About our frames cont'd: Our enclosure method

Roof

The roof is “built up” on site with materials from local suppliers.  Over the frame, V-groove sheathing, or the less modern tongue & groove (without the “V” ), is nailed over the timber rafters. This is covered with vapor barrier in an unbroken envelope, all seams taped, with a couple of feet hanging down to later be joined to the vapor barrier on the walls.

Next, rigid foam is applied in two staggered layers.  It is held down with horizontal 2x4s on 16’ centers, on top, nailed through the foam and into the timber rafters. On the gables the 2x4s are run out past to be chalklined and cut off to form the overhang.  The foam is installed in an unbroken envelope,  not pieced between other members like pink insulation in a stud wall.  Some foams, like P2000, have a foil vapour barrier with handy “sticky tape” overhangs to make an easy seal.

Another layer of 2x4’s are installed vertically, with the tails running out to form the eave overhang. This layer is much easier to put on as there now is handy 2x4 strapping to walk on.

The plywood or board sheathing is applied, then shingles, or steel roofing. If the latter is chosen, the sheathing can be foregone.
 
A roof insulated this way will perform much better than R-value “rules” would indicate.  The double air space created can breathe easily in all directions; around valleys and hips, from the soffit vents up to the ridge vents.

This air space seems to be the secret. The radiant floor in the Newcomb (link) is heated by an everyday electric 60-gallon hot water heater, bought new for $300.

It turns out that this roof system can be built more cheaply than factory-made roof panels, even with the extra time it takes to install. As all work is done on site, there are no unhappy surprises.

Walls:

We use an “out fill” stud system on the walls, with either 2x6s or 2x4s.  The contractor builds sections of walls the length of each bay which butt together on the back of the posts. These sections are framed like a normal wall with window and door openings, except there is no need for 2x10 headers,  just 2x6 to give something solid for the inside and outside trim. Remember, the timberframe is carrying all of the weight.  There is also no need for built up corners (drywall corners), so in the end, you use much less 2x stock than a conventional stud wall.  These wall sections are often built on the floor, and boomed off out of the way by us when we arrive with the frame.

The first step is to attach drywall to the outside of the frame. If it is a windy day, one wall is done at a time. The drywall is screwed to all of the timbers. This keeps it tight even after the timbers shrink. Next, vapor barrier is stapled to the outside of the frame, wrapping around the house and joining back at the beginning, and taped.  Remember the 2’ of vapor barrier hanging down from the roof?  That is now taped to the wall barrier. You now have a complete one piece vapor barrier over the whole house, in one step.

Next, the stud wall sections are installed from the outside and spiked to the frame.  Inside, the drywall is now screwed to the studs, keeping away from studs that are less than 6” from a beam.  This insures that the drywall will curve slightly as the beams shrink over time, leaving no gap.

The 2x6 walls can be filled with pink, or with blown in cellulose for a bit better performance.  If more insulation is required, we often add rigid foam to the outside in an unbroken envelope,  held on with 1x3 strapping on the outside to attach siding, while creating the important air space.

In the last few years, many clients have been using 2x4 walls with no pink, and installing the vapor barrier over the outside sheathing. Many are using P2000 1” “foil on foil” as it has its own foil barrier.

The manufacturers claim that this system, with the proper air space, will perform at the equivalent of R27 in a pink-filled stud wall.

This product has been around for a few years. There has been a little controversy about the R-value claims. So far, the only critics I have heard are competitors. I haven’t heard of an unhappy client.