7.3N Block U-Value

[Sophiae]

Good morning everyone

 

The SE specified 7.3N blocks for the new (single story rear extension with a beam for the bifold doors) partially filled cavity wall. 

With the new regs I am trying to lower the U-Value as much as possible taking in consideration that this wall now is going to eat up so much for my intended space. 
 

Blocks outer leaf 100mm finished with Render

100mm PIR insulation 

50mm Residual cavity

Blocks inner leave 100mm

Plasterboards

 

My question is are there any 7.3N blocks with a u-Value below 18 out there? 
All I found online was 18 and above. 
 

All suggestions are much appreciated. 

Edited June 8, 2023 by Sophiae

[Carrerahill]

The makeup will be 0.18 - the block on its own is not as good as that. 

 

If you can, use thermalite blocks on the inner, that will help too. 100mm con block, 50mm cavity, 50mm PIR, 100mm thermalite block gave us the requirement on a recent build (signed off last month) and we are in Scotland with more onerous targets to hit.

 

I realise the whole thing is in connection with the floor and ceiling, but nothing we had was too bad to comply. 

 

 

 

Edited June 8, 2023 by Carrerahill

[Sophiae]

34 minutes ago, Carrerahill said:

The makeup will be 0.18 - the block on its own is not as good as that. 

 

If you can, use thermalite blocks on the inner, that will help too. 100mm con block, 50mm cavity, 50mm PIR, 100mm thermalite block gave us the requirement on a recent build (signed off last month) and we are in Scotland with more onerous targets to hit.

 

I realise the whole thing is in connection with the floor and ceiling, but nothing we had was too bad to comply. 

 

 

 

Thank you for your response and suggestions. 
my floor and roof will have 150mm PIR. The builders suggested the 100mm PIR for the walls as they knew I wanted to get below the target 18 for the walls over all. 
 

[Sophiae]

This is what I am looking at, so if there is any other option as most require about 100mm PIR insulation boards to get below the 0.18. 

[Sophiae]

Here is another one

 

[Dave Jones]

Use the cheap 3.6n lightweight aerated concrete blocks on the inside skin, that will give you a pass with 100mm celotex

 

 

 

[Sophiae]

Am I ok to use the 3.6N on the inside leaf with a bean sitting on top? 
I’ll have a look again at the SE’s design. 

[Caversham Passivhaus]

Also doing a single storey, SE recommended 7.9N/mm2 "a standard strength" - but as we are looking at a single storey section of wall we can reduce, looking at Part A: Structure pg. 24, 2.9N/mm2 blocks are allowed with the best thermal u-values.

[LSB]

it's interesting that you can possibly do something different from SE recommendations, our BC checks everything we do against the SE drawings to make sure we comply, and we are single storey.

That said we always specified 3.6 internal, although as they are not particularly good for some things we are using 7.3 for walls where we want to hang things, such as the kitchen.

We have 150 full fill cavity.

 

[Caversham Passivhaus]

It was the initial SE recommendation, after questioning the SE stated we can reduce.