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Building Regs, retained thermal elements question, adding an extension to a garage wall

Discussion in 'Building Regulations and Planning Permission' started by lora272, 12 Sep 2021.

  1. lora272

    lora272

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    I am drawings the plans for a client who is having a small room, a gym (10msq) added onto the back of their garage. The new room will be sharing the existing wall to the rear of the garage.

    The garage is not insulated, and adding insulation and plasterboard to the gym side of the wall will still leave a thermal bridge by the bricks. Are there any solutions to this problem?, other than demolishing the wall and rebuilding it?

    The building regulations is quite confusing, it talks about retained thermal elements and 50% (the extension will cover more than 50% of the rear wall). But then has U values for retained elements and updating them etc.

    Im quite lost and would appreciate any advice.
     
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  3. ^woody^

    ^woody^

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    Lining with insulation deals with any thermal bridge doesn't it?
     
  4. lora272

    lora272

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    The new inner block layer meeting the old outer brick layer would thermal bridge I believe.

    Here is a diagram, pink being the insulation, blue the new inner layer of the extension, red the old external layer of the garage
     

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  5. ^woody^

    ^woody^

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    The blue should not be touching the red
     
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  6. lora272

    lora272

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    But doesnt the blue inner layer need to tie into the existing red wall for support, it cant just float there.

    Or Ive just thought should there be an extra leaf added to the existing such as the new image, that way the insulation would be continuous? But then I guess the foundations would need redoing for that exisiting wall?
     

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  7. Swwils

    Swwils

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    The garage is presumably uninsulated space (or close enough) and so the new gym is all treated like external walls, even the one where the garage is forming part of it.
     
  8. lora272

    lora272

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    Yes, it is the connecting of the walls that is the problem for the thermal bridging. I was hoping there might be a way to do it without having to demolishing the existing garage wall.
     
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  10. Swwils

    Swwils

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    Is the existing garage single leaf? If so the traditional method of breaking into the cavity and extending it around won't work ( newer method of leaving cavity closed but using a thermabate vertical DPC is now typical)

    The bridge won't be significant, but you are right to recognise it. A 25mm thermal plasterboard in those areas would be a solution.

    Would also take care for any possible damp bridge
     
  11. lora272

    lora272

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    Yes, its single leaf.

    Do you think that a timber frame construction with a brick outer leaf would be a better design for the new parts rather than the traditional brick and block? That way the shared wall could just have some rigid insulation and plasterboard added and there is not an inner block leaf to worry about not being supported.
     
  12. tony1851

    tony1851

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    Why not just stop the inner skin short? A few extra ties at the end will ensure robustness.

    Suggest don't use timber framing - most builders are used to brick-and-block; anything different tends to put the cost up.
     

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  13. ^woody^

    ^woody^

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    Do building regs even apply
     
  14. tony1851

    tony1851

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    They might, or might not - depends...........
     
  15. lora272

    lora272

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    Thanks Tony, I was thinking of this but was worried about the structural support for the inner wall, but maybe the extra ties on the end will be enough.

    Ill keep that in mind about he builders
     
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