Flat roof under-insulated?

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redcoatonline

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Hi,
I've recently had a flat roof (warm) installed by a local contractor, who used 100mm Kingspan over the main deck, followed by torch-on felt. BC now advise that the insulation is too thin: 100mm gives 0.22W/m2K, requires 0.18W/m2K. Is that reasonable? What is my recourse? can anything besides stripping the roof back to the deck and adding insulation be done? A quick googling reveals that 130mm should be OK: can 30mm be added under the main deck (between the rafters), or does this then stop being a warm roof?

Thanks.
 
If you consider it?

Why not [if you can afford it] fixing something thicker than the minimum 30. mm required? this will "future proof you?"
noseall said:
Yes, they will accept this.
Click to expand...
As an aside? would the additional thickness be jammed hard up to the decks underside or will there have to be a vent gap between top of the insulation and the underside of the deck? just wondering??
 
I make it 120mm insulation for a warm roof, although that might be influenced by the type of fixings.

You will need thicker than the difference, if making it in between rafters -as they create an element of bridging.

Strictly speaking this would be a hybrid roof which celetex etc dont recognise.......
 
KenGMac said:
will there have to be a vent gap between top of the insulation and the underside of the deck?
Click to expand...
This is what worries me: if you add insulation below, then the deck isn't as 'warm' as the room, so could collect condensation, requiring ventilation, like a cold roof. Not sure how likely that is with 100mm of solid insulation above though.
 
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