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Housing - Renovation: Thermal break at wall starters?

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  1.  
    • CommentAuthorShevek
    • CommentTimeApr 29th 2013
     
    I'd like to thermally break the connection where we're starting some new blockwork off an existing solid brickwork wall, to help minimise the thermal bridge we have coming through the brickwork wall.

    Any good ideas for doing this in a cost-effective way? Should we just use a normal wall starter kit and then fill gap with PU foam instead of mortar?
    • CommentAuthortony
    • CommentTimeApr 29th 2013
     
    Does the insulation barrier cross the wall at the junction?
  3.  
    You need something with reasonable compressive strength if the wall starters are to work as intended. I've seen Foamglas used in this application.

    David
    • CommentAuthorShevek
    • CommentTimeApr 30th 2013 edited
     
    Here's the junction in plan view. The dark grey is existing brickwork. If I can thermally break this joint I'll probably add a bit of insulation along the inside of the dining room wall there too.

    There's a perimeter upstand of floor insulation going under the blockwork where it meets the brickwork wall too:
    http://www.greenbuildingforum.co.uk/forum114/?PostBackAction=Download&AttachmentID=4027
    • CommentAuthorShevek
    • CommentTimeApr 30th 2013 edited
     
    Posted By: davidfreeboroughYou need something with reasonable compressive strength if the wall starters are to work as intended. I've seen Foamglas used in this application.

    I think that's further than I want to go at this stage (cost us loads to get out the ground!).

    Why the need for compressive strength? What about some mineral wool?
  6.  
    Wall starter ties work by holding the new wall tight against the face of the old wall. Its the compressive strength where the walls meet which provides the resistance to relative wall movement, not just the wall tie itself. Imagine the loads when the new wall is hit by a gust of wind. It will bow inwards like a sail & the new block nearest the old wall will want to rotate about the face where they meet.

    That said, you may not need much compressive strength & EPS100 may be enough.

    David
    • CommentAuthortony
    • CommentTimeApr 30th 2013
     
    I wouldnt bother with insulation behind starters, or starters for that matter!
    • CommentAuthorShevek
    • CommentTimeMay 7th 2013
     
    Posted By: davidfreeboroughYou need something with reasonable compressive strength if the wall starters are to work as intended. I've seen Foamglas used in this application.

    David

    Maybe I misunderstand you David but if you look at the literature, which shows the joint being sealed with a compressive sealant, it seems to me there shouldn't be any problem simply filling the gap with mineral wool.
    http://www.strongtie.co.uk/pdf/c2k.pdf
  9.  
    If the wall starter ties are restrained by just a few screws then the rated wind loads are quite modest. The literature doesn't seem to have any requirement for compressive strength between the two, but they do require that the new masonry is built tight against the old & that both have a compressive strength above some minimum (around 3.5kN).

    Building the two walls apart means the ties will need to take the entire shear load without the bracing/stiffening provided by the masonry/mortar bed.

    Perhaps one of the steel frame ties would be more appropriate? Or could you use TeploTie cavity wall ties bonded to the old wall with resin?

    David
    • CommentAuthorTimSmall
    • CommentTimeMay 7th 2013
     
    Unless I'm not really reading the plan correctly, doing stuff at the joint of the new and old wall isn't going to do much, unless you also have a short bit of (tapered?) IWI on both the original wall and the internal wall.

    Given that your neighbour is going to be heating their bit the other side of the boundary, I'd guess that bridge there isn't going to be too serious. In my case I tackled the bridge in a somewhat similar situation by stitching in ~400mm of aircrete "coursing bricks" into the original external wall i.e. just above where it says SVP in your plan. In my case, I was building a new load-bearing engineering brick pillar at this point, so taking a couple extra of the original bricks out at the same time wasn't too much hassle, I only had space for 400mm, but more would have been better.

    Model it in Therm?

    Tim.
    • CommentAuthorShevek
    • CommentTimeMay 7th 2013 edited
     
    Posted By: davidfreeboroughThe literature doesn't seem to have any requirement for compressive strength between the two, but they do require that the new masonry is built tight against the old...

    But how can it? The starters themselves are about 8 mm thick.

    Edit: I've read a number of instructions for starters now and none of them are clear but I they all assume a vertical mortar joint between the new and old it seems to me, even if there is a flexible sealant as well.
  12.  
    I agree that its not totally clear, but due to the relatively light loads involved its probably not critical if you build the new wall against the old.

