N
Nickam
The original post did say 'Flat roof' did it not ?
Position of Celotex in cold flat roof.
- Thread starter JonB123
- Start date
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NO downlights 
celotex against the plasterboard - air gap above and vents @ soffit . Just like one I did here earlier. After letting it all dry out for a week where the old downlights had allowed loads of water vapour into the roof
celotex against the plasterboard - air gap above and vents @ soffit . Just like one I did here earlier. After letting it all dry out for a week where the old downlights had allowed loads of water vapour into the roof - Joined
- 24 Aug 2009
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Yes, you're right and I had overlooked that so since I know nothing about flat roofs, I'll withdraw my advice.
so since I know nothing about flat roofs, I'll withdraw my advice.
N
Nickam
No Probs. We all sometimes look at something quickly and don't always see what's there, especially at my age
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Warm deck is by far the most sensible.
However if you decide to go cold deck remember that the joists will act as a cold bridge. You WILL need to ventilate the void with through ventillation.
However if you decide to go cold deck remember that the joists will act as a cold bridge. You WILL need to ventilate the void with through ventillation.
Hi
As already mentioned create some 'fire hoods' to protect the insulation, you can use 1/2" plasterboard - not sure of the size of your lamps, but imagine a hood similar to a small empty can of baked beans - if your fittings are larger imagine a larger tin of beans - find an object of the right size, first create an perimeter to the hood using the object as a template, cut the plasterboard to the correct height, then on what is going to be the external face cut vertically through the backing paper to the plasterboard and then snap the plasterboard along the cuts, place around the object until the perimeter is covered, then fit a lid on by cutting a piece of plasterboard to suit - looks pretty ugly by this stage, then finish with multi-coat plaster and hessian tape to bound the lot together, allow to set, remove template and you have your hood!
You may need to include a bearing plate between 2 joists to support the hood - 2 pieces of 2x1 batten fixed on facing sides of joists and fix the ply across the gap. You may need to adapt to suit cables, but this will provide you with a 'fire hood'.
Ideally, you need to maintain around a 50mm gap between the top of the insulation and the underside of the roof (this is a must) as it provides a ventilation path, as condensation will form in the void and the ventilation will allow the moisture to evaporate and escape to the outside.
Polystyrene or PIR insulation board can be used for insulating the void, just cut to suit over the fire hoods, and go full depth to all other areas. Both insulation materials are very good insulants although PIR is a slightly better insulant, but you will need to consider cost!
Before you re-plasterboard the ceiling remember to add a vapour barrier - again this is a 'must' as the warm air holds more moisture than cold air and when the warm air meets the cold air behind the insulation condensation will form, the vapour barrier reduces the amount of moisture getting through and minimises condensation.
Regards
As already mentioned create some 'fire hoods' to protect the insulation, you can use 1/2" plasterboard - not sure of the size of your lamps, but imagine a hood similar to a small empty can of baked beans - if your fittings are larger imagine a larger tin of beans - find an object of the right size, first create an perimeter to the hood using the object as a template, cut the plasterboard to the correct height, then on what is going to be the external face cut vertically through the backing paper to the plasterboard and then snap the plasterboard along the cuts, place around the object until the perimeter is covered, then fit a lid on by cutting a piece of plasterboard to suit - looks pretty ugly by this stage, then finish with multi-coat plaster and hessian tape to bound the lot together, allow to set, remove template and you have your hood!
You may need to include a bearing plate between 2 joists to support the hood - 2 pieces of 2x1 batten fixed on facing sides of joists and fix the ply across the gap. You may need to adapt to suit cables, but this will provide you with a 'fire hood'.
Ideally, you need to maintain around a 50mm gap between the top of the insulation and the underside of the roof (this is a must) as it provides a ventilation path, as condensation will form in the void and the ventilation will allow the moisture to evaporate and escape to the outside.
Polystyrene or PIR insulation board can be used for insulating the void, just cut to suit over the fire hoods, and go full depth to all other areas. Both insulation materials are very good insulants although PIR is a slightly better insulant, but you will need to consider cost!
Before you re-plasterboard the ceiling remember to add a vapour barrier - again this is a 'must' as the warm air holds more moisture than cold air and when the warm air meets the cold air behind the insulation condensation will form, the vapour barrier reduces the amount of moisture getting through and minimises condensation.
Regards
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