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Housing - Renovation: Major renovation and extension of 1960's detached house

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  1.  
    • CommentAuthorkaicasswell
    • CommentTimeApr 3rd 2022 edited
     
    Looking for any input on the following design:

    The old part is cavity wall - uninsulated - and the new part (shown as the whole right hand half of the elevation pdf) will be solid concrete block 220mm wide.
    200mm EWI all around. with 65mm XPS down to foundations. The floor is 150mm kingspan type with screed on top. The roof will be kept as it is, and the loft insulated as much as possible (no loft conversion, ignore the velux shown). Air tightness inside with lots of tape/wet plaster. MVHR system.
    The new extension also sits on a new ICF basement,
    Once we have the shell watertight and finished i was planning on measuring the heat loss before deciding on final heating arrangements, but probably small gas boiler/unvented DHW or thermal store/UFH/solar thermal and maybe PV/battery.
      side elevation.png
  2.  
    Welcome to your first thread!

    Does ''200mm EWI all around'' mean ''over the old house as well as the extension''? If so can you be certain that there is absolutely no air movement in the cavity? Unless you can I would strongly suggest you have it filled with graphite EPS.

    If this is to be a comprehensive retrofit will there be insulation in the floor of the old house?

    Can I ask why the 'plinth' layer of XPS is so much thinner than the 'main EWI'?

    And have you considered a HP instead of a gas boiler? Could you have UFH in the screed?
    • CommentAuthortony
    • CommentTimeApr 3rd 2022
     
    How/where is the insulation barrier in the roof, how is it joined to the wall insulation?

    Will you do an airtightness test?
  4.  
    +1 about (properly) filling the cavity
    I would take the EWI down to the foundations with 200 EPS. (I presume the above ground EWI will be EPS). No need for the thin film render below ground but the adhesive + mesh layer should be applied.
    • CommentAuthortony
    • CommentTimeApr 3rd 2022
     
    +2 all good comments Nick and +1 on taking EWI down below ground full thickness.
    • CommentAuthorjamesingram
    • CommentTimeApr 4th 2022 edited
     
    sounds good.
    After discussion here I take the EPS 200mm down rather than use xps and use a drip bead to create the look of a dpc break in the rendered finish if required.
    • CommentAuthorkaicasswell
    • CommentTimeApr 4th 2022 edited
     
    thanks for all the comments it is much appreciated.

    To answer the questions, it is a complete renovation and the house is stripped right back, last year we broke out the whole existing floor, lowered it and fitted the 150mm insulation.

    The EWI down to foundations sounds good - I will look into that. Someone had told me i needed XPS below ground and not as thick. I had some 65mm insulation left over. We are not going for any passiv standards but trying our best with the renovation. I will do some air tightness testing as we go along.

    The cavity is open now, and I have had a quote for liquid type foam injection. However because the walls and windows sills etc are all stripped back i can access all the cavity quite easily so i could blow EPS beads into it-what is special about graphite beads? alternatively i could fill the cavity with concrete...

    I can link the EWI to the roof/loft insulation in the eaves - its a steep pitch roof that comes down into the first floor rooms, which only have half height vertical external walls

    I was planning UFH and have considered an ASHP. Still undecided. Was also interested in the Viessmann fuel cell units but doubt i could afford one..
    •  
      CommentAuthordjh
    • CommentTimeApr 4th 2022
     
    Posted By: kaicasswellSomeone had told me i needed XPS below ground and not as thick. I had some 65mm insulation left over.
    Some people think XPS is better, other think EPS is better. I'm in the latter school (my house sits on 400 mm of the stuff). I was convinced when I learned that it is used to build embankments for railways and roads, so there are no concerns about longevity.

    We are not going for any passiv standards but trying our best
    Interesting. Any particular reason for not trying for EnerPHit, for example? I think the discipline of having the goal can help. It sometimes can help in making decisions too.

    i could blow EPS beads into it-what is special about graphite beads?
    Graphite EPS has a better lambda value, so in a fixed volume like a cavity it gives better insulation.
  9.  
    If I remember rightly white EPS has lambda of about 0.038. graphite EPS 0.031-0.033.

    Re beads, professional installers bond with PVA, otherwise you get buried in EPS if you make a later hole! Genuinely filling with concrete (or 'semi-dry' mix) would be fine. I had mine filled, not for thermal reasons - cavity too variable, and full of crud - but to still air movement. How wide is your cavity? Beware PVA really stinks, and sets off your smoke alarms!!
    •  
      CommentAuthorfostertom
    • CommentTimeApr 4th 2022 edited
     
    Yes, 200 EPS down abs as far as poss but not a whisker below u/s of found, to avoid danger of ground extrusion from under the found. To my surprise, calcs showed that if anything a greater thickness of insul is justified as the 'coffer dam' of perimeter insulation below GL. To my taste, no drip "to create the look of a dpc break" - on traditional buildings a bit of splashback helped make the building look 'settled' into the ground.
  11.  
    Again thank you all, been very helpful. Regarding the question about Enerphit - i did join passivhaus and got a lot of decent info but the costs of the design architect for it were far too high.

    I managed to persuade our own architect to design the works based on a consultation i had with Green Building Store which helped a-lot. Building control and the architects are still struggling with some aspects of the design though.

    As a plumber, and now rapidly becoming a builder, we are doing most of the works ourselves and we have finished the basement and are just about to start building the extension part. For anyone else thinking of building a basement in winter for your first project i can highly, highly recommend the experience!

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