Green Building Q&A Part 5: Windows, Siding, and Roofing

Part 5 of our 15-part Q&A series on all aspects of green building from the publishers of HealthyHouseInstitute.com. Click here for the introductory post and furthur details.

Question: Aren’t wood windows best from a health standpoint?

Answer: Wood windows are usually treated with water-repellent and fungicidal chemicals. So, while wood is a natural material, treated windows can certainly bother some sensitive people. Also, they’re usually made of pine which can have a strong natural odor. Furthermore, wood windows require routine painting. However, wood windows usually aren’t strong outgassing sources. Therefore, these concerns are only important for very sensitive people.

Vinyl windows are a less-expensive option. While they never need painting (a real plus), the vinyl itself can outgas a little—especially when new—which can be enough to bother some sensitive individuals.

Personally, we prefer aluminum-framed windows. Most are available prefinished in white or brown, and they require little maintenance. In cold climates, you should look for frames with thermal-breaks to minimize sweating. Aluminum windows generally have rubber or plastic seals that have a slight odor—but it usually isn’t significant.

Multiple panes of glass are a good idea in harsh climates for energy efficiency. Low-E coatings and argon-filled windows rarely cause health problems, and we think they’re important to conserve energy.

Question: Is there a healthy window putty I can use?

Answer: In the past, window putty used to be made with linseed oil and other ingredients, but today vinyl compounds are more common. Either can be odorous when fresh, but because the putty is applied to the exterior of a window, it’s outside the living space, so it’s usually not a serious problem. The putty tends to be less bothersome after aging for a while, or after being painted. We aren’t aware of one brand that’s less odorous than others.

Question: Are there any healthy caulkings and construction adhesives?

Answer: All caulkings and adhesives have an odor when wet, but once cured, they tend to outgas very little. The goal is to select a long-lasting product (so you won’t have to reapply it very often), and one that will outgas most of its odor within a short period.

Most water-based latex caulks are good choices because they outgas less than other types of caulking. Personally, we’ve had good luck with 100%-silicone caulking for most outdoor applications. It’s reasonably priced, durable, and very long lasting. It does have a strong odor when fresh, but once it’s had about a week or so to air out, it’s quite inert. Silicone’s a little messy to work with because it can’t be cleaned up with water, and while it can’t be painted, it’s usually available in some basic colors.

For a healthy construction adhesive, several companies now make water-based products, and some offer zero-solvent adhesives. While they’re all odorous during application, they air out fairly well, and are almost always covered up, so they’re rarely exposed directly to the living space.

Question: Is it all right to use vinyl siding on my new healthy house?

Answer: Vinyl siding does outgas a small amount, especially when warmed by the sun. And, in a fire, it melts and burns very quickly producing toxic gases. On the plus side, vinyl’s big advantages include low-cost, availability, durability, and the color goes all the way through so scratches aren’t noticeable.

Because siding is outside the living space, it usually doesn’t have a significant impact on indoor air quality. But, some sensitive people are bothered by warm vinyl siding on a hot summer day when they’re next to it, or indoors when the windows are open. We like aluminum or steel siding because it usually has an inert baked-on finish. Brick is also a popular, low-outgassing, low-maintenance siding. The big drawback to wood siding is the fact that it requires regular painting or staining.

We’ve talked to many people on a tight budget, for whom brick, aluminum, or steel are simply too expensive. They often choose vinyl siding, then concentrate on spending any extra money indoors where it will do the most good. We think that can be a wise decision.

Question: What healthy paints and clear finishes can I use on my home’s exterior?

Answer: Some of the most long-lasting paints contained toxic lead. Fortunately, they’re no longer on the market, having been replaced with oil-based and water-based products. In general, the water-based varieties are less toxic because they air out much faster, so we prefer them.

There are a number of healthier-than-average interior paints but, because outdoor paints must withstand much harsher conditions, conventional off-the-shelf paints are the only ones we feel should be used outdoors. Alternative paints simply won’t hold up to the rain, temperature extremes, and sunlight.

Very sensitive people may want to test two or three different brands to see if any one is less bothersome. But, in general, as long as you choose a good-quality water-based product, exterior paints generally don’t affect the indoor air quality very much once they’re dry.

One of biggest enemies of an outdoor finish is the ultraviolet from sunlight. Clear wood finishes don’t last very long outdoors (sometimes only a year or two) because the sunlight goes through the finish and damages the wood itself. Once the wood is damaged, the finish no longer adheres very well, and soon flakes off. Stains last a little longer (depending on how much pigment they contain), but they often need to be reapplied every few years. So, to avoid regular reapplications and reexposures to fresh materials, we prefer paints outdoors rather than stains and clear finishes.

For outdoor metalwork (doors, railings, etc.), you might consider automotive paints. They’re available in a wide variety of colors and, if you go to a body shop that has the equipment to bake the paint on, you’ll end up with a very durable and inert finish.

Question: Can the foam insulation inside a steel entry door be a problem?

Answer: Usually not, because the steel outer skin tends to minimize outgassing from the insulation inside it. Actually, we like insulated steel doors for other reasons, as well. For example, they’re warp-resistant and long-lasting. They're also energy efficient. Many have magnetic weather-stripping (like a refrigerator), and an adjustable threshold, so they seal very well. Finally, when painted with a baked-on automotive paint, they’re inert and virtually maintenance free.

Wood doors, on the other hand, often don’t seal well, and they require frequent repainting. Plus, most wood doors are chemically treated with water-repellents and fungicides—although this usually isn’t a serious issue.

Question: Aren’t cedar shingles or shakes the logical healthy choice for roofing?

Answer: Roofing materials are not only outside the living space, but they’re also way up on the roof. Therefore, they usually don’t affect the quality of the indoor air. However, cedar shingles are actually one of the most bothersome roofing materials because cedar is so aromatic. We’ve heard of cases where sensitive people reroofed with cedar and the odor permeated their homes.

Fiberglass and asphalt shingles are, by far, the most common residential roofing material. They can have an asphalt odor, but it’s rarely a problem indoors. About the only time we’ve heard of people being bothered is when there’s an open dormer window overlooking a hot roof in the summer.

In most cases, roofing is chosen because of its appearance, expected life, and cost—rather than healthfulness.

Question: Why do you use metal roofs on the healthy houses you build?

Answer: Granted, roofing usually doesn’t affect the air inside a house. But our own personal philosophy is to use materials that are as inert as possible wherever we can.

Most metal roofing is coated with an baked-on finish that’s quite inert. We like to use sheet roofing that can be screwed down to 2x4s that are attached to the rafters every 24" (the 2x4s are called purlins). That way, we don’t need a plywood roof deck or asphalt-impregnated felt paper for an underlayment. Plus, we like the appearance of sheet-metal roofing.

(Note: This article is part of the original HHI Archives, and was believed to be accurate at the time of writing.)