New insulation refurb regs. Bld control not sure

[trevorbayliss]

I am doing a refurb on a top floor flat. So i have ripped out all the old Pb and small lath walls to reveal a shell.

The building control guy is not sure on the new regs and said he will get back to me on what i need to put back.

He is saying i can leave the 50mm rigid foil insulation in between the roof joists and under board with 50mm. So 100mm rigid insulation on the roof.

The flat dorma can have the same, so 100mm.

The dorma sides he wasnt sure, It is 75mm deep here.

On the small eave walls he wants 150mm rigid which doesnt seem right.

Uvalue to achieve is 0.16 on any roof part and 0.3 on walls (i think).

Anyone know about this topic ?

 

[oldbutnotdead]

Check your U values, I'm sure 0.3 was the old number for walls. 100mm in the roof sounds very skinny...

 

[trevorbayliss]

0.3 in walls seems to be the new regs from my reading. Not new build, but renovation / upgrade on a building.

100mm does seem skinny, but what happens when you cannot add too much insulation under the rafters ?

Do you just not carry out any improvement works then. Surely a bit more insulation is better than not upgrading.

 

[oldbutnotdead]

Fair enough. Yes if you've got limited headroom any is better than none but specially now (with energy costs where they are) it'll be worth overinsulating an otherwise naturally cold space if you can.

 

[tony1851]

The 150 he wants in the eaves walls is off the top of his head and will not be as cost-effective as extra insulation in the roof, as per O.B.N.D. Consider just a little more on the underside of the roof - say 75 instead of 50 if the headroom still works for you, and just 100 in the dwarf wall.

The bottom line is that the level of refurbishment insulation is down to what's reasonable, and cutting down floor space and headroom is pointless if you can't use the room for lack of space. Is your inspector private or LABC? The latter tend to be a bit more picky.

 

[trevorbayliss]

He’s private but doesn’t seem to know the regs.

I have read some of part L and it says what is practical and functional.

50 under the eaves is the most I can add really as it was tight in places with just plasterboard. So this has been removed, but I need to add it back plus the 50 mm. Insulation

 

[jeds]

You should be referring to regulations for 'renovation of thermal elements', which is table 4.3 column b.
Roof; 0.16
Walls - internal or external insulation; 0.30
Which concurs with your figures.

It then gets a bit confusing because 100+50 in the roof gives you 0.18, so 50+50 is nowhere near?

 

[tony1851]

He’s private but doesn’t seem to know the regs.

To be fair, I doubt anyone does now!
They can quote the required U-values for each element, but ask them how to achieve that and it's another matter.

 

[trevorbayliss]

Thanks for info.

I have seen the manual and the 01.6 U value and then you have 100 plus 50 and it doesnt get there. So it is all a bit confusing.

I think i will get away with 100 in the slopes due to the practicalities of getting more in.

The eave walls looks like 75-80mm rigid will be ok. I wonder if BC was referring to soft insulation at 150mm ?

The flat roof is being redone and i think i can get 150mm in there to make it a warm roof.

I will ring technical for some of the companies this aft to see what they say.