Thu, 07 May 2026 16:49:00 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178669#Comment_178669 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178669#Comment_178669 Wed, 26 Jun 2013 11:28:22 +0100 sparklyfish
First time poster here! Have been reading as many threads here as possible for a month or so, and am very grateful to you regular posters as I've learnt a lot already.

I'm interested in floor insulation. We've just agreed to buy a larger house, and as we'll be able to get possession before vacating our current house, I'm wondering what is really worth doing before we move in.
Here's the house in question:
http://property.cheffins.co.uk/more_details.php?profileID=100539034191
So it looks to be a not-very-remarkable 1972 house (the remarkable bit is personal; it has a lovely view, and is a short nice walk to school and work). Suspect the cavities were filled some time ago, and the loft insulation could no doubt do with a bit more. But wall and loft insulation are jobs that can be done later, unlike the ground floor. The floor is a solid concrete slab, which I presume is uninsulated, and has the odd bit of central heating running through. Ceiling height is pretty average - i.e., not enough to raise the floor comfortably.

So, my question is whether you knowledgeable people think it is worth excavating and insulating the floor before we move in?

I can probably justify the cost of excavation, insulation, and a chipboard floor, but that would have to be it until we've sold off our current house. Having said that, does anyone have any rough ideas for how much excavation might cost?
I'd have to put down new pipes to keep the current radiators, until such a time as we could afford to put in UFH (hopefully the probably-original boiler will last that long so that we can go for a whole new system at that point). I'm also trying to learn more about external perimeter insulation, in case this is more suitable than breaking up the slab in a hurry.
Anything I do is always going to be more bodge than build, so I'd be grateful for your thoughts!]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178675#Comment_178675 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178675#Comment_178675 Wed, 26 Jun 2013 12:24:59 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178686#Comment_178686 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178686#Comment_178686 Wed, 26 Jun 2013 14:11:48 +0100 davidfreeborough
Lightweight Expanded Clay Aggregate (LECA) can also act as a perimeter drain to help keep the base of the wall dry, but it is the least insulating of all the options. Other options worth considering are GLAPOR recycled foamed glass gravel, Foamglas foamed glass slabs, expanded polystyrene (EPS) & extruded polystyrene (XPS).

XPS is the most insulating of these, but is not going to do anything to help keep the wall dry, so make sure the drains are in good order, that no land drainage is required & that the all your gutter are doing their job & draining away from the property.

David]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178692#Comment_178692 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178692#Comment_178692 Wed, 26 Jun 2013 15:10:32 +0100 fostertom
It's a 70s house with suspended timber floor over void - all bone dry within. The Building Inspector has approved blocking up the thro ventilation, and insulation round the perimeter as shown, so no disturbance to extg ground floor. Only catch is poss radon build-up - so we've put a 110 VP up and out at ridge level - works by vapour dispersion, not chimney effect, so no lower air inlet needed - tho it will no doubt be 'pulling' inside air down 'thro the floorboards' (actually chipboard), for permanent ventilation - mixed blessing perhaps.

Geotextile lining the trench bottom and side; from mid-height extra-tough polythene cuts across to the house wall as root barrier, topsoil on top for planting right right up to wall, Leca below. The EPS EWI only carries down thro this tapering Leca-insulation-zone; rely on Leca alone below that. Leca is one-third as insulative as EPS, which is fine as it's naturally used, here, at 3x the thickness.

The idea of the 'coffer dam' is to create a v long path-length thro soil, for heat traveling from the underfloor space and the block of subsoil beneath it within the found, out and up to the cold ground surface. The soil acts as a decent insulator, given large 'thickness' i.e path-length.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178695#Comment_178695 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178695#Comment_178695 Wed, 26 Jun 2013 16:08:18 +0100 RobL It definately works, though I haven't any sensors in it I'm afraid.
At first I used XPS, but having used both insulation types, I found foamglass much easier. It was easier to form into a shape, and easier to fit to a brick wall - jiggle it a bit against the wall, and it wears itself to the right shape! I had the foamglass type without bitumen on it, in large sheets (100*600*900mm from memory).
Took a lot of digging:-(
I would check how deep you foundations are with an exploratory hole, before deciding - ours were quite deep, some are less so.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178726#Comment_178726 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178726#Comment_178726 Thu, 27 Jun 2013 08:44:04 +0100 jamesingram https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178730#Comment_178730 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178730#Comment_178730 Thu, 27 Jun 2013 09:14:03 +0100 jamesingram https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178749#Comment_178749 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178749#Comment_178749 Thu, 27 Jun 2013 13:44:18 +0100 jms452
But if you aren't planning on EWIing and are planing underfloor heating then I woudl imagine the perimiter insulation won't be as effective as conventional floor insulation.

