Floor insulation and building regs

juraj.kecso

Hi All,

I am planning to insulate our ground floor suspended timber floor (between the joists). I will probably use 200mm mineral wool supported by netting with DPM on top as it is a lot cheaper than using Celotex/Kingspan.

Has anyone done it this way?

I have all this worked out, but am slighlty struggling with how this works regarding building regulations. Do I need to tell someone that I am planning to do this work? Who will I have to tell, my local council? Will they have to send an inspector? How much would that cost?

How would they ever find out if I didn't tell them?

bengalknights

Dont believe this falls under building regs, but if it did your installer should report it to the council.

Davesnave

You'd only have to report it to the council if it was part of measures to make an extension (or converted part of your property, like a garage) compliant with the regulations for energy efficiency in habitable spaces. It would then be part of a package of work monitored by a building inspector or other qualified person.



So you don't need to tell the council.

juraj.kecso

I am planning to do this myself, it seems to be easy enough job; pull out the floorboards, insulate pipes, put down the netting and insulation, replace floorboards.

According to Energy Saving Trust:

"If you are adding extra insulation to your floors, the work will need to comply with the relevant building regulations for where you live. Your installer will normally arrange this for you, but if you are doing it yourself, it is your responsibility to comply."

Doozergirl

I'm sure they're wrong and Davesnave is right.

When you own a house, the building regs that apply were the ones in force at the time it was built. You are allowed to improve on that, but you can't make it worse.

If you replace the roof or knock the plaster off the walls, there are regs to comply with for energy efficiency. Probably if you dig out the floor and replace it as well, but not to apply to the underside of existing boards.

Davesnave

juraj.kecso wrote: »

According to Energy Saving Trust:

"If you are adding extra insulation to your floors, the work will need to comply with the relevant building regulations for where you live. Your installer will normally arrange this for you, but if you are doing it yourself, it is your responsibility to comply."

Yes, it ought to comply, if possible, but that is not the same as stating a need to report it, have it inspected, or meet current standards if it's a one-off small improvement.

FreeBear

Does it need to comply with building regulations - Probably, and it is as well to meet or exceed the required standard.

Does Building Controll need to be notified and the work signed off - It doesn't fall under "notifiable works" as far as I'm aware, so BC do not need to be informed unless it is part of a much larger program of works that would fall under their remit.

As for putting in 200mm of insulation - Be very careful not to block air flow under the floor. I did consider doing something similar when I was renovating my lounge. The boards are lounge & groove, so would be a right royal pain in the ... to lift. The joists, only 3x2 resting on small sleeper walls - The effort to fit minimal insulation outweighed the projected savings. Ended up putting down a thin layer of wood wool boards topped with decent underlay and carpet. Has been nice and toasty in there for the last couple of winters (the new stove probably helps there).

king132

The joists need to 'breathe' so putting a layer of DPM underneath as netting is a bad idea, you'll end up with condensation which can't go anywhere.

I did this work on my suspended floor and i used Celotex in between joists - was told by BC to leave a 15mm gap from joist level down to Celotex level and i stapled breathable roof membrane instead underneath to act as a net.

I'm not sure how effective mineral wool in between floor joists would be, but i'd personally just go Celotex or even polystyrene and go for a tight seal in between joists to stop any heat dissipating through the floor.

juraj.kecso

Hi All,

Thanks for clarifying the difference between complying with building regs and reporting it. How would it work if selling the house in the future? Can the prospective buyers insist on building regs inspection/sign-off?

Also, I was planning to place DPM on top of the joists before replacing floorboards. I will make sure that the space underneath joists is well ventilated and put a thinner layer in over sleeper walls to leave a gap.

troffasky

juraj.kecso wrote: »

How would it work if selling the house in the future? Can the prospective buyers insist on building regs inspection/sign-off?

If you weren't legally obliged to have it inspected and signed off in the first place then nobody can insist on anything.

Doozergirl

I wouldn't put the DPM there. No need. And the joists will be able to breathe from above without it.