I read your article in the Sunday Free Press every Sunday. The info you give is great. I see that you take questions, so thought I would ask you this one.
We recently did some renovations to our house this past summer. We renovated the kitchen by taking out a dividing wall between the old kitchen and dining room. Along with the kitchen renovation, we upgraded the number of plugs in the kitchen more than what code required. The problem we had with the wiring was that we had to come from the attic down the wall to where the plug is located. There were 5 new outlets on the south wall and one on the west wall. With having a larger kitchen (19 x 12) we notice that the exterior walls are cooler.
The house was built in 1952. It has gypsum board interior covered by sandstone and then a layer of plaster. Under the gypsum is a layer of buffalo board and behind that is yellow fiberglass insulation. The exterior is shiplap wood, covered by stucco. The stucco has b een painted approx 3 times.
In fishing the wiring down the exterior walls, I suspect that the insulation has been disturbed in a few spots. All boxes on the exterior walls have vapor barrier behind them, but the wall in those areas is cold. My first instinct was to shoot expanding foam behind the electrical boxes. Would this cause any problems by doing this?
We are looking at adding more insulation to the exterior. I have seen blue Styrofoam insulation added on top of the stucco and have also seen stucco removed and the insulation added onto the shiplap, itself. Which way is best? I would like to do as much of the work as possible, myself.
After the insulation is added, we would be adding stucco to match the new garage. The front of the house might have some updated details like brick or decorative brick.
Thanks again for all you comments and great column.
To answer your first question, I would like to know what kind of vapour barrier was put behind the electrical boxes in your renovated kitchen. Although it is proper to put vapour barrier behind outlets in exterior walls, the existing wall, built in 1952, would not have a proper air-vapour barrier. The vapour barrier behind the new outlets would only be fully effective if sealed to an original vapour barrier.
I am assuming that the vapour barrier behind the new boxes is a small sheet of poly or a pre-manufactured plastic box. If either of these was installed, it may have been to prevent condensation behind the new metal box, since a hole was cut in the old exterior wall and some insulation disturbed. The old wall may not have had a proper polyethylene air-vapour barrier installed behind the interior wall sheathing, but the many coats of paint on the old plaster may provide a reasonable vapour barrier. If this has only been disturbed to cut a few holes for the new outlets, foaming behind the outlets may be a good idea. The expanding foam may seal the area around the electrical boxes and partially seal the new vapour barrier to the old wall sheathing, preventing air and moisture leakage into the wall cavity.
This brings me to your next question about using rigid blue Styrofoam over the exterior walls for insulation. Unfortunately, rigid foam insulation of this kind is not normally suitable for use on the exterior of an existing wall, due to its lack of permeability to moisture. This insulation has a relatively high vapour barrier rating, if properly sealed at the joints. Installing this over the old wall may create a vapour barrier in the wrong location and trap moisture in the old wall cavity and cause moisture damage. Other types of rigid or semi-rigid insulation are available for exterior wall application that is breathable and often has a housewrap-style of membrane on the outside. This membrane acts as a good air barrier, if properly installed and taped at the seams, but allows moisture to escape to the exterior, preventing wall damage. Check with your local home centre or building supply centre for availability and pricing.
Installing over the old stucco may be possible, depending on the condition of the stucco, but removal and installation directly over the shiplap is preferred. This will allow for easier installation of the insulation and will minimize or eliminate the need to build out the existing door and window jambs or brick moulds. Removal and discarding of the old stucco is a big job, but may yield a superior finished product and will allow for repair or replacement of any moisture damage to the old sheathing behind the stucco.