How To Sheathe Roof Rafters

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Fluffy Is Disgusting

We got several days of heavy rain, right in the middle of sheathing the roof rafters on our new earthbag-walled home. The forced delay was bad enough, but what the wetness did to the OSB (oriented strand board) sheathing material was worse. Much worse. The boards got all fluffy, especially at the edges. What used to be 15/32 of an inch thick is now 3/4 of an inch thick, sometimes even thicker than that.

Gr-r-r-r! And even *%$!#@! To someone like me who takes pride in his work and who will go to considerable lengths to make things look artistically beautiful as well as structurally sound, the irritation is–um, not overwhelming. Not that. But deeply irritating, to say the least.

True, it’s not such a horrific mess that I have to rebuild anything. Once the tarpaper is applied and the steel roofing panels are screwed down tightly, it won’t really matter that the underlayment (sheathing) boards are all swelled up from getting soaked. After all, they only have to be there to keep the metal from flapping all over the place; they’re not in a beauty contest.

But, oh, the ugliness! Wanna see? Here’s a photo of the ultimate fluffiness at the southeast corner of the roof.

Fluffy

The Basic Steps

Okay, if you’re done vomiting, we can let the underage children back into the room. I promise not to show anything that hideous ever again in this hub. There was nothing I could do about the sudden multi-day rainstorm that fluffed stuff; it’s just one of those (admittedly revolting) things. Let’s get to discussing the usual factors involved in sheathing the roof.

#1. Run the sheathing boards horizontally. This makes a stronger roof because of the way they’re manufactured and because each board crosses more supporting trusses.

#2. Nail a 50-inch support piece of two-by-four under one end of each board for extra support. You don’t really have to do this; most roofs have two board-ends sharing a single edge of one truss. I just like it better with more lumber under every board-end.

#3. Stagger the layers like you were building a brick wall. Just another aid to providing the strongest final structure possible.

#5. Be generous with the nails. Sheathing works well with 8d size nails. I tend to space the nails between 5 and 7 inches apart, ending up with a minimum of 40 nails per board.

#6. Work in layers/rows, beginning at the outer, bottom edges and progressing to the peak.

#7. Trim the final board in each row on the roof, not on the ground. I didn’t do this at first and wound up wasting three “wrong cuts” that didn’t fit right before getting the message and lugging the Skilsaw up to the roof. Adjusting the depth of cut to just reach through the sheathing board eliminates any chance of ruining the underlying truss, and you can get the edge of the strand board cut exactly where you want it.

#8. Use a straightedge to help every nail hit its truss dead center. I use a strip of sheathing board snugged against two nails which are nailed down only part of the way near either edge of the board. The six to eight nails that will run in a straight row between these two are then started right next to the straightedge. After that, the straightedge is removed and the entire row of nails (8 to 10 total) gets hammered down the rest of the way.

It also helps if you switch from working alone to putting your newest household member to work. Justin pitched his tent behind our camp trailer a few days ago and is more than earning his keep by helping Pam take her medication on time and helping me with constructing the home. His homebuilding contribution for today was to roll paint onto the exposed earthbags to protect them from UV rays, allowing me to concentrate on adding sheathing boards to the roof.

The roof boards are placed horizontally.

The roof boards are placed horizontally.

Justin paints the earthbags for temporary protection against the sun's UV rays, allowing me to concentrate on the roof.

Justin paints the earthbags for temporary protection against the sun’s UV rays, allowing me to concentrate on the roof.

The beautiful southeast corner before it did the Ugly Fluff Rain Dance.

The beautiful southeast corner before it did the Ugly Fluff Rain Dance.

A 50 inch board is nailed to a truss, ready to receive the end of a roof sheathing board.

A 50 inch board is nailed to a truss, ready to receive the end of a roof sheathing board.

Two nails and a straightedge guarantee every additional nail will hit the truss board below the sheathing.

Two nails and a straightedge guarantee every additional nail will hit the truss board below the sheathing.

The first row at its west end finale, trimmed with the Skilsaw to fit the rafter edge exactly.

The first row at its west end finale, trimmed with the Skilsaw to fit the rafter edge exactly.

Harrassing Home Depot

Basically, that’s about it. As of this writing, 27 of 40 total 4′ x 8′ boards are in place (most of them fluffy to extra fluffy, but they’re there) with 13 to go. Tomorrow morning, I need to call Home Depot first thing, ask them when my special order steel roofing panels are going to show up–preferably before we get too many more Sky-Niagra dumps and those fluffy boards expand into tulip trees or something.

Next: Roofing felt application….

Note: The top photo is of the finished home, now called the Border Fort. We’ve been living in it for 3 1/2 years to date with no roof problems to date (October 2, 2013). The photo was taken on December 31, 2012; we’ve added a front porch since then.

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