Roof insulation - HELP asap please

muz39 · 12 Mar 2014

We live in a 1930s semi and are due to have the roof retiled next week. Can anyone advise me please - our roofer said he is going to use 50mm unsulation between the rafters, but then said this won't satisfy the inspectors?
The bit of research I've done since suggests we need a 50mm airspace and 100mm+ of insulation. If we go with what he is suggesting, what are the likely consequences??

we are on a really tight budget so if its something we can easily change, ie if we need to sell up at some point, Id rather do it later.

the attic space is fully boarded out and was used as a part time room by previous owners.

thanks so much!

Toproofer · 12 Mar 2014

So the attic as stairs up to it and plaster boarded out?? If so you can only put in so much insulation depends on rafter thickness!,so if rafters are 3"x2" then 50mm max cellotex between rafters in be fine,building control shouldn't have a problem with that surely,

tony1851 · 12 Mar 2014

If you are incorporating breathable felt when re-tiling, a 25mm airspace would be fine.
But why 100mm insulation? Are Building Control involved?
Just go with 50mm. If there is no fixed ladder or staircase to the room, you can pretty well do as you like.

jonez · 13 Mar 2014

Since October 2010 if more than 25% of a roof is replaced then it falls under building control notifiable to the LABC. To be compliant the average U value must be 0.15U or better and any individual element must be 0.7U or better.

The consequences of using less are that your heating bills will be higher and if it's obvious that the roof was done after the regulations changed then if you sell the property a buyer may want to see the sign-off documentation from building control.

JohnD · 13 Mar 2014

do you mean you want it to be a loft conversion?

theoldun · 14 Mar 2014

jonez said:
Since October 2010 if more than 25% of a roof is replaced then it falls under building control notifiable to the LABC.

Thie above part is correct, how ever to comply with L1B 2010, the U value required for insulation between the rafters is 0.18Wm2/K (This is due to change 6th April 2014). To achieve this target, you need either 165mm Celotex between rafters or 100mm between and 65mm below.

The other reason for being notifiable is that if you are stripping the roof of say slates and replacing with concrete tiles is that he roof will with stand the additional loading.
Make sure you use a breathable felt
oldun

Toproofer · 14 Mar 2014

jonez said:
Since October 2010 if more than 25% of a roof is replaced then it falls under building control notifiable to the LABC. To be compliant the average U value must be 0.15U or better and any individual element must be 0.7U or better.

The consequences of using less are that your heating bills will be higher and if it's obvious that the roof was done after the regulations changed then if you sell the property a buyer may want to see the sign-off documentation from building control.

It's all well and good trying to follow building control protocol but common sense must prevail when stripping a old roof off, most of the time rafters are 2x2 or 3x2 inch and if its a attic room which as been plasterboarded out max celotex you can get in is 50mm, I've done some jobs where you can only get in 25mm celotex,due to ceilings been old lath and plaster!! Building control officer was fine about it,like he said,some insulation is better than none

tony1851 · 14 Mar 2014

Yes, where space and headroom are at a premium in loft conversions, Part L allows a reduced standard of insulation.

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Roof insulation - HELP asap please

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