Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)


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.

Buy individually or both books together. Delivery is free!

powered by Surfing Waves

Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.

    Cavalok are promoting a new "structural" cavity closer for use in cavities up to 300mm. It seems to be the existing BigBlok with CompacFoam instead of EPS insulation & additional cill support brackets.


    The key advantage is that the CompacFoam will take a screw & the brackets will take the weight of the frame. So there's no more need for long frame fixing straps &, if using a membrane as the air barrier around the opening, no more need for a plywood box.

    • CommentTimeJul 25th 2012
    Cd be used in EWI situation, rendered EPS, no masonry outer skin?
    • CommentAuthortony
    • CommentTimeJul 25th 2012
    I can't see why a cavity closer needs to be structural
    • CommentTimeJul 25th 2012
    To carry the window 'outboard' without it needing to touch or get support from the outer skin?
    • CommentAuthortony
    • CommentTimeJul 25th 2012
    Did that by fixing mine to the outer skin only, inside the outer skin.
    Posted By: tonyDid that by fixing mine to the outer skin only, inside the outer skin.
    As you've proven, this can work if you're building it yourself, take time to build templates/formers for the offset openings and take responsibility for filling the gaps around the frames.

    Without a template/former the bricklayer is unlikely to get the offset openings right. Fixing the windows to the inner face of the outer leaf also requires a substantial gap to be left around the frame which subsequently needs to be filled with insulation. The average bricklayer will leave a gap here which is either too big or too small and the average window installer isn't going to take the time to cut pieces of insulation to precisely fill these gaps. I also have concerns about the long term airtightness of solutions based on PIR/PUR insulation & polyurethane foam.

    A cavity closer which is able to take the weight of the frame allows the frame to be placed more centrally in the cavity without using fixing straps or plywood boxes minimising cold bridging. A cavity closer which is made from something which can withstand the UK climate provides a durable template for bricklayers to implement a check reveal without the risk, for example, of plywood delamination. And a cavity closer which is rigid provides a solid substrate for proven airtightness solutions based on tapes &/or membranes.

    All-in-all I think its a better solution than the plywood box & well suited to how things are done on a typical building site. The downside is likely to be cost, but I don't have the numbers yet.

    • CommentAuthorlineweight
    • CommentTimeMar 26th 2019 edited
    davidfreeborough - (if you are still around) I'm bumping this thread because I've come across it in trying to find solutions for the situation I describe here:


    Don't know if you're able to offer any comment on whether this Cavalok system is likely to be of any use.
    • CommentAuthortony
    • CommentTimeApr 3rd 2019
    I can’t see why a cavity closer needs to be structural or even strong, mine are all plasterboard and no sign of problems even after ten years.
    • CommentAuthortony
    • CommentTimeApr 4th 2019
    Yep behind it I had pir wedged tight into the open cavity and then fibreglass batts, nothing biodegradable or structural
    I'd have thought plasterboard touching the outer leaf would be liable to get damp.
    • CommentAuthortony
    • CommentTimeApr 5th 2019
    Doesn’t touch the outer leaf, only the window frame does that and then only the inside of the outer leaf.

    Fail safe by design
    Posted By: tonyDoesn’t touch the outer leaf, only the window frame does that and then only the inside of the outer leaf.

    Fail safe by design

    Fair enough, I see. Being pedantic I might argue it's not really a 'cavity closer' in that case, just the internal finish; your cavity is closed by the insulation instead.
    • CommentAuthortony
    • CommentTimeApr 5th 2019
    I could agree with that, though the final airtight layer is the plasterboard
Add your comments

    Username Password
  • Format comments as
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   

© Green Building Press