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RSJ has been installed and it is thermally bridged

Discussion in 'Building' started by TofuSpaceship, 22 Apr 2018.

  1. TofuSpaceship

    TofuSpaceship

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    Hi all.

    Undergoing some renovation, i.e. a wall has been knocked off and creating one unique space from two rooms.
    The room at the back used to have a cold pitched roof, will now have a flat warm roof and the RSJ will be exposed, we want it as a feature.

    The steel is sitting halfway on the external padstone, I am confident this will cause thermal bridging. When challenged the builders on two occasions, I have been dismissed with things like "it is how it is always done", "there is no other way".

    [​IMG]
    [​IMG]

    I suppose some TB will be happening, but is it indeed an acceptable thermal bridging or is it going to be very compromising?
    If it is very compromising, how to minimise thermal bridging as much as possible, seeing the steel is actually already in situ and we really wouldn't want to start from scratch? Our house has been exposed for 10 days already (instead of the 2 days originally planned) and it is really impacting our lives.
    I was thinking to pad the face and top of steel with some XPS, but then it would still be sitting on cold concrete padstone and slates, so in my mind having some XPS is just going to slow down the rate of heat exchange, but the final heat exchange is going to be exactly the same?
    Is there such a material that has compression strength (like a padstone) but it is also insulating?

    Or solution B, cutting that steel corner and have a padstone sitting on the internal skin, at a 90 degree angle with the current internal padstone.
    Unfortunately the internal wall of the extension has just been rebuild with breeze block sitting on top of each other (not interlocked). When I challenged the builders they said you cannot have a padstone on top of breeze blocks (which is incorect according to what I read online) but indeed I think having a padstone on top of a pillar of straight freeze blocks is now what someone would want?

    [​IMG]

    Anticipating your questions ("why have they done this?"), essentially when it came to replace the window (located where the hop-up bench is) the wall appeared to be really crap with lot of broken, misplaced bricks and further opening up of the wall made it clear was not going to be able to have a load bearing RSJ sitting on it. Unfortunately also the extension appeared to be very badly tied to the main building (which we imagined already), so they essentially have had to cut two blocks width on the outside of the extension wall and one block width on the inner leaf (as you can see above) to have staggered bricks interlocked between the main building and the extension to effectively tie them (that's how it is on the outer leaf). It escapes my mind why they haven't cut two blocks width on the inner leaf too and interlocked blocks between main building and extension in the inner corner as well. Surely if that would have been done, you could have safely had just one padstone there holding the steel?

    Thank you all really
     
  2. Notch7

    Notch7

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    Can you have the rsj exposed?

    Is there no requirement for fire protection? -is it holding up a 1st floor and roof?
     
  3. TofuSpaceship

    TofuSpaceship

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    We are on the first floor here, RSJ is holding up the roof - and we have interest in one day going up into the loft.
    BC will be here tomorrow, apparently with intumescent paint you're good to go.
     
  4. ^woody^

    ^woody^

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    Insulate the end
     
  5. TofuSpaceship

    TofuSpaceship

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    Isn't it pointless to insulate the end only, when the bottom part of the RSJ is sitting on an outside padstone?
    Surely it is going to slow down the heat exchange, but it is not going to limit the whole amount of heat exchanged?
     
  6. iwanttodiy

    iwanttodiy

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    As it’s a cavity wall, I would have though the SE would design twin beams or a twin PFC. One for outer leaf and one for the inner leaf? 1B9975FA-5D31-49EB-AB0C-E18050EF10D1.jpeg Then insulate the cavity and the web?

    A solution to your problem could be, £100 buys a 1200x1200 10mm aerogel blanket. Maybe wrap it up using double sided tape and follow it through with plasterboard on the outside? You would lose the feature though.
     
  7. ^woody^

    ^woody^

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    Won't the room be heating the padstone?

    But its hard to see what is inside and what is outside from that camera angle. It looks like the inner leaf of a cavity wall. If the padstone is on an external leaf, then damp will be a bigger problem than thermal bridging
     
  8. iwanttodiy

    iwanttodiy

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    Btw, I’ve been talking to proctor group technical recently about the best way to reduce cold bridging on steel structures. They mentioned they have made a product specifically to do that - spacetherm cold bridging strips (https://www.proctorgroup.com/images...ation/Spacetherm/Spacetherm_CBS_Datasheet.pdf)

    Maybe you could talk to them and ask if you can put that between the padstone and beam. You only need a 10mm to mitigate any impact of cold bridging. PHstore sell them at £25 a strip + £15 delivery.
     
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  9. John D v2.0

    John D v2.0

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    Well, steel is one of the best conductors of heat there is. You either want it entirely inside your insulation, or outside. Our architect said it's not as uncommon as you think to have a soaking wet beam due to incorrect spec/installation.
    We had specified a beam by the SE and architect to only stay on the internal leaf for that reason, however the builder took it upon himself to get a huge flange i.e. thermal bridge welded on the bottom. Then the architect redesigned it twice based on other design changes the builder made, and in the end the builder refused to do any remedial work because as far as he was concerned it didn't matter.
    Anyway the up shot is, you might get away with it, you might not.
     
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  10. TofuSpaceship

    TofuSpaceship

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    The steel is having one corner sitting on an inner padstone and the corner next to sitting onto an external padstone; I am honestly worried about TB + condensation.

    It is really annoying. Our builder is really not that bad or cowboy-ish. But of course there are aspects that find me much more concerned than he is. I find it so astonishing that they are paid by the customer to do the job and if they really want to, they can shrug their shoulders and build according to their own wishes and disregarding SE and customer reqs.

    BCO was around and did not mention anything at all about TB. When interrogated by me, her answer was something on the line of "it's a period house, you probably have more important things to be concerned about".

    Anyway, in the end we mediated and the builder agreed to put a little jacket on the end of the steel, as the steel is sitting only on 3.5cm of the 10cm width of the padstone. I suppose compromise is the key as always.
     
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