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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorward32
    • CommentTimeFeb 22nd 2015
    I am building a cold roof loft and am planning a robust vapour control layer at ceiling level so there shouldn't be much moisture getting in to the loft. Loft space will house a couple of water tanks for the open vented systems and these will be enclosed in a thick insulation tent. I was planning on making the roof unventilated under the 'felt' and double battening the tiles and ventilating under them. I was going to use vapour permeable underlay (SolitexPlus) taped and sealed all round. I am now reading that vapour permeable only underlays may not be good enough as the NHBC are recommending ridge ventilation where they are used. An alternative is vapour and air permeable underlay (like Roofshield) but then there will be more air movement in the loft negating the purpose of sealing the space. I suspect having open vented water tanks in the loft may generate some vapour but what would be the best choice of underlay?
    • CommentAuthortony
    • CommentTimeFeb 22nd 2015
    Robust vapour control will not stop condensation in the loft, this will happen anyway. It can be made far worse by not having vapour control or air sealing.

    Cold loft void should be ventilated or use breathable membrane.

    Cold water tank will not add vapour to the air in the loft, a warm heating header tank might.
    Vented dry ridge systems are good and easy to fit as are over fascia vents ,they help set out the sprocket/eaves tile angle. I'd use the even if ventilation wasn't an issue
    • CommentAuthorCWatters
    • CommentTimeFeb 24th 2015 edited
    Pretty sure cold lofts must be ventilated.


    It is generally prudent to work on the assumption that all cold roofs will require ventilation...snip... Advice on ventilating roof voids has been removed and instead Approved Document C indicates that the requirement to resist damage from interstitial condensation will be met by designing a roof in accordance with clause 8.4 of BS 5250:2002 and BS EN ISO 13788:2002, with further guidance provided in BRE Report BR 262.
    • CommentAuthorGreenfish
    • CommentTimeFeb 24th 2015 edited
    Posted By: CWattersPretty sure cold lofts must be ventilated.
    BCO was happy with my non vented cold roof, but had well sealed ceilings, breathable membrane and battens/counter battens.

    Ironically the (old school) roofer was determined to vent it, so ended without taping the membrane and with a potential vent at the apex. Builder sealed the soffit as requested (no vents in it). Outcome there is some external air movement in the loft, but not a lot and the 500mm of mineral wool does not suffer wind wash.
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