Progress on Net Zero Home in Fairfax

Weather has been a killer, but we are finally out of the ground, and framing lumber is onsite and ready to go up. This spring has had the longest stretch of rainy days since the 1880’s, which has been great for my garden and our trees, but not so good for excavation and the pouring of concrete. Here are photos of progress to date..

DSCF4709 The site, cleared and with excavation equipment ready.

DSCF4712 Excavation work in progress.


DSCF4918  A dry day with footings in place. On this project we used our standard high density eps foam footings over a mudslab. At sides and top of footings, however, we used 2 layers of 2″ Roxul Comfortbat CIS mineral wool.

DSCF4922 Note the waviness of the sides of the footings. We used rebar set into the ground to hold the side insulation in place to work as our formwork. Whereas a foam would have withstood the pressure, the mineral wool, less stiff, gave way to the pressure.

DSCF4920 It was also difficult to keep the mineral wool in place after pouring, as this picture shows.

DSCF4935 Here you can see the high density EPS sitting on the mudslab. We ran it out 4″ past the edge of the concrete to provide a base for the mineral wool at the sides.

DSCF4939 April 5th. Formwork now in place.


DSCF4952 Note the haunches that will carry the slab under the front entry stone.

IMG_5786 April 18. Formwork is down. Ready for waterproofing.

DSCF4982 Footings may be wavy, but the walls are true!

DSCF4963 The mineral wool did not stand up well to the setting up and taking down of forms. Much was knocked loose and abraded. We had to come back later and replace some, and fill gaps with canned foam. This is an example of the damage.

IMG_6690Foam enclosure around sump crock.  Where before we had a circular piece of foam made up to wrap the crock, we found it easier to make a simple box and then fill in with gravel behind after setting crock.

IMG_6678 A mountain of 4″ EPS foam waiting to go under the slab. Our intention was to use Roxul Comfortbats, which have a much lower global warming potential (GWP). While it has been widely used under slabs in Canada and Europe, because Roxul has not produced an ICC report for that application the city wouldn’t allow it. We resorted to the foam we have used on our past PH projects.

DSCF5037 May 5. Carlisle MiraSeal waterproofing in place. This is amazing stuff. Great bonding to the concrete, tough and flexible.

DSCF5029 A wall penetration. No need for any further sealing after using the MiraSeal!

DSCF5024 The entire underground insulation and wall drainage system is being installed by Aird, Inc. The also did the Sto EIFS system on our Rockville passive house. Rob Aird has been a great partner in the planning and construction of these houses. Here the Aird crew is installing the second 2″ layer of the Comfortbats. Note the staggering of the joints to prevent air gaps that would reduce thermal performance. Notice  also all the cans of glue and adhesives lying on the ground. This stuff is hard to hold in place and doesn’t adhere well to much of anything. In the end they used Liquid Nails to adhere to the Carlisle MiraSeal and Carlisle Hardcast Travel Tack spray adhesive to adhere the two layers of insulation.

DSCF5026 The southeast corner, with mineral wool application in progress.

DSCF4992 Izumi, David and Matt on a site visit.