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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorwholaa
    • CommentTimeJan 15th 2021
     
    Hi,

    I have a pretty typical house, end of terrace, semi cavity wall. There is some under screed insulation (PIR) but it's not great and I know great attention is paid to make cold bridge free foundations. Some corners of the house's ground floor screed get cold. One area gets to 7 Celcius on cold days. I wonder is it wise to dig a deep trench around the strip foundations, say a metre deep and line it with glass foam gravel insulation to get better floor insulation? Has anyone done this and could it damage the structural integrity of the structure?
    • CommentAuthorRobL
    • CommentTimeJan 15th 2021
     
    I fitted foamglas insulation sheets from dpc down to foundations.
    I think the blocks were 600x450x100mm, and the foundation concrete slab was about 700mm below ground level. I didn’t go below the top of the foundation concrete slab. The foamglas is hard to find, but easy to use. I used fake skates made from cement fibre-board in front of them, to prevent the odd bit of spade damage. Above dpc we now have EWI, but if you don’t do the Ewi, make sure rain drips off away from the wall.
    In one location I used XPS instead- it was much more difficult to lay it flat against the wall.
    • CommentAuthorLF
    • CommentTimeJan 15th 2021
     
    I think putting insulation in makes a difference since perimeter to area makes a big difference.
    I was looking at a while ago and thermally it made sense but work is on hold/slow at the moment. It seems like a good compromise when you cannot take solid floors up.
    Big warehouses only insulate at edges. I will try and find the info.

    Not sure of best way to insulate and it will be interesting to get views of experienced people on here.
    There are some good photos I remember on here from someone doing it the back of the house.
    • CommentAuthorLF
    • CommentTimeJan 15th 2021
     
    Not read it yet but this was what I was thinking of. back to work !

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13794
  1.  
    Posted By: wholaaHi,

    I have a pretty typical house, end of terrace, semi cavity wall. There is some under screed insulation (PIR) but it's not great and I know great attention is paid to make cold bridge free foundations. Some corners of the house's ground floor screed get cold. One area gets to 7 Celcius on cold days. I wonder is it wise to dig a deep trench around the strip foundations, say a metre deep and line it with glass foam gravel insulation to get better floor insulation? Has anyone done this and could it damage the structural integrity of the structure?

    As a general rule you an dig down to the bottom of the foundations without problems (but no lower). I'm not sure how much insulation value you will get out of the glass gravel because the voids will quickly fill up with water and/or soil. If you use geotex type sheet to keep the soil out the water will still get in and conduct away the heat. (all you would need then is an outflow and you will have a very good french drain)
    Depending upon how flat the outside of the strip foundations are you could use EPS fixed to the foundations by a perimeter bead of adhesive and a few blobs in the middle of each sheet. It would not matter if water got behind the EPS because the perimeter bead would stop flow so anything behind the sheets of EPS become inside the insulated envelope. EPS retains most of its insulating properties even after prolonged submersion in water.

    Edit - after thought - 2or 3 cm of EPS over the floor screed with OSB over that then carpet, (or if wood strip flooring then leave out the OSB) will make a tremendous difference and might be easier, less work and cheaper.
    •  
      CommentAuthordjh
    • CommentTimeJan 15th 2021
     
    Perimeter insulation is a very good idea. It might be sensible to make the trench into a French drain outside the insulation unless you live on very well drained land and assuming you can find somewhere to drain the drain. :bigsmile:
  2.  
    We created a French drain around the perimeter of our house. We dug a trench down to where the foundations rested on the earth and laid a perforated land drain pipe at the bottom, covered it with geotextile and filled the trench with foam glass. We then covered it with another geotextile sheet and added a thin decorative layer of medium sized broken slate on top. The land drain was connected to a junction where a solid pipe takes the water off to our stream.

    I have no idea if the house is warmer because the house is still a work in progress. We do get a large flow of water going off to the stream though, so at least the French drain part is doing its job.
      Screenshot 2021-01-15 153410.png
    • CommentAuthorbhommels
    • CommentTimeJan 15th 2021
     
    Same here: semi with 50mm cavity walls. I dug down 30-40cm, to the top of the foundations, no further as I did not want to take any risk, they are quite shallow. After repointing the sub DPC brickwork using lime mortar, I fitted 100mm of XPS with frost resistant EWI adhesive to the wall, creating a nice fillet. Where there is adhesive, there can't be water, after all.
    Later I added 50mm of EPS (leftovers), and finished it off with mosaic render and cement fibre boards, depending on location and access. The mosaic render is really sturdy but tricky to apply, the cement fibre boards look nice.
    It is difficult to say whether it made much of a difference as most of the floors were dug up and insulated at the same time, it is one huge cold bridge I don't have to worry about any longer though.
    • CommentAuthorwholaa
    • CommentTimeJan 15th 2021 edited
     
    <blockquote><cite>Posted By: Peter_in_Hungary</cite><blockquote><cite>Posted By: wholaa</cite>Hi,

    I have a pretty typical house, end of terrace, semi cavity wall. There is some under screed insulation (PIR) but it's not great and I know great attention is paid to make cold bridge free foundations. Some corners of the house's ground floor screed get cold. One area gets to 7 Celcius on cold days. I wonder is it wise to dig a deep trench around the strip foundations, say a metre deep and line it with glass foam gravel insulation to get better floor insulation? Has anyone done this and could it damage the structural integrity of the structure?</blockquote>
    As a general rule you an dig down to the bottom of the foundations without problems (but no lower). I'm not sure how much insulation value you will get out of the glass gravel because the voids will quickly fill up with water and/or soil. If you use geotex type sheet to keep the soil out the water will still get in and conduct away the heat. (all you would need then is an outflow and you will have a very good french drain)
    Depending upon how flat the outside of the strip foundations are you could use EPS fixed to the foundations by a perimeter bead of adhesive and a few blobs in the middle of each sheet. It would not matter if water got behind the EPS because the perimeter bead would stop flow so anything behind the sheets of EPS become inside the insulated envelope. EPS retains most of its insulating properties even after prolonged submersion in water.

    Edit - after thought - 2or 3 cm of EPS over the floor screed with OSB over that then carpet, (or if wood strip flooring then leave out the OSB) will make a tremendous difference and might be easier, less work and cheaper.</blockquote>

    Just insulating over the floor is a nice idea but I have so many kitchen units in the way and in my country, internal floors and door thresholds are built to be level with the outside ground level so the house is fully accessible to wheelchairs.So it would require new door that is higher and against the regulation although no one checks.
    • CommentAuthorjms452
    • CommentTimeJan 15th 2021
     
    Posted By: RobLThe foamglas is hard to find, but easy to use. I used fake skates made from cement fibre-board in front of them, to prevent the odd bit of spade damage. Above dpc we now have EWI,


    Hi Rob,

    Have you had a look with a thermal camera now it's all installed? You've gone gold standard so interested to hear how it looks thermally.
    • CommentAuthorRobL
    • CommentTimeJan 16th 2021
     
    I have, and it's generally good. There's a sliver of heat escaping that I still need to fix - I did the below ground stuff years before the EWI, and I made the top of it sloped to keep rain draining off it correctly. The EWI needed a starter track - and between the two things there's a wedge shaped gap, which actually looks pretty bad on the camera!

    Pic attached is thermal pic of chimney breast (plat EPS on house, rockwool on chimney).
      FLIR0483.gif
    • CommentAuthorRobL
    • CommentTimeJan 16th 2021
     
    And here's a regular photo, so you can see what you're looking at:
      FLIR0484.gif
    • CommentAuthorRobL
    • CommentTimeJan 16th 2021
     
    Here's a "paint" schematic of a side cross-section of the wall.
    Black is pre-existing CWI walls, foundations

    I dug around the house, bit by bit (before the patio flasgstones in the pic placed)
    Orange is 100mm foamglas
    Purple is cement fibre-board
    Cyan is flashband fake lead

    then done this last year:
    Yellow is 150mm EWI
    Red is starter track
      SideViewFoundations.png
    • CommentAuthorLF
    • CommentTimeJan 16th 2021
     
    Looks fantastic.
    How did you fix the foam glass to foundations?
    Do you insulated floor inside ? Did foundation make s big difference to bottom of wall and floor temps?
    • CommentAuthorRobL
    • CommentTimeJan 16th 2021
     
    Hi LF
    The foamglas was put in place, and rubbed against the wall - any bits that don't quite fit just grind away a bit of the foam easily - very satisfying. Then I sprayed a bit of water on both surfaces, and a bit of expanding-foam glue, and pushed against the wall. I held them in place using sticks or anything while the glue set, then filled back the hole in.
    The foamglas has all been fine.
    In contrast, the small bit that I used XPS with I had to subsequently fix in place with a few mechanical fixings. As the earth nearby heaves a bit as it dries out, the XPS picked away from the wall slightly.

