My Roof windows are just a bit too wide

[Phil A]

I am starting the conversion of space over my double garage into habitable accommodation.

The roof is constructed with attic trusses at nominally 600mm spacing and are fit to support floor loads and there are no intrusive beams etc. The room is not very large so does not require large windows. I plan to install a couple off 55cm wide velux windows between between the rafters.

With 47mm wide rafters the actual free space between rafters is pretty tight for a 55cm window so my thoughts were to bolt a full length rafter (same size as original) to the side of one of the existing rafters then then cut out a section of the original rafter thereby giving me an extra 47mm space to fit the windows. (Hope that made sense). Since the rafter would still exist this would ensure tension in the joist and connect to existing webbing to take some of the roof load. The spacing between complete rafters would only extend by 5cm.

I am sure I have seen a diagram of this in a guide on the web before (its where I got the idea) but I can't for the life of me find it again.

Does anyone know if this is a safe approach to gaining a couple of extra cm space or has anyone experience of similar mods? Does anyone know what the building control might say to this proposal?

thanks

 

[vinn]

Who says that the trusses "are fit to support floor loads"?
Trusses are not to be altered without guidance from BCO and, if possible, the truss Mfr.

 

[Phil A]

Thanks Vinn,

I have the floor and tile loadings the trusses were designed to cope with and BC have seen and approved them.

I have the guys I want to install the windows coming around on Monday so will get their view on whether they will fit first without any mods and if need be chat with the BCO and if they wont comment engage the structural engineer I used for the main loft conversion. I was hoping to avoid engaging him as he does tend to be a bit belt and braces with his solutions - not to mention expensive.

 

[catlad]

Why don't you cut your trimmers and then release the batons
on either side of were you want the windows to go and then squeeze
the trimmers in, that will get you the extra bit of space you need.