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    • CommentAuthortbhulse
    • CommentTimeJul 18th 2012
     
    Hi,

    I'm looking at putting external insulation on a '70s brick house with a 2inch cavity. Can't see any new threads on this in last couple of years. I'm thinking it would be a good idea to fill the cavity with a coated polystyrene bead to cut down on air circulation behind the external insulation. Will have to close the external air bricks. I am thinking of a Baumit lime render on top of PUR - can't see the advantage of natural material. All the single glazed windows will be replaced - up-front cost is a significant factor, so no TG, but will be weighing up wood vs uPVC. Wood is preferred but may be beyond budget. New windows can be extended into external insulation. I am upgrading the loft insulation too - should I be closing the cavity at the top and how? Am concerned about air tightness in the loft - any ideas on improving this other than a big can of spray foam? Any other comments appreciated.

    Thanks,

    Tim
    • CommentAuthortony
    • CommentTimeJul 18th 2012
     
    best to have a well insulated but well ventilated loft.

    I think foam might be best in your cavities as it will be the most air tight choice to stop draughts whipping away your heat.

    Love the idea of EWI, I would use eps if it were mine

    all power to your elbow.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 18th 2012
     
    3G Uw1.1 Scandinavian-style cheaper than 2G from the likes of Russell Timbertech £350/m2 - beat that in timber! PVC 30% cheaper, but problems problems, from bitter experience.

    Like Tony, skip expensive PUR unless really limited on feasible thickness - thicker EPS is greatly superior in environmental credentials - and breatheable.

    I'd fill the cavity with weak concrete, so you don't isolate half your precious thermal mass (inside the EWI teacosy) from the interior.
  1.  
    Posted By: tbhulseI am upgrading the loft insulation too - should I be closing the cavity at the top and how? Am concerned about air tightness in the loft - any ideas on improving this other than a big can of spray foam? Any other comments appreciated.
    I would take off any soffit boards & carry the EWI over the top of the wall closing the cavity.

    The best way of making the ceiling below the loft airtight is to fit a layer of polyethylene to the existing ceiling, batten over it to create a service void for running electrical cables & fit a new ceiling to the battens. If this is not practical then you could fit polyethylene to the top side of the ceiling, but unless you have a simple purlin roof, its likely to require a lot of cutting & taping around ceiling joist hangers, etc.

    David
    • CommentAuthortbhulse
    • CommentTimeJul 20th 2012
     
    Thanks for the feedback guys, EPS sounds good - I like cheaper.

    Fostertom - any recommendations re: sourcing 3g scandi windows cheaply? Other forum link? I like the idea of the weak concrete but the foam sounds easier! Need to think about that a bit more.

    Like the idea of carrying the EWI over the wall, as long as I can do that without blocking the airflow.

    Trying to do anything inside the house itself if possible so can't install new ceiling. The rafters are trussed, quite complicated because of the width of the building so poly will be awkward, but would be doable.

    Tim
    •  
      CommentAuthorfostertom
    • CommentTimeJul 20th 2012 edited
     
    The ideal is EWI to walls, continuous with similar EPS on OSB boarded over the top of the rafters, tiles/slates replaced but a bit higher up. The roof OSB is adequately airtight, without any problems with interruption by internal trusses etc. Unfortunately EWI can't be relied on to be airtight, so either an external rough-render (breatheable) on the brickwork before EWI-ing, or the internal plaster wd be your wall airtight barrier.That (like IWI) is problematic because of joist penetrations and joists so close parallel to wall that you can't make the internal plaster continuous through the floor thickness. Also needs connecting up with roof OSB (or with over-joist membrane if trying to air-tight at loft floor level).