    No, I haven't insulated the floor. It's a bit of a weakness - I'm currently monitoring to try to understand how important it might be. Everything's in flux this year - we still have the EWI scaffolding up on the South face so the windows are covered, and I've only just sealed up the porch which was a dreadful thermal bridge for the foundations as the slab was effectively exposed there.
    • CommentAuthorLF
    • CommentTimeJan 16th 2021
     
    Rob, thanks for info.
    It seems like if perimeter insulation is good then you do not need to insulate under the floor and get a pretty good U value. If so, then seems a good cost effective mod if you can get at footings easy enough.
    • CommentAuthorLF
    • CommentTimeJan 16th 2021
     
    Rob. What grade of foamglas?
    • CommentAuthorRobL
    • CommentTimeJan 16th 2021 edited
     
    They were Foamglas Perinsul T4+, 450mm x 600mm x 100mm.
    I can't remember the internet site I got them from. Maybe £800 for all of it. It's oddly hard to find.

    I've just re-analysed my temperature sensors - there's one inside (pretty much 21C all the time), one outside in the shade and with a rain-hat on. They've both "sht35-d" parts, typical 0.1C accuracy, measured every second, hourly means stored on a little stand-alone micro. There's a nice pic of the data gathered attached, and I've split in into pre and post porch. I only made the lockdown-project logger recently, so nothing before it to compare!

    Pre CWI, MVHR, as we bought the house we actually used 18MWh / year of gas
    Pre EWI (but perimeter insulation done) we actually used 8MWh / year of gas
    Post EWI but pre porch I think we would have used 5MWh* **
    Post porch I'm now hoping for 3.5MWh / year gas* **

    Before we added the porch, there was a huge thermal bridge. The original front door was inset by 1m, with the slab bridging inside to outside, so effectively 2m^2 of slab was fully exposed to outside air. Worse still, a central heating pipe actually runs in the slab by the front door, making sure there was a good heat flow straight out! I think it shows there's a lot to be gained by insulating the slab & foundations.

    *Using the equations on the plot, and degree days .net for our area

    ** edited as I think I calculated it wrong first time. Answers not quite as stellar now. Still, gives me something to strive for :-)
      Gas V Temp.png
    • CommentAuthorPetlyn
    • CommentTimeJan 16th 2021
     
    If anyone is looking for Foamglas T4+ we have 40 off 50mm x 1200 x 600 sheets available surplus to our build.
    • CommentAuthorjms452
    • CommentTimeJan 17th 2021 edited
     
    Looks awesome Rob - Even in the new area where we've got perinsul in our walls and 200mm celotex under the floors is nowhere near that good.

    Some self adhesive neoprene strip in the sloping gap?
    • CommentAuthorLF
    • CommentTimeJan 17th 2021
     
    Excellent work RobL.

    I searched harder and found you had generously shared more info back in 2013 on this.
    Nice to know you are still happy with what you have done and you managed to add the EWI afterall.

    http://www.greenbuilding.co.uk/GBF_Forum/discussion/10829/floor-insulation-is-it-worth-it

    I will do a bit of digging to see what doing on once the water table has dropped a bit from current very high level!
    • CommentAuthorRobL
    • CommentTimeJan 17th 2021
     
    Thanks all! Frustratingly I made a mistake in my calculation from degree.days, and my yearly gas prediction is now not as stellar as it was - I've mended the numbers above, and added some more in I found before works started. It gives me a new target to get to though :-)
    Insulating the slab is still a great improvement !


    And yes, I did talk myself into it, then managed to persuade Mrs RobL that brick doesn't look that great, and EWI was the future, and we really should just get on with it. Then I went on an EWI training course, did all the prep & insulation, but am paying a pro renderer to finish off.
    • CommentAuthorjms452
    • CommentTimeJan 17th 2021
     
    Posted By: RobLThen I went on an EWI training course, did all the prep & insulation, but am paying a pro renderer to finish off.


    You should do that professionally - many installers seem to consider the rendering the specialist bit and everything else trivial!
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