How do I maintain pressure-treated wood framing at the base of my NB garage?

Pressure-treated lumber at the base of your garage requires very little active maintenance, but there are a few key things to inspect and address each year to ensure it lasts the full 30-50 years it's rated for.

Pressure-treated wood used for garage sill plates and low-framing members in New Brunswick is typically treated with alkaline copper quaternary (ACQ) or copper azole (CA) preservatives, which resist rot and insect damage even in persistent moisture conditions. The treatment does the heavy lifting — your job is mostly to keep the conditions around that wood as dry and well-drained as possible so the treatment never gets overwhelmed.

Annual Inspection Is Your Most Important Maintenance Task

Once a year — spring is ideal, right after the frost leaves the ground — walk the perimeter of your garage and look at the base of the framing where it meets the foundation. You're looking for a few specific things. First, check that the grade still slopes away from the foundation on all sides. NB's freeze-thaw cycles shift soil every winter, and it's common for the ground to gradually settle toward the garage over several years, creating a bowl effect that directs water toward the sill plate. If you see soil sitting level with or above the bottom of the wall sheathing, add topsoil or gravel to restore a slope of at least 1 inch per foot for the first 6 feet out from the wall.

Second, look at the sill plate itself where it's visible (often at the base of the exterior sheathing or inside the garage at floor level). Healthy pressure-treated wood is firm and slightly greenish or brownish depending on age. Soft spots, dark discolouration, or wood that crumbles when you press a screwdriver into it are signs of rot — which means moisture is consistently reaching the wood faster than the treatment can handle. This is almost always a drainage or grading problem, not a failure of the wood itself.

Keep Moisture Away from the Wood — That's the Whole Job

The most common maintenance failures in NB garages involve water finding its way to the sill plate from multiple directions. Gutters and downspouts that discharge too close to the foundation are a frequent culprit — extend your downspout splash pads or underground drain pipes at least 4-6 feet away from the garage. Inside the garage, make sure your concrete slab has no low spots against the walls where meltwater from snow-covered vehicles pools and sits against the framing. A simple broom-out after driving in on a snowy day goes a long way.

If your garage has exterior sheathing (OSB or plywood) that runs close to grade, check that the bottom edge is at least 6-8 inches above the finished grade. Sheathing that wicks moisture from soil contact will rot from the outside in, eventually reaching the framing behind it regardless of how well the sill plate is treated.

Sealing and Finishing Pressure-Treated Wood

Pressure-treated lumber does not need to be painted or sealed to perform its rot-resistance function — the preservative treatment handles that. However, if your sill plate or low framing is exposed to view (inside an unfinished garage, for example), you can apply a penetrating water repellent after the wood has dried for 6-12 months post-installation. This reduces surface checking (the small cracks that develop as the wood dries) and keeps the wood looking cleaner. Use a product rated for use on pressure-treated lumber — standard exterior stains and sealers are fine once the wood is fully dry.

When to Call a Professional

If your annual inspection reveals soft or rotted wood in the sill plate, don't ignore it. Sill plate replacement is a structural repair that involves temporarily supporting the wall framing, removing and replacing the damaged section, and ensuring the new plate is properly isolated from the concrete with a sill gasket or sill seal. This is work for an experienced carpenter or contractor — it's not dangerous DIY territory, but it requires knowing how to safely transfer load while the repair is made. A rotted sill plate that goes unaddressed will eventually compromise the wall framing above it, turning a straightforward repair into a much larger and more expensive project.

If you're planning a new garage build or noticing moisture issues around an existing one, New Brunswick Garages can connect you with local contractors through the New Brunswick Construction Network — find garage builders and general contractors in your area at newbrunswickconstructionnetwork.com.