"Neil Jones" wrote in message
...

. How much does it
cost
to
buy 70 m2 loft insulation, at a depth of 300mm?


What was the answer to this?



I'll answer my own question. About £300, as far as I can tell.

For the same price I can get enough boards of 25mm Kingspan to dryline
the solid walls downstairs, which would reduce the U-value to 0.6.

So the heat loss here would become

Walls = (27*2.1 - 5.9 - 3) * 0.6 * 24 = 688 W
+( 8*2.1 - 2.2 - 3) * 0.6 * 24 = 167 W
Walls Total = 855 W
Previous Walls Total = 2462 W

Saving = 1607 W

So I can either spend £300 to save 588 W, (£1.96/W) or I can spend the
same and save 1607 W. (£5.35/W)

If I go for 50mm Kingspan, the price goes up to £400, but the saving
goes to 1870 W. (£2.63/W for the extra £100, which still gives a
better
return than more loft insulation).

Alternatively, I could spend another £300 on 25mm Kingspan for the
upstairs and get another 1573 W saving, at £5.24/W.

[If Andy is right, and I'm only saving 392 W with the extra loft
insulation, it's £1.31/W.]

Extra loft insulation comes well down the priority list for my house,
because the cost/Watt saved is easily beaten elsewhere.


Whoops! These are all in Watts saved / £ spent, not the other way
around.

Neil