pergola fascia fixing - newbie

It all depends on how much weight you're going to put on the end of the eaves. I'm guessing that Spanline is a pretty light weight roof.
I wouldn't like to see this type of structure, weighing two tonnes by TEEJAYS estimate being erected without engineering and inspection (and possible strengthening) of existing eaves structure.

In a worst case scenario you may have a situation where a birdsmouth is cut one third of the depth of the rafter. The carpenters may have been slack, and simply overcut with a circular saw instead of stopping short and tidying up with a hand saw or recipro. The rafter would then be effectively reduced from a 90x45 to a 45x45. If they haven't pulled the birdsmouth tight against the load bearing wall, and there's a gap there, then the rafter is free to pivot downwards. If they haven't framed their eaves support back to the framework, but instead simply stopped it above the brickwork and nailed a vertical from the rafter down to the eaves support to hold it down, then there's no triangular support for the end of the rafter overhang and the rafter is free to sag at the end.

If someone doesn't check all of this and proceeds to attach deep long span rafters to a ledger attached through the fascia into the existing rafters, then there's every chance that it will begin to sag, and just keep going until something breaks.

Failures are very rare with the safety margins built in and I'm sure you could remove half the timbers in a house, and double the spans allowable and you still wouldn't have a collapse. It might be a bit springy to walk on, but I've walked on some very springy ceilings before any hangars have been attached.

One thing is for certain. According to the code, and the span tables, you would not be allowed to design a new home with a roof attached to the end of an eaves overhang without engineers approval. And I'm almost certain that he would suggest that the roof should be carried directly by the wall, or he would design extra support for the eaves overhang, above and beyond what the framing code calls for.

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Originally Posted by pawnhead

It all depends on how much weight you're going to put on the end of the eaves. I'm guessing that Spanline is a pretty light weight roof.
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John

That is true that Spanline is a light weight roof and when they construct it all the ends of the rafters are carrying is the roof and not any beams. Any beams that they may have in the structure are usually carried back to the wall such as on a gable in the middle of a skillion roof.

The one thing you have to remember when an engineer designs a roof the dead load is a secondary consideration. What they usually consider most important is the live loads which are created by the upward and downward pressure from the wind which is usually far greater than any dead load.

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What they usually consider most important is the live loads which are created by the upward and downward pressure from the wind which is usually far greater than any dead load.

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That's why I don't understand how they can accept a roof that is attached with hanger brackets and a few screws to the ends of the rafters. They go to great lengths to specify tie-down and then just let you go and do that. It makes no sense at all.

The other thing is that tie-down requirements for a roof are different when there is a verandah attached (what they refer to as Dimension "A" in the framing code). The dimension for tie-down on the external wall is half the span of the rafters on the main roof plus half the span of the verandah for a rafter roof, or half the span of the truss + half the span of the verandah for truss roof.

I suppose the saving grace is that in a big wind storm, that verandah roof would be torn off like the lid off a tin of sardines, leaving the main roof behind.

the biggest problem in this example is alot of weight is being supported on the creeper trusses at the ends that have hardle any (or none) backspan. For something like that i would feel more comfortable with post support. If a descent beam is fixed to the facia this can cantilever to make up the shortfall in the weak creeper trusses at the ends of a hip roof.