Hi,  Looking for some advice on roof windows.  I am about to have a timber frame kit erected which has attic trusses with room in the loft.  My drawing shows 4 roof windows (no particular reason I can think of as it was not an architect who drew up the drawings.  The attic room was a late addition to the plans due to a simple roof design and as it is quite a large house it seemed a good idea to put a room in the attic even though it may not get used immediately.  So if my trusses will be at 600mm centres can someone explain the different sizes options of roof windows.  I looked at a site recently and the windows comes in a variety of widths.  For example 55cm, 66cm, 78, cm 114cm.  Which ones fit between the joists and which ones need bridled.  Joiners will be erecting timber frame and fitting roof windows so probably bread and butter for them.  I would just like to understand a bit more about roof lights and appreciate and advice from those with a bit of experience.  Longer term the attic room could be used as an extra bedroom and en suite. Should I stick with 4 narrow windows or perhaps 2 wide windows.  Any advice much appreciated 

You'd get the size of roof lights you want to fit the room. The rafters can be moved and doubled (or tripled) up on either side to accommodate them. Just make sure the TF manufacturer is happy to accommodate the change to the new structural opening size!

Yes you basically make them whatever size you want, the trusses will be designed around them. 

 

Here is a screenshot of part of my truss plan showing 4 x roof windows 1140x1180mm.  They are doubled each side and the truss that goes through the middle is cut onsite and bridled (600mm centres).

I know someone with 4 walk on roof lights !!

If it might be a bedroom in the future you should consider fewer but larger windows that confirm to fire regs. The window manufacturers will know which of their sizes are suitable as fire exits.

31 minutes ago, Sensus said:

Obviously, if the trusses are at 600 centres, the gap between them will be 600mm - the timber thickness of a truss, which you'll usually find is no thicker than 50mm. (but if it is, it's no big deal to nudge the trusses across by a few millimetres to give sufficient clearance).

Do you mean that..? If they are 600 centres then the gap will be 600mm minus truss thickness. 

Oh, I missed the tiny minus symbol too and thought it was an error.

Thanks to everyone who has contributed with some advice.  Much appreciated.