Velux windows

[akist]

If a standard roof has rafters at 400, and we take one rafter out, that gives us 800 opening less 25mm + 25mm on either side (assuming 50mm rafters) leaving a net of 750.

I'd expect a "standard" Velux to be 750 (or a bit less) but it is 780.

If the rafters are at 300, the opening after taking a rafter out would be 600 - 25 - 25 = 550.

And they DO make a 550, even though I suspect a tight fit.

The ideal standard size should be like 800 - 25 - 25 - 20 = 730
And 600 - 25 - 25 - 20 = 530

Could someone please explain it to me?

 

[^woody^]

Could someone please explain it to me?

Only if you explain your question first.

 

[Wayners]

Just fit the smallest option because of the heat (like radiators in summer) and noise from rain ( fit outside blind)
Pack frames with timber to make up the gap around.

 

[akist]

Pack frames with timber to make up the gap around.

Yes, I now realise that you are meant to close large gaps with additional timber pieces.

My carpenters did a net 600mm, I am not sure why So we have to pack 50mm or so, as the standard size is 550mm. Maybe use some expanding polyurethane too.

 

[noseall]

Yes, I now realise that you are meant to close large gaps with additional timber pieces.

My carpenters did a net 600mm, I am not sure why So we have to pack 50mm or so, as the standard size is 550mm. Maybe use some expanding polyurethane too.

You don't pack anything rather you use the correct gap filling method to ensure airtightness and accurate cradling of the plaster board. The fitting gap is important if you wish to use Velux proprietary weathering collars etc.

 

[datarebal]

read the instructions , its all there

 

[gonch69]

You don't have to pack 50mm there ment to be over sized openings put 25 mm insulation either side of windows then you're plasterboard will slot in

 

[catlad]

Standard roofing tiles are 300mm wide, so 780mm x 60mm drainage channels either side = 120mm. 780mm + 120mm= 900mm which is 3 standard roofing tiles wide. I fitted 2x CK06 today which are 550mm wide these are suited to truss roofs which are 600mm centres normally. Old cut roofs are 16" centres normally, and if your lucky you will be able to get an MK = 780mm skylight in with only needing to cripple one rafter. They also do one the FK range which used to be 700mm wide! Velux is an international company with an annual turnover of 20 billion! it wasn't building its empire on old cut roofs in England with 16" rafters centres.