    What concerns me is separating the two by 50-100mm & using the wall tie to carry that shear load unsupported. Normally its buried in masonry/mortar & so cannot twist or bend. If its effectively spanning a cavity then the safe working load may be significantly reduced.

    That's what made me think of using a cavity tie instead (but these are not usually rated for shear).

    David
    • CommentAuthorlineweight
    • CommentTimeJul 13th 2023
     
    10 years later... I have the same question.

    This kind of situation comes up quite often: here a new cavity wall is meeting some existing solid brickwork.

    I'd like the insulation layer to be continuous, as drawn, but as drawn the inner blockwork leaf is not attached to the brick wall it needs to tie into - other than by my red "what can this be" rectangle.

    Some kind of "insulated wall starter" that would do this, would be very useful. As of yet I've not found any off the shelf product that deals with this.
      Screenshot 2023-07-13 at 14.10.35.jpg
  14.  
    When we did the barn conversion we IWI it, I built internal block walls for some of the downstairs rooms and to support the stairs, so to avoid a cold bridge at the edge I just went through the 100mm PUR with a s/s wall starter kit from Scr***ix and long screws. See picture attached. The walls in our case had other bracing though as well, with walls at right angles and concrete lintels spanning across.

    In terms of compressive strength, the screws were done up incredibly tight with no noticeable compression of the PUR. Not sure if in your case the bit of P/board would compress easier?

    Please note I am not a Structural Engineer nor an Architect.
      avoid cold bridge.jpg
    • CommentAuthorlineweight
    • CommentTimeJul 13th 2023
     
    In the case I describe above, the blockwork inner leaf is loadbearing. And I'd need to get it OK-d with a structural engineer.

    I suspect that even if what you did would work fine - the structural engineer would not be able to calculate it. If there was an off the shelf product designed for the particular situation then it would be easier to prove it was appropriate.

    Perhaps the wall ties between the inner & outer leafs, in conjunction with the fact that the outer leaf can be bonded in to the existing brickwork, can be considered to provide suitable restraint. At some point I will just have to ask.
    • CommentAuthorlineweight
    • CommentTimeJul 13th 2023
     
    Posted By: davidfreeboroughYou need something with reasonable compressive strength if the wall starters are to work as intended. I've seen Foamglas used in this application.

    David


    In that case, were there foamglass blocks, toothed in with the bricks/blocks either side, simply as if a few bricks/blocks had been swapped out for foamglas ones?
    • CommentAuthorwookey
    • CommentTimeOct 24th 2023
     
    The big thermal bridge people leave when adding a new wall bugs me. It's very obvious in lineweight's drawing.
    I cut in foamglass blocks for our extension, or just cut out some wall so the insulation was continuous, depending on how much structure was needed.
    Slot for insulation and wall tie-ins
    http://wookware.org/pics/house/extension/html/104-image00225.jpg.html
    inner leaf tied in:
    http://wookware.org/pics/house/extension/html/113-image00238.jpg.html

    New wall tied in here, then slot cut for insulation once one leaf built:
    http://wookware.org/pics/house/extension/html/105-image00226.jpg.html

    Row of foamglass where extension roof joins wall:
    http://wookware.org/pics/house/extension/html/105-image00226.jpg.html

    This bit would offend structural engineers - it's rather relying on the wall-ties (it's a cavity wall) to hold everything together - smaller stepped blocks would have been more kosher:
    http://wookware.org/pics/house/extension/html/123-image00265.jpg.html
    No sign of cracks or movement 10 years later now, so looks like it was OK.

    Doorway going in here - roof timbers provide bracing to hold things together.
    http://wookware.org/pics/house/extension/html/126-image00268.jpg.html
    http://wookware.org/pics/house/extension/html/180-image00335.jpg.html
    http://wookware.org/pics/house/extension/html/152-image00307.jpg.html

    Nearly all extensions just leave massive thermal bridges at all these locations.
    Some more robust ways of doing this for when you haven't got a cavity wall would be good, so the wall can be tied in tension across the thermal break. Something like the schock products for balconies
    • CommentAuthorlineweight
    • CommentTimeOct 31st 2023
     
    Posted By: wookeyThe big thermal bridge people leave when adding a new wall bugs me. It's very obvious in lineweight's drawing.
    I cut in foamglass blocks for our extension, or just cut out some wall so the insulation was continuous, depending on how much structure was needed.
    Slot for insulation and wall tie-ins
    http://wookware.org/pics/house/extension/html/104-image00225.jpg.html
    inner leaf tied in:
    http://wookware.org/pics/house/extension/html/113-image00238.jpg.html

    New wall tied in here, then slot cut for insulation once one leaf built:
    http://wookware.org/pics/house/extension/html/105-image00226.jpg.html

    Row of foamglass where extension roof joins wall:
    http://wookware.org/pics/house/extension/html/105-image00226.jpg.html

    This bit would offend structural engineers - it's rather relying on the wall-ties (it's a cavity wall) to hold everything together - smaller stepped blocks would have been more kosher:
    http://wookware.org/pics/house/extension/html/123-image00265.jpg.html
    No sign of cracks or movement 10 years later now, so looks like it was OK.

