Timber frame insulation - most cost effective?

10 May 2011
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West Midlands
United Kingdom
What is the most cost effective insulation to acheve a u value of 0.18 roof, 0.22 floor, and 0.28 wall

Based on the celotex calculator, the following thicknesses are needed.

Roof cold deck - 100mm between plus 52mm
Suspended Timber floor 120mm
Timber frame wall. 60mm between plus 24.5

However celotex seems rather expensive. Is there a more cost effective option?
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I cant confidently answer your question, perhaps google can.
But FWIW: cold flat roofs are frowned on nowadays, Councils prefer warm roofs.
Just a thought, basildon.gov.uk ... download documents ... guidance on Part-L Insulation
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The only other real alternatives are polystyrene and fibreglass. Although a lot cheaper, both these products will only give you roughly one-half the insulation value of the PUR/PIR boards.
So, for example, to achieve the same U-value, a roof would need around 280mm thick fibreglass. How practical would that be if it was - say - a flat roof?
Thanks for the link re Basildon Council.

I have tried google, other altenative looks o be multi foil. Some ranges such as YBS Superquilt seem to have approval for building regs.

Roof seems to need 2 layers, or 1 layer plus 90mm PIR (rather than 100m PIR plus 40mm PIR). For suspended timber plus, just one layer.

For floor use, superquilt works out at £7.50/m2 rather than £14.50 for 120mm PIR.


if i'm giving wrong advice, i apologise and thank you for correcting me.
But my experience, and the experiences of others, submitting for cold flat roofs this last ten years or so, was why not go for a warm roof where applicable.
For floor use, superquilt works out at £7.50/m2 rather than £14.50 for 120mm PIR.
Floors are more problematic - you can't just assume a certain thickness of insulation will give you the required U-value.
You may need more - or less - thickness than that to achieve the required value. It depends on the relationship between the area of the floor and its' perimeter.
eg a floor 4m wide x25m long will loose more heat that a floor 10m x10m, even though they are the same area,so the latter will need less insulation than the former. In some cases, the need for additional insulation can be almost marginal.

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