Rafter is the Best Medicine

Over at the timber frame, all the inner and outer leaves of the stud walls are up, and the open-web-joist rafters are on their way to forming the gable roof. Lifting these rafters into place is a real team effort, so it was nice to have seven guys on site for a busy day last week. We have set up temporary cleats and ladders to help us navigate the gable’s 16-on-12 pitch.

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Rowan and Chris lift rafters onto the roof, while Ben preps near the new dormer window.

Ben and I spent half a day prepping the shed roof for insulation. The job began with shoveling snow off the roof and casting off our protective tarp (which keeps the inside dry while construction is in progress). Then we cut and installed X-braces between the rafters at midspan. Bracing helps the rafters share loads, so if there’s a snow drift or a heavy carpenter standing in one spot then a single rafter doesn’t need to do all the work.

Next, we stapled a tight mesh called Insulweb on the side of each rafter, and along the bottom and top of the roof area. Insulweb encloses each bay of the roof area and enables us to blow cellulose insulation without stuff leaking out. Installation got tricky at the end, when the only place left to stand was balancing atop each rafter.

I remarked many months ago that I would hate to have the job of loading bags of cellulose into the blower machine. Well, that was precisely my job today… and it wasn’t half bad. The paper-fiber material doesn’t itch like fiberglass, but it does produce lots of dust, so wearing a respirator is essential (not so uncomfortable in today’s sub-freezing temperatures). Opening one 25-pound bag at a time with a utility knife, I fed the cellulose into the hopper and tried not to let too much fall on the ground.

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Loading a bag of cellulose into the blower machine.

The machine did most of the heavy lifting, pulling cellulose from the hopper into a hose and blowing it up to Ben at the other end. I don’t envy Ben’s job. Perching carefully atop the roof, Ben wrestled the hose into one bay at a time and then stood by until the bay was tightly packed with insulation. Ben also managed a switch that turned the blower on and off from afar. We operated at two speeds: a very fast initial pack and a more leisurely dense pack.

Apparently, in the early days of cellulose insulation, walls and ceilings were loose-packed, and R-values were satisfactory. But the material settled to the bottom over time, leaving air voids that offered no insulation at all. That’s why today’s standard practice is to fill the voids up front with as much material as possible, leaving no space for it to settle. Today it took 38 bags of material (just under 1000 pounds) to fill two thirds of the northeast gable roof (about 500 cubic feet) with dense-packed cellulose. That’s a lotta shredded newspaper between those rafters.

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Dudley Do-Right Ben looks down from the roof.

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