Sill Plates

Last week we installed the sill plates, which are the base for the frame that will support the roof. The straw bales themselves are not weight bearing in this particular structure, although there are straw bale buildings where the bales are the structural support as well as the insulation. I am sure that it can be done, however there is the worry of compression. That is why Mark is building a frame, and why we install the sill plates.

Here is a drawing of the whole set up.

A cross-section of the foundation and wall structure.
Drawing by Mark Rogers

The sill plates are kind of hard to see. They are represented by the rectangle with an "x" that is connected to the j-bolts, which are the smaller, j-shaped hardware that stick into the foundation. As you can see from the drawing, the sill plates and the frame will be closer to the inside of the thick walls, supporting the roof with a post and beam system. The insulation will go between the stone wall and the frame of the house. The straw bales, when we get to that stage of the construction, will have to be cut out to fit around the beams. 

Instal ling the sill plates was challenging, but there is a trick. I hope Mark won't mind me sharing it. :)

Sill Plate installation

The first step was to measure 19 inches in from each edge of the foundation and mark that with a chalk line. This is about the thickness of the wall, though it may extend farther into the interior space when the plaster is applied. You can see the blue chalk line a little bit in this picture. The j-bolts were installed already, when the foundation was poured. The challenge, then, is to drill the holes exactly where they need to be in order for the plate to sit right along the edge of the blue line, since the bolts are not placed at exact, regular intervals. 

The next step is to set the plate parallel to the blue line, behind the j-bolts, by measuring and equal distance on both ends. This will ensure that the following measurements are accurate. Then, using a rafter square... 

Rafter Square
from www.irwin.com

we drew two lines, one on either side of the bolt (which you can see in the photo). The lip of the square would go on the far edge of the sill plate and keep the line square. The bolt would go in the middle, between these two lines.

The next measurement is from the blue line to the middle of the j-bolt. Then we measured that same distance from the bottom edge of the sill plate to determine where to drill the hole. There was always a bit of anticipation after drilling the holes and checking to see if the plate will fit over the bolts. Mark let me install 3 plates by myself, and I got pretty good at it by the end, if I do say so myself. Its a shame they are all finished now!

The last step is to put a layer of tar paper on the underside of the sill plate. Wood and masonry (concrete) are generally not supposed to touch, so it just adds a layer of protection. You can see a little bit of it sticking out at the corner in this picture. It doesn't have to be exact since it won't be seen. 

The sill plates I installed. All by myself!

The next step in the process will be to add foam insulation to the outer vertical edge of the foundation. This will ensure that the insulated envelope around the whole house will be complete and there will be no heat leaks. Then, we will install flashing to protect the foam from wheel barrows.

That's all for now! 

Laying the Foundations

This spring, I am very fortunate to have the opportunity to work with a natural builder on his very own straw bale house. Mark Rogers is one of a few builders in the area, with experience in stone masonry as well as straw bale construction, and he has graciously allowed me to tag along and "help" (learn) from him through the process.

I met Mark towards the end of last summer (2014), when he was in the process of pouring the concrete foundation for his small house. It is about 1000 sq ft, not counting a second story loft, and the floating slab foundation serves as the floor of the interior space. Here is a quick diagram of a basic floating slab foundation, though there are several variations. 

Image from:
http://www.barntoolbox.com/foundation-types.htm

Mark's foundation is a little different. There is not only rebar in the thicker portions that will support the walls, but there is also welded wire reinforcement throughout the slab. The concrete is also completely insulated with 5 inches of foam insulation underneath. This way, he can take advantage of the foundation/floor's thermal mass. He has also put in a radiant floor heating system, which will run hot water through small pipes embedded in the concrete and heat the floor. That will be super cozy and nice during the winter. Here are some pictures of the form before the concrete was poured. 

Another thing that is different about Mark's foundation is that there are a few dozen pieces of rebar sticking up about 3 feet high all around the edge of the slab. This is a picture of the slab covered for the winter. Mark used straw and foam insulation underneath a sheet of plastic to help protect the concrete from thermal stress and the elements. You can see here the rebar I was talking about. These rebar posts are anchored into the concrete slab and will serve to anchor the stone wall that will lie underneath the straw bales. 

There are a few advantages to having a stone wall. Not only will it be very beautiful when completed, but the stone wall will raise the straw bale up from the ground and protect it from water damage. Plaster often gets worn away by the splash of rain water falling off the eaves of the roof. It seems minor, but years of splash can really damage the plaster and straw bale. 

Hopefully I will figure out a way to scan and upload some of the technical drawings to illustrate the plan for the next stages of construction. I'll keep you posted!