SOS: eco -retrofit of a 1960s ex council house

[Philippa]

Hi fellow AECB members

I am hoping this is the place where someone is going to tell me they have done this all before 😉

I have a house that was built in 1964 which is very tired and in need of some TLC. We are moving the kitchen to the rear of the house and thought it was worth wrapping in some works to improve air tightness. The floor at the front of the house is solid concrete and at the rear it is suspended timber with airbricks ventilating the subfloor (only on two sides of the room) and there is a chimney which we will need to remove.

There seems to be two trains of thought on this:

1) fill the floor in –

Remove the floor joists, fill with hardcore, then line with membrane taped at the perimeter, then insulation (contractor would use “ecoboard” something like this – https://www.insulationsuperstore.co.uk/browse/insulation/insulation-board/ecotherm-insulation/eco-versal.html) , underfloor heating then a concrete screed.

( I would be interested in a lower embodied carbon alternative/ less plasticky alternative if this is the way to go)

2) Leave the joists in place and sag a breathable membrane between them and fill with loose fill natural insulation. top with wood fibre board (making sure to leave 150mm of air gap in the subfloor)

We are intending to externally insulate our cavity walls (that are filled with polystyrene balls) so I am unsure if the later is appropriate as I suspect we will need to block up the air bricks and create a french drain detail? Also I may struggle with head space in the lounge as the ceiling is already pretty low.

Any advice would be much appreciated – on the method and on the materials.

Thankyou, PB-W

 

[X Wookey]

My 1960s retrofit already has concrete floors so I’ve not done this personally, but as no-one else has offered an opinion, here’s mine.

Unless the space is too deep to make it practical, I’d fill it in. so you can get a properly insulated floor with some thermal mass. and get decent airtightness. Building control people get very difficult about airbricks, airtightness and suspended timber floors so getting rid of it is both technically and ‘politically’ better.

Hopefully the space is just right for 200-300mm of insulation. I default to XPS rather than PUR underground just in case it ever got soaked (flooding), but that’s carbon-intensive too, so if you’d prefer to avoid that foamglass agreegate is very green (but also expensive when I looked). https://www.mikewye.co.uk/product-category/brands/geocell-foam-glass/ You’d just pour that in instead of the hardcore, then put a floor on top. Lithotherm UFH floor blocks directly on top of the foamglass is one way to do concreteless solid floor: https://www.backtoearth.co.uk/product/underfloor-heating-tiles/ I’ve not tried it myself but I’ve seen one and it looks like a reasonable plan. Backtoearth are great so I’d certainly have a chat to them about it.

You could take the view that having this nice space to fill in with some insulation is a bonus. Dealing with an existing concrete floor is a pain because digging it up is a big job and insulation on top is technically limiting, especially with UFH.

[X Wookey]

{no sign of post so trying again – maybe this will be here twice?]

My 1960s retrofit already has concrete floors so I’ve not done this personally, but as no-one else has offered an opinion, here’s mine.

Unless the space is too deep to make it practical, I’d fill it in. so you can get a properly insulated floor with some thermal mass. and get decent airtightness. Building control people get very difficult about airbricks, airtightness and suspended timber floors so getting rid of it is both technically and ‘politically’ better.

Hopefully the space is just right for 200-300mm of insulation. I default to XPS rather than PUR underground just in case it ever got soaked (flooding), but that’s carbon-intensive too, so if you’d prefer to avoid that foamglass agreegate is very green (but also expensive when I looked). https://www.mikewye.co.uk/product-category/brands/geocell-foam-glass/ You’d just pour that in instead of the hardcore, then put a floor on top. Lithotherm UFH floor blocks directly on top of the foamglass is one way to do concreteless solid floor: https://www.backtoearth.co.uk/product/underfloor-heating-tiles/ I’ve not tried it myself but I’ve seen one and it looks like a reasonable plan. Backtoearth are great so I’d certainly have a chat to them about it.

You could take the view that having this nice space to fill in with some insulation is a bonus. Dealing with an existing concrete floor is a pain because digging it up is a big job and insulation on top is technically limiting, especially with UFH.

[Philippa]

Thankyou for your advice on this. We have filled in the floor. We explored the limecrete build up but the void was not deep enough (and digging any deeper would compromise the foundations) so we have resorted to seconds and co PIR insulation and will have an exposed polished screed over the top – if we have to use cement we better cherish it rather than cover it! (/avoid the additional CO2 emissions from tiles/flooring on top). We will definitely consider XPS for the slab at the front of the house where the levels need to be dead on.

[Gabriel Hyde]

Hi Philippa. It looks like you sent a new forum query yesterday but the link in the email notification doesn’t work, not for me anyway. It looks like there is a glitch in the system, maybe you can try re-posting the query? Or contact the administrator.

This is the link that doesn’t work:
https://aecb.net/forums/topic/insulation-internal-step-detail/
When I click on it, I get to a page that says: “Not Found. Sorry, but the page you were trying to view does not exist.”

I’m posting this message here because I don’t know how else to contact you.

Regards
Gabriel

[Philippa]

Hi Gabriel

I don’t think I am having much luck uploading my doodle. I tried to share an image but it didnt work, then I tried to share a link to the detail I’ve drawn uploaded on imgur – but that isnt working either?

I can try again and explain it without the image but as they say – an image is worth 1000 words 😉

 

• This reply was modified 9 months, 3 weeks ago by Philippa.

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