Framing this week has been productive. We deferred setting the trusses until next week to be sure we have all of the details right. Of particular concern is the air seal of the building envelope. This is a continuous layer that will serve to prevent air infiltration. In this building it will occur at the plywood sheathing on the walls and at the ceiling. Partly due to the weight of the attic insulation, we are installing a plywood ceiling (“lid” in construction lingo) where we will tape all of the construction joints.
To be certain we have an air tight seal, we have extended this layer to the outside wall. The design of the lid becomes the cap for the double wall system, and the trusses then also bear on top of the lid at the outside wall. The strip was installed with a wide enough rip of plywood to close off the top of the wall, tie the two walls together, and provide a seam far enough away from the wall that when we install the tape seal we will not scrape our knuckles on the wall during the installation.
Window headers are normally doubled up 2 x 12 boards with a sandwich layer of plywood to match the width of the wall and so that the header height matches the door heights. The headers noted in the picture are engineered plywood laminated beams that are furnished in increments designed to minimize waste. With this engineered header we only need one piece allowing more insulation in the wall cavity, however we need to fill in above the header to provide adequate bearing to the top plate.
Under the exterior wall we have installed a sill sealer that is a 3" wide rubber strip with two ½” bulbs one each side to prevent air infiltration. Typical sill sealer is closed cell foam that does not have the compressive qualities of this product. When we test the building envelope for air tightness with a blower door test and a smoke machine, we will see how effective this strategy will be. This close-up picture of the seal shows the profile which is placed under the main bearing wall.
In this detail you can see the plywood we have added to the window frames to prevent the insulation from falling out of the wall before the drywall is installed. It served to stiffen the wall during the construction process, and will provide a surface area for the drywall to fasten to after the windows are installed.
The boring rig for the heat pump had difficulty getting through a layer of boulders that begins about four feet below the grade. Once they got through that, they spent nearly two days boring the better part of two – two hundred foot loops at depths of 12 to 18 feet for the closed loop hydronic heating system before their hydraulic rig broke down. The hydraulic head is in for repairs and they expect to be back on Friday to finish up the job.
We deferred the excavation due to all of the activity on the site and will get that started next week as well. The completion of the site concrete is contingent on getting the grading done around the house. We need the sidewalks poured if we are going to get an occupancy permit which we are anticipating in late January. It is very hazardous to pour concrete this time of year, and few contractors will warrant work done after Nov 15. We go at risk on this knowing the potential problems.
It is gratifying to begin to see the views we had hoped to capture through the windows framed in lumber. Manifesting your vision is no simple task even with all of the skill and resources we have available. Drawings and the assistance of 3D modeling can only take you so far in the process. We staked out the building in the field and marked out the views, then moved the building on the site to optimize for solar radiation and views. It will take at least a year to determine if all of our expectations will have been met.
The trusses in the background should be up in the air for next week's entry. The plywood is covering a window temporarily to brace the corner during the installation of the trusses. Next week will be a big one.
