Hello Ari, I have multiple chemical sensitivities. The builder putting up my house insists that YT Building Code requires PWF on the concrete slab for the floor to lay on. What alternatives are there to chemically treated woods for the foundation? Similarly, what alternatives are there to plastic vapour barrier?
Thank you, Margot Simonot
Many building materials may contain various chemicals, especially when first installed. While there may be an acceptable alternative to PWF wood for a subfloor, many other products may also affect you, as well.
I have a frequent client with similar health concerns, and a few other individuals that I know, who have developed chemical sensitivity at a certain stage in their lives. While not an expert, I have learned that it is an unusual disease, with largely unknown causes, and can act like an allergy but to many items that contain artificial chemicals. The degree of sensitivity varies and it may also affect individuals who have problems with electronic devices, various noises, and other irritants. Like allergies, the effects can range from mild to severe, depending on numerous factors. For those reasons, I am quite surprised that you are undertaking construction of a new home, which may have significantly more chemicals than older buildings, which may have off-gassed most of these compounds long ago.
Preserved Wood Foundation (PWF) is a type of wood treated with liquid chemicals, under pressure, to help prevent rot and insect infestation. It is a very effective process, which has been modified since it was developed a few decades ago. The main component that helps prevent moisture damage is Copper, which is mixed with other chemicals that help transfer it into the wood. I am not sure what the basic composition of the most modern solution is, but it is far superior to the original ones that contained Arsenic. The reasons for discontinuing the use of that is the same reason that railroad ties no longer are preserved with Creosote. Both are quite toxic and can be very harmful to the environment they are installed in. One of the more recent compounds was labelled as ACQ, which I believe was an abbreviation for Aqueous Copper Quat. If you understand what that compound is, your chemistry knowledge is superior to mine.
The liquid preservative solution is driven into the dried wood or plywood, often through small incisions in the surface, under pressure. This helps it to penetrate much deeper into the pores than simple surface applied preservatives or wood finishes. The deep penetration also ensures that the majority of the treated wood is protected, but any cuts should still be surface treated. This may also be an issue for you if the sawdust from the cut material is not thoroughly removed.
To deal more directly with your question, there may be a simple alternative to the PWF material, if it is only used for a subfloor over your concrete basement floor slab. I am unsure from your description if this is the limit of its use, but I will presume that is the intended goal. It is now commonly used for any wood that is in direct contact with a concrete slab-on-grade, to prevent wicking moisture from the concrete. That is a common cause of rot in untreated wood, as the cooler concrete is much more likely to have condensation on the surface, or absorb moisture from the soil beneath, if it is saturated. Your solution may be to substitute the PWF treated wood, normally pine, with cedar. Cedar has natural phenols in the wood that are a built-in preservative. They make cedar a good choice for any area where moisture damage is likely, but may not have as long-lasting effects as PWF does in standard lumber. Many older homes used cedar firing or strapping on top of basement floors, below plywood or solid wood sheathing, to prevent damage to the flooring.
As far as replacing 6MIL polyethylene sheathing for the air/vapour barrier, the only alternatives are likely sprayed-on polyurethane or extruded polyurethane foams, which likely have more off-gassing of chemicals than the plastic sheathing. There are various air barrier options that may not be as problematic, but to control water vapour there is nothing more effective than some form of plastic. There may be alternatives using special vapour barrier paints, but these would have to be approved by the local building officials and may require additional work when installing the drywall.
My overriding concern is still with all the other materials that will be installed, which can contain even more chemicals that the PWF floor components. Cabinets, carpets, laminate flooring, drywall compound, roofing, vinyl windows, and even pre-finished hardwood flooring may have a huge amount of chemicals that can initially bother even homeowners without your sensitivity levels. Most cabinets and countertops are composed of particleboard or MDF that are held together with large amounts of adhesives. These have been known to contain formaldehyde, as well as other very volatile compounds. While it may be possible to paint the walls and ceilings with very low VOC paints to help seal in some of the irritants, that won’t work for the rest of the components. Even ABS plumbing drains are glued with highly volatile adhesive. Don’t forget the amount of plastics in the electrical wire sheathing, switches, receptacles, faceplates and circuit breakers.
Using cedar instead of PWF wood and plywood for your basement subfloor may help with one aspect of your chemically sensitive issues, but don’t forget about the rest of the home. Preventing installation of new materials that may also cause issues with your condition may be much more difficult than just the basement subflooring.