Roof Sheathing

First two rows of sheathing: complete

Today Dad and I started attaching the plywood sheathing to the rafters. Great! Except...

We had an exchange that pretty much summarizes my feelings about this portion of the tiny house project:

Me: "I guess I shouldn't consider a career in roofing."

Dad: "You'd be the slowest roofer in the world."

Me: "Slow, but very careful... not to fall off."

Yeah. I'm not a huge fan of heights.  Not scared, exactly, just--shall we say--respectful. Wisely respectful.

View from below

But despite my caution, and some issues with rafters not being quite where we meant to put them, we got 2/3 of the sheathing up today! The space is starting to feel nice and closed in--and shady, which is nice, since it is definitely high summer in the Pacific Northwest. And since I'm Pacific Northwest born and bred, 75ºF is about the upper limit of my comfort zone, and I'm sure it's been topping that inside the house where the breeze doesn't reach.

We decided not to install the shou sugi ban'ed fascia boards at this point, since they'll probably get in the way of the housewrap and siding installation. What we did instead was install a temporary fake fascia of the same thickness made from plywood scraps, just to be able to tell how far to hang the sheathing over the ends of the rafters in order to cover the real fascia. We also screwed scraps of wood to the fake fascia to act as "stops," so that the plywood couldn't a) fall off the roof or b) extend too far over the fascia. 

Glue and screw! + Fake fascia and "stops"

 The key points to remember when installing sheathing seem to be:

1. Install the plywood perpendicular to the rafters. The sheets have more strength lengthwise than crosswise.

2. Cut the plywood so that the edge falls about halfway across the rafter, so there will be some space on the rafter for the next piece of plywood to sit on.

3. Glue and screw for greatest wind resistance. We used a 1/4"-3/8" bead of Liquid Nails on the rafters and outriggers, and drove 2.5" deck screws (they could have been 2" or even 1.5", but 2.5" was what we had) every 8" on the edges of the plywood and every 12" in the field. Since the outriggers are only 1.5" thick, we used shorter deck screws from the random screw bucket to attach the sheathing to them, so no screws poke through the 2x4.

4. Stagger the seams in the plywood. In other words, if there is a seam between sheets of plywood on rafter X in row A, make sure the seam is not on rafter X in row B. This increases the structural integrity of the roof assembly.

Nails to maintain gap between sheets, + Point #2: share the rafter

5. Use plywood sheathing clips, or h-clips, to attach the plywood sheets of one row to the sheets in the next row up. Use one clip per bay between rafters. These clips help support those free-hanging edges.

 6. Try to leave about a 1/8" gap between plywood sheets, so that if they get damp and have to expand, they have some space to expand into. The h-clips will maintain the gap between rows the sheets. Drive a couple of thin-ish nails into the rafter right at the edge of the installed plywood to provide the gap between sheets in the same row.

7.  Measure as you go and try your best to keep things square!


Full disclosure: We messed up on one sheet and ended up breaking rule #4 by accident. Oh, well. Plus, now I have to use an extra sheet of plywood. Oh, well...

And we don't even know how we're doing on squareness, yet. I guess we'll find out when we're done and we measure the diagonals.

But you know what? I'm positive that houses are built every day without the kind of care that we're putting into this one, and you don't hear of houses spontaneously collapsing all the time. So it'll be okay.