    Posted By: tbhulseLike the idea of carrying the EWI over the wall, as long as I can do that without blocking the airflow.
    By that you mean airflow to underfloor? Not confusing with wall airtightness or water vapour breatheability. My approach is to dig a perimeter trench down to bottim of foundations, carry the EWI down into the ground as deep as feasible, backfill with Leca (lightweight expanded clay aggregate, little malteser balls, usefully insulative), optionally making a french drain out of it. Then the underfloor subsoil is kept warmish and bone dry (if french drain), so the underfloor void not liable to condensation, so you can block the air vents (which actually just import moisture) and you have a draught free fairly insulated ground floor without having to disturb it at all.
    • CommentAuthortbhulse
    • CommentTimeJul 22nd 2012
     
    Thanks. Re:airflow I was referring to eaves ventilation - going to be doing airtightness at the loft floor level. Like the suggestion re: perimeter insulation and Leca though.

    Cheers,

    Tim
    • CommentAuthorSwarm
    • CommentTimeOct 27th 2012
     
    I just wondered if you had any update on the EWI + CWI? I'm thinking of doing the same and would be interested if you had worked out the U value you might achieve.

    From my research so far and my very limited understanding, the remaining interior wall should still provide enough thermal mass. In fact one source mentioned that beyond a certain depth of wall (something like 10cm), there are greatly diminished returns on the thermal mass effect.

    I'd not considered air bricks at all in this. What side-effects could there be of covering those with the EWI?
    • CommentAuthoreniacs
    • CommentTimeOct 29th 2012
     
    Swarm I am looking at the same thing, my cavity walls are insulated already and i am looking at 100mm phenolic insulation as EWI. The phenolic gives a U=0.18 which is already fairly good. Add to that the minor effect of the remianing cavity insulation and you may be onto U=0.16 at best.

    If doing EWI on a cavity walled house, make sure the cavitys are filled with somthing, otherwise they will have a negative effect on your toasty warm EWI coating!
    •  
      CommentAuthorfostertom
    • CommentTimeOct 29th 2012
     
    Posted By: eniacsIf doing EWI on a cavity walled house, make sure the cavitys are filled with somthing, otherwise they will have a negative effect on your toasty warm EWI coating!
    Why so? (can guess, but just checking)
    • CommentAuthoreniacs
    • CommentTimeOct 29th 2012
     
    Best way i can think of explaining it is wearing a huge loose coat on a windy day.
    Imagine that you have a nice toasty coat, then that it is too big and doesnt touch your skin, the wind would blow around you under the coat and would completely negate the effect of the coat.

    Same thing in a cavity walled house, air movement within the cavity will allow heat to escape, bypassing the toasty layer of your chosen insulation type.

    I believe Tom (above) will recommend a concrete fill, I however would recommend a insulant fill like polystyrene beads. You should think about the house's occupation profile as to which one you decide to go with.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 29th 2012
     
    What if the airtight layer is outboard of the cavity, so it's not open to outside air?

    I'm not so sure these days about recommending conc cav fill, unless converting the wall into a uni-directional thermal store as per http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9743&page=3#Item_12
    Posted By: Swarmbeyond a certain depth of wall (something like 10cm), there are greatly diminished returns on the thermal mass effect
    • CommentAuthorCav8andrew
    • CommentTimeOct 29th 2012
     
    Tom, why the change in heart re. conc. fill ?
    •  
      CommentAuthorfostertom
    • CommentTimeOct 29th 2012 edited
     
    Don't ask me - it's a mystery! Perhaps what Swarm summed up, ST's ongoing back yard experiment, realisation that uni-directional mass storage works so clearly, hoping that simple 'in the room' massiveness would come equally clear, but it hasn't.

    Mind you, if using a cavity wall as uni-directional storage (heat input from collectors into outer face of wall, traveling uni-directionally inward), then wd certainly conc fill it, plus think about adding more mass, wood fibre or Hempcrete as EWI perhaps. Or the cavity could be kept for an air-as-thermofluid system.

    I still think the outer leaf is a mass asset that should be used, rather than thermally isolated and lost.
  2.  
    Great read chaps, and learning quickly!
    Bought a '50s house 12months ago, and now experiencing our second cold winter. Room temps of 8-10degs are the norm at the moment :( With two young kids I am desperate to get this house suited and booted for this time next year.
    We have plenty of space around the bungalow for EWI, but am a little naive abou the cavity wall insulation situation. Allegedly it has been filled (I've seen something resembling a duck down/synthetic pillow filling) but I have no idea how well, or how thoroughly.
    I'd rather not tackle the outside without knowing its going to be effective, and that sounds like its dependant largely on what the cavity situation is like! But how do I check??
    Regarding the top and bottom of the cavity, should these be blocked up? Isn't it bad trapping air and water in there with no way of getting out?

