Ask the Remodeler: The floor is uneven, and the basement is cold

Ask the Expert Home Improvement
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Q. I have a small two-bedroom condo in an old building. I want to get bamboo floors installed, but the contractors I’ve contacted have told me that they don’t install floors on uneven surfaces. This cannot be a deal-breaker. How can I get new flooring in an old building?

A. Wood flooring and uneven subfloors are a problem for many of us. Bamboo flooring is typically prefinished, and you cannot just put a prefinished floor of any species over an uneven subfloor. If it is important that you have wood floors, then you have two options depending on the severity of your floor’s undulations:

If they are not too severe and widespread, you can pour a liquid floor leveler in the offending areas to even out those spots with the rest of the floor. As long as the leveler is not too thick, nails should be able to penetrate it and catch the wood below. This may allow you to use a pre-finished floor.

If the undulations are too great, you should consider a natural wood floor that is installed, sanded, and finished in place. Typically, the wood can be shimmed in place to take the worst curses out of the floor, and because the flooring is not prefinished, it can “float’’ across some of the undulations. The flooring installer can then sand over the entire floor and blend everything together. The floor won’t be as level as the prefinished floor, but it will roll more with the contours of the house, which is not always a bad thing. You always need to be careful leveling one space as it can create awkward transitions into the adjoining rooms. The floor should then be sealed with at least three coats of a water-based or oil finish. Installing a natural-wood floor takes longer but gives you more options in an old house.

Q. We have a walk-out basement, and one wall and portions of the side walls are above grade with no insulation. During the winter, the temperature in the furnace room (which is unfinished) can dip into the 40s. What would be the easiest way to insulate the walls?

A. There are several ways to tackle this.

For the most effective basement insulation, the more involved (and costly) process is to have a stud wall framed with a ½-inch gap between the back of the wall and your foundation, and then have a professional insulator apply high-density and non-permeable closed-cell foam in the bays. In this case, the rim joist (the space between the top of the foundation wall and the bottom of the floor above) also should be foamed. This is where most drafts originate.

However, if you’re looking for a more cost-effective way to insulate, I’d recommend using a rigid foam board. The best type is polyisocyanurate panels, which typically have a finished face on both sides and an R-value of around 7 to 7.25 per inch, similar to the closed-cell foam mentioned above. (R-value refers to the effectiveness of insulation; you want R values of at least 7 per inch of thickness.) For your situation, I’d recommend a panel thickness of 1 ½ to 2 inches.

When installing, I suggest applying a moisture barrier first. This is typically a product sold by the gallon at any paint store and can be rolled on. Next, apply wood strapping to the walls and attach your panels to that. Apply foil insulation tape to the seams between the panels, and fill the corners with a high-density, non-permeable closed-cell spray foam, paying particular attention to the rim joist area.

Mark Philben is the project development manager at Charlie Allen Renovations in Cambridge. Send your questions to [email protected]. Questions are subject to editing. Subscribe to the Globe’s free real estate newsletter — our weekly digest on buying, selling, and design — at Follow us on Facebook, Instagram, and Twitter @globehomes.