Update on the Womelippi passive house project

Regular readers will know that I'm engaged in a personal experiment of sorts -- to see if an effective passive solar building can be built using common and local materials for around $20 or $30 a square foot using my own labor.

This is not actually a stand-alone building. It's an extension, essentially a new wing to our existing but very small farmhouse, which was listed as 1,250 square feet, but that includes the full porch, which is around 200. But it might as well be a stand-alone new building, for the purposes of experiment. It doesn't actually need to be connected to the main house to hold itself up, so the costs and construction specs are much the same as if it had been stand-alone.

I also plan to fit an air-sealed interior door between this building and the main house, to keep it isolated as far as air-space goes, purely for the purposes of experiment.

Here's a report of what went into the building so far:

The basic foundation used a small amount of concrete, around 300 bags of ready-mix and about 300 regular concrete blocks. This is about half the concrete that a regular foundation would have used, a savings made possible by the fact that the building sits on solid rock all around. It was then insulated with 2-inch Foamular ® closed cell styrofoam board insulation. This stuff releases HCFCs in production, but Foamular is one of the better brands. You have to use a closed cell foam for underground use. Open cell foam like urethane or polyisocyanate falls apart underground.

Here's the partially completed foundation, showing how little concrete was needed -- because this grade beam is pinned to solid complete rock.

Here's the completed concrete work, with the joist structure now on top.

This structure, like all the framing we'll do for this building, uses hemlock lumber grown and milled locally, produced by and purchased from Gerald Fowler's mill in Thorndike, Maine. This is one of the best sustainability features of the building.

Hemlock is a superior framing lumber overlooked by commercial operators because it's generally produced locally by small industry and so the lumber isn't "stamped", meaning it doesn't have the black stamping found on "big box" two by fours, and so hasn't been inspected: ie, that a large commercial lumber company did not produce it. Commercial contractors essentially can't use this material because building regulations and/or insurance companies require that stamped lumber. If the structure fails because of poor quality lumber the company that stamped it can be sued.

Obviously, I'm not a commercial operator, and there's no building regulation in Jackson, Maine that calls for the use of stamped lumber. I can use this material and reap the benefits. Apart from the fact that it's a local product and grown sustainably, in the sense that almost all the hemlock-producing woodlots in the north Waldo County area are logged on a very low-intensity basis -- we're adding to our forest cover here, mostly by abandoning farm fields, not reducing it as they are in many parts of the world -- it's also almost twice as strong as planed spruce or fir lumber of the same (nominal) dimension from the box stores and lumber yards. And all the money for lumber costs will go into the local economy.

Hemlock is also cheap. My 2 by 6 hemlock studs cost the same as 2 by 4 regular studs in the box store, but are probably three or four times as strong.

The floor decking used a commercial "engineered wood product", a tongue and groove subfloor panel made of 23/32 oriented strand board. Oriented strand board uses smaller trees to produce, which, although it means that plantations are grown on short rotation, also means that it's commercially viable to properly replant them. "Proper" plywood uses lamination and so requires big trees for veneer. OSB is more sustainable.

In this case this is not a local product -- this came from North Carolina, and was probably made from lumber from the southern forest plantations of Georgia, north Florida, and from the southern Appalachians. But I needed a product that could stand up to rain, because with only one of me working on the building, there was no way that I could get all the framing done and the roof on before normal plywood flooring warped. This material was rated for 100 days of wet weather.

Here's the finished foundation structure, showing the special decking, as well as the complete sheath of R10 Foamular ® foam board insulation that will insulate and air-seal the basement.

Once the foundation and joist work was done, we could move to framing. Again, we're using local hemlock lumber. We're using 2 by 6 inch material, instead of 2 by 4, which will allow for an addition thickness of stud bay insulation. We're also using recycled foam board insulation, bought from the Unity Amish community, as an additional layer on the outside, glued at the edges for air-sealing.

That requires the use of let-in cross-braces, since the foam board must lie under the sheathing, because we plan to use local cedar shingles. (You can't nail shingles to foam board.)

The alternative would be to use the sheathing itself directly over the studs, which would provide cross-bracing, and then add a "nailer" of additional plywood or OSB over the foam board, which is wasteful. The let-in or inset cross bracing requires a little more skill from a carpenter -- you have to know how to properly use a chisel to cut a traditional joint! Heaven forbid!

But that's enough to prevent this technique from being used on almost all commercial construction sites, and so foam board insulation is rarely added to a stud wall, even though it is needed to get the insulation up to super-insulated levels.

Just for the record, the contractor that generally builds the college's buildings, alum Joe Bellerose, uses a steel let-in cross brace system, which allows all the campus buildings to be super-insulated with additional foam board insulation under the sheathing.

In this case we'll finish up with R19 fiberglass in the stud bays and 1.5 inch polyisocyanate foam board insulation under the sheathing, a total of R28, plus an inch or so of shingles, sheathing, and drywall, making an R30 wall. This is less than would be required for passive house certification, but more than 50% more than is required for Maine code. With superior air-sealing and two feet of cellulose insulation in the attic crawl spaces, we'll have a very warm, tight building here when we get done.

Here's the hemlock framing work partially complete. Weather permitting, it will be all done by next weekend. I'd like to get a roof over this building quickly if I can. I don't trust that subfloor to hold up under all the wet weather we're having.

But of course, if it continues to rain as much as it has, I may not be able to work!

There's an element of luck in any project.

For more details at any point, go to the farm blog at www.womerlippi.blogspot.comwww.womerlippi.blogspot.com