Assistance required Brick, Cavity Brick Wall - Building Regs

[NatalieB]

Hello, 

I'm currently looking for a bit of advice or guidance as i am completing a rear single storey extension. (Foundations have been done needed to change to piling which was a bit of a nightmare but its now done). We originally had the plans drawn up for 103mm brick external skin:100mm cavity filled  with earthwool dritherm 32 ultimate insulation batts and inner skin of 100mm thermalite turbo blocks and 13mm plasterboard. We have decided to change one of the inner skins to reclaimed bricks (already purchased as unaware this would be an issue, in hindsight we should of released this would change our insulation requirements ) We have spoken to building regs who have advised we need to unsure we are adhering to 0.18uvalue which could require a change in insulation or maybe cavity depth. I'm currently trying to work out if i need to change the insulation type and or make the cavity wall deeper. Any assistance would be great 

[Declan52]

Use insulated plasterboard on the inside to get your u values acceptable to the building control officer. How deep will be a trade of of how warm you want it to be plus how much you can afford to lose inside. 100mm insulation would be great for heat loss but can you lose that much on each wall.

[Mr Punter]

Just now, Declan52 said:

Use insulated plasterboard on the inside to get your u values acceptable to the building control officer. How deep will be a trade of of how warm you want it to be plus how much you can afford to lose inside. 100mm insulation would be great for heat loss but can you lose that much on each wall.

 

I guess they wanted exposed brickwork inside.  Increase of cavity would be easiest.  You could use Kingspan insulation.  You are allowed a poorer u value if you compensate elsewhere.

[markc]

Are you looking at using the reclaimed bricks as a feature? I.E. exposed brick instead of the plasterboard?

damn! Mr Punter bet me to it.

Edited January 8, 2021 by markc

[Jason L]

Hi   look at using a PIR insulation in the cavity for that part, such as Kingspan, ( other are available )  that will provide the u-value

[NatalieB]

Thank you everyone for your assistance, its really appreciated ?

 

[A_L]

4 hours ago, NatalieB said:

We have spoken to building regs who have advised we need to unsure we are adhering to 0.18uvalue which could require a change in insulation or maybe cavity depth.

 

Why? Table 2 (page16) of Part L1B says 0.28 for new thermal elements in an extension

 

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/697629/L1B_secure-1.pdf

 

The Thermalite/Plasterboard option is 0.24

Edited January 8, 2021 by A_L
to improve jpg

[MikeGrahamT21]

@A_L is right, extensions have a higher allowable U value so your BCO has made a mistake there... either way you want it as low as possible, take a look at xtratherm cavitytherm, it’s full fill cavity insulation which should get you around or just below the 0.2U mark with that build-up

[NatalieB]

Hello All,  Yes you are right building regs have confirmed they made a mistake it should be 0.28. I have put the question to Kingspan just waiting on a response will also look at xtratherm cavitytherm Thank you everyone ?