Questions About Flat Roof

[securespark]

Looking for a few answers as I have made enquiries to my local BC, but they didn't seem to be aware of the regulations as I found them on the internet.

This all came about because I want to insulate the room better because in winter it is freezing and in summer, very hot.

I had a replacement EPDM flat roof carried out in July 2011.

As far as I know, the roofer replaced the deck and the felting with a fresh deck and Firestone EPDM.

When I asked about insulation, he said it was adequate.

The extension was built circa 1970 with an unheated garage under and bedroom over, with a flat roof on top. AFAICT, the roof just has some thin rockwool between the ceiling and the deck. So, AIUI, it's a cold roof.

Coming to the crunch, the regulations say that after 2006, even refurbished flat roofs should have their insulation upgraded.

My BC did not recognise this and said if it was a "like-for-like" replacement, BR (or improvement of the insulation) would not have been required.

All the advice I see recommends if there is any flat roof refurbishment required, a warm roof installation is strongly recommended.

Could anybody enlighten me please?

Thanks!

 

[^woody^]

the regulations say that after 2006, even refurbished flat roofs should have their insulation upgrade

The regulations actually state that insulation must be considered, rather than being compulsary.

You are permitted to take into account the cost, the payback time, and the practicalities of any potential improvement.

You can felt over the existing covering, but if the covering is removed from more than 25% of the roof area, the regulations apply.

 

[securespark]

OK. So, given they stripped off the old felt and deck and replaced both, should they have upgraded the insulation or left it as a cold roof after considering the upgrade?

 

[^woody^]

The 'considering' involves a bit of working out, not just a quick rub of the chin. But strictly, it's not the builders job, but yours as the homeowner. However, the builders should perhaps of been aware of any regulation that might apply and notified you

But if your own building inspector had passed it, then that's it you're covered - colder but covered.

 

[securespark]

Thanks, woody. Hmm. That's the problem.
There was no building inspector. As above, my local BC reckoned it did not need an application as it was a like for like replacement (her words).

 

[John D v2.0]

I think to be honest, you just have to decide what you want to be done and specify that to the roofer. Building control are just a nice to have but may miss or misinterpret things. The roofer just wants to do whatever makes you happy and move on to the next job. You're the person who lives there so you're the only one who has an incentive to do better.

 

[securespark]

Thanks, John.
This all came about because I wanted to insulate the bedroom. Advice seems to suggests conversion to Warm Roof.
Can this be done without ripping off what has already been done?
Cheers.

 

[John D v2.0]

No because the insulation has to go where the felt is now, and the felt on top of that.
You could put the insulation on the felt and then felt again on top of that then it'd be a warm roof but there would be no real saving against ripping off the old felt. You'd ideally have to remove the existing insulation too, and certainly block up the cold roof ventilation to it.

 

[securespark]

5H1t.

I only had it done in 2011 and it cost 5K....

 

[John D v2.0]

Just ignore all that as it's a sunk cost. Just decide what you want to do going forward and if it's worth it then do it. Another option is to ree board the ceiling with celotex plasterboard but that's not a good way generally due to loss of height and you'd have the cost of ree skimming. Also keeping the timber within the insulation is better as you mentioned before.

 

[securespark]

Thanks, John.

Skimming is not an issue as the whole room is hopefull going to insulated (with Celotex?).

My first thought was to drop the ceiling and board with Celotex-backed board. A loss of about 60mm is bearable.

But there are two snags:

1. I was told I couldn't do it, as it would cause condescension.

2. I'm not sure if 50mm Celotex meets the insulation requirements.

3. Woody reckons if the void between the plasterboard and deck is filled chock-full of insulation, condensation would not be an issue.

 

[John D v2.0]

Any insulated buildup can cause condensation, you have to make sure the cold side is either vapour open enough relative to the warmer sides, or ventilated to outside before any less permeable surfaces.
If the ventilation is not great to stary with then it'd be a worse idea. Perhaps your ventilation is too good, hence the thermal issues!
50mm is similar to 100mm wool, so nowhere near the requirements, but still a lot better then a solid wall or an uninsulated timber floor. You'd probably need around 120mm to meet building regs if that's the level you'd be happy with.
Theoretically if no air movement can occur through the insulation there's no way of getting condensation. Some people make passiv haus designs that have almost no air leakage and little heat loss, with a relatively fanatical approach to detailing. However it's not something I've seen recommended elsewhere. If you're adding any cables or you don't have a sealed vapour barrier on the inside then airs going to move through.

 

[securespark]

Thanks very much for your advice. I shall add it to the list of stuff I am going to talk about with the architect and SE.

 

[geraldthehamster]

I see no reason why you couldn't, in principle, fit 100mm+ of Celotex on top of the existing EPDM covering, and cover it again. Either EPDM directly onto the new Celotex, or another deck of 11mm OSB on top. The existing EPDM below would provide an excellent, albeit expensive vapour barrier. Of course if height is an issue this might be difficult. And you would need to make sure that any ventilation above the existing insulation was prevented.

EPDM roofing is a pretty easy DIY job, by the way.

 

[securespark]

Thanks, GTH.

I'll check the headroom.