Chainsaw Retrofit - Energy Efficiency Renovation
Most of the work to date has been focused on updating the home's services, layout, and amenity. While the new HVAC systems (Combi Boiler & HRV) offer industry leading energy efficiency, the real energy savings come from upgrading the home's building envelope. For comparison, the new HVAC likely reduces consumption by ~20% over the old furnace/hot water tank, while the envelope upgrade will reduce consumption by an additional 60%. Overall, we're targeting an 80% reduction in energy consumption.
Our exterior work gives credence to the Saskatchewan pioneers, Harold Orr & Rob Dumont, and could be described as a Chainsaw Retrofit. The idea is to strip the home down to roof & wall sheathing, and cut off the roof eaves so that you have a smooth surface to work with. You then apply a continuous poly air/vapor barrier over the entire surface, sealing it to the exterior foundation wall. This poly is followed by copious amounts of insulation, supported by framing, new sheathing, and then new roofing/siding.
For our project, we're targeting R10 slab, R40 walls, and R60 roof. Our Duxton windows are R8.3 cog, with fibreglass frames. The old envelope was R2 slab, R12 walls, R12 roof, and R1 windows. To achieve an R40 wall, we're building out a 2x4 stud that sits 3.5" offset the sheathing, supported by the rafter eave and by a ledger bolted onto the foundation wall. This gives us 3 x 3.5" Roxul batt, nominal R42, and roughly R40 effective. For the roof, we're adding 12" TJI purloins + new 3.5" rafters, which supports 5.5"+3.5"+3.5" Roxul batt, leaving a 2" venting space. Add in the 3.5" Roxul batt in the original rafters, and we have 16" Roxul for R64 nominal, and roughly R60 effective. Our window detail involves a plywood buck box with sloped sill, Prosoco FastFlash to waterproof the sill, followed by a metal sill plate and Hardie trim. We have a primary air/vapor/weather barrier at the poly level, and then a secondary barrier at the Tyvek/shingle level on the new exterior sheathing level. Belt AND Suspenders!
We started with the wall stucco demo, and then had a volunteer roofing bee with Peter Amerongen, Dave Butterwick, Jamie Davis, and Vince Tsang. Over a weekend, we stripped the shingles, cut off the eaves, got the roof poly down, and the new 12" TJI's installed. We cut off the old chimneys at this point as well, and carried the poly over top. Huge thanks to the guys for their help with this!
Shortly after this, Meg and I got the news that Baby Fix is on the way, so we decided to fast track this exterior work.
We hired Dave Butterwick's crew, www.Butterwick.ca, to handle this scope of work. We've rounded out the retrofit with a new cedar front porch, which gives credence to the old front overhang, which giving us a bit of deck space on the South. Butterwick did a great job, I highly recommend them!