Key Takeaways
- Tack strips will leave nail holes in hardwood—unavoidable with standard stretch-in installation
- Hardwood needs to acclimate and be checked for moisture before carpet goes down
- Use breathable underlay to prevent moisture trapping between layers
- Reversibility is the main advantage—you can remove carpet and refinish hardwood later
- Hardwood in poor condition (warped, cupped, or heavily damaged) is a poor base for carpet
- Floating floors (engineered hardwood, laminate) should not be carpeted—they need to expand and contract
Why Homeowners Carpet Over Hardwood
Hardwood is expensive to refinish. Hardwood is cold underfoot in Ottawa winters. Hardwood shows every scratch if you have dogs or children. Carpet is softer, warmer, and quieter.
Some homeowners inherit hardwood they dislike—wood that’s dark, dated, or damaged beyond easy repair. Refinishing costs $3–$5 per square foot. Carpet installation costs about the same but delivers immediate warmth and sound dampening.
Others plan to sell in a few years and want neutral, cozy flooring now without destroying the hardwood underneath. Carpet is reversible. Tile and vinyl are not.
The hardwood stays intact under the carpet if you install carefully. When you’re ready, you pull up the carpet, patch the tack strip holes, sand, and refinish. The hardwood returns.
But there are risks. Moisture. Damage from tack strips. Hardwood movement beneath a fixed carpet. You need to understand what you’re doing to the floor before you cover it.
How Tack Strips Damage Hardwood Floors
Tack strips are thin wood strips with angled nails that grip the carpet backing. Installers nail or glue the strips to the floor around the perimeter of the room. The carpet stretches over underlay and hooks onto the nails.
On hardwood, the tack strip nails penetrate the wood. Each nail leaves a hole. Standard tack strips have nails every inch. A 12-by-12-foot room has roughly 200 nail holes when you’re done.
These holes are small—about 1/16 inch in diameter. They’re repairable. Wood filler, sanding, and refinishing will hide them. But the holes are there. If you’re trying to preserve museum-quality hardwood, carpet is the wrong choice.
Some installers use adhesive-backed tack strips to avoid nailing. The adhesive is strong enough to hold the carpet but removes cleanly when you’re done. This works on hardwood you want to keep pristine. The tradeoff is cost—adhesive strips cost more, and not all installers stock them.
Gluing tack strips to hardwood can also pull finish off when you remove the strips later. Test a small area before committing to a full room.
For most residential installs, nailed tack strips are standard. The damage is minimal and reversible. Expect to spend $500–$1,000 on refinishing after carpet removal, depending on room size.
Moisture Trapping Between Carpet and Hardwood
Hardwood absorbs and releases moisture based on indoor humidity. It expands in summer. It contracts in winter. This movement is normal. Carpet on top interferes with that process.
Carpet and underlay create a barrier. Moisture that would normally evaporate through the hardwood gets trapped. The hardwood can develop mold, mildew, or cupping (where the edges of each board rise higher than the center).
Ottawa’s seasonal humidity swings make this worse. Summer humidity can hit 70%. Winter indoor humidity drops to 20% when the furnace runs. Hardwood needs to breathe through these changes. Carpet blocks airflow.
Use breathable underlay. Avoid rubber underlay and moisture-barrier underlays designed for concrete slabs. Those trap moisture. Choose felt or synthetic underlay that allows vapor transmission.
Run a dehumidifier in summer if your basement or main floor tends toward high humidity. Keep indoor humidity between 30% and 50% year-round. This protects both the hardwood and the carpet.
If the hardwood was previously finished with polyurethane, moisture trapping is less of a concern—the polyurethane already seals the wood. Unfinished or oil-finished hardwood is more vulnerable.
Choosing Underlay for Hardwood Floors
Felt underlay is the traditional choice. It’s made from recycled fibers, compressed into a dense pad. It breathes. It doesn’t trap moisture. It’s firmer underfoot than foam, which some homeowners dislike, but it’s the safest option for hardwood.
Rebond foam underlay (the common recycled foam type) works on hardwood if the wood is sealed with polyurethane. It’s softer. It’s cheaper. But it doesn’t breathe as well as felt. If your hardwood has an oil finish or is unfinished, skip the foam.
Synthetic underlays (polyurethane-based) fall in the middle. They offer cushioning and some breathability. Look for products labeled as “moisture-permeable” or “vapor-permeable.” Avoid anything marketed as a moisture barrier.
Thickness matters less than density. A thin, dense underlay protects the hardwood better than a thick, soft one. Aim for 6–8 pounds per cubic foot density.
For carpet installation over hardwood, felt underlay is the conservative choice. It’s been used for decades. It works.
When Hardwood Condition Makes Carpet a Bad Idea
Cupped hardwood—where the edges of boards are higher than the centers—indicates past moisture problems. Carpeting over cupped hardwood traps moisture and makes the problem worse. The boards will continue to move. The carpet will develop waves and ridges.
Warped or buckled hardwood means the subfloor beneath has issues. Water damage, foundation settling, or joist movement. Carpet won’t fix it. The carpet will follow the contours of the warped wood. You’ll see every dip and hump.
Loose or squeaky hardwood telegraphs sound and movement through the carpet. The squeaks get worse under the weight of furniture and foot traffic. Secure loose boards before installing carpet, or choose a different flooring solution.
Heavily damaged hardwood—deep scratches, gouges, missing boards—can be carpeted over, but you’re wasting the reversibility advantage. If the hardwood is too damaged to refinish later, there’s no point in preserving it under carpet. Consider removing the hardwood and installing carpet over the subfloor.
Check for insect damage. Termites and powderpost beetles leave holes and sawdust. Carpet hides the problem. Inspect the wood closely before covering it. If you see damage, treat it before proceeding.
For hardwood in good to fair condition—minor scratches, dull finish, outdated color—carpet is reversible and safe. For hardwood with structural issues, fix the wood first or remove it entirely.
Floating Floors and Engineered Hardwood: Special Considerations
Floating floors are not nailed or glued down. They click together and “float” over the subfloor. Engineered hardwood and laminate are common floating floor types. These floors need room to expand and contract. Carpet on top interferes with that movement.
The weight of carpet, underlay, and furniture can prevent a floating floor from expanding. The floor buckles. Seams separate. Boards crack.
Most manufacturers void the warranty if you install carpet over a floating floor. Check your flooring warranty before proceeding.
If you proceed anyway, do not use tack strips. The nails will puncture the floating floor and prevent movement. Use adhesive tack strips or a glue-down carpet method. Neither is ideal.
For engineered hardwood that’s glued or nailed to the subfloor, the same rules apply as solid hardwood. Use breathable underlay. Expect tack strip nail holes. Keep humidity stable.
For floating floors, the better option is to remove the floating floor, install carpet, and reinstall the floating floor later if needed. This avoids warranty issues and floor damage.
Reversibility: What to Expect When You Remove Carpet
Removing carpet from hardwood takes a few hours. Pull up the carpet and underlay. Remove the tack strips. Pull out the nails or scrape off adhesive residue.
You’ll have nail holes around the perimeter. Fill them with wood filler that matches the floor color. Let it dry. Sand the filled holes smooth.
The hardwood may be lighter under where the carpet was. Hardwood darkens with UV exposure. The covered areas stay lighter. Refinishing the entire floor will even out the color.
Expect to sand and refinish the floor after carpet removal. Budget $3–$5 per square foot for professional refinishing, or rent a floor sander and do it yourself for $100–$200 in rental and materials.
If the hardwood was in good condition before you carpeted it and you controlled humidity while the carpet was down, the wood will refinish well. If moisture got trapped, you may see cupping, dark stains, or mold. Minor cupping can sometimes be sanded out. Severe cupping requires board replacement.
For homeowners planning to keep carpet down for 5–10 years, the hardwood underneath will survive if you used breathable underlay and maintained stable indoor humidity. For longer periods, inspect the hardwood every few years by pulling up a corner of the carpet.
When to Call a Professional for Hardwood-to-Carpet Installs
Professional installers know how to minimize hardwood damage. They carry adhesive tack strips for floors you want to protect. They know which underlay works best for hardwood. They check for moisture and floor movement before starting.
If your hardwood is valuable—original old-growth hardwood, exotic species, or high-grade oak—hire a professional. Mistakes are expensive.
If the hardwood has existing issues—cupping, warping, squeaks—a professional can assess whether carpet is appropriate or if the wood needs repair first.
For standard oak or maple hardwood in average condition, DIY installation is feasible if you understand the risks. Use felt underlay. Use adhesive tack strips if you want to avoid nail holes. Control indoor humidity.
For a quote on carpet installation over hardwood in Ottawa, contact installers who specify their process for protecting existing floors. Ask whether they use adhesive tack strips. Ask what underlay they recommend for hardwood. If they don’t have answers, find someone else.
FAQ
Will carpet damage my hardwood floors? Tack strips will leave nail holes. Moisture can get trapped if you use non-breathable underlay. Hardwood can be refinished after carpet removal, but expect to repair nail holes and possibly sand the floor.
Can I install carpet over engineered hardwood? Yes, if the engineered hardwood is glued or nailed down. Do not install carpet over floating engineered hardwood—it needs to expand and contract. Check the manufacturer’s warranty before proceeding.
What type of underlay should I use over hardwood? Felt underlay or moisture-permeable synthetic underlay. Avoid rubber or moisture-barrier underlays designed for concrete. Breathability is critical to prevent moisture trapping.
How do I avoid damaging hardwood when installing carpet? Use adhesive tack strips instead of nailed strips. Use breathable underlay. Maintain indoor humidity between 30% and 50%. Inspect the hardwood before installing to ensure it’s in good condition.
Can I install carpet over unfinished hardwood? Yes, but the hardwood is more vulnerable to moisture. Use felt underlay and control indoor humidity carefully. Consider finishing the hardwood first to seal it against moisture.
Will carpet adhesive damage hardwood? Direct glue-down carpet methods use adhesive that bonds to the floor. Removing it later will damage the finish and possibly the wood itself. Stick with stretch-in installation using tack strips for reversibility.
How long can I leave carpet over hardwood? Indefinitely, if you use breathable underlay and maintain stable humidity. Inspect the hardwood every few years by lifting a corner of the carpet to check for cupping, mold, or moisture damage.
Can I install stair carpet over hardwood stairs? Yes. Stair tack strips are smaller and create fewer nail holes. Use felt underlay on the treads. Hardwood stairs can be refinished after carpet removal just like floors.
What happens to hardwood under carpet in a humid basement? Basements have higher humidity. Hardwood will cup, warp, or develop mold under carpet in a humid basement. Use a dehumidifier or choose a different flooring type. Basement carpet works better over concrete with proper moisture barriers.
Should I remove damaged hardwood before installing carpet? If the hardwood is too damaged to refinish later, there’s no advantage to keeping it. Remove it and install carpet over the subfloor. This saves the cost of underlay and eliminates the risk of hardwood movement under the carpet. Contact us for an assessment: contact page.