Flat roofs, celotex and downlights...

[Octopus]

Got an extension to fit down lights into - can anyone please point me in the direction of the latest regs and guidance regarding this thorny issue

Thanks

 

[Rpa07]

What have you done with Murdoch?

 

[jackhammerJIM]

A very grey area . Better speaking direct to the building inspector and builder .

 

[Octopus]

What have you done with Murdoch?

Nothing yet..... the roof structure and extension is under construction.... not ready for 1st fix yet.

 

[Toneyz]

We all know that downlights are available to be installed with insulation covering I don't think that you will be able to fit one with remote LED driver as it burns them out .How much of the insulation would you have to cut away?.I think that you will have to fit one with LED GU10 lamp however the danger is someone installing a 50watt gu10

 

[jackhammerJIM]

Never had a problem installing them personally . However a fussy building inspector could refuse to sign off .

 

[jackhammerJIM]

We all know that downlights are available to be installed with insulation covering I don't think that you will be able to fit one with remote LED driver as it burns them out .How much of the insulation would you have to cut away?.I think that you will have to fit one with LED GU10 lamp however the danger is someone installing a 50watt gu10

The insulation will likely be solid celotex/kingspan . whoever insulates leaves a gap .

 

[Toneyz]

The insulation will likely be solid celotex/kingspan . whoever insulates leaves a gap .

In theory your going to have heat loss/cold spots hence why manufactures have developed downlights which insulation can cover I think that a lot will depend upon the exact construction detail.

 

[jackhammerJIM]

In theory your going to have heat loss/cold spots hence why manufactures have developed downlights which insulation can cover I think that a lot will depend upon the exact construction detail.

I understand that but when you have a 100mm downlight sat in 100mm of celotex there won't be much insulation covering it

 

[J.C.E]

get builder to cut 100mm hole out where you coil for a downlight
or a slot is slightly easy job when it comes to fitting the downlight in

 

[Octopus]

^^ so a 100mm hole all the way through the celotex? Not sure about that!

 

[Des 56]

Once you ask of the building inspector the problem will not be yours,it seems to be a wise sparky who will ask the question but I have always just gone ahead and cut

What about making separate compartments,I wonder if that is a solution for a long discussed problem ?

 

[Toneyz]

As I posted a lot is dependant upon construction of the roof the joist depth and where the Kingspan/celotex sits etc.

 

[J.C.E]

The u value will not be effected enough to worry

Dont suppose they are having veluxs are they...well theres a bit more that a 100mm hole

 

[jackhammerJIM]

As I posted a lot is dependant upon construction of the roof the joist depth and where the Kingspan/celotex sits etc.

7"x 2" joists , 125mm kingspan in between joist + 25mm kingspan on underside of joist.
2 inch air gap above .

 

[stummish]

I've asked a couple of building inspectors about this. If you take the whole roof area and m2 and calc the u value, then minus off the total u value lost by cutting 100mm holes for downlights at (as a rough guide) 1 every 1000mm on x and y axis, the total uv lost is almost nothing.

I normally have a chat to the builder and try make sure there's a minimum 70mm gap between plaster and insulation, then cut out 100mm hole but only 20-30mm deep into the kingspan. Don't remove at this stage. On 2nd fix if I need the space I'll then knock out the cut section. I almost always fit the collingwood halers h2 pro 700's so you need less fittings per m2, they're only 60mm deep so usually they have enough breathing space. Plus integrated led dls dissipate their heat better than canned gu10s. And if all else fails cut straight through the kingspan. Get the building inspector to calculate the lost uv to prove it's negligible loss.

Also the seal fairy's cousin, the kingspan fairy, may appear if you're lucky!

 

[Midwest]

I had a similar installation a while back. Phoned my LBC and was told in no uncertain terms, not to cut holes in the celotex/kingspan.

A while later, had another similar installation, this time emailed LBC and got the response that stummish & Jim received, in this case the customer was having velux installed, and was given them as an example, effecting the U value.

Then the BO turned up to inspect part of the extension, and the subject of DL in the Celotex was mentioned, and we were told we should not. I showed the email advice, and he back tracked somewhat. In the end, my customer decided not to bother.

Clearly with all the wonderful manufacturers pictures you see of DL's in vaulted etc ceilings, its allowed, just getting LBC to commit.

So Murdoch, I would get LBC approval in writing, before proceeding.

 

[stummish]

As @Midwest says, getting it in writing will always win the he said she said battles.

 

[Pat H]

Yes the effect on a few downlighters on the whole ceiling U value is negligible. But you will end up with cold spots round and of the DLs and depending on the design of the DL you may well punch a draught hole straight through from the air gap to the room.
Its a real issue. I've tended to stick with surface mount lights and just avoid it.
But I'd agree its down to what the LBC will sign off.

 

[Midwest]

Think there is an issue with damp forming by warm air going into a cold air designed roof void (not the correct terminology) thru DL, but I was told by my LBC these roof designs are not very common.