Home  5  Books  5  Magazines  5  News  5  GreenPro  5  HelpDesk  5  Your Cart  5  Register  5  Green Living Forum
Not signed in (Sign In)

Categories

This month's favourite choices





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.




    • CommentAuthorPDobson
    • CommentTimeSep 2nd 2007
     
    What cavity insulation would you recommend for a new build Brick & block house with a 100mm cavity. I have currently got 100mm standard Dritherm specified. Dritherm 32 gives a slight (.04) improvement in U value but is apparently double the price. I would like to improve the insulation but the better insulants don’t seem to allow full fill and so give relatively little improvement.

    Any ideas?
    •  
      CommentAuthorfostertom
    • CommentTimeSep 2nd 2007 edited
     
    Just wait till multifoils become available for CW insulation - hung in a 50mm cavity, touching nothing, not even counterbattening (under development - not avail. yet). Equivalent of 200mm of Dritherm, in a back-to-the-60s basic easy cavity wall.
    • CommentAuthortony
    • CommentTimeSep 2nd 2007
     
    Dream on!! wind will blow both sides and the bellows effect will suck and blow loads of heat away even if the house was air tight which is exceedingly unlikely. Might work a little when there is no wind but how much use would that be.

    You were OK with the insulation specified though I would go for 300mm of it.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 3rd 2007
     
    Unh? I don't understand your point, tony - bellows effect affects any and all CW insul systems? Multifoil wd be skewered on spacer/wall ties to keep it central in the cavity and wd probably be the stitched type, allowing pressure equalisation through it.
    • CommentAuthortony
    • CommentTimeSep 3rd 2007
     
    How ever it is fixed within the cavity it will blow around and move when the wind blows. When this happens warm air will be repeatedly sucked out of the house and replaced by cold air like a pair of bellows puffing big dollops of cold air into the house increasing heating bills.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 3rd 2007
     
    So the movement of an autumn leaf causes the wind? In your house, is airtightness by other means "exceedingly unlikely"?
    • CommentAuthorPDobson
    • CommentTimeSep 5th 2007
     
    Having enough trouble getting multifoil approved for use in my roof & I need an immediate solution so I don’t think Multifoil is for me - in the cavity at least. I think its either Drytherm or celotex. I have been warned off Celotex in cavities at least as far as using their 25mm cavity is concerned. With only room for 50mm of celotex I may as well stick with Drytherm. I could put in an insulated plaster board – I would ideally like one that adds only say 25mm to the wall thickness– using celotex doesn’t seem practical as they want 25mm battens between the insulation board & the plasterboard. Does anyone have any recommendations?
    • CommentAuthortony
    • CommentTimeSep 5th 2007
     
    100mm cavity full of what you propose -- it would be better to have 300mm in the cavity.

    I worry about sheet materials in cavities as cold wind can access both sides of if so how is it insulating?
    •  
      CommentAuthorfostertom
    • CommentTimeSep 5th 2007
     
    Posted By: PDobsonI don’t think Multifoil is for me - in the cavity at least
    No, multifoil's not yet for use in cavities - that's for the future.
    Posted By: tonyI worry about sheet materials in cavities as cold wind can access both sides of if so how is it insulating?
    Same applies to any insulation in any position - all joints should be sealed, no reliance on sticky tape, to prevent convection, with or without wind to drive it, bypassing any kind of insulation. How often is that done, for *any* insulation? It's not only a problem for sheet materials in cavities.
  1.  
    Are you allowed to fully fill a cavity with Cellotex type insulation? If not, why not?
    • CommentAuthortony
    • CommentTimeSep 5th 2007
     
    Even if it was fully filled I still think that in the real world there would be all kinds of gaps and cracks around it letting the wind reduce its effectiveness.
    • CommentAuthorMike George
    • CommentTimeSep 5th 2007 edited
     
    Posted By: Chris WardleAre you allowed to fully fill a cavity with Cellotex type insulation? If not, why not?


    No, though I don't know why, only that the certification for such products always stipulates this. BCO's enforce this also. I suspect it may be to ensure that rainwater running down the external leaf of brick/blockwork cannot track across the cavity to the inner leaf. The clear cavity ensures that any such moisture ingress quickly evaporates [together with the heat lost via wind howling around the insulation] :bigsmile:
    • CommentAuthorPDobson
    • CommentTimeSep 6th 2007
     
    I would have liked to fill the cavity with celotex but you are right BC wont let me - I haven’t investigated but I suspect the warranty providers wouldn’t either. As the stuff is foil backed and you could tape up the joints I don’t think it would actually be a problem but the powers that be wont have it so that’s that.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 6th 2007
     
    Dritherm is allowed to fill the cavity due to some supposed layering effect that prevents moisture tracking inward from layer to layer. Seems over-hopeful to me - Dritherm gets totally saturated if left out in the rain, for example. Blown-in min wool or polystyrene beads ditto. Cellotex with aluminium-taped joints would seem much more waterproof to me, so why not full-fill?
  2.  
    More appropriate to green building than products dependant on the oil industry would be to fill the gap with something nice such as oak shavings. Remember to build the wall with lime mortar, not cement. You don't want any water getting trapped inside, do you?
    • CommentAuthortony
    • CommentTimeSep 6th 2007
     
    I cannot imagine a bricklayer applying tape to dritherm in a cavity. Unrealistic -- they dont even fit bats properly a lot of the time.

