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Sheathing a Simple Gable Roof

Sheathing a roof begins with placing the first sheet in the right spot
November 09, 2022

Now that you’ve got the rafters where they’re supposed to be, it’s time to slap some sheathing down so you and Ruff can take lunch.

The first part of sheathing the roof is figuring out where that first sheet goes.
Obviously, it doesn’t go in the middle. It goes in one of the bottom corners, but you need to account for a couple of overhang dimensions.

Account for the gable overhang

The main overhang hasn’t been framed yet, but in order to frame it, you need to know where the plywood is going.

The other overhang is how much the plywood extends past the rafter tail. It should cover the subfascia and most of the fascia.

It should be a bit shy of the full width of the fascia because, unlike animation land, the real world has humpy lumber. Leaving the plywood shy of the fascia edge means you won’t be running a Skilsaw along that roof edge tomorrow morning.

Covering the fascia edge means more protection from water with nefarious intentions.

There are a couple of ways to frame the gable overhang, and they both involve ladder-style blocking.

Determine where the bottom of the roof sheathing will go

Any self-respecting carpenter is going to make sure the plywood breaks on a ladder block, and THAT’S why we want to figure out where that sheet is going to land.

You can use your little rafter jig from a couple of videos ago to see where the plywood should stop.

Draw the 1-1/2 inch subfascia and the fascia. I’m using ⅞ inch-thick fascia to make the math less typical—for a two and ⅜ inch extension.

The diagonal is 2 and 11/16, so that’s the MOST you can hang the roof sheathing past the rafter tails.

But you should cut about a quarter inch off that to account for bumps or irregularities. So, two and a half is an easy number to remember and communicate.

Sheathing the roof

Burn 2 and a half on the end of the rafter tail, mark 48 inches, and snap a line across the rafters.

Before going much farther, if you haven’t done it already, make sure the rafters are standing plumb and that the post is braced to keep them plumb.

If they’re not plumb, the plywood will break at the bottom of the rafters, but it will run diagonally off very quickly from there.

Ok, that 48-inch mark is where you should center one of the ladder blocks.

Frame the overhangs either as a ladder block system or outlookers extending back to the second rafter if the overhang is large. We cover that in a different animation.

Ok, NOW we can nail that first sheet down to the framing. And the second, third, and fourth…

Keep the sheets on the line and split the sheets on the rafters. The tails down at the bottom of the sheet are not going to move much, but four feet in from the wall, the rafters can wobble.

It’s important to pull the rafters to the layout if they’re not sitting perfectly.

Stagger the second course half a sheet from the first, and keep checking the layout as you work up the roof.

Inevitably, you’ll need to rip the final row to fit. If there will be a ridge vent installed, hold the sheathing back for whatever the manufacturer recommends, probably between one and two inches.

With the roof sheathed, you can pop the inside braces and get BARK to looking for your lunchbox.

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