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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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Building Regulations and Standards: BR Doc A - Structure: Wall Thickness and height

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  1.  
    Hi folks - my first post to the forum.
    I've been reading a lot of good stuff here - keep up the good work :-)

    I'm researching how to refurbishing and extend our 1930's bungalow to maximise it's energy efficiency.
    The current plan is to remove the roof and build a highly insulated timber frame upper storey and roof.

    However I'm not sure how to interpret the height I can go to based on the current wall thickness.
    Can you folks help?
    ----
    The original cavity walls are nominally 2 x 4" leaves with a 50mm cavity.

    From Document A (http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_A_2004.pdf)
    Para 2C6 suggest a wall thickness of 1/16th the height of the wall
    Para 2C8 for cavity walls say to use a wall thickness of "the combined thickness of the two leaves plus 10mm"
    Does this thickness include the cavity?

    As I want to add another floor the gable end wall height will between 3.5m & 9m.
    Although most walls are less than 9m in length - the L shaped building does have two walls over 9m long (but less than 12m).
    Table 3 suggests I'm OK for short walls - but it means my longest 250mm thick walls are limited to a 3.5m high.

    Is this right?
    Do these regs apply to a timber frame upper floor?

    Cheers
    C.T.
  2.  
    I've seen somebody do exactly this near my old house except they made the two floors into two separate flats. They used a timber frame for the upstairs.

    I think I would use 250mm aircrete blocks straight on top of the existing walls laid with thin joint adhesive. I'd have the cavity filled downstairs and externally insulate, mesh and lime render the whole house to bring the walls to a U-value of about 0.15 and make it all look nice. I'd try and re-use the existing roof struture and coverings and stick 500mm of mineral wool in the loft, perhaps with a false ceiling below the roof void to get the full depth in without blocking off ventilation at the eaves (unless you want to convert the loft space as well while you are at it?).

    I can't see how a 250mm wall could be an inadequate thickness for a 2 storey house.
  3.  
    Draw up your plans and send them off to see if they pass building regs, if they don't they will tell you why they have failed and what to change so that it will pass.
  4.  
    I spoke with the local building control department and they said that deviation from the guidelines is OK as long as the submission is backed up with appropriate calculations.

    C.T.

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