The first part of the house framing that is unusual, is the roof structure. Instead of setting the trusses directly on the second floor framing a roof deck is established; essentially a lightweight floor structure framed from 2x8's. All the seams in the sheathing are sealed with a tape from the SIGA company designed for this purpose. This additional deck simplifies the air sealing of the house by removing the framing connection between the trusses and the second floor framing.
The trusses go up normally, except you have a nice solid deck to move around on! You may note the energy heels on the trusses in the right hand photo.
Now begins the key to this homes extreme energy efficiency: the Larsen truss! A Larsen truss allows a large insulation space with a minimal amount of thermal bridging, In this case an additional 12" beyond the 2x4 structural wall. You can see the SIGA tape is used for sealing just as in the roof system.
Work here continues, and we will update this page as new photos become available.
On the left the exterior sheathing nears completion. You can see the completed rain screen on the adjacent wall in the photo. The center photo shows the air sealing of the window opening and on the right the water dam installed on the sill.
The windows are installed with interior brackets. With no nailing flange we are using a two-step weather sealing process. The secondary seal is created with a foam backer rod followed by silicone caulking. On the right are the first three windows in place in the rain screen wall
The crew from the solar company arrived last week and installed the solar-thermal panels on the roof. (First two photos) This week they have returned to begin work on installing the Photovoltaic (PV) panels. The third photo shows them installing the mounting rails on the roof. You can also see we have finished installing all the southern glazing as well.
The crew continues work today installing the PV panels. The center photo shows the passage of the solar water pipes through the attic/house interface. So far this is the only attic penetration of the building envelope.
Our insulaters arrved today. They are here to insulate the Larsen truss wall. Because of the size of the bays to fill (12" x 24" x20' ) they showed up with two blowers in stead of the single they normally use. The photo right shows the view down the larsen truss from the attic to the first floor level.
A short video of the process to insulate the Larsens.
The next day we set up for an initial test of airtightness, a key element of Passive House design. We found the house was already so tight at this "framing only" stage that we were unable to use my blower door and needed to use a duct blaster instead. Duct blasters arenormally only used for pressurizing a duct system, not an entire house!
Passive House requires that the completed home has a final measurement of .6 ACH @50p. This means that at 50 Pascals of pressure (equal to a 20mph wind blowing on all sides of a building simultainiously) the house can only lose 6/10th of it's air in one hour. A standard completed house would commonly have a number 20 times this high! Our initial numbers were 1.04 pressureized and .66 de-pressurized. This showed we still had some work to do. The leaks we went for first were the windows as they are the major penetrations in the shell.
The brackets used to mount the windows created both a difficult area to seal as well as requiring the rough opening (RO) to be shimmed 1/2" before the drywall would fit. We solved both problems by laying in a heavy bead of caulk between the window and the R.O. and pressing a piece of 1/2" foam board into the joint seal it. The metal brackets were then filled with expanding foam and sealed with Siga tape.
After the window work and some other minor air-sealing the air tightness test was redone.
Our new numbers are .59ACH for depressurizing, and .34 for pressurizing!
After finishing the air sealing, we began work on the three season room and utility space to the rear. This space will be connected to the house by an covered breezeway. After leveling the site and installing a weed barrier fabric and gravel, 6x6 posts were installed on the existing piers. Framing was built on the piers (photo left). 1/4" cedar plwood is wrapped with two layers of chicken wire to deter animals, and installed between the joists. (center photo) Finally, the same high-density foam used for the slab is installed between the joists.
Because of the extreme tightness of the house, controlled air exchange is required. A Heat Recovery Ventilator (HRV) is installed to insure healthy indoor air quality. This HRV removes air from the bathrooms and kitchen and exhausts it to the exterior while transferring its latent heat to the incoming fresh air. This HRV is 92% efficient!
The main HRV unit is mounted in the back of a small closet (left). Both exhaust and fresh incoming air is moved through flexible pipe placed in the ceiling (center). The air connects to the living spaces through individual ports (right).
The biggest bypasses through the air envelope are the data and power cables traveling from the house to the main panel located in the storage room. Once all the lines were run through the access conduit I installed expanding foam into the center of the conduit run with an with foot long nozzle on the foam application gun. Once the foam had fully hardened silicone sealant was forced into the cable bundle starting in the center and working out. While wearing gloves I worked the sealant into all the spaces between the separate lines. After 24 hrs. for the silicone to cure the entire joist bay was then was then filled with a two-part high-expanding foam. The drywall was then able to be installed. Elsewhere, the insulaters were back and installed dense-pack cellulose into all the structural 2x4 walls. The walls for the interior bedroom walls were also filled to help with sound transmission.
The finishers came to complete the concrete on the first floor. The concrete is being given a "polished" finished. This is the basically the same as terrazzo. The concrete mix was specified with river stone for the aggragate giving a final finish as shown at right.
Doug Hurth is doing our drywall, and doing a great job. There are several unusual aspects to the sheetrock: All the drywall is 5/8" instead of 1/2, this allows for the 2 foot spacing of the framing as well as helping keep noise levels down between rooms. In addition to the depth of the window surrounds Doug also had to finish the small clerestory windows abve the upstair doors. These were
installed to allow daylighting for the interior hallway. Finally, since the upstairs ceiling was dropped to allow for all the HRV piping he had to rip drywall sheets to fit the less than 8' wall height.
Siding begins with installing our primary water seal for the windows. We take metal flashing and apply a bead of silicone along one side and press that into the edge of the window frame. The exterior trim is then installed and caulked as normal.
At the bottom of the wall we install vent strips between the rain screen nailers. This will allow plenty of air movement behind the siding but help keep bugs out. At butt joints in the field a piece of roofing underlayment is installed to keep wind driven water on the surface of the wall.
Above we see Dan Johnson installing the last piece of exterior siding! In addition to finishing the siding, the shade arbor and entry porch (right side of center photo) have also been completed. The shade arbor (right photo) Is designed at a height and depth for this lattitude that will allow full sun into the house during the depth of winter when we need heat, and near full shade at the height of summer when cooling is the issue.
The roof of the entry porch has been fully lined with a rubber roof that drains to the back corner (away from the house). The roof is going to have a drainage mat installed under soil that will be planted for a living roof. The interior 3-season room has been completed as well (photo right). The 3-season room is covered in the same ship-lap siding as the exterior but with a natural clear finish instead of stain.
The upstairs sink turned out to be too large to fit in the upstairs cabinet and counter. As a result it fell to me to enlarge the existing cabinet and build a new counter in order to mount the sink for the plumber. It all worked out well in the end.
The house reaches completion and the owners are moving in next week. Following are a series of photos of the completed interiors, starting with the three season room
The three season room - Sleeping loft and main sitting area
Large southern windows are a major heating source
Living room -west S.E. Bedroom S.W. Bedroom
S.W Bedroom showing sleeping alcove and HRV unit in back of closet
S.E. Bedroom closet above and additional storage behind door.
Linen Closet with laundry hamper behind large door below
Main floor, looking toward kitchen. Seating bench for dining table has storage below and, when needed, opens....