All houses need a strong foundation, but that’s not enough for a passive house. The whole envelope of the house needs to be insulated, and the foundation needs to do its part in keeping the heat in (or out).

Here’s a basic diagram of a slab foundation, with footings under the outside walls as well as the interior load-bearing walls. Without any insulation, heat will escape through the concrete slab.

Finally – our lot now has something other than dirt and a porta-potty: the concrete footings around the house have been poured!

It took some steps to get there. After the clay had been removed, that big hole had to be filled with good dirt, compacting it along the way. And some of the trenches had to be dug again.

The foundation has made significant progress. The rough plumbing was put in.

Then those trenches were covered back up.

New trenches were dug for the interior footings.

The forms for pouring the stem wall were completed.

The insulated foundation looks clean and simple on paper: 4 inches of insulation everywhere around the slab, making sure there’s no way for heat to escape from the concrete slab to either ground or stem wall without going through at least 4 inches of insulation. (That amount of insulation provides an R-value of about 20; 4 inches of concrete has an R-value of less than 1.)

When I arrived to check on the work in progress, the reality was not quite as simple, and would definitely not insulate as required. The stem wall is where the temperature differences are biggest, so that’s where the insulation matters most.

The slab was poured on Monday July 15, starting at 7 am. The whole operation went very smoothly. They were careful to push the insulation into place as the concrete was poured, to avoid the concrete flowing into cracks.

Moving the house a few feet westward paid off: the ready mix truck could get through on the east side and deliver concrete from the back, eliminating the extra cost of pumping the concrete.

The wall panels need a base plate to stand on. The base plate goes around the perimeter of the house – the red ring in the following image:

The base plate fulfills several functions:

• It moves the straw panels a few inches off the ground to protect them from any future water mishap.
• It’s firmly tied down to the concrete, and in turn gives a solid base to screw the panels into.
• It’s the first step in creating an airtight layer around the whole house.

In essence, the base plate consists of two support beams with insulation in-between. Underneath, a waterproof layer separates the wood from the concrete. Here’s an image of the base plate under construction:

After a long trip from Lithuania, the EcoCocon wall panels finally arrived at the site.

The panels consist of a load-bearing wood frame densely packed with straw (110 kg/m3, about 7 lb/ft3).

The panels are light enough to be moved by two (strong) people.

It’s amazing when you’ve been carrying a design around in your head for so long, and it finally gets realized. With the walls almost completed, I’m very happy to see the plans come to life.

Here’s the last beam being placed in the front.

The current state as seen from the hill.

And here it is as seen when you’re coming up the street. A few panels are still missing.

Lots of progress in the last week. The walls are now complete; the last panel was a very tight fit.

Interior walls

Meanwhile, the interior walls are being built: first assembled on the floor, then raised to vertical.

I was on a family trip to Norway and Portugal for two weeks. We got updates and handled some house questions while traveling, but it’s good to be back and see the progress with my own eyes. A lot has happened.

Roof

We have a roof! As the roof is at a low angle (4°), TPO works really well. We looked into a standing seam metal roof, but it would have been twice the cost, which was not worth it for a roof that’s mostly hidden.