fear of rafters falling like dominos

I am almost ready to raise a 12'x16' Shaker Garden Shed which is shown in Jack Sobon's TF book. I'm concerned about the rafters being able to withstand windstorms that can occr once or twice a year where I will raise it (NH). The rafters are simply pegged into the top plate (step lapped) and pegged at the peak with an open mortice/tenon. The step laps cut into top plate are only 2" deep which hold the 4"x6" rafters in at a 45 degree angle. Once the rafter is set into the step lap top plate it looks like they will not provide much support for side loads (wind hitting gable end). Of course the roofing boards (1"x10"x10') will offer some support against side loads but that wouldn't totally prevent the rafters from "dominoing" somewhat in the wind.

I could always nail a 1"x6" long board diagonally across the rafters on the inside (bottom of rafters, seperate from roof) but that wouldn't look to good.

Instead of nailing the roofing boards perpendicular to the rafters, is it unheard of to nail the roofing boards diagonally across the rafters to offer some extra support?

Thanks in advance.

Hi Josey, I built the same shed in Maine two years ago. It's in an open location, windswept area. The frame hasn't budged at all and we've been hit with some strong winds. I think the roof sheathing helps hold everything together (we used 1x10 shiplap boards). The boards are perpendicular to the rafters so I don't see how the rafters could possibly "domino"; it seems like it would have to move as one. Also, the step-lap rafter seat is holding the rafter foot securing in place. Maybe you're over thinking this?

Ok, yeah I'm probably over thinking it. Thanks.

Also, 2 of my rafters are warped a bit. I had the rafter pieces stored outside away the elements for about 6 months while I finished the other timbers. I might have to redo these 2 rafters. I guess warping is a common problem that even the builders of 200 years had to deal with.

You gonna pull those pistols or whistle Dixie?

Have you tried to perform or learn the loading calculations and the stresses at the joints? When you do, you'll typically see that they are build with enough margin of safety for just about anything if done right. That shed has been build quite a few times according to people I've seen mention it here. If there were any doubt, I'm sure we'd have heard about it. I'm sure this frame has been examined numerous times. As long as you have followed the plan and used materials that were up to spec... you shouldn't worry. If you're still worried, find out how much a TF outfit would charge you to do the calculations. Heck, even someone on here might have done it and have them.

Hi Josey:

Have no fear about your rafters collapsing, just look at any historic structure that has survived the test of time an you will see just nailed on rough boarding over the rafters, in many cases on very large buildings with very high roof peaks.

the only case that I can recall is of the rafters being lifted out of their seatings at the bottom due to a vicious storm some years ago. Even partly exposed frames will withstand high winds.

According to what you say the rafter seatings are let into the plate approx. 2", this in itself after pinning will cause the whole rafter network along with its boarding to be very rigid, and no doubt stay with the frame when the wind picks the whole structure up and carries it away!!

NH

I nailed my sheeting boards on a 45 degree angle. It really did stiffen up the frame. I'll try to post a picture of it here.



-Thomas

the 1x6 you refer to is a good idea, let it into the outside faces of the rafters just under the sheathing and it will look great... framers around here call it wind bracing and install by tacking the board in place, tracing around it, then rough out the rafters with a circular saw set to match the thickness of your board. After that use a ripping hammer to clean out the cuts, a chisel is not usually neccessary.

I agree that you may be over thinking this. if the rafters were going to fall then all the roofing boards would have to shrink to nothing and/or all the nails would have to shear off. Don't sweat it.
bloveland

But, I'll take a triangle over a square any day. There is a lightly framed corn crib I pass every day, no bracing, vertical framing and horizontal skip sheathing. It leans about 18" this year as each board has let it drift from square to paralellogram. Next big snow will take it. I'd figure its lasted 50-75 years. It can take awhile for a flaw to creep enough to show itself. Each degree out puts it under more stress which will make it lean more and put it under more stress until... It's always worth thinking about.