    Also, where can I find definite instructions on how to insulate my loft? I'm petrified of causing condensation in spaces I can't get at, and want to do it right the first time. I have an old concrete tiled roof, with a bitumen type felt on top of 4 inch timbers and nothing else. How about a 40mm gap with tiled vents at the top between each rafter, and matching vents in the plastic sophet to allow for ventilation along its length?

    Many thanks for any help!
    • CommentAuthortony
    • CommentTimeDec 6th 2012
     
    Loft insulation between and over joists total 300mm+ of insulation, easiest with quilt, leave no gaps, dont block the air path at the eves leave 25mm clear gap
  3.  
    <blockquote><cite>Posted By: tony</cite> easiest with quilt </blockquote>

    Thanks Tony. Only 25mm gap? Cool! More space for insulation!

    What's 'quilt' though?
  4.  
    I did a little sketch of what I think is correct for OSW and roof insulation. Please could you offer a critique?
    • CommentAuthortony
    • CommentTimeDec 6th 2012
     
    I see no sketch (save file reduced for web pages?)
  5.  
    Sorry, trying again....
  6.  
    'Quilt' = any roll-type insulation, from glass fibre to sheep's wool, and all between.

    Nick
  7.  
    Photo above finally.

    Isnt board better for the roof? easier to maintain a vent gap?
  8.  
    No comments on my sketch?

    I cant seem to find any best tried and tested EWI system for a 1950s Cavity wall bungalow. Can anyone point me to a good thread/blog/info source please?
    • CommentAuthortony
    • CommentTimeDec 22nd 2012 edited
     
    In Europe 200mm of eps is common with thin coat hitgh tech render in a thin plastic mesh for EWI
  9.  
    SVV: I don't know if we are talking at cross purposes. I am fairly sure that Tony's suggestion was for an on-the-top-of-the-bedroom-ceiling-below installation, and the 25mm was not a gap between tiles and imnsulation on the sloping plane, but a ventilation 'slot' at eaves level. Now that we have your pic, we can see that you propose to insulate up the slope of the roof, but I do not understand why. Can you explain?
    • CommentAuthornikhoward
    • CommentTimeDec 23rd 2012
     
    Posted By: samuelvincentvellaNo comments on my sketch?

    I cant seem to find any best tried and tested EWI system for a 1950s Cavity wall bungalow. Can anyone point me to a good thread/blog/info source please?


    We have similar, see below
    • CommentAuthornikhoward
    • CommentTimeDec 23rd 2012
     
    Posted By: tonyIn Europe 200mm of eps is common with thin coat hitgh tech render in a thin plastic mesh for EWI


    What we are doing
    • CommentAuthornikhoward
    • CommentTimeDec 23rd 2012
     
    Posted By: samuelvincentvellaPhoto above finally.

    Isnt board better for the roof? easier to maintain a vent gap?


    That's what we have done, but we have done a loft conversion
    • CommentAuthornikhoward
    • CommentTimeDec 23rd 2012 edited
     
    Summary, double skin rendered block 1961 bungalow, same roof make up as you, 50 celotex between old rafters to leave 50 mm vented gap above, 50 mm below that between new rafters (below old ones), another 50 under all of that, then boarded, new vented ridge, with over fascias vent. Celotex runs from ridge to eaves all taped as VCL and air tight layer, sealed at ridge and to rendered block at eaves (a right pain), top of (rockwool filled cavity) closed with eps and foam.

    Almost complete and in the last few days when friends have popped in they all said how warm it is (I have not fitted rads upstairs yet) we have had the windows open while working up there, but it is 10C outside (19 inside)

    Hope that helps
  10.  
    ''when friends have popes in''

    Are popes more or less likely to feel the cold tan members of the general population? And anyway, I thought the nature of the beast was that you could only have one in at a time.
   
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