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Housing - Renovation: Suspended Floor Insulation - Design & Experience

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  1.  
    • CommentAuthorTomB
    • CommentTimeAug 28th 2012
     
    We recently insulated with 200mm of fibre-glass under our Edwardian sitting-room floor, to a design that should achieve a a U-value of 0.25W/m2K, the current standard for new-build.

    This article discusses our design choices and lots of practical detail we learnt doing the job. No expecting to learn more from your comments!

    http://cambridgecarbonfootprint.org/under-floor-insulation/
    • CommentAuthortony
    • CommentTimeAug 28th 2012
     
    Top class job and very nice, I wish the whole country was like you!!
  3.  
    What a well written and helpful document, well done.
    • CommentAuthorowlman
    • CommentTimeAug 29th 2012
     
    I'm doing a similar job for my clients at the moment. After lifting the floorboards I found they were the only thing that was holding the floor together. No strutting or noggins between the joists. The sleeper walls were uneven, loose and built directly off compacted hardcore, which itself was crumbly, - no site concrete here. Once the floorboards were up the joists simply twisted, bowed and were unusable. Moral is, be very careful and be prepared for some serious renovation if it goes pear shaped. But, well done TomB, a good job.
    • CommentAuthorseascape
    • CommentTimeAug 29th 2012
     
    Great job and good that others can see how to do it - very helpful article.
  6.  
    Well done for the guide. Can I add my 2.5d (1+p)-worth?

    I always used to do it this way, and it works fine if you've managed to track down all the air-leakage (since most disappointment with u/fl insulation usually relates not to the insulation but to remaining unsolved air-leakage, in my experience), but I now use breather membrane instead of netting, Pro-clima taped between sheets, and taped at te perimeters where the surface allows, or battened-and-mastic-ed (mastuck?), as a belt-and-braces air-tightness layer. (Note that you must still chase down the leaks and remedy by normal means as much as poss first).

    I used to do a lot of work in similarly-confined u/fl spaces, but have got ratther claustrophobic after a particularly tight job. Your photo gave me the shivers!

    Nick
    • CommentAuthorEd Davies
    • CommentTimeAug 29th 2012
     
    Nick, they put a polythene sheet over the top of the joists for air tightness. Doing that, would you still use a breather membrane? I could see that it would help stop air movement in the glass fibre which would be a good thing.
    • CommentAuthorskywalker
    • CommentTimeAug 30th 2012
     
    The nice thing about the breather membrane method is that if you can get under the floor you do not need to use a plastic sheet over the top and can leave the boards in place. Then hunt the air leak as Nick says. Worked a treat on my front room. After a short intermission (couple of years!) I will be doing the rest of the floor soon.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 30th 2012
     
    Posted By: Nick Parsonsbattened-and-mastic-ed (mastuck?)
    Yes!
    • CommentAuthorMikeRumney
    • CommentTimeAug 31st 2012
     
    Posted By: tonyTop class job and very nice, I wish the whole country was like you!!


    Posted By: PeterStarckWhat a well written and helpful document, well done.


    ... what they said! ....

    Any burrowing creatures with long teeth where you are?
    We're having to consider which membrane will keep them out. :cry:
    Anybody have info on, or experience of, different membranes from this point of view?
    (Mesh would probably cost too much, tho' not fully researched yet)
    • CommentAuthorTriassic
    • CommentTimeAug 31st 2012
     
    Direct link to the original article -- http://cambridgecarbonfootprint.org/wp-content/uploads/2012/08/Get-Snug-Underfloor-Insulation.pdf

    Must say I find this type of case study helpful.
  12.  
    +1
    Nice blogs Tom I liked your other eco home case studies, like GD .

    When I did this job I wish I had taken opportunity to make an insulated airtight hatch to get under floor without lifting boards. Would have been handy for couple of subsequent electric plumbing type jobs.

    I need to get back under to replace pipe insulation, mice shredded the foam stuff.
  13.  
    • CommentAuthorJTGreen
    • CommentTimeAug 31st 2012
     
    The Cambridge Carbon Footprint ecohomes events were what first got me going with my whole house insulation project. I'd had an idea about making some home improvements, but it was going to see other people's 'ecohomes' that raised the bar a bit for me. It also got me into doing the carbon conversations sessions, which helped me look at food and consumption as well as housing. And CCF also arranged the thermal imaging of our house pre-building work. Stuff like this really does work in pushing people to do the right thing (certainly did for me).
    • CommentAuthordjh
    • CommentTimeSep 2nd 2012
     
    Posted By: JTGreenThe Cambridge Carbon Footprint ecohomes events were what first got me going ... it was going to see other people's 'ecohomes' that raised the bar a bit for me. It also got me into doing ... CCF also arranged the thermal imaging of our house ... Stuff like this really does work in pushing people to do the right thing

    I agree with all of this and that it is excellent. What I want to ask is, how to progress this into other areas, which aren't quite as special/enlightened/whatever as Cambridge?

