Earlier in the year, I discussed the idea of “replacing concrete with wood” in our pier and beam foundation design. For the construction of our timber frame house, we decided to go high and dry, and eliminate as much concrete as possible with this style foundation. I wanted to take this opportunity to go more in-depth about the plans for our pier and beam foundation, with a bunch of images to illustrate the design.
Read ahead more for details.
Pier and Beam Foundation Construction
We used very heavy material in our foundation, because of the weight of the house. A timber frame with straw bale walls (and plaster), and a living roof is quite a bit of weight, and the foundation reflects that. Here is a checklist of the size of pieces we used:
- 8×12 sill beams (longest single span = 16 feet, longest span with scarf joint = 26 feet)
- 3×10 floor joists (16 foot span)
- 3×10 rim joists
- 8×10 floor beams (just two of these in strategic locations)
We used white oak for all of the beams, because of course the wood is somewhat exposed to the elements, and white oak is highly rot-resistant. I doubt most of it will ever get wet or even damp, but better to be safe than sorry in these situations.
You can read about the details of planning and pouring our concrete piers here, if you’re interested to know more about that process.
Before placing any of the beams into position, we snapped lines on the concrete piers to determine exactly where the beams would fall. Thankfully, we did a fairly good job of locating the piers and there were no major mistakes in locating any beams.
Placing the Beams
The first thing to go in place, of course, were the perimeter beams, a relatively straightforward process. There were two scarf joints, one on each side of the long axis of the building, both of which were located right above a pier. In these cases, the beams were dropped into place, and later pegged.
As you can imagine, a 16′ white oak 8×12 takes a lot of muscle to move into place. That’s over 600 pounds of green wood!
Of course, we like to make things complicated. Why settle for a square house when you can have half of an octagon on one side? These 45° angles required some tricky cuts, with a half lap joint. They were somewhat difficult to fit, since the joinery was extremely tight, and we had to simultaneously drop the scarf joint in place with the half lap. No small trick!
It was a real treat once we squeezed the pieces together, though, and we were especially pleased that nearly every beam was perfectly level.
Floor Insulation Joists
The floor joists in the main portion of the house are not dovetailed, but simply lay on edge over the perimeter beams, 24″ on center, and cantilever a full 18″ to support the straw bale walls. We toe-screwed the joists, and spike nailed a rim joist to the outside faces. (Yes, we used some hardware in this case.)
Also, because we took this approach, we had a whopping 22″ cavity under the (future) floor that could be later insulated. So before we actually laid the floor joists in position, we installed a series of insulation joists, or 2x6s mounted on joist hangers, on the bottom end of the perimeter beam. We would later installed recycled roofing metal on the underside of these 2x6s to contain blown-in cellulose for insulation.
Finally, we installed the floor joists, checked for level and made some small corrections in the necessary locations, and spike nailed (with 6″ landscape nails) our rim joists in place.
On the north porch, we let in the floor joists in shallow pockets in the 8×12 beam, since the floor here would not be insulated, and not hold nearly as much weight as it would indoors.
There ya have it.