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    • CommentAuthorgravelld
    • CommentTimeJan 15th 2018
     
    Next one: plinth insulation.

    As a reminder, the target of this retrofit is a 1950s cavity walled property:
    - Existing partial fill mineral wool insulation
    - No air bricks
    - All solid floors

    I don't actually know how deep the foundations are, or the nature of the footings.

    Here's a first attempt at the foundations then.
    - EWI on the wall, then continued in EPS below the foundation (see below)
    - Air barried continued from existing render with a S+C coat on the plinth as low as possible.

    I have opted for EPS on the plinth, even though XPS is often suggested. My understanding is that EPS is more "fault tolerant" in that it may get wet, but it can dry.

    Questions (other than points others raise):
    - I have separated the plinth and wall insulation, even though it's all EPS. Is this required or can I just continue it down?
    - Do I need to mark the existing DPC, and how to treat it?

    Refs: https://retrofit.support/detail/20/
      plinth.JPG
    • CommentAuthorgravelld
    • CommentTimeJan 23rd 2018
     
    Just wondered if anyone had any comments about this... Not enough detail to comment on?
  1.  
    The EWI installed by others on a job of mine was separated from the plinth layer (of high density EPS) by an alu base-rail. I don't really like this as it introduces a thermal bridge, and if cut boards are used, the possibility of voids.

    2 installations I worked on had EPS (in one case HD and in one case graphite) immediately below the main EPS. One had no drip to the plinth, and on the other I used an angle-bead as a drip (see pic), with the EPS slightly relieved so that the joint was otherwise all tight. I sat the EPS on the HDEPS with low expansion foam as 'belt and braces'.

    I am not sure what you mean about marking the dpc, and how to treat it.

    I am intrigued, though this is not part of your Q, how the cavity is partly filled. Given that it would not have been filled in 1955, how is there a vertically-defined gap to fill? I can understand there being the odd void due to slumping or 'picking up', but I don't understand how retro-fitted EWI could leave a fillable vertical gap.

    Have I misunderstood that bit?
      DSCF5830 - Copy.JPG
    • CommentAuthortony
    • CommentTimeJan 23rd 2018
     
    Nice job, I worry about air in the cavity bypassing the EWI if wind can get in there cooling the block adjacent to the edge of the slab.

    How many houses need the same treatment?
    • CommentAuthorgravelld
    • CommentTimeJan 24th 2018 edited
     
    Thanks Nick. Nice pic.

    Posted By: Nick Parsons
    2 installations I worked on had EPS (in one case HD and in one case graphite) immediately below the main EPS. One had no drip to the plinth, and on the other I used an angle-bead as a drip (see pic), with the EPS slightly relieved so that the joint was otherwise all tight. I sat the EPS on the HDEPS with low expansion foam as 'belt and braces'.

    I've not seen mentioned before using different _types_ of EPS for above/below DPC. In fact I haven't seen much mention of types of EPS at all other than some have lower conductivity. So why would different types be used, something to do with how it deals with water?

    Posted By: Nick Parsons
    I am not sure what you mean about marking the dpc, and how to treat it.

    The DPC is always the first subject builders bring up (well, three of them...) when I talk about doing this part of the project. I'm wondering whether it has to be continued somehow from the blue course of bricks across the EPS and how this should be drawn.

    Posted By: Nick Parsons
    I am intrigued, though this is not part of your Q, how the cavity is partly filled. Given that it would not have been filled in 1955, how is there a vertically-defined gap to fill? I can understand there being the odd void due to slumping or 'picking up', but I don't understand how retro-fitted EWI could leave a fillable vertical gap.

    The house is extended many times. There's actually as much extension wall as original. The original wall is retrofit fully filled EPS bead. This wall pictured is actually more like 1980s build. We will need to add the white layer, ideally something like walltite but pouring EPS if not.
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