Passing the Porch

Milestone: No more plywood. We finished paving the final roof!

The screened porch roof was the trickiest by far. This roof uses trusses for framing, while the adjacent wraparound porch roof uses rafters. The problem is that the rafters need to be 2x8s because they carry the entire roof load in bending, whereas the truss top chords are 2x4s since they share their axial loads with the rest of the truss. As a result, when we aligned the bottom of the trusses for a uniform drip edge, the peak fell about 4 inches below the top of the rafters. How do you solve this huge 3D geometry problem and make the roof look good?

The porch roof problem.

The porch roof problem.

As usual, it was Terry who brainstormed the simplest solution – the kind that makes you slap your forehead and say, “Why didn’t I think of that?” He and Colin added a 2×4 to the top of each truss, increasing the height to match the rafters. They cut the new lumber to get the exact peak elevations we needed, and they toe-nailed it to the trusses at regular intervals for a strong shear connection. As an added benefit, the improved trusses have stronger top chords to support the heavy snow loads they will receive (we hope!) every winter.

Adding lumber to make every truss the right height.

Adding lumber to make every truss the right height.

Then it was back to 5/8-inch plywood to cover the roof. We’ve been using our plywood supply as a temporary walking surface on all our as-yet-unpaved porches (although the decking finally arrived yesterday), and now Colin and I scooped up every full sheet we had. Terry also laid out all our plywood scraps on the grass for a visual. With so many edges to this roof, we needed to cut lots of triangular pieces, and each new set of measurements became a puzzle to use our existing scraps efficiently. Sometimes we even used scraps upside down, fitting grooves into tongues instead of vice-versa, to finish the job with the pieces we already had.

So many scraps to choose from!

So many scraps to choose from! (On the driveway you can see $5000 worth of decking.)

The valley where the open porch meets the screened porch was our last challenge. Terry pulled a string tight to indicate the valley’s location, installed the north-facing plywood to run a bit long, then called down measurements for mini-rafters to sit atop that roof for the west-facing plywood. It took a compound cut, 18-degree run with an 18-degree miter, to make each rafter sit properly. We nailed down our last bit of plywood around 4pm… and then it was full steam ahead with vapor barrier and shingles until we ran out of daylight.

What a relief to finish the plywood. Colin, Carson, and Terry unroll asphalt paper.

What a relief to finish the plywood. Colin, Carson, and Terry unroll asphalt paper.

One thought on “Passing the Porch

  1. Pingback: Two Hundred Fifty | PERCH ENGINEERING PLC

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