I think its a case of where you are going?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178756#Comment_178756 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178756#Comment_178756 Thu, 27 Jun 2013 14:30:03 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178764#Comment_178764 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178764#Comment_178764 Thu, 27 Jun 2013 15:35:19 +0100 CWatters https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178768#Comment_178768 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178768#Comment_178768 Thu, 27 Jun 2013 16:04:49 +0100 fostertom http://www.diamondbead.co.uk do a healthy business removing CWI - easy. Even with CWI, totally inadequate - EWI it anyway.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178838#Comment_178838 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178838#Comment_178838 Fri, 28 Jun 2013 11:22:44 +0100 sparklyfish
I haven't got any experience of living in a house with EWI, although I have seen how UFH makes a house comfortable with a lower temperature required - I helped build my parents' house, which has UFH but is quite conventional cavity build. So it's really helpful to know that decent EWI (inc perimeter insulation) could mean that we simply wouldn't need to use the conventional heating system very much anyway. We're pretty hardy types anyway, mainly due to our rubbish condensing combi boiler which I'll be very happy to say goodbye to!

I was mainly thinking that this is the only opportunity we'll have to have a completely empty house, and wondering whether it's worth seizing that opportunity! But we won't have a significant amount of money to spare, so EWI inc perimeter sounds like the route for us. Just a small question on that front, though - how does fitting EWI around an existing conservatory work? Would the builder butt the EWI down to the conservatory roof, with flashing between the EWI and the roof?

Thanks again for all your advice - much appreciated.

Yasmin]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178839#Comment_178839 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178839#Comment_178839 Fri, 28 Jun 2013 11:29:58 +0100 RobL I got the foamglas from "insulationdirect2u.co.uk"... but just checked & they don't stock it anymore. I remember it was hard to find a stockist at the time. It was ~£300 all in for ~72 slabs each 450*600*100mm, 3 years ago. I think it's the less dense type of foamglas, and was bare (no bitumen). I don't know why it's not a more common material, seemed easy to use, very stable, can't burn, made from recycled glass even. Rotten egg smell when you cut it - don't do it inside, don't breathe the dust (like glasswool dust).]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178841#Comment_178841 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178841#Comment_178841 Fri, 28 Jun 2013 11:42:02 +0100 jms452 Posted By: sparklyfishBut we won't have a significant amount of money to spare, so EWI inc perimeter sounds like the route for us

Perimiter plus EWI is the lowest heat loss route with the largest thermal mass which is great.

But just to reitterate you need to do both to get the full benefit.
As you mention cost being a limiting factor you should be aware that you are looking at £100/m2 plus for EWI at current prices i.e. the perimiter plus EWI option is definitely not the low installation cost option.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178843#Comment_178843 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178843#Comment_178843 Fri, 28 Jun 2013 11:53:36 +0100 fostertom
That relocation is at least as important, perhaps more so, than replacing old(?) double glazed windows with latest triple glazed. However, not really practical to take out and reinstall/relocate existing windows.

Not that triple glazed are expensive nowadays, as windows go - cheapest in PVC (yuk) but still incredibly good price and lovely in timber - £250/m2 incl french doors etc, delivered, glazed and finished.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178849#Comment_178849 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178849#Comment_178849 Fri, 28 Jun 2013 13:05:59 +0100 sparklyfish
I hadn't quite understood that renewing/relocating the windows was so important; I've been watching EWI go on some local council houses, where the existing windows have been left in situ. But maybe they've been using IWI as well, or just not bothering?!]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178855#Comment_178855 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178855#Comment_178855 Fri, 28 Jun 2013 15:19:58 +0100 fostertom In hitherto quite thin (like 50-75mm) EWI installations, that is less noticeable than the disaster it becomes with 150-200mm EWI.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178863#Comment_178863 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178863#Comment_178863 Fri, 28 Jun 2013 16:55:51 +0100 jms452
Not nearly as good as Tom's gold standard but much better than doing nothing.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178883#Comment_178883 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178883#Comment_178883 Fri, 28 Jun 2013 21:14:36 +0100 WillInAberdeen (part of larger job, which included IWI)
It transformed the livability of the room so very pleased. Wont payback in energy costs savings tho.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178884#Comment_178884 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178884#Comment_178884 Fri, 28 Jun 2013 21:21:25 +0100 WillInAberdeen
Necessary to remove wall linings so was good chance to IWI as EWI no good for us.

