Here's a link to the last installment: Roofing
We talked enough about bracing earlier that I thought it deserved it's own entry. Buildings are subjected to all kinds of forces when the wind blows and can cause it to rack, or twist, or for the roof to lift off, or for the trusses and gable ends to domino over. Racking is not much of an issue if plywood or some other sheathing is used to sheath the building, and hurricane clips help keep the roof structure anchored to the walls. To mitigate twisting and the domino effect on the trusses you need bracing, as some of you rightly pointed out to me. Some building designs don't require much if any added bracing, hip roofs, for example. Each section of roof braces the adjacent ones. But with a simple gable roof some added bracing is needed. Today, I took care of it by adding two sets of diagonal braces. One set goes under the bottom chord of the trusses to the midpoints of the walls. The other and likely more important set goes from the top of the gable ends down across five trusses, crisscrossing along the way. You can see both sets in these photos.
The braces are double screwed at each point they cross the trusses and also to the walls. I think it will shrug off most anything short of a tornado. The commercial sheds I've looked at often address the twisting forces by installing a 3 ft or so deep storage shelf at the top plate at one or both ends. But I haven't seen any bracing of the gable ends. Maybe it isn't required, and/or maybe it's not a real problem with the low pitch that most commercial shed roofs have.
John
We talked enough about bracing earlier that I thought it deserved it's own entry. Buildings are subjected to all kinds of forces when the wind blows and can cause it to rack, or twist, or for the roof to lift off, or for the trusses and gable ends to domino over. Racking is not much of an issue if plywood or some other sheathing is used to sheath the building, and hurricane clips help keep the roof structure anchored to the walls. To mitigate twisting and the domino effect on the trusses you need bracing, as some of you rightly pointed out to me. Some building designs don't require much if any added bracing, hip roofs, for example. Each section of roof braces the adjacent ones. But with a simple gable roof some added bracing is needed. Today, I took care of it by adding two sets of diagonal braces. One set goes under the bottom chord of the trusses to the midpoints of the walls. The other and likely more important set goes from the top of the gable ends down across five trusses, crisscrossing along the way. You can see both sets in these photos.
The braces are double screwed at each point they cross the trusses and also to the walls. I think it will shrug off most anything short of a tornado. The commercial sheds I've looked at often address the twisting forces by installing a 3 ft or so deep storage shelf at the top plate at one or both ends. But I haven't seen any bracing of the gable ends. Maybe it isn't required, and/or maybe it's not a real problem with the low pitch that most commercial shed roofs have.
John