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Housing - Renovation: Floor insulation; is it worth it?

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1 to 29 of 29

  1.  
  1.  
    Hello,

    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!
    •  
      CommentAuthorfostertom
    • CommentTimeJun 26th 2013
     
    Especially if you're going to EWI it, excavate for a french drain all around the perimeter, run EWI down to base of found, backfill with Leca as insulating no-fines french drain aggregate - a sort of 'wing' insulator in addition to the EWI. In other words, instead of underfloor insulation, leave it undisturbed, and move that insulation to a downstanding perimeter 'coffer dam'.
  3.  
    I'd agree with Tom. If you're sure its a ground bearing concrete slab then its an ideal candidate for perimeter insulation. Dig down the outside of the outer leaf until you reach the top of the concrete strip foundations without disturbing the ground which supports them. Then fill the trench with moisture tolerant insulation & cover with a thin layer of gravel.

    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
    •  
      CommentAuthorfostertom
    • CommentTimeJun 26th 2013 edited
     
    Here's how the principle has evolved, so far, for me.

    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.
    • CommentAuthorRobL
    • CommentTimeJun 26th 2013
     
    I did as DavidFreeborough just said, digging down 3-4 feet to the top of our foundations in our 1963 house (brick 55mm cavity block construction, no insulation under the concrete floor). I used 100mm thick foamglass from the foundations up to a brick away from the DPS level. The top of the foamglass was shaped with a nice slope for rainwater, and then painted with bitumen. If ever we get EWI, then I'll join the two things up at the DPC.
    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.
  6.  
    Rob , where did you source the foam glass ?
  7.  
    sparky , you mentioned future UFH , would you be using the overlay thin build up system ? think you need some floor insulation with UFH .
    • CommentAuthorjms452
    • CommentTimeJun 27th 2013
     
    With EWI I would second, Tom, David and Rob.

    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?
    •  
      CommentAuthorfostertom
    • CommentTimeJun 27th 2013
     
    But for heavens sake do EWI it - piece of cake, by the pics. Then you prob wouldn't need more than extreme-winter heating, which the extg system would cover amply, even with several inconvenient rads etc removed - save yourself doing UFH.
    • CommentAuthorCWatters
    • CommentTimeJun 27th 2013
     
    The EPC says it's already got filled cavity wall insulation.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 27th 2013
     
    Pity - cavities better filled with weak concrete, inside EWI. The likes of http://www.diamondbead.co.uk do a healthy business removing CWI - easy. Even with CWI, totally inadequate - EWI it anyway.
  12.  
    Thanks so much for your comments, everyone - very much appreciate the time you've taken.

    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
    • CommentAuthorRobL
    • CommentTimeJun 28th 2013
     
    Hi James
    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).
    • CommentAuthorjms452
    • CommentTimeJun 28th 2013
     
    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.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 28th 2013 edited
     
    And you really need to renew the windows at the same time - or rather, to be quite accurate to relocate the windows outboard so they sit within the EWI zone i.e. completely outboard of and not touching the masonry.

    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.
  16.  
    Good to know a rough price on EWI. I'd anticipate doing it in a year or so; once we've sold off our current house, we'll have money to spare again - just won't have much to hand with the two houses. We'd know what the new house is like to live in, then, and know more about hot and cold spots.

    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?!
    •  
      CommentAuthorfostertom
    • CommentTimeJun 28th 2013
     
    Just not bothering prob - the effect is an extremely thin (if any) bit of insulation lining the existing external window reveals. So masonry around the windows is almost unproteced from outside temps.
    In hitherto quite thin (like 50-75mm) EWI installations, that is less noticeable than the disaster it becomes with 150-200mm EWI.
    • CommentAuthorjms452
    • CommentTimeJun 28th 2013
     
    We fitted the windows flush with the outer masonry and then got the phenolic of the EWI to overlap with the frames by 1cm.

    Not nearly as good as Tom's gold standard but much better than doing nothing.
  19.  
    We paid about 3k to break out 20m2 concrete floor and relay over kingspan and dpm.
    (part of larger job, which included IWI)
    It transformed the livability of the room so very pleased. Wont payback in energy costs savings tho.
  20.  
    Including 5% vat for insulation projects, and various pipe runs under floor.

    Necessary to remove wall linings so was good chance to IWI as EWI no good for us.

    Cost some more for replacement floor coverings.
  21.  
    Rob, what did you use to fix the foam glass sheets to the wall?
    • CommentAuthorRobL
    • CommentTimeJun 29th 2013
     
    Phil
    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.
    • CommentAuthorShevek
    • CommentTimeJul 1st 2013 edited
     
    We've broken out slabs and replaced with insulated slabs. As Will notes it won't pay financially but we're doing it for comfort (we're also installing underfloor heating) and because it seems like the sensible thing to do in the long run.
  24.  
    Thanks Rob.

    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.
  25.  
    sparklyfish - I wonder if you're still reading this as I am going back to your original question.
    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.
    • CommentAuthorSeret
    • CommentTimeJul 3rd 2013
     
    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.
    • CommentAuthorRobL
    • CommentTimeJul 7th 2013
     
    Hi Seret
    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....
  28.  
    Thanks, everyone, for your input! Sorry if it looked like I asked a question then ran away; been busy with gigs (I play in a steel band - not very 'green' but at least the basic material is re-used).

    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
    • CommentAuthorjms452
    • CommentTimeJul 8th 2013
     
    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!

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