Wood is a cornerstone of North American homes, especially in timber-frame construction, forming the structural skeleton of many houses. Beyond the framework, lumber is used for roof construction, including beams and sheathing. Unless floors are concrete, tiled, or carpeted, they rely on wooden joists, girders, and decking. Wall cladding, door and window frames, and both interior and exterior doors are often wooden as well.
Since most wood components are exposed, they must be treated to resist weather, insects, and rot. Treated lumber is critical for framing, but not all treatments are equal. Effectiveness, longevity, and toxicity must be considered. National standards and building codes in many countries regulate treated wood use, mandating preservation standards and specifying where treated lumber is required.
Why Lumber Is Treated
Treated lumber lasts longer and ensures structural safety. Treatments primarily prevent:
- Fungal attacks causing staining and rot,
- Insect damage from carpenter ants, termites, beetles, and borers, which accelerate decay,
- Water and mold damage.
Some woods, like heart-grade Canadian redwood, red and white cedar, and cypress, naturally resist rot and insects but are costly. Treated lumber offers a more affordable option for timber-frame homes.
Traditional and Modern Treatment Methods
Traditional treatments include vacuum and pressure methods, with pressure-treated lumber preferred for timber-frame structures. Historically, three main preservatives, all containing inorganic arsenicals (pesticides), were used:
- Chromate copper arsenate (CCA),
- Ammoniacal copper arsenate (ACA),
- Ammoniacal copper zinc arsenate (ACZA).
These impart a green tint due to waterborne salt preservatives. However, they contain toxic arsenic, a known carcinogen, and CCA includes chromium, listed among the U.S. government’s 20 most hazardous substances. A 1980s EPA study concluded that CCA’s benefits outweighed its risks, making it a global standard. Properly treated CCA lumber fixes chemicals to wood fibers, becoming insoluble with no odor, and can be stained or painted. However, Health Canada (www.hc-sc.gc.ca) advises wearing masks and gloves when handling CCA-treated lumber, washing exposed skin and clothes afterward, and disposing of waste per local regulations. Burning CCA-treated wood or exposing it to drinking water poses serious risks. By 2002, producers voluntarily phased out CCA for non-industrial use, though it remains in some applications. ACZA, considered more eco-friendly, is marketed as Chemonite by Arch Chemicals (www.archchemicals.com).
Pressure-Treated Lumber Today
Modern pressure treatments prioritize environmental safety. Alkaline copper quaternary (ACQ), using copper instead of arsenic, is a newer preservative. Great Southern Wood Preserving (www.greatsouthernwood.com) uses ACQ-treated lumber with preservatives from Osmose Inc. (www.osmose.com), offering a lifetime warranty against fungal decay and termite damage for residential and agricultural use. ACQ-treated lumber starts dark green, fading to light brown or gray if unsealed. It can corrode metal fasteners like screws or nails if wet, so hot-dipped galvanized or stainless steel fasteners are recommended. ACQ is registered as a non-restricted use pesticide by the EPA.
Eco-Friendly Wood Preservatives
Some, like Wood Preservation Canada (www.woodpreservation.ca), argue CCA is eco-friendly, as its components—copper, chromium, and arsenate—occur naturally. They emphasize using less toxic inorganic pentavalent arsenic. However, alternatives exist. LEED (Leadership in Energy and Environmental Design) certification, developed by the U.S. Green Building Council and adopted in Canada, rates products from certified (40–49 points) to platinum (80+ points). When choosing lumber, ensure compliance with building codes, Forest Stewardship Council (FSC) certification, and LEED standards. Columbia Forest Products, with its “keep it green” motto, exemplifies such compliance.
Non-toxic options like BluWood and NexGen (www.nexgenprotection.com/) use a two-part coating that prevents chemical leaching, suitable for green or kiln-dried wood. Applied in factories, it’s non-corrosive, non-hazardous, and guaranteed for a home’s lifetime. Featured on Extreme Makeover: Home Edition in 2010, BluWood’s bright blue hue draws attention, while NexGen offers a clear or tinted finish, earning LEED points. Ironically, blue may be “greener” than green, making it an appealing choice for eco-conscious framing.
7 Responses
This article is complete horse dung. Treated lumber does not make your lumber structurally safer. In fact it makes it weaker.
The proper solution to moisture problems is to keep moisture out of your walls, with proper cladding, moisture and vapour barriers, architectural detailing, etc.
Treated lumber should only be used in outdoor applications, for example, decks.
Is the article dung for the bugs?
The article did not say it made wood safer. It said safe and that could mean multiple things. For instance, if you use untreated wood where treated should be used, that may eventually create an unsafe condition. Additionally Matt, weaker does not mean less safe.
if there is bugs eating your wood, your wood has turned to dung. termites and carpenter ants only eat soft, juicy saturated wood. No different than how you like your dinner. Soft, moist and fragrant, or bone dry, tough and hard?
Hi guys I live in South Africa and want to construct my own house out of wood as it is going on the farm more info will be great .Every body warning me of bugs that is going to destroy
my house any advice will be appreciated
Burt, if done properly, pressure treated wood can be used for a large portion of the framing or perhaps all. I have built a small building completely out of pressure treated wood and it has functioned perfectly for 20+ years. It is best to dry your lumber properly. I chose not to and did fine because I framed and sheathed the walls and floor before the wood had a chance to twist etc. I have noticed no problems due to shrinkage. You must use approved fasteners which are readily available. In my opinion the modern coated fasteners perform as good or better than hot dipped galvanized.
I’m thrilled at the idea of interior framing construction with treated wood. But I always balked at the idea due to expected shrinkage and warping. I only find references to width shrinkage which I would see as a nightmare if you’ve screwed sheetrock in place. Maybe it supports a return to interior shiplap?