until the house is completed.


To answer the question, we’re going to rephrase it a little: “Should we install a radon mitigation system as the house is being built, or should we wait until the house is completed, then measure the radon level indoors and determine if we need a system at that time?”


Because most radon comes from the soil, we think what makes the most sense is to design the foundation to prevent radon from entering the house. And, as the house is being built, install part of a mitigation system. Don’t install the whole ball-of-wax, just put in enough to make it easy to hook up the rest of a system later—if you need it. After the house is finished, if you find radon mitigation is necessary, it’s easy and relatively inexpensive to install. If you don’t need radon mitigation, you really haven’t spent much extra money. This is just like buying insurance.


If you’re building a basement, for example, you might install some inexpensive perforated plastic pipe under the basement floor slab and connect it to a capped tee fitting that sticks up through the floor. Then after the house is finished, you can measure the radon concentration in the basement. (You can buy radon test kits at many hardware stores.) If the concentration is too high, you simply hook up an exhaust fan to the tee and connect the fan to the outdoors with another length of pipe. This will pull the radon from under the slab (before it has a chance to enter the basement) and blow it outside into the atmosphere. If you measure a low radon level in the basement, you don’t need to do anything further. You can get more information about radon testing and mitigation from the EPA’s indoor-air-quality infoline at 800-438-4318.


27. I’m very concerned about having toxic chemicals around my home’s foundation. How do I safely deal with termites?


There are several types of termites in the U.S., but the most common, and most destructive, is the subterranean termite. They live in nests in the soil, and continually travel back and forth from their nest to the wooden parts of a house. If they’re exposed to the air for very long, their bodies dry out quickly and they die. So, they often travel inside hollow concrete blocks, or they build mud tubes to move through.


For decades, toxic chemicals called termiticides (termite killers) have been routinely used around foundations either as a preventive measure or to halt an existing termite infestation. Now, fortunately, there are some less noxious control methods available.


There are actually several less-toxic alternatives, some of which look promising. For example, Dow Elanco (9330 Zionsville Rd., Indianapolis, IN, 46268, 800-352-6776) has developed a Sentricon system that involves placing underground bait stations around a house to attract termites. The bait contains a low-tox chemical that prevents termites from molting. As a result, after they eat it, they eventually die. This can be used with either new or existing houses.


U.S. Borax (26877 Tourney Rd., Valencia, CA 91355, 800-984-6267) has a low-tox chemical called Tim-Bor which can be sprayed on wood to permanently poison it so termites won’t eat it. While Tim-Bor shouldn’t be ingested, it’s basically a mineral, so it doesn’t release any odors or gases into the air. It’s big drawback is the fact that it remains water soluble, so it can’t be exposed to rain. In new construction, you wait until the house is under roof and is closed in, then you can walk around the inside and spray a Tim-Bor/water solution on all the wood in the house. In an existing house, you can certainly spray any exposed wood in a basement or crawl space, but there will usually be some parts of a house that are hidden and can’t be sprayed.


Another solution for new construction is called a sand-barrier. It involves placing a layer of sand around the perimeter of the foundation. The sand must be a certain grain size—the particles must be too big and heavy for the termites to move out of the way to tunnel through, yet too small for them to fit between the grains. Termites will go to great lengths to find wood to eat. Therefore, sand barriers must be placed carefully to avoid pathways around the sand.


Termite shields are made of galvanized steel or aluminum and they’re placed on top of the foundation to block the termites on their way to the upper wooden parts of a house. However, shields often aren’t totally effective because the termites can build their mud tubes around the shields and get to the wood portions of a house anyway. What the shields do is force the termites out into the open, so you’ll be able to see their mud tubes early—before any structural damage is done.


One of the best sources for information about alternative or less-toxic control of termites (or any pest for that matter) is the Bio-Integral Resource Center (P.O. Box 7414, Berkeley CA 94707, 510-524-2567).


28. My contractor wants to use salt-treated lumber for my outdoor deck. Is there anything unhealthy about it?


Most of this lumber is pine that’s been pressure treated with toxic copper, chromium, and arsenic salts—not table salt. Sometimes there’s a white arsenic powder on the wood. Manufacturers warn that you should wear gloves and respiratory and eye protection when working with it, and that you should wash your clothes separately from other laundry. Furthermore, treated wood should not be used for eating surfaces (picnic tables), and you should never burn the scraps.


Workers are at much more risk than homeowners because they can easily inhale the chemically laden sawdust. However, we’re also concerned about children playing on treated decks and playground equipment.


The simplest solution is to use redwood instead of salt-treated lumber. It has little odor, so it’s often tolerable to people who are bothered by the smell of pine, it’s naturally resistant to insect attack, and it needs no sealer. It does cost more than treated lumber. But, construction-grade redwood (it has a few knots in it) isn’t excessively expensive. As a reasonable compromise, you might use treated lumber for the support structure (the posts embedded in the ground and the floor joists), then use redwood for all the exposed surfaces (the deck itself and the railings).


Redwood ages to a natural gray color, but can eventually get quite dark. To clean it, we use a scrubber sponge and low-tox liquid detergent, then rinse.


29. I like the convenience of an attached garage, but aren’t detached garages healthier?


Garages are routinely filled with exhaust gases and gasoline odors. A hot automobile can also smell of oil or rubber. Garages also often contain lawn chemicals, paints and solvents, insecticides, etc., all of which can leak into the living space through unseen gaps and cracks in the common walls or ceiling. Contaminants can also get into the indoor air if there are leaky heating/cooling ducts in the garage. It’s not unusual for odors and combustion gases to rise up into bedrooms located above a garage.


The easiest way to prevent these pollutants from getting into the living space is to build a detached garage. This works best if the garage is downwind of the house. If you have your heart set on an attached garage, you should build it as airtight as possible. In other words, every possible pathway between the garage and the living space should be sealed. This typically involves using gaskets in some places between the drywall and the framing, caulking or aerosol foam insulation, weather-stripping around the service door leading into the house, and airtight electrical boxes and light fixtures. But even if all this is done, some pollutants will enter whenever the service door is opened.


Something that can improve the air quality in all garages is an exhaust fan controlled by a spring-wound crank timer. After pulling a hot automobile (or motorcycle, or lawn mower) into the garage, you can crank the timer around for an hour or so. This will air out the garage while the vehicle cools down, then the timer will shut the fan off automatically. An exhaust fan can also help when you first start up an automobile in the morning, but it's best to pull the car outdoors and let it warm up there.

(Note: This article is part of the original HHI Archives, and was believed to be accurate at the time of writing. The views expressed in this article are those of the author, and do not necessarily represent those of The Healthy House Institute, LLC.)


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Healthy Home Basics - Foundations, Decks, and Garages:  Created on February 1st, 2008.  Last Modified on February 28th, 2011


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