This week saw the first flooring boards go down in the main house–an exciting development for those of us who witnessed this happening in the in-law suite more than three months ago (and wished we were the ones moving in). But before laying the floor boards, several layers first had to materialize in between concrete slab and finished fir. Here’s what that looked like:
1) Polyethylene membrane: This thin layer of plastic will protect our flooring from the whims of moisture, which causes wood to warp and crack with its changes in temperature and humidity. All seams are sealed together, and all edges sealed to the airtight drywall, creating another layer of air sealing. It should be noted that our slab is 24″ above grade and under it is a 12″ layer of 3″ rock as a capillary break and drainage plane, as well as 4″ of foam insulation and another layer of plastic. The slab is one year old. Fresh slabs have a higher moisture content and can be problematic. There are some more expensive dimpled plastic products as well as thicker membranes that provide more robust moisture control for more challenging situations.
2) Two layers of 1/2 ” plywood stapled and glued together to form a floating floor layer: While a single layer of plywood may do the job in some cases, our architect and Fine Home Building advised a double layer to prevent the hardwood from curling at the edges due to changes in interior temperature and humidity. We also didn’t want to puncture the membrane beneath by screwing a single layer right through to the concrete slab. Using 7/8″ flooring staples ensures this won’t happen on the floating double floor. The first layer is oriented with the long axis parallel to the final flooring orientation and spaced 1/2″ around the edges and 1/4″ between sheets to allow for expansion. The second layer is oriented 90 degrees to the first and staggered and overlapped with the first layer so no seams line up. (This layer is also spaced like the first layer.)
3) Flooring paper: After the membrane, a thin layer of dry sheathing paper goes down to cushion the flooring and prevent squeaks. You can also use cork on the second floor to provide more sound proofing but we opted to use the plain paper to save on the significant added expense. We do have 4″ of Roxul Safe and Sound insulation between the floor joists. Some people would use a vapour retarder membrane like Aquabar or rosin paper, but we felt that was unnecessary in our case since we had the plastic layer on the slab and vapour retarder paint on the ceiling under the second floor (as well as an inch of plywood).
4) Installing floor boards: We had 3.5″ Douglas fir boards milled up off our property. We find that the narrow boards shrink less than wide plank floors and leave less noticeable cracks. First we snapped a chalk line an average of 1/2″ off the starting wall. We adjusted that line a bit to ensure that it was parallel with the stairs and future stove tile across the room. This process squared up the area that would have flooring and allowed room for expansion by leaving a gap under our future baseboards which will be 3/4″ thick. We used straight boards for the first row along the chalk line and face-nailed these with a pneumatic 16 gauge nailer and 1.5″ nails. Most of the holes would be covered by baseboard and the others would be filled in after. For the second row I used a pneumatic stapler with 1.5″ staples going into the tongue. I used a scrap chunk of flooring and a hammer to help tap the pieces together as needed. I also had a pry bar that hooked onto the end of the board and with a bend at the other end I could hammer on to draw the last pieces together as I approached the wall. I alternated lengths to avoid nearby joints and randomly laid out a variety of edge grain, knotty and sapwood patterns with various colour tones. The staples go every 12″ and sometimes closer to persuade a tighter fit.
Next comes sanding, filling and sealing (and perhaps a set of blinds for those windows).