    Doorway going in here - roof timbers provide bracing to hold things together.
    http://wookware.org/pics/house/extension/html/126-image00268.jpg.html
    http://wookware.org/pics/house/extension/html/180-image00335.jpg.html
    http://wookware.org/pics/house/extension/html/152-image00307.jpg.html

    Nearly all extensions just leave massive thermal bridges at all these locations.
    Some more robust ways of doing this for when you haven't got a cavity wall would be good, so the wall can be tied in tension across the thermal break. Something like the schock products for balconies


    Thanks, interesting to see these and good to know I'm not entirely alone in worrying about these things.

    You are right, in general domestic extensions are built with massive thermal bridges everywhere and people tend to look at you like you're crazy when you suggest these kinds of mitigations.

    The other day I was looking at these:

    https://www.ancon.co.uk/products/windposts/thermal-windpost-twp2

    and wondering if they could be re-purposed in this situation.
    • CommentAuthortony
    • CommentTimeNov 1st 2023
     
    I also worry about the fact that there can be a cavity wall inside the newly extended building with all the possibilities of air ingress, ‘in house winter cooling systems’ thermal bypass on top of the relatively minor thermal bridging at the junction.

    We frequently took down the outside skins completely when building extensions adding 15mm or mor space in the new room(s)
  20.  
    Posted By: tonyI also worry about the fact that there can be a cavity wall inside the newly extended building with all the possibilities of air ingress, ‘in house winter cooling systems’ thermal bypass on top of the relatively minor thermal bridging at the junction.

    We frequently took down the outside skins completely when building extensions adding 15mm or mor space in the new room(s)


    You're describing a situation where you extend onto a building that has cavity walls itself, right?

    Agreed that in that scenario the outside skin should be removed where it becomes part of the interior - I guess the reason it often isn't is to avoid having to provide structural support for it at higher level.

    Assuming it is removed though - it's then fairly easy to tie the new cavity wall to the old one, without any thermal bridges because inner leaf can tie to inner leaf, and outer to outer, at the corners. It's more difficult when the junction is to a solid wall, because whether it's internally or externally insulated, you can't tie in both leaves of the new wall to the existing one without a cold bridge.
    •  
      CommentAuthordjh
    • CommentTimeNov 1st 2023 edited
     
    Posted By: lineweightIt's more difficult when the junction is to a solid wall, because whether it's internally or externally insulated, you can't tie in both leaves of the new wall to the existing one without a cold bridge.
    Why not build a new solid wall in that situation? Then the insulation can just continue whatever was chosen for the house.
    • CommentAuthortony
    • CommentTimeNov 1st 2023
     
    Line weight,

    ‘Assuming it is removed though - it's then fairly easy to tie the new cavity wall to the old one, without any thermal bridges because inner leaf can tie to inner leaf, and outer to outer, at the corners. It's more difficult when the junction is to a solid wall, because whether it's internally or externally insulated, you can't tie in both leaves of the new wall to the existing one without a cold bridge.‘


    I saw a guy cut through the corner and internal walls of a solid wall house and join the internal wall insulation to the new cavity wall insulation seamlessly, he had to strap the cut walls together during the process.
  23.  
    Posted By: djh
    Posted By: lineweightIt's more difficult when the junction is to a solid wall, because whether it's internally or externally insulated, you can't tie in both leaves of the new wall to the existing one without a cold bridge.
    Why not build a new solid wall in that situation? Then the insulation can just continue whatever was chosen for the house.


    If it's an option to externally insulated both the existing house and extension that would make sense yes. Otherwise I don't think it would.
    • CommentAuthorcjard
    • CommentTimeNov 3rd 2023
     
    Return the inner leaf into the cavity some way to buttress the corner. Embed a couple of 45 degree supports from inner leaf end face to outer for a minimal bridge and put more efforts to elsewhere

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