Trimmer height for Velux

[sgg123]

Hello all,

Hopefully an easy one to answer.

I will be installing a couple of FK06 - 66 x 118cm Velux windows in a roof space. As per the structural engineers advice I have strengthened the roof rafters and added double trimmers above and below the proposed window spaces.

I have decided to set the top and bottom trimmers at exactly the same height dimensions as the window opening (see sketch attached), so the space between each set of double trimmers is 1225mm (118 + 45mm) as per the Velux installation illustration - also attached.

My question is - is it OK to have the rafter trimmers at these intervals - or do they need to be further apart? The only issue I can think of right now is that this would force the window reveal splays to be at a right angle to the window rather than say spilling toward the floor. Is there any other reason why I should consider

repositioning the trimmers?

 

[RandomGrinch]

The only issue I can think of right now is that this would force the window reveal splays to be at a right angle to the window rather than say spilling toward the floor.

All the MI I have seen, have been along these lines; aiding air circulation and avoiding condensation ...

 

[sgg123]

Thank you for this. Probably best to move the trimmers then!

 

[noseall]

Thank you for this. Probably best to move the trimmers then!

We never fit the horizontal trimmers until we have the window handy. What we actually do is fit the trimming rafter doubles each side AND fix a sacrificial rafter up the centre of the Velux opening. We then fix the first two, three or four courses of tile batten (depending where we want the Velux bottom to start), fix the bottom Velux bearer batten, fix the top Velux bearer batten, lay the roof widow temporarily in place and then decide where the horizontal trimmers go. We then cut out the material required out of the sacrificial rafter THEN fit the (horizontal) trimmers.

 

[sgg123]

We never fit the horizontal trimmers until we have the window handy. What we actually do is fit the trimming rafter doubles each side AND fix a sacrificial rafter up the centre of the Velux opening. We then fix the first two, three or four courses of tile batten (depending where we want the Velux bottom to start), fix the bottom Velux bearer batten, fix the top Velux bearer batten, lay the roof widow temporarily in place and then decide where the horizontal trimmers go. We then cut out the material required out of the sacrificial rafter THEN fit the (horizontal) trimmers.

Thanks for this. So, would you also agree that the trimmers need to be spaced out away from opening to allow for horizontal and vertical plays?

 

[sgg123]

I meant splays

 

[noseall]

Thanks for this. So, would you also agree that the trimmers need to be spaced out away from opening to allow for horizontal and vertical plays?

If you are reliant on the horizontal trim's to actually form the reveals, then there is no other way to do it, as the window needs to sit in a pre-determined position, relative to the tile battens. You can't just guess, lol.

 

[^woody^]

Does means of escape apply? If so, be mindful of the height requirements.

 

[catlad]

I would advise to just screw your trimmers in loosely for the time being until a decision is finalised as to where they are going to go. Try not to fall into the classic builder mistake of deciding where they are going to go ,without taking into account the flashing kit , which is relative to the tile/slate coursing.

 

[sgg123]

Yes, they need to be top hung and no more than 1100mm from floor for means of escape

Does means of escape apply? If so, be mindful of the height requirements.

 

[sgg123]

I would advise to just screw your trimmers in loosely for the time being until a decision is finalised as to where they are going to go. Try not to fall into the classic builder mistake of deciding where they are going to go ,without taking into account the flashing kit , which is relative to the tile/slate coursing.

I've planned for the top edge of the bottom installation batten to be 80mm from the top of the next course of tiles - which should allow for the EDW flashing kit.

 

[catlad]

Correct, although I sometimes measure 100mm from bottom of frame as its the same difference.
If its a new roof I put the brackets and the batons on the frame so I can rest it on the rafters until I am happy with its position, if you put a couple of screws ( halfway in ) on the rafter where you think it will go it stops the skylight sliding down the rafters and keeps your hands free.

 

[sgg123]

Correct, although I sometimes measure 100mm from bottom of frame as its the same difference.
If its a new roof I put the brackets and the batons on the frame so I can rest it on the rafters until I am happy with its position, if you put a couple of screws ( halfway in ) on the rafter where you think it will go it stops the skylight sliding down the rafters and keeps your hands free.

Great advice, thank you!

 

[sgg123]

Thanks to all of you for your advice on this. It's unfortunate that I will need to go back and trim some rafters to allow the trimmers to sit further out from the window - but I understand that this will make it a better job. Time to get to work!

 

[catlad]

Just seen yours are top hung! you need to pay a bit more attention for level and square on that design.