Cold Roof Warm House (Part 1)
This morning the thermometer outside my kitchen window read -20 degrees Fahrenheit. That's TWENTY BELOW! Okay, you Canadians shrug, but even for us hearty New Englanders, that's pretty cold, and by March, we're starting to think Spring (or at least Mud Season) so it's not all that welcome. But thanks to my efforts at bundling-up Chez Melendy early on in the renovation, we're cozy inside.
As I mentioned earlier, one of the principal reasons for gutting my house in the first place was to insulate the walls and ceiling. There was no insulation in either place for the prior residents. No cornhusks, newspapers, or rags were found inside the walls, just airspace. The original walls were covered with plaster, though, and this provided some brake against the cold. Most of the cold air that enters a house is through infiltration. Cold air comes through the tiny cracks in the outside walls and then finds its way through the interior walls via electrical outlets, holes for plumbing, window casings, etc. Plaster does a good job at sealing up the places were infiltration can occur. But the fact is that the prior residents burned 1,300 gallons of oil the last year they lived in the house. That's a lot for a smallish (1400 sq. ft.) house. Even if the Melendys had put some pink fiberglass insulation in the upstairs attic they could have cut down a little on the heating costs.
Since I was going all-out to increase the R-Value of my house I decided to hire a contractor to apply polyurethane foam to the rooflines and the sill perimeter. This would help cut down on the chimney effect of losing heat through the roof while having it replaced with cold air that is drawn in where the foundation comes into contact with the frost line.
The biggest hurdle with polyurethane foam insulation is the cost. After all, it's a petroleum product and it requires special equipment for application. There are DIY kits available but I had a large job to do and plenty of tasks to keep me busy, and if you've ever used the spray foam cans, which spray a similar material, you know that applying foam insulation is a messy and unforgiving business. The pros came in and had the job done in one and a half days. As much as I prefer to tackle every task on my own, this was one I decided to let go of.
Applying foam
to an old house is especially beneficial because of its ability to seal off areas of infiltration while adding R-Value at the same time. Chez Melendy was sheathed with rough sawn pine boards and then covered in clapboards. Tyvek building wrap wasn't even part of anyone's imagination at the time, and tarpaper must have been considered a luxury because it wasn't used either. The foam sealed all those cracks right up.
Another benefit of the kind of foam I used (known as closed cell) is that it saved me from having to vent the roof, which would include cutting vent holes in the soffit and installing a ridge vent.
The need for venting comes from the fact that in a well-insulated house, moisture can get trapped between the interior and exterior walls and eventually start rotting the wood there. Think of a cold glass of water on a hot day. Moisture condenses on the cold glass. In the winter, moisture from inside the house can condense on the cold roof if no vapor barrier prevents it from getting there. In the same way, during summer, outside moisture can condense on the out-facing side of the interior walls if the house is kept cool. Venting the space between the walls provides airflow to help carry this moisture away.
Closed-cell polyurethane foam provides an automatic vapor barrier, though, so that moisture created by people breathing, taking showers, etc. inside the house can’t pass through to where it might eventually rot the wood sheathing.
In the next installment I’ll write about insulating the walls and how the results of my efforts paid off in the first winter.
p.s. Check out the following Builders Square animated How-to Tutorials associated with this post:
Climate Control: Installing a Soffit Vent
Climate Control: Installing a Ridge Vent
Climate Control: Insulating an Unfinished Attic
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