In an effort to make our newly purchased, older home, a little cozier, we’re going to be adding ridged John Mansville polyiso insulation board (made right here in Cornwall, by the way) to both sides of our exterior walls.
Why insulate both sides? Because our dated walls have too many holes, or weaknesses in its construction. Weaknesses that may not have been a concern 50 years ago, when gas was cheap and chopping wood was still in vogue. However, with the price of energy today, this barn is really going to be a heating money pit.
Holes do as poor a job keeping the cold out, as they do keeping the heat in. So, we address the comfort issue by insulating both sides of the wall. Basically, if we could replace the exterior walls, we would. But assuming our budget doesn’t include removing the roof with the same crane that was commissioned to lift and lower the lengths of International Bridge one section at a time, the next best solution is to bolster the insulation value of the exterior frame.
Further bonuses to choosing the John Mansville board solution. One, it won’t disturb an often delicate wall structure that may contain anything from lead paint to asbestos filled insulation. And two, wrapping both sides of the exterior wall will make things absolutely air tight. So, that cool draft you feel up the wazoo every time you step out of the shower will soon be a forgotten morning ritual.
Step one, remove the existing wood, vinyl, or composite siding. Brick homes can be covered directly with John Mansville board, while covering a stone house (for aesthetic reasons) should be avoided. Step two, install the John Mansville polyiso board to the wall studs, with the reflective side facing the interior. Next, cover the John Mansville board with a house wrap. If the John Mansville polyiso board serves as a heavy sweater, the house wrap is its light windbreaker jacket over top. Although the ridged insulation board will basically seal the home, house wrap is a good idea because it effectively protects the John Mansville product from the elements during the construction phase, and against any moisture that infiltrates the siding in the future.
Next, install 1×3 spruce strapping vertically over the house wrap, fastening it through the John Mansville board and into the exterior wall studs. The 1×3 strapping provides a can’t-miss target for installing your siding. Plus, it provides a key, ¾ inch air space for wood and composite sidings, which require this type of drying zone behind the product in order to avoid rot or paint peeling issues. Now, with 1-1/2 inches of JM insulation board, along with the ¾ inch strapping, and considering the thickness of the siding, won’t all these exterior coverings cause a challenge to finishing around the windows? Very likely, but nothing a roll of aluminum flashing in the hands of a qualified installer can’t correct.
Is it a good strategy to install an insulation board and siding before replacing the windows? Or, shouldn’t the windows be replaced before replacing the siding? There’s no doubt that in a perfect renovation world, and with the budget to do so, replacing the windows along with the siding is as good a 1-2 punch as you can get when it comes to turning around a home’s curb appeal and value. However, if budget constraints will allow you one renovation per year, insulation and siding, in most cases, is cheaper than window replacement, and the better value.
New windows are terrific, but you’re still replacing glass with glass. So, start with the furnace, then the siding, and put the money saved on heating towards new windows the following year.
Inside the home’s exterior walls and ceilings? Basically the same procedure as we did outside. John Mansville board (3/4 inch) glued directly to the existing drywall or plaster, 1×3 strapping overtop, followed by a 6 mil. vapour barrier, then regular drywall to finish. As is common practice, be sure to start with the ceiling insulation panels and drywall first, then the walls.