Porch 2 inch cavity

mrbg07546

Hi.

I am building a porch and also want to maximise space.

Is there anything wrong with a 50mm/2inch cavity? I know they recommend 100/4inch?

Anyone against this?

Doozergirl

As long as you have a separate front door.

The 4 inches allows a sensible amount of insulation, but if it's unheated and outside the front door, it isn't going to make a huge difference.

It's except from building regs, so no one is able to have a strong opinion.

Furts

Doozergirl wrote: »

As long as you have a separate front door.

The 4 inches allows a sensible amount of insulation, but if it's unheated and outside the front door, it isn't going to make a huge difference.

It's except from building regs, so no one is able to have a strong opinion.

But the crux here is countless people then move the front door to the wall of the new porch and the porch becomes habitable space. Then it all becomes a breach of Regulations, so it is up to OP how to play this one.

It is a certainty that the porch will be cold, all the more so if the new inner leaf is brick or concrete block.

mrbg07546

Ok well tHe intention is to adhere to building regs.

So is 100mm ideal? What's the minimum recommended as per building regs?

Doozergirl

mrbg07546 wrote: »

Ok well tHe intention is to adhere to building regs.

So is 100mm ideal? What's the minimum recommended as per building regs?

It's 100mm for rockwool to meet 0.3 uvalue, but if you use solid insulation, you can get away with less than a 300mm depth wall. It's not really the cavity that needs to meet BR, it's the insulation.

It's not subject to BR. If it were, I'd negotiate insulation and method with the BC officer.

Furts

Doozergirl wrote: »

It's 100mm for rockwool to meet 0.3 uvalue, but if you use solid insulation, you can get away with less than a 300mm depth wall. It's not really the cavity that needs to meet BR, it's the insulation.

It's not subject to BR. If it were, I'd negotiate insulation and method with the BC officer.

Even if partial fill with Celotex, Kingspan, Xtratherm or whatever there must still be a 50mm clear cavity. I would be surprised if OP could negotiate below a 300 nominal wall because even 50mm Celotex is old hat now. My walls are to this and fail to meet current Buildings Regulations.

Could be OK with appropriate dry lining - up to OP to check out the permutations here.

Doozergirl

Furts wrote: »

Even if partial fill with Celotex, Kingspan, Xtratherm or whatever there must still be a 50mm clear cavity. I would be surprised if OP could negotiate below a 300 nominal wall because even 50mm Celotex is old hat now. My walls are to this and fail to meet current Buildings Regulations.

Could be OK with appropriate dry lining - up to OP to check out the permutations here.

Note, I talked about reducing the width of the wall, not cavity in that post, and discussing methods.

KazB14

Use a 50mm kings pan board and not mineral wool. The mineral wall is what is being extracted and has too many down sides. Xx