Cost some more for replacement floor coverings.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178894#Comment_178894 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178894#Comment_178894 Sat, 29 Jun 2013 03:43:23 +0100 Phil.Chaddah-Duke https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178919#Comment_178919 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=178919#Comment_178919 Sat, 29 Jun 2013 15:57:22 +0100 RobL I dug a hole about 300mm wide, 900mm deep down to the foundations. Then filled the bottom with "bricks" of foamglas - offcuts really. Then the top bit was made with one sheet of bitumined foamgas glued to the wall carefully level. I think I used "unibond extreme repair sealant" (35 year guarantee, ok damp outdoor) as a glue to the wall - It didn't take much. I left the foamglas pushed against tlhe wall overnight to set, filled any little gaps with expandy foam then sealant to make watertight then covered back over with earth. It won't be moving after that. I intended to use flashing over the top, but instead just sealed to the brickwork with more sealant. seems ok 2 years later.
I've seen loads of housess EWI-ed now out of interest, but I've not noticed perimeter insulation ever. After doing it, I'd guess it's because the digging is too labour intensive for the benefit, compaired with EWI on a (typically) non-cavity wall.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179022#Comment_179022 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179022#Comment_179022 Mon, 01 Jul 2013 13:03:06 +0100 Shevek https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179091#Comment_179091 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179091#Comment_179091 Tue, 02 Jul 2013 22:12:18 +0100 Phil.Chaddah-Duke
Our house is on a hill so the external insulators took a line from the back all the way around the house (kind of nominal damp proof line) so we have a good 2 feet of uninsulated wall above ground a the front. I am sure its losing loads of heat as the UFH on the other side only just above bottom of EWI. This means the foamglas will be very visible anyone know if we could paint the foamglas with masonry paint or maybe as its not buried in the ground XPS rendered would be better but don't fancy render touching the ground.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179098#Comment_179098 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179098#Comment_179098 Wed, 03 Jul 2013 09:42:42 +0100 piersadler I think the answer depends on your ultimate aim.If you are trying to go for a very low energy completed house even in years to come this might be the only realistic opportunity to insulate the ground floor. If you are more pragmatic then the perimeter solution is a good compromise. I agree with others that UFH to be avoided if you are strapped for cash. It won't give you any significant energy benefit.
EWI definitely the most effective way of reducing heat loss, but expensive due to the large wall areas.
No one has mentioned the roof. You will need to insulate your loft if you have one. If you are going for EWI you will also need to pay attention to the eaves.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179108#Comment_179108 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179108#Comment_179108 Wed, 03 Jul 2013 12:54:55 +0100 Seret Posted By: piersadler
EWI definitely the most effective way of reducing heat loss, but expensive due to the large wall areas.


Definitely expensive yes, and not necessarily the only effective way of improving performance in this type of building. Make sure you actually do the numbers, if you've already got cavity insulation and are on a budget you're likely to find EWI is way down the list in terms of cost effectiveness.

Looking at my own place (also CWI) fitting EWI turns out to be the absolute least cost effective way of reducing heat demand. EWI is excellent at bringing solid walled buildings with little or no insulation into line, but it's extremely expensive for improving a wall u-value from 0.6 down to 0.1, for example. You're likely to find there are a raft of other measures you take take that will result in similar carbon savings for less money. These could include airtightness, loft and floor insulation, new boiler and/or controls, and all those million and one little bits and pieces like loft hatches.

Collect some data on how the building actually performs before committing to any improvements. A thermal model of a building is actually very simple, many people on here can give you a spreadsheet, all you need to do is plug in some numbers and experiment with changing various parameters. That way you can determine where the low hanging fruit are instead of embarking on big jobs that may actually give smaller benefits.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179338#Comment_179338 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179338#Comment_179338 Sun, 07 Jul 2013 14:47:03 +0100 RobL I think we're in a similar position to you- CWI on 4 bed house in UK (SE) am having trouble justifying EWI to myself, never mind Mrs RobL. I've been going round our house doing all the other things as you say, and our total gas heating load last year was 8000KWh. In comparison 10 years ago our gas use was 18000KWh/year.
Optimistically, EWI would knock off another 5000KWh/year , at a cost of £10000-£15000. In comparison, PV makes a more valuable 3500KWh(elec)/ year for only £6000.
Oddly, that's the kind of maths that allows me to justify a DIY energy saving task, but not to pay somebody else to do it - it might end up being "cost effective", but it takes me forever and I'd be better off just doing my day job....]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179373#Comment_179373 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179373#Comment_179373 Mon, 08 Jul 2013 09:10:46 +0100 sparklyfish
I suppose I was asking the question about excavating the floor as it's an ideal opportunity, but given that our budget will be very tight (mortgage company said one thing, and then changed their minds in the wrong direction...), I think we'll have to live with it as it is for a couple of years. But I'll know now to take plenty of measurements about how the house is currently, in order to inform a decision on what to do next!

Thanks again - much appreciated.
Yasmin]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179377#Comment_179377 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10829&Focus=179377#Comment_179377 Mon, 08 Jul 2013 09:32:09 +0100 jms452 Posted By: sparklyfishI'll know now to take plenty of measurements about how the house is currently, in order to inform a decision on what to do next

Here here - wish we had done more before getting started. imeasure is good!]]>