If two of the rafters are cut a Velux window 1340 wide will fit in the loft. There are 6 rafters in total that reach the ridge, it would be two of these, the roof is hipped and sarked with planks.
It gets 100mph windy here, would this be too big a weakening of the loft? thanks
I think the correct procedure is to double up the rafters either side of the opening to compensate.
Normally you would put stringers above and below the window - those will pick up and support the cut rafters. If you want to add extra strength then nail a pair of additional rafters beside the pair that take the edge of the window.
So if you start with:
Add extra like this:
go on stick in a couple of criple rafters.........
Is this not a question for a surveyor and a structural engineer? You would not get much sympathy from the planners either if you caved in the roof without asking for permission, at least not around here. Brian
Ha ha. very funny.
Tiles are havy things. also if its a semi or terraced design anything like this can bring grief to the neighbours who will look to you for the cost of repair when their ridge goes up in the air as yours sinks.
Brian
When I looked at cutting a rafter my tame structural engineer said I would need a steel frame around the hole to pass the tension on it around the cut. It was a trussed rafter though, and I could have built a couple of new ones either side and removed it altogether if I could pre-stress them to take the same load without the roof moving at all.
If its a typical over engineered Victorian roof you can probably put in stringers and chop it out but I wouldn't do it without expert advice first, especially on a hipped roof as I don't know where the stress runs while I do on a trussed rafter (maybe!).
The hole was to get a solar cylinder into the loft space and it wouldn't fit through the hatch or where the original cylinder was in the airing cupboard.
In the end we measured all the spacings and found one with 6mm clearance so they took the tiles off the roof and carried the cylinder up the ladders and put it through the hole.
Pick a different shape and size of Velux window, I always use Rota.
Often the adjacent rafters to the opening are doubled up with screws/bolts linking them at intervals.
It's important that the trimmers (above and below the opening are well secured to the doubled rafters. Usually with metal brackets
Leave the rafter in the middle of the Velux. [g]
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