    PS I don't think membranes keep sharp-toothed animals out. Metal, stone or something else hard and strongish might.
    • CommentAuthorSeret
    • CommentTimeSep 3rd 2012
     
    Just did a similar job myself in the dining room last week, wish I'd taken some pics now but was trying to get the work done as quickly as possible!
    • CommentAuthorJTGreen
    • CommentTimeSep 3rd 2012
     
    Obviously Cambridge does have some special characteristics (e.g. historic university city, high level of cycling etc....) as will any town or city but it's has its share of 'ordinary' too.

    The idea of a 'green open house' is not unique to CCF at all, (see http://ecovation.org.uk/ ) I think there's quite a bit of 'ecovation' activity going on in different places under different auspices - superhomes is another example. Transition does a bit of the same sort of thing (there's definitely an overlap in Cambridge). The carbon conversations model, which is at the heart of what Cambridge Carbon Footprint do, is attempting to be replicated nationally - this aspect of CCF work was taken on by COIN - http://carbonconversations.org - not necessarily with massive take up at the moment, but no reason to think it's not replicable in other places given the catalyst of just a few people who want to lead it/do it.
    • CommentAuthorTomB
    • CommentTimeSep 16th 2012
     
    Thanks for the positive Comments.
    Yes, djh, there's plenty of community action on eco-renovation, nationwide. YouGen has a growing list describing Open Homes around the country: www.yougen.co.uk/blog-entry/1978/Open+homes%273A+see+how+others+have+improved+their+homes/

    Let's consider carefully who we're trying to inform and inspire and what will appeal to them.
    For example "Eco-Homes" may sound too expensive and "green" to many. But emphasising pay-back times and money-saving only reaches some people considering low-hanging improvements. Common Cause champion appealing to people's values. See the recent debate with Tony Juniper: http://valuesandframes.org/responses-to-tony-juniper/
  19.  
    We're completing on our purchase of a late Victorian terrace house in the next couple of weeks, with typical suspended floors (over probably quite a deep void, at least at the front, given the slope of the ground, but no-one has been able to look as we can't take boards up before completion!). We've had a couple of quotes from local firms (really hard to find anyone who offers underfloor insulation) around Bath/Bristol, but the work they propose seems at odds with some of the advice here. Could anyone comment on whether the approach they proposed is sensible, or should we look to do it ourselves (maybe getting a professional to lift and relay the floor boards for us, as we want to keep the existing exposed floorboards)?

    First quote proposes to "100mm sheet insulation fitted in and between (sic) existing floor joists", and then to relay the floor boards "directly to existing joists using needle pin technique". The rest of the quote solely deals with the floor boards (they are a wood flooring specialist, but claiming underfloor insulation as one of their services).

    The second quote proposes to use "100mm of Celotex sheet insulation between the joists". We specifically asked him about using loft-style insulation layed into "bags" of breathable membrane, as per the work done in Cambridge near the start of this thread, but he was dismissive of this, saying he "always" uses Celotex.

    From searching the web people spend a lot of thought on controlling the humidity to avoid any risk of the joists jotting. I'm concerned that neither quote mentions anything about vapour control barriers or membranes, is there any need for these if using Celotex sheets? I've picked up that we should be asking them in detail about how they seal the edges of the Celotex to the joist etc, but are there any other questions we should be asking?

    I noticed that in the Warmer Bath leaflet looking at how local houses can be made more eco-friendly (http://www.cse.org.uk/warmerbath.pdf) lauds under floor insulation, and the pictures (p44) look like they simply placed the breathable membrane over the joists. This looks easier than the more thorough approach of securing them under the joists that the Cambridge example took. Can anyone see any difficulties with this? (I realise it leaves the joists uninsulated, which would reduce the effectiveness a bit, but should mean there are no changes in their risk of rot etc.?

    Which approach is likely to yield better results? Many thanks in advance for everyone's help.
    • CommentAuthortony
    • CommentTimeSep 22nd 2012
     
    Air sealing is crucial what ever you do, most dont think a vb is necessary, I like to see one and it can double as the air tightness barrier too.

    Sheet insulation has its technical problems and poorly fitted or fixed negates a lot of its benefit, it is also expensive to but and to fit, so I prefer and generally use glass or mineral quilt on netting which is much cheaper even for the same theoretical U-value.

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