To Insulate or not that is the question

[moraz]

Hi DIY Gurus,

I've stripped my kitchen ceiling as part of renovation work and noticed that we have no insulation under our flat roof.

I would like to fit insulation using the cold roof method but building regulation states that it can cause serious condensation issues if I don't have ventilation from opposite sides.

I only have one side ventilation and will be unable to create ventilation on the other side. Is it possible to insulate my roof or should I just give it up?
I thought to do the following but I am no expert and I don't know if the single side ventilation will create problems which I'll better avoid.

If it is possible can I do the following or is there a better way?

1. Fit 100 mm Kingpsan at the bottom of the Joist. (This will leave 50mm gap on top of the insulation).
2. Fit 2 layers of vapor barrier (1 layer from west to east and 1 layer from north to south)
3. Fit fire resistant plaster board.
4. Skim it all


Many thanks for your input!

Untitled

• moraz
• 1 Aug 2014
• 2

 

[freddiemercurystwin]

If you were doing a garage conversion and you did not wish to re-roof, which is a very common scenario, you would typically add Celotex fitting it tight up against the underside of the deck, Building Control would pass it as you have no other choice when keeping the roof. There is a slim risk to the structure and that the joist lines may show up behind the plasterboard but there is little else can you do.

There seems little point trying to utilise your vents when they won't allow cross ventilation.

 

[moraz]

Thank you Fred,

Just to clarify, the work will not require the approval of the Building Control.

Regardless, I've spoke to Celotex technical team and they said that they can only recommend their product if I have ventilation from both sides and won't be able to advice otherwise. This brings me back to the beginning.

 

[freddiemercurystwin]

That's because they have not had it tested it in this scenario, they have only tested it in either a completely warm roof scenario or a completely cold roof scenario. However when you have an existing roof finish that is being retained it is difficult (to say the least) to achieve either a proper cold roof or a proper warm roof, you have a hybrid roof or a combination of the two and you have to compromise.

BTW I'm not suggesting you apply for Building Regulations merely pointing out that if you were then this method would be approved.