The Kingston Passive House team has had a busy (and very toasty!) 3 weeks. There was not as much soil as we were hoping for, so we opted to hammer through the top 14″ layer of limestone (subsequent layers are much harder) and resigned ourselves to the fact that Kingston Passive House will just have to sit a bit higher on the lot. One benefit of the increased elevation is the basement floor will be higher than the sewer and storm laterals – no sewage-ejector required for the basement bathroom rough-in!
Since the house sits on bedrock, we also reduced the footing and pad sizes; we used less concrete and lowered the house by another couple of inches as a result. The “blue” you see on the footings is a capillary break. Although the Permanent Wood Foundation (PWF) SIPs are designed to function in a moist environment, we still want to keep them as dry as possible. The stepped footing in the back is for the garage; no need to pound through rock for that. Here you see the first four SIP sections are in place… the beginning of a very well insulated home. The water-filled hole is for the sump pump and tank. If you look closely (click on the image for a better view) you can make out the six PVC conduit sections through the footing at the back. These are for the three loops of 3/4″ PEX that will make up our Subsoil Heat Exchanger (SHX). The pipes will exit the house, and travel around the perimeter of both the garage and house before coming back in. You might also notice the footing extensions; A SIP can not handle a concentrated load (such as the end of a beam) so you can either carve out insulation and embed a post in the wall, or place the posts right beside the wall and avoid creating a thermal bridge.
This next photo shows our hemlock posts in place.
They sit on a galvanized steel saddle to keep them secure. The saddles also act as a capillary break between the hemlock and the concrete footing. Why hemlock? Placing 9 hollow steel posts through the basement floor and sub-slab insulation would represent a significant thermal bridge. The wood posts will not conduct heat energy into the ground to the same extent as steel. You could also argue that wood posts have a lot more character than steel. Even the offcuts were destined for a higher purpose; inspiring the crew to create “Hemlockhenge”.
The piles of recycled EPS are only half of what is required for sub-slab insulation. There will be two layers (ten inches total) below the concrete slab. Radiant heat would be overkill in this house, so the only thing in the slab will be some reinforcing steel.
This final picture shows the open web floor joists. They span greater distances than dimensional lumber and will allow us to run services in any direction within the floor cavity. Being an engineered product, they are also more consistent in terms of being straight and do not have to be overlapped at the beams, making subfloor installation that much easier: