Nothing But the Roof

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.

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.

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Habitatting

Habitat for Humanity is building a house in East Montpelier. Last fall I tried to contribute to this project as an engineer, but a team of Norwich University students designed the house and I wasn’t needed. Now that it’s under construction, I can lend a hand in a much more literal way.

It’s been more than a year since I last worked on rough framing, and it felt great to lug materials and climb around like a monkey. Even better, I got to test my competency. Head carpenter Chris put me in charge of a roofing crew: a team of five from the Montpelier USDA office who took an outing to join us. Also on site were longtime volunteer Lisa and project manager Bruce.

Our primary task for the day was to install as much tongue-and-groove sheathing as possible atop the scissor trusses that support three quarters of the roof. Chris and Bruce snapped a chalk line on the south side of the gable to get us started. For our first row we aligned each tongue (pointing uphill) with the chalk line. Subsequent rows we pounded into place with a sledgehammer and beater board. While Chris, Bruce, and Lisa puzzled out the geometry of the remaining rafters, the task of the roofing crew was relatively simple.

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Chris and Ben install a rafter in the southeast quadrant of the roof.

But no carpentry task is without pitfalls, and we encountered plenty. The scissor trusses are pretty squirrely on their own, free to sway until the sheathing provides shear strength. So we had to take care when we walked on them, and as we nailed down the sheathing we had to continually straighten the trusses so they’d line up perfectly. Usually we accomplished this task by marking the sheathing two feet on center, measuring periodically from the previous seam. Getting those seams right took some sledgehammer magic, too. When we hit one end in, the other end liked to seesaw out, unless we hit in just the right place or tack-nailed a corner to keep it from sliding.

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Snapping a chalk line to align the remaining sheathing panels.

The USDA team was a delight to work with. Ben actually built many houses while he was in school, and I appreciated his problem-solving intuition and acrobatics. Polly, Megan, Mike, and Ted learned fast, and what they lacked in experience they more than made up for in enthusiasm. Fears were overcome as everyone got up on the roof; the adage “many hands make light work” rang true. By day’s end we had over 90% of the roof sheathed – major progress toward getting the interior dry for the electricians who arrive next week.

(Did you know? The USDA provides rural housing mortgages and renovation loans with super low interest rates! Apply here and see if your income qualifies you.)

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Mike and Megan nail the last panel of the day into place.

Truss-Tease

Over the course of a week, we assembled two trusses to lift up the timber frame. Apart from the challenge of cutting the truss members to the right size, I think we were all surprised by the number of steps required for assembly.

First we set up a low platform at each node and laid out the truss. We measured diagonals to confirm the corners were square. Each node eventually gets sandwiched by a pair of plywood gusset plates, which connect the vertical, horizontal, and diagonal members via a pattern of screws… if not for the gusset plates, there would be no transfer of forces between the members. We attached the first set of gusset plates at this stage. Then it was time to lift the truss into position.

Truss laid out and ready to lift.

Truss laid out and ready to lift.

Cillian climbed to the second floor of the timber frame with two cargo straps, wrapped them around a post, and sent the straps down to Ben who tied off the top corners of the truss. With Ben and me lifting the truss and Cillian ratcheting the straps, we slowly swung the truss into its vertical position beside the timber frame. We used a couple of Timberlock screws to hold the truss tight against the timber frame, and then attached the second set of gusset plates.

Ratcheting in progress.

Ratcheting in progress.

Timberlock screws weren’t enough to transfer loads from the timber frame to the truss. For that task I drew up a pattern of four ½-inch lag bolts centered about each node. We drilled a hole for each bolt running clear through the gusset plates and about 3 inches into the timber frame. (If the bolts went all the way through the timber they’d be called through bolts; since they only go partway in they’re called lag bolts.) Then we used an impact driver to bury the lag bolts, each 8 inches long, into our holes. The timber frame weighs about 9000 pounds, so a solid connection is critical.

A solid connection is what I was worried about when I noticed a few pieces of plywood had delaminated, with one ply separating from the next. I reinforced these locations by cutting an additional gusset plate out of some scrap Advantech and screwing it on. Nothing to worry about now.

Screw and lag bolt patterns. The node on the left has an extra gusset plate for reinforcement.

Screw and lag bolt patterns. The node on the left has an extra gusset plate for reinforcement.

The trusses will carry the weight of the timber frame out to four corners, jacked two feet off the ground. We were all set to start jacking last Thursday when we discovered to our dismay that one jack couldn’t hold a load. It was busted. Friday came and the rental store could neither fix the broken jack nor locate a working one, so our great lift was postponed for the weekend. I’ll report next time on how it went.