Century-old houses have their charms, but energy efficiency is not one of them. They were built using a different heating philosophy than we use today. Back then, houses had no real thermal barrier (therefore cold) or air barrier (drafty). Instead, folks stoked up the stoves and fireplaces and the heat would pour out every window and crack in the building envelope. When they reached a point where the massive heat production exceeded the massive heat loss, the house became relatively comfortable. Not a bad system when fuel is cheap and plentiful. When fuel costs started causing pain in the early ’70s and that cartoon of dollar bills flying out the window became popular, insulation started making sense.
Unfortunately, my place had not evolved to the point of insulation and was still in pre-oil-embargo condition. There is evidence of three stoves and two fireplaces in five rooms covering less than 660 sq ft. That’s a lot of BTUs to make up for a lot of heat loss. Given that the insulation value of a 12-inch brick wall is about R4, it is understandable why they needed so much heat even with unexposed sidewalls. These days the fireplaces are blocked up, the stoves have all been removed and the space heating is provided by electric baseboards. Not my ideal heat source, but there really is no room anywhere for a furnace of any sort. I decided to stick with electric heat but air seal and insulate so the energy demand is significantly reduced. As my grad school supervisor was fond of saying about well designed building enclosures, “You could heat that with a fart!”
I knew I had to insulate, but what are the options for insulating a solid brick wall? The best way to insulate any building is on the exterior, a nice continuous blanket covering it like a big old down parka. Of course you have to protect the insulation with some type of cladding like clapboards, vinyl siding, metal panels, etc. (You know I would never, but just bear with me.) The brick will stay warm and protected from the elements and actually store heat to help moderate interior temperature swings, thereby reducing overall heating energy. Awesome, right? Well no, it turns out most people are not down with destroying the character defining element of a brick exterior. I am not either, but in some projects this approach would definitely make sense. Such as a non-heritage building of dubious brick quality. Since this is a Heritage property, exterior insulation is OOTQ – out of the question. (I have been using the phrase OOTQ a lot lately so I have deemed it acronym-worthy.)
Ok then, interior insulation it is. The front and back walls, the roof and pretty much the entire bathroom except the floor. I already mentioned my unvented roof strategy, the wall strategy is similar but there are some different considerations since we are insulating brick rather than wood. One would think the goal is to maximize wall insulation, but with brick too much insulation could cause problems. Interior insulation means the wall is colder throughout the winter because less heat is escaping. If the wall gets wet and the exterior temperatures go through a few freeze-thaw cycles, not at all OOTQ here in Halifax, then the brick could become permanently damaged. As in crumble to bits and fall out of the wall. A problem, you could say. That is a severe outcome and it requires a perfect storm of factors lining up – like crappy cold brick exposed to lots of rain to the point of saturation while the temperature hovers around freezing. Unlikely, but not impossible. How much rain on average does Halifax get every year? More than Vancouver.
However, the brick is fairly intact after 110 years of simultaneous wet and cold weather, so I am not so worried about those uncontrollable factors. What I can control is keeping the bulk water off the wall by making sure the eavestroughs and downspouts are in good repair. The only other factor I can control is how much heat escapes into the wall. I want to insulate it, but not too much or else it will be too cold. The code requirement for new construction is R24, but I don’t have to meet that. I am going to go with R12 of insulation which would be equivalent to the R-value of fibreglass in a 2×4 stud wall. All told, the wall assembly including the brick, the drywall and the cavity airspace will total R17.
I could get into the gory details of this decision, but I will cut to the chase and say I decided to go with two inches of closed cell spray polyurethane foam (ccSPF) on the walls. Spray foam is a magical product that is perfect for this type of project. It provides excellent thermal insulation, R6 per inch, one of the highest available. It eliminates air leakage and reduces vapour diffusion, all while forming a continuous covering that adheres tenaciously to the irregular cavities and surfaces of the roof and wall framing. ‘Nuff said. If you want my long-winded story of why I am a SPF believer, you can read about it here. If you want a much shorter story about interior insulation on brick, John Straube et al explain it nicely in this article.
With that, the guys from Trinity Maintenance Solutions arrived yesterday with their truck full of magic and 10 hours later, ta-dah! I cannot believe how warm it is in there already. Some before and after pics: