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Green Building Bible, Fourth Edition
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    • CommentAuthormarsaday
    • CommentTimeJun 15th 2017
    I am doing my extension this summer and have been going through the workings for my concrete floor.

    I have to dig out 370mm depth and then fill back up again. I am now thinking a suspended timber floor using 8" joists will be easier for me to lay as doing work myself. I am also using oak boards anyway.

    Do i have to lay a screed of concrete for BC to stop the weeds, just read this may be required.

    What sort of insulation would i use between the joists? Would it be soft hung in nets or rigid board insulation ?

    Any help appreciated on deciding what to do.
    • CommentTimeJun 15th 2017
    Sounds like this, which I keep posting up here. Click my name above, email me, and I'll send the pdf, which is properly legible.
      285Ja-ufloor 330KB.JPG
    Tom, I will be in touch, if I may, for a legible copy, too. In the meantime I read (with difficulty! - I am getting old!): '' The only safe way is with insulation under the joists as well as between, and a water vapour-impermeable membrane (VCL) below that...''

    This puts the VCL on the cold side of the 'sandwich', contrary to normal VCL practice. I raised a similar issue in http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14961&page=1#Item_9 - 'Basement waterproofing - VCL 'on the wrong side'?'.

    The thread did not reach an unequivocal conclusion, though (thank-you, all) there were some useful thoughts. Your thoughts re this and similar situations (where the VCL appears to be 'in the wrong place') would be useful.


    • CommentAuthormarsaday
    • CommentTimeJun 16th 2017
    This looks too technical for me. I am not an experienced builder and taking on my own DIY extension is a massive task. I can do it, but looking into something like the design above and getting build control to understand it is a lot of work for me.
    Moisture in suspended timber floors can be a vexing and at times apparently fairly inexplicable issue (actual happenings vs expectations based on theoretical behaviour) . If it's 'technical' but does the business, it is arguably worth it.
    • CommentTimeJun 17th 2017 edited
    Nick, you are right to question the VCL location.
    Not sure what I had in mind in writing that (VCL belolw the insulation) on the drawing - except that I was summarising supporting document
    that was referred to (now clickable here, as it isn't (I now discover) on either the jpg or the pdf that I submitted to Bldg Control!).
    So 'VCL below' is not part of the solution I illustrated, just part of the supporting document. I'd have done better to not mention it!

    And that supporting document relates to mid-west USA conditions, of hot humid summers, cool (hopefully) interiors - in which "vapour drive is upward" - conditions and vapour direction that rarely apply in UK.
    In UK the critical time is winter, with cold humid air beneath, warm humid interior - in which case the VCL should def be on the top side. In UK, vinyl flooring would be ideal, but in mid-west USA is shown to be a big no-no.

    In the solution illustrated, I in fact show 'no VCL at all', relying on free breatheabilty of the floor, any water vapour passing downward being condensed-out on cold surfaces well remote from the floor structure, within free-draining water-impervious insulation and draining away from there.
    • CommentAuthorborpin
    • CