"Neil Jones" wrote in message
...

"Andy Hall" wrote in message
Supawrap from BuilderCenter is £12.66 exc. for 4sqm and 150mm thick.

So for 70sqm coverage you would need 35 rolls to achieve a thickness
of 300mm at a total cost of £520. This appears to be the cheapest
they have on a volume basis. You could probably get 20% discount,
so say £400.

On your assumed U value of 0.5, which is worse than it probably is,
you are saving 588W worst case.

If the temperatures were worst case all year all day then at 1.4p a
unit for gas you would save £72 per annum.

If you work on the 10 degree average which is closer to reality, then
the loss is going to be 8/21 x the figure - i.e. 220W and £27 per
annum.

In reality, the insulation you have is probably better than 0.5 and
the saving perhaps £20 per year.

A 20 year payback or 10 years if energy costs double today....

Doesn't seem interesting to me.

I'd think about using even a thin Celotex layer on a few outside walls
during redecoration first, if that's practicable. This is about
£5/sqm for 50mm, 25mm is about £3.50.


Exactly, although I'm looking at Kingspan rather than Celotex.

Do both. Loft and walls.



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