Sheathing

Nothing But the Roof

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A Yestermorrow semester program built an apartment property for Jas. In a win-win arrangement, Yestermorrow students gained real-life skills in design and carpentry, while Jas got free labor. Unfortunately, the class ended this week and the students left the house incomplete. Jas hopes to at least get a cover on the roof before winter sets in.

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The 400-square-foot apartment one week before end of semester.

So I found a free afternoon to get started. As soon as the Yestermorrow class finished installing roof rafters, I joined Allen to begin sheathing the north side. The tasks were familiar: start in a bottom corner, use tongue-and-groove Advantech with the tongue pointed downhill, install sheets so they break in the middle of a rafter. We snapped a chalk line across the rafters to align the top edge of the first 48-inch-wide sheet, wanting a bottom overhang of 1.5 inches. Then we cut the first sheet of Advantech with a circular saw to trim the length for a ¾-inch outside overhang. Once the first one is in place, the rest follow smoothly.

Several characteristics of this project were unique. The rafters are 16 inches on center, which leaves too narrow a space to pass a 96-inch-long sheet out without endangering someone’s safety. Therefore we raised the Advantech from below, with Allen and I sliding each sheet up a pair of ladders before ascending ourselves. The other concern was the location of the rafters in space – alignment is always a concern when you inherit a project from somebody else. The sheathing must stay in one plane so the finished roof doesn’t look wavy, and it should bear on every rafter for structural reasons. I used a long skinny half-inch-thick piece of Advantech to shim out one rafter that sat a half-inch low, sliding and squeezing it between the lumber and the sheathing.

Allen and I lift the sheathing…
…and align it on the rafters.

Jas and Allen soon completed the north side of the roof with Advantech, and then I helped sheath the south side using salvaged T-1-11 siding from the shed removal. It’s a race against the clock to get the sheathing installed and covered with Ice & Water Shield before the weather gets too cold and snowy to work safely. (People do it, but I’m no fan of outdoor construction in the winter.)

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Jas installs a safety harness system to finish the south side with T-1-11 sheathing.

Roofless

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Sunshine and highs above 50… it didn’t take much to get us outdoors, where we started on the long-awaited project of removing and replacing Bob’s roof.

We began by building a scaffold around back. The scaffold components fit together like very heavy K’nex, with pins between vertical sections and x-braces for lateral stability. Two platforms sandwich a ladder, and some deep planks span across the lower roof to a third platform. Together they give us a place to stand along the full length of the dormer eave 15 feet above ground level.

The scaffold is a lot of fun to climb.

The scaffold is a lot of fun to climb.

The old roof was standing-seam aluminum, attached via hidden clips to the plywood below. With no need to puncture the metal, these clips were key to the water-tightness of the roof. Not that it did much good: the plywood was completely rotten and we were careful to step only on the rafters. Everything came off! For a couple glorious hours the home interior was bathed in sunlight, a lid off a jar.

But with rain in the forecast overnight, we needed to install a new lid quickly. We built it out of Advantech, same as Colin’s house. I have a bad habit of calling this stuff “plywood,” but strictly speaking Advantech is something else. It’s an engineered panel made from wood strands and resin pressed together under heat. 10½ sheets of 4-by-8-foot Advantech nicely covered the 12-by-30-foot dormer roof, and with ring shanks in the nail gun and a bead of adhesive on every rafter the crew resheathed the roof well before sunset.

Advantech sheathes the roof. Great view of Sugarbush.

Advantech sheathes the roof. Great view of Sugarbush.

The old roof sagged quite a bit at the eave. While the rafters were exposed, Mark pulled a string across the edge and cut shims to fill in the sag. The new sheathing follows a nice straight line at the eave, and for our next step we installed fascia across this line. Directly in the path of water coming off the roof, the fascia is extremely vulnerable to rot, so Bob chose a plastic product called KLEER with an imprinted wood grain. It looks like painted lumber and cuts as easily, but it requires no maintenance. It’s also as floppy as a stick of string cheese.

KLEER installed - the white woodlike material around the upper eave.

KLEER installed – the white woodlike material around the upper eave.

Hans and I held up the 1×12 KLEER to run straight along the eave and took turns with the drill to secure each piece of fascia. We used finish screws with threads that run both clockwise and counterclockwise on the same shank. This innovation helps squeeze the fascia to the lumber behind, but it’s a huge pain to remove a screw once it’s in… so we try to get it right the first time.

Tarp on for a rainy night.

Tarp on for a rainy night.

Sealing the Ceiling

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It was pretty easy to make the walls airtight. Zip-Systems sheathing around the exterior, Zip-Tape on the joints, foam to plug every incidental hole. The ceiling is much more difficult because we must think in three dimensions to seal “inside” the house entirely from “outside” the house.

From an HVAC perspective, the attic is “outside” the house. We’ll install a thick layer of blow-in insulation directly above the second-floor ceiling to match the R-value of the house’s 12-inch-thick double walls, and the ceiling drywall will serve as the air barrier. To join the ceiling drywall to the Zip-Systems sheathing, we included an overhanging 16-inch-wide plywood nailer around the perimeter back when we built the exterior walls, as you may recall. Since the nailer fits between the walls and the roof trusses, it leaves a 1/2-inch gap between the ceiling drywall and the truss bottom chords. And if we can’t nail the drywall to the trusses, we need some other way to support the ceiling in the middle of a room.

The colorful parts of this diagram constitute our air-seal system.

The colorful parts of this diagram constitute our air-seal system.

Don’t worry if that last paragraph confuses you… it took a long time for me to get it, too. The important thing for construction is that we need strapping above the second floor so we have a place to nail the ceiling drywall. Slowly but surely, Carson and I are installing 2-1/2-inch-by-1/2-inch straps across each second-floor room, spaced 16 inches on center measuring from the insulating stud walls. Carson made a guide by marking 16-inch intervals on a scrap piece of strapping, and I can hold up the guide to a truss bottom chord to mark where I should align each strap. Then we cut the materials to length and attach them with sheathing nails. Lots of working above our heads, standing on stepstools and ladders, eyes pointed skyward. The strapping fills in that 1/2-inch gap I mentioned, and the regular spacing will inform us where to nail the drywall when we reach that step.

Strapping, spaced 16 inches on center above the master bedroom.

Strapping, spaced 16 inches on center above the master bedroom.

Above the mudroom was a different story. There’ll be blow-in insulation below the shed roof here, but the ceiling to support it is 12 feet above the floor, which is uncomfortably high for a traffic-heavy space. Instead, we’ll build a false ceiling 9 feet above the floor. The true ceiling, 12 feet up, we built from leftover pieces of Zip-Systems, and we sealed it just like we did the exterior sheathing. It took some tricky sawcuts, some awkward lifting, and some even more awkward holding-in-place to get the mudroom ceiling up… so Terry helped me.

The mudroom's true ceiling, sealed with Zip-Tape.

The mudroom’s true ceiling, sealed with Zip-Tape.

Colin closes up above the mudroom ceiling so the insulation won't fall out.

Colin closes up above the mudroom ceiling so the insulation won’t fall out.

We’ve made fantastic progress on the electrical front in these last few days, including Colin’s first attempt to turn on power for the whole house. Did he succeed? I’ll give a full report next time!