    Biff -- filling a cavity with wood shavings?? were they to get damp it would not be long before dry rot would set in with horrific consequences.
  3.  
    Hence the importance of lime mortar to wick the damp away.

    I find bats fly in and out on their own. They don't need fitting.

    Come on folks - we need a bit more imagination to build in a green post-oil age. Celotex is not going to save the planet.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 6th 2007
     
    Posted By: tonyapplying tape to dritherm
    Noooo - to Cellotex
    Posted By: biffvernonI find bats fly in and out on their own. They don't need fitting
    but they can't live without flitting.
  4.  
    What do you recon is the U-value of your oak shavings then Biff? Would be good to come up with a "green" cavity wall insulation. Why can't you use sheeps wool? I thought this was still a good insulator when wet?
  5.  
    I haven't got any sheep but I have lots of wood shavings. Other people will have a surplus of wool, hemp, straw, newspaper, rags, heather, bracken, christmas trees etc.. If it's free and it stores carbon there's not too much point in worrying about the exact U-value. Just make that gap more than the standard 100mm.
  6.  
    Posted By: biffvernonI haven't got any sheep but I have lots of wood shavings. Other people will have a surplus of wool, hemp, straw, newspaper, rags, heather, bracken, christmas trees etc.. If it's free and it stores carbon there's not too much point in worrying about the exact U-value. Just make that gap more than the standard 100mm.


    Biff, I can see why you may think oak shavings would be okay because of their resistance to rot, but newspaper in full fill masonry? No chance of this staying dry, lime or no lime, and wet insulation is useless.
  7.  
    I agree, Mike. But come on, be positive, let's have some ideas that don't depend on the petrochemicals industry.
  8.  
    I agree, my viewpoint is that we should be allowed to accept higher [worse] u-values if we can use non petrochemical insulants. We have got to a stage with regulation where the improvements being enforced are producing savings which are miniscule when compared to the that gained with the initial inclusion of insulation. This is being driven by lobbyists from the petrochemical industry who sit blissfully happy that the Government are gullible enough to believe that doubling the thickness of insulation will double the savings in energy used for space heating. Solid floors is a classic example of this and in order to comply there is often not a viable alternative to PC's

    Quality of build is also completely ignored in the steady state u-value calculations used to predict heat losses. This is the area where significant savings can be made through air tightness, though I accept your viewpoint about living in a plastic bag. The trouble is we cannot have it both ways. If we want to make significant fabric improvements than that is the only way left for it to be done
    • CommentAuthorwookey
    • CommentTimeJul 17th 2010
     
    Apoligies for resurrecting this old thread, but I was wondering if there had been any movement on this 'You can full-fill with (silicone-treated) mineral fibre, but not with PUR' BC stance. It makes no sense at all to me. How can foil-faced taped-seam PUR boards be less water-resistant than mineral wool? I can fit either 200mm dritherm32 or 150of PUR for nominal 0.15U in a dense-block/brick cavity wall. I picked the dritherm but my builder recommends the PUR for a narrower cavity (shorter argument with BC), and is happy to build the inner leaf first (carefully de-snotted, fit all the PUR, goop and tape it, and then build the outer leaf. Which should avoid the usual problems with bardly-installed insulation boards.

    But if a 50mm cavity is still insisted-upon then I might as well go with the fluff? And why 50mm? 20 would be plenty if you are just trying to avoid wall and insulation touching.
    •  
      CommentAuthorjoe90
    • CommentTimeJul 17th 2010
     
    I have just had plans drawn up for an extension and the BCO has told me 100mm full fill cavity required for brick outer and thermalite inner to meet insulation regs but not specified what insulation???? any suggestions? perhaps I will ask him what he would suggest (then I will post it here).
    •  
      CommentAuthorali.gill
    • CommentTimeJul 17th 2010
     
    I've just spec'd Springvale Ecobead Platinum 150mm blown insulation (internally - U=0.2) with brick outer leaf and lime mortar. Queried the BCO and his only observation/concern was the mortar profile being flush but this matches the existing build anyway.
    Great/fast technical help with Uvalues.
    http://www.springvale.com/products.asp?InfoID=525&mySub=517
    http://www.brick.org.uk/mortar-joint-profiles.html
    • CommentAuthorDarylP
    • CommentTimeJul 18th 2010
     
    Wookey,

    I am interested in your points regarding the 50mm clear cavity. Did you get any resolution with BC?
    We are in the middle of a similar dialogue with BC. When asked why they insist on 50mm clear cavity with PIR/PUR boards, they don't seem to have a definitive answer....why wouldn't 20mm be enough?

    Cheers..:confused:
    • CommentAuthorJulio
    • CommentTimeMay 16th 2011
     
    Resurrecting the thread again, sorry!

    Has anyone used either LECA or expanded glass within a cavity (about 100mm). Would work like the polystyrene beads do presumably, without the associated oil dependance. How would 100mm poured into an existing cavity work do we think? Would be interested to know. Different R-values etc? Thermal bridging issues of the LECA due to the fact it does not pack down as tightly as the polystyrene balls.

    Cheers

    Jules
    • CommentAuthortony
    • CommentTimeMay 16th 2011
     
    Try to aim at the U value that you want 0.1 is a good target --- I didnt use polystyrene but at least the oil is being used for insulation rather than being burnt
    •  
      CommentAuthorfostertom
    • CommentTimeMay 17th 2011
     
    Leca has only one third the insulation value of expanded polystyrene - presumably taking into account the freer passage of air between the granules.
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press