- Basement finishing


The proper way to insulate and finish inside concrete walls is as follows: Identify the outside grade level, then transmit that to the inside of the concrete wall. Take that line and draw a line on the wall 6" above the grade line all the way along the interior concrete wall. This now becomes the height of your poly vapor seal - 6mil polyethylene. On this line spread a bead of acoustic adhesive available from your local building supply store in tube form. This adhesive will retain your 6mil polyethylene to the concrete. The 6mil polyethylene in 10 foot width will adhere to the acoustic adhesive, go down the inside of the concrete wall and out onto the floor. This stops any moisture emanating from the concrete to the wood studs.

Build the stud walls 1 1/2" shorter than the wall height. This allows the walls to stand up in position and you can screw them to the underside of your floor joists up against the concrete wall. Cut styrofoam or polyurethane foam blocks 1 12" thick and position them every 2ft. along the bottom of the wall. Pound a 4" common nail (it doesn't have to be a concrete nail) through the bottom plate and foam block and into the concrete, stopping when your hammer rings. The wall will remain in place being screwed at the top to the underside of the joist and nailed into the concrete floor.

Now, you are ready to prepare the wall for insulation. If there is any pony wall above the concrete, remove any polyvapor seal from this wall. Stack R12 insulation batts behind, lying on their side above the concrete wall and the joist above thus covering the poly wall section if it exists. Put insulation batts in green garbage bags making insulation pillows. Put in the joist header areas (where the joist runs over the plate to the outside joist fascia). Run insulation batts between the newly studded wall from the joist line to the floor.

Finally take the polyethylene vapor seal that is lying out on the floor (the excess of the 10ft width) and bring it up around the studded wall to the point that it will reach and staple in place. Staple another piece of polyethylene from the top area onto the underside of the joist 12" out from the studded wall bringing it down the wall to meet the polyethylene coming up from the floor. Overlap them and seal with acoustic adhesive. You have now totally encased the finished interior framing wall not allowing any mois-ture that may emit from the concrete to get into the wood fibre and or insulation causing a musty odour.

Proceed to drywall or panel. Now no moisture will ever get near a wood fibre. If there is ever a crack in the wall of floor, the moisture will run up against the polyethylene, run back in behind and out onto the floor and will be identified at the floor line rather than up in behind your panelling or drywall.

Article courtesy of: Shell Busey

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September 30th, 2023