Is this gap causing the draught?

[u/junglist1]

I have a room below this roof which was made as part of an extension in 2019. It is like an ice box in winter and doesn't warm up at all even with the heating on. There is definitely insulation above the ceiling.

I've felt the draught coming from under the skirting and have blocked it with foam strips. Also had the windows and french doors checked and they have no gaps when closing.

I had a roofer around today and asked him to have a look at it. In his opinion, the gap is there for any drips from the tiles to come down the felt and into the drain. He lifted the felt and found a gap above the cavity wall which he filled with expanding foam. However, the room still feels cold.

Calling the original builder back isn't an option as he left the work unfinished and I had to get someone else to come and do the finishing.

Any help is greatly appreciated.

[u/LondonCollector]

I can’t make out what that is.

Have they created a platform to lay tiles over a felt roof?

[u/junglist1 → u/LondonCollector]

Yes I believe so. Roofer said they must have done it this way due to the pitch of the roof.

[u/Massive_Worker5827]

This detail is called counter batten, but you would normally have the felt between the horizontal and vertical battens.

Not sure if they did it all the way up the roof or just for the first few courses, but it's normally part of a ventilation detail.

It's normally required with a vaulted ceiling where the insulation is placed between the joists. However, the ventilation detail would normally flow under the felt, not above it as here.

The other option is your roof just wasn't flat and they've packed battens up to make the slate neat. And the foam is blocking the intended ventilation gap.

[u/junglist1 → u/Massive_Worker5827]

I've checked some photos of the construction phase and this sounds like what they've done. But the felt is below the battens not above for some reason.

[u/M0ntgomatron]

Sounds like the extension is poorly insulated. Foaming up that section will stop the airflow needed above your insulation and will cause more issues. That was absolutely not the solution.

[u/junglist1 → u/M0ntgomatron]

Thanks. I think so too. I know they put in probably 200mm wool insulation but that would have left a considerable gap between the felt and insulation at the highest point of the pitch.

Now I need to find an easy way of topping it up.

[u/M0ntgomatron → u/junglist1]

It's most likely the wall insulation that's the issue. 200mm wool isn't quite enough in the roof.

Stopping the draught at the skirting boards will certainly help. Cold air coming in means warm air is being pushed out somewhere.

Be careful not to create a sweat box. Airflow is needed, but in the right places. If you have e trickle vents on the windows, open them once a day for an hour or so. Or you'll have mould.

If you top up the roof insulation, make sure you leave air flow at the eaves (even though that foam is stopping the air flow.....)

[u/Professional-Stage76]

Im no detective, but if you felt a draft and the room is cold and it wasn't drafty and cold before.

Then yes, is your answer

[u/seifer365365]

Keep the roof cool. Healthy and in good condition

[u/nearmiss2]

Hi, It depends on whether you had a cold roof or warm roof installed.

I suspect it's a cold roof design, so the roof will have airflow built in, the airflow is in the cold area above the insulation. It should not cause draughts or be much less efficient than a warm roof design.

Mineral wool type insulation should have been 300mm deep in 2019, to achieve u value below 0.2 as per building regs at the time or 120mm of PIR insulation.

If its less than that top it up to 300, but don't block the ventilation at the perimeter

Is there an access hatch, is it insulated and draught proofed? I always add a 120mm pir board to the back of any access hatches and use door draught seal if it hasn't got any seal.

Edit... Walls and floor should have been insulated too as they loose just as much heat as roof. 100mm pir or 200mm wool.in the walls, 100mm pir between solid floor and top screed or 200mm wool between joists of suspended floor. Buy a cheap thermal.heat detector off amazon and scan the whole extension, roof, floor, walls, it'll show you where the cold spots are

Infrared Thermometer, Helect Digital Laser Infrared Thermometer Pyrometer (-50 °C to 550 °C) with LCD Lighting https://amzn.eu/d/eDFXeo6

[u/junglist1 → u/nearmiss2]

Thanks for the detailed reply. The floor and walls were insulated properly. I will have to make a hatch and check the ceiling insulation.

[u/homer994 → u/nearmiss2]

Sound advice. Additionally, inspect the areas around any spotlights, as these are often significant sources of air leakage.

The external eaves detail is clearly incorrect. While it’s uncertain whether this directly contributes to internal air leakage, the gutter height and overall build-up are evidently flawed. Could it be that the bottom slate has been pushed upwards?

I recommend removing all joints around doors and windows (including heads, cills, and jambs) and applying a high-quality airtight tape. Once sealed, the plasterboard should be reinstated. I’m happy to recommend suitable products for both airtight tape and spotlight covers, if they’re accessible.

That said, nearmiss2’s advice is correct. The roof build-up and design are likely contributing to internal air leakage within the property.

[u/Strong-Potatoes]

What in god's name am I looking at , Jesus Christ never seen that before

[u/Competitive_Time_604 → u/Strong-Potatoes]

It can only be described as a slate storage rack, serving little purpose other than to keep slates ready to repair the other roofs.

[u/Strong-Potatoes → u/Competitive_Time_604]

Honestly wild bro lol

[u/Cartepostalelondon]

'Part of an extension built in 2019'? Why wasn't it properly insulated?

[u/junglist1 → u/Cartepostalelondon]

I mistakenly assumed it was. In hindsight I should have checked how it was done. Got a feeling they just stuffed some wool above the ceiling plasterboard

[u/Cartepostalelondon → u/junglist1]

Did building control have to sign it off? Did you check the work would be guaranteed through an insurance scheme? Did you receive a detailed quote, invoice and receipt for payment?

If I were you, I'd give them a chance to rectify it. If there's no satisfactory outcome, pay a surveyor (not a builder or anyone else with a vested interest in being payed for work) to come out and look at it and give you their considered opinion in writing and take legal action.

Though the question of why it's taken nearly five years to complain may arise. Any warranty may have expired in any case.