Frequently Asked Questions

Interested in learning more about pressure treated wood and its applications? Here are some answers to commonly asked questions.

A. Wood is a renewable building material and is used in a variety of residential, commercial, industrial and agricultural applications. Wood products are safe, strong, and yield many advantages as a construction material. Wood products are versatile, easy to work with, economical, store carbon, and provide natural beauty in the places we work, live and play.

A. Pressure treatment is a process that is used to preserve wood. Wood is placed inside a closed cylinder and pressure is applied, which forces the preservatives into the wood cells. The end result is a more durable and lasting product.

A. Wood preservatives in Canada are governed by the Pest Control Products Act and must be registered with the Pest Management Regulatory Agency (PMRA) of Health Canada. The PMRA determines if the wood preservatives can be used safely and if they will be effective for their intended use. Once on the market, PMRA monitors the use of pesticides through a series of education, compliance and enforcement programs. Did you know that each preservative is reviewed every fifteen years?!

A. Pressure treated wood products can be used in a variety of applications for structures that require resistance to fungal decay and termites. Residential applications include decks, fences, gazebos, playground equipment, docks, raised flower planters, and landscaping. Agricultural and industrial applications include utility poles, fence posts, bridges, rails and railway ties.

A. Wood treated for above ground applications can be used in exterior construction where the wood is NOT in contact with soil. Lumber treated for ground contact has a higher preservative retention level than above ground. This is to improve the performance of pressure treated wood when it comes in direct contact with the ground (soil), fresh water, high moisture areas etc., where it is highly vulnerable to deterioration. The end tags attached to pressure treated lumber will identify if the wood has been treated for Above Ground or Ground Contact applications.

A. Do not use pressure treated wood for the following applications:

  • Projects where the wood may come into direct or indirect contact with drinking water, except for uses involving incidental contact such as freshwater docks and bridges.
  • Projects where the preservative may become a component of food (like a countertop or cutting board), animal feed or beehives.
  • As mulch.
  • Firewood. Never burn pressure treated wood.

A. Use quality, exterior, corrosion-resistant fasteners (and other metal products) that approved within the building code with all pressure treated wood products. 

alkaline copper quaternary compounds (ACQ)Use hot dipped galvanized or stainless-steel fasteners that are building code approved. 
copper azole (CA)Use hot dipped galvanized or stainless-steel fasteners that are building code approved. 
micronized copper azole (MCA)Is no more corrosive to fasteners than untreated wood. Use exterior fasteners and hardware that are in compliance with the manufacturer’s recommendations and the building codes for their intended use. 
    • Stainless steel fasteners and hardware are recommended for use with pressure treated wood in other severe exterior applications such as swimming pools, saltwater exposure, etc.

A. Aluminum building products (such as aluminum siding, flashing, and door and window frames):

  • Can be placed in direct contact with wood pressure treated with micronized copper azole (MCA) used for interior applications and above ground, exterior applications where the wood is not exposed to frequent and prolonged wetting, such as decks and fences.
  • Cannot be placed in direct contact with wood pressure treated with alkaline copper quaternary compounds (ACQ) or copper azole (CA). When using ACQ or CA pressure treated wood in close proximity to aluminum products, a 1/4″ minimum space must be left between the pressure treated wood and the aluminum products. Polyethylene or nylon spacers can be used to maintain the 1/4″ spacing. Another option is to use a polyethylene barrier, with a minimum thickness of 10 mils, between the pressure treated wood and the aluminum product to prevent direct contact of the wood and the aluminum.

A. Pressure treated wood may be used indoors for applications where protection against termites and fungal decay is needed. Pressure treated wood should not be used for indoor applications where it can come into contact with drinking water or food, such as countertops or cutting boards. Follow safety practices when working with wood products – cleanup and dispose of sawdust and construction debris after construction.

A. Yes, you can use pressure treated wood for a raised garden bed project if the wood has been treated with one of the following three preservatives: alkaline copper quaternary compounds (ACQ), copper azole (CA), or micronized copper azole (MCA). If desired, a suitable thin plastic material can be used as a barrier between the pressure treated wood and the raised bed garden soil. The use of a plastic barrier will also help keep the raised bed garden soil within the bed area. For proper drainage, the plastic material should not be used underneath the raised bed garden. Learn More

A. The use and handling guidelines for pressure treated wood are similar to safety practices used when handling all wood products. Wear appropriate safety equipment such as gloves, eye protection and a dust mask. Work in a well-ventilated area and avoid the potential for the inhalation of sawdust.

A. Here are a few best practices that should be followed when storing pressure treated wood:

  • Ensure that the lumber is unloaded in a dry place.
  • Elevate the lumber on stringers to prevent absorption of ground moisture, as well as to allow air circulation. Do not store lumber in direct contact with the ground.
  • Cover the lumber stored in an open area with a material that will protect it from the elements. The covering material should be porous to allow for moisture to escape. Note: if you use polyethylene or similar non-porous covers, loosely cover the wood so that there is air circulation, preventing moisture from being trapped.

A. For outdoor projects, it is important to protect the cut ends of pressure treated wood from fungal decay. All cuts and holes expose untreated wood and should be brush-coated with two applications of a registered end-cut preservative before the wood is installed (copper naphthenate for in-ground contact, and zinc naphthenate or a copper-based end cut wood preservative for above-ground contact). Always follow the manufacturer’s recommendations.

A. Do not burn pressure treated wood. Pressure treated wood approved for residential use should be disposed of by ordinary trash collection or at a landfill. Commercial and industrial users should dispose of pressure treated wood in accordance with local, provincial and federal regulations.

A. No. Do not burn pressure treated wood. Pressure treated wood must not be burned because combustion breaks the unique bond formed between the preservative solution and the wood. When this bond is destroyed, the components of the preservative can be released in the form of ash and particulates, which can be harmful if inhaled.

A. Mold growth can occur on the surface of many products, including untreated and pressure treated wood, during prolonged exposure to excessive moisture conditions. To remove mold from the pressure treated wood surface, the wood should first be allowed to dry. Once dried, use a mild soap with water to remove any remaining surface mold.

A. To protect your investment, regular maintenance is important. Here are some important construction tips:

  • Use a registered end-cut preservative (copper naphthenate for in-ground contact or zinc naphthenate or copper-based end cut wood in above-ground contact) on all cuts and holes that expose untreated wood.
  • Use a fastening system that provides maximum holding power and corrosion resistance and follow the manufacturer’s recommendation for all metal products.
  • Use screws to add extra holding power for decking and all applications where appearance is important.
  • Drill pilot holes, especially when working near the edge of the board, to minimize splitting.
  • Apply a weather resistant finish. Any exposed wood, pressure treated or not, should be protected from the weather. Application of a high-quality clear water repellent or semi-transparent stain will minimize the wood’s moisture uptake and loss. For maximum protection, a weather resistant finish should be applied as soon as the wood is dry to the touch after construction is completed.
A. Any exposed wood, whether pressure treated or not, should be protected from the weather. For any application of a paint, stain, clear water repellent or other finish, consult the finishing product manufacturer’s instructions for use with pressure treated wood. Prior to applying a finishing product on an entire project, it is recommended to do a test patch on a small exposed area to ensure that it provides the intended result.

A. Unless the finishing product manufacturer states otherwise, you can apply a water repellent or semi-transparent stain to pressure treated wood as soon as it is dry to the touch after installation. Pressure treated wood may still be damp from treatment when purchased from a store. Too much moisture in the wood may prevent the finishing product from penetrating the wood sufficiently and result in a blotchy appearance or poor adhesion. To test to see if the wood is surface dry, sprinkle water droplets on the surface. If the water droplets are absorbed into the wood, it is ready for the water repellent or semi-transparent stain. 

A. Pressure treated products have specific applications and can only be used for approved uses. Agricultural products must only be used in an agricultural setting and residential products must be used in residential applications.