Current building regs for a cavity wall.

[Russell griffiths]

Having a discussion with a builder. 

Can anybody tell me what amount of insulation is needed in a cavity wall to meet current regs. 

I was under the impression it has changed a lot and you now need substantial cavity insulation plus insulted plasterboard. 

 

He is saying 75mm of cavity batts in a 150 cavity is good enough, I’m disagreeing. 

 

Can i I have it for a new build as well as an extension please. 

Sorry to be a pain, but I might have to buy him a beer if I’m wrong 🤦🏻‍♂️

 

Anybody point me at current levels. 

Cheers. 

Edited December 10, 2022 by Russell griffiths

[SteamyTea]

Think the current value is 0.3 W.m^-2.K^-1, changing to 0.26.

Really up to you to tell him what u-value you want.

Sounds like he is going to do a crap job anyway, as he probably thinking any insulation, no matter how badly fitted, is all that is needed.

How you going to deal with airtightness and vapour migration?

[ADLIan]

Effective June this year 0.18 for new wall in an extension. May get away with a little higher in new build dwelling. Your wall need a total redesign.

[Russell griffiths]

21 minutes ago, SteamyTea said:

Think the current value is 0.3 W.m^-2.K^-1, changing to 0.26.

Really up to you to tell him what u-value you want.

Sounds like he is going to do a crap job anyway, as he probably thinking any insulation, no matter how badly fitted, is all that is needed.

How you going to deal with airtightness and vapour migration?

I’m not. 

Im sitting in a pub having a heated discussion. 

[Russell griffiths]

4 minutes ago, ADLIan said:

Effective June this year 0.18 for new wall in an extension. May get away with a little higher in new build dwelling. Your wall need a total redesign.

Any idea what insulation is needed to achieve this. 

[Russell griffiths]

Exact information. 

 

Im sitting in a pub with a bunch of builders. 

This isn’t a house I’m building, or an extension. 

Builders are saying they are currently using 75mm wool type batts in a 150mm cavity with no other insulation and this is fine. 

Im saying it’s shite and doesn’t come up to current regs. 

 

Who's right. 

 

Beer is at stake. 

 

[SteamyTea]

Download the regs 

 

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1082748/Merged_Approved_Documents__Jun2022_.pdf

 

 

[Canski]

I'm just getting through with 100 mm thermalite, 125 mm beads blown in and 102 mm facework this is on the new regs.

 

[nod]

75 mil is pretty normal 

Insulated pb is unusual 

Weve recently plastered a self build that had specified 100 mil Celotex in a 125 cavity which wasn’t practical to build So he went 75 mil batts in a 125 cavity 

man’s insulated pb on the inside of the house 

Expensive mistake on the Architects part 

[saveasteading]

38 minutes ago, Russell griffiths said:

Who's right

You are of course, unless they can tell you where the offset is.

They can offset a shortfall in the wall as long as it reaches minimum standard, with extra elsewhere.....but they probably use the same argument for the floor and roof and windows.

The build quality is more my worry., having seen affordable housing with complete gaps.

Ask them about airtightness?

 

Actually my main concern is builders who just ignore the drawings, through ignorance and sometimes arrogance.

[Gone West]

48 minutes ago, Russell griffiths said:

Beer is at stake. 

Brick and Thermalite with 75mm batt in 150mm cavity is coming up as U=0.28.

[Radian]

48 minutes ago, Russell griffiths said:

Im sitting in a pub with a bunch of builders. 

This isn’t a house I’m building, or an extension. 

Builders are saying they are currently using 75mm wool type batts in a 150mm cavity with no other insulation and this is fine. 

Im saying it’s shite and doesn’t come up to current regs. 

 

U-value: 0,267 W/(m²K)

 

[Radian]

2 minutes ago, Gone West said:

Brick and Thermalite with 75mm batt in 150mm cavity is coming up as U=0.28.

I always put the cavity as being at the rear ventilated level (outside air) because most janky builders leave walls like sieves. If I make that installation level, it drops to 0.254 which puts my calcs either side of yours. The Knauf Insulation was only available in 80mm so that helps them. Couldn't be arsed to find a 75mm batt. Either way @Russell griffiths has to win the pint.

 

[saveasteading]

Except that 0.27 is better than the minimum 0.3.

But a long way off 0.18 so there will neeed to be an awful lot in the roof. 

I wonder who is supervising.

[Russell griffiths]

18 minutes ago, Gone West said:

Brick and Thermalite with 75mm batt in 150mm cavity is coming up as U=0.28.

That’s what I made it. 

It needs 50mm of insulated plasterboard on the inside as well in my opinion. 

[ETC]

3 hours ago, Russell griffiths said:

Having a discussion with a builder. 

Can anybody tell me what amount of insulation is needed in a cavity wall to meet current regs. 

I was under the impression it has changed a lot and you now need substantial cavity insulation plus insulted plasterboard. 

 

He is saying 75mm of cavity batts in a 150 cavity is good enough, I’m disagreeing. 

 

Can i I have it for a new build as well as an extension please. 

Sorry to be a pain, but I might have to buy him a beer if I’m wrong 🤦🏻‍♂️

 

Anybody point me at current levels. 

Cheers. 

Irrespective of what the Guidance say you should be putting in as much insulation as possible. 75mm is a bit on the low side. For 0.18W/m2K you’re looking at 190mm of Rockwool. Other insulants will vary in thickness.