Loft insulation from the outside and building regs

[Jim]

A friend has a house in the chalet bungalow style where access to a lot of the roof is difficult because it is behind sloping areas of plasterboard or low stud walls in the bedrooms. If he were to insulate in between the rafters by removing tiles from the outside of the roof would this count as notifiable work under building regulations?

I think it would be troublesome to bring fully up to current specs because the rafters aren't deep enough.

I've read through the Part L document but I can't find a bit specifically about loft insulation - I was convinced there was some kind of one-time get out for it?

[RobertL]

Doesn't it depend on what percentage of the roof area you change. I thought if you modified more than 25% of a thermal unit it then became a BC matter and you had to bring it all up to part L.

BTW, if he does this, make sure the insulation doesn#t block the ventilatiopn of the space leading to damp problems.

Robert

[John Rumm]

The other thing to consider is that many BCOs will take the pragmatic approach anyway, and recognise that any improvement is a good thing, even if the limits of the existing building dictate that modern standards are not realistically achievable.

[geraldthehamster]

Yes, it would be notifiable. And obvious ;-)

I know it might seem like a lot of faff to him, but mightn't it be easier (not to say safer) to do it the "proper" way, rather than removing the entire roof? A day to pull out the plasterboard, then

50mm Kingspan between (leaving one or two inch air gap depending on whether 3x2 or 4x2 rafters), 50mm below, new PB, and skim? That doesn't quite conform to regs (50mm air gap and 5 inches Kingspan) but, who's to know he's doing it?

I also don't see how you could easily install a proper vapour barrier from the top - which is taken care of if you install foil-backed Kingspan underneath.

Cheers Richard

[geraldthehamster]

PS - he'd also need to remove all the roofing felt/membrane, as well as the tiles, to get to the rafters, and then replace it again. While he's doing the work, his roof is off and his first floor is exposed to the elements.

I really don't think this is the way to do it ;-)

Cheers Richard

[Phil L]

If the roof is in bad shape and needs replacing then it would be feasible, other than that I wouldn't bother as the whole roof will have to come off.

re-roofing isn't notifiable, provided he's not changing the skyline, that is to say if he is raising or lowering the roof, he needs PP.

It would by cheaper, easier and more effective to retrofit kingspan over his existing ceiling, plasterboard and skim.

[dom]

Exactly what I would suggest too.

Or if it's feasible, use kingspan backed plasterboard, and bond it directly to the areas where the ceiling follows the roofline.

[Jules]

Can't he use blow-in insulation? It should be possible to do that with a minimum of disruption. Or is blow-in insulation not allowed in the UK for some reason?

cheers

Jules

[geraldthehamster]

Surely if you blow insulation into the spaces between rafters, between the roofing felt on the outside and the plasterboard on the inside, all the moisture from the interior will condense amongst the insulation, and on the timbers? Where's your vapour barrier?

You could fix Kingspan or insulation-backed plasterboard over the existing internal finish, but you'd lose space from the room. Better to do it properly; the result will be much warmer.

Regards Richard

[geraldthehamster]

On 15 Feb, 19:54, geraldthehamster wrote: insulation, and on the timbers? Where's your vapour barrier?

Actually, and replying to myself, he's going to lose space from the interior anyway, isn't he, if he insulates between and over? So he's probably not going to lose any more interior space if he simply adds

50mm Kingspan and PB over the existing finish.

However, it won't be as warm as if he insulated between as well, and IME it's worth stripping the old out to take the opportunity to uncover any horrors.

Cheers Richard

[Jim]

I agree :) - especially the fact that you can't just remove the bottom section of the roof easily because of the way the tiles overlap.

I think he's trying to avoid causing a lot of damage/redecoration inside however.

[geraldthehamster]

Probably, though that's a bit like my endless quest for a way to insulate under my suspended ground floor without lifting the boards - there isn't one ;-)

Cheers Richard

[Hugo Nebula]

It would be notifiable, as a renovation of a thermal element.

Approved Document L1B (2006) is the one applicable. Sections 54-55 & Appendix A gives the advice you're looking for. To summarise; "if such an upgrade is not technically or functionally feasible... the element should be upgraded to the best standard that is technically or functionally feasible". Appendix A describes what to do in your friend's situation.

Is it detached? If so, and they intended to replace all the roof covering, they could consider insulation over the rafters.

[geraldthehamster]

If they raise the roof level by insulating over the rafters, wouldn't they need to re-do their fascias, soffits and guttering as well?

Cheers Richard

[John Rumm]

The soffits ought to be ok, the facias will need to be taller. You might get away with uPVC facia capping that is taller than the current board, nailed over and the gutter refixed a tad higher.

[Andrew Gabriel]

I've done this a few times (for other reasons, such as replacing the felt), and it's not difficult, although it will depend on the tiles.

Slide the third row of tiles up under the 4th row. Now you can unhook the second row (although still a bit fiddly), and then the first row.

If you intend to pile them up on scaffolding, make sure you specified that before the scaffolding was built, as piles of building materials can be very heavy.

[terry]

Suggestion; use blown in insulation to more tha fill in and cover the ceiling joists, and make sure there is a vapour barrier on the warm side, i.e. the ceilings below the attic. A vapour barrier can sometimes be provided by certain types of impermeable (probably 'oil' based paint)?

[geraldthehamster]

And create an air gap for ventilation between the insulation and the roofing felt how, exactly? ;-)

Hmm.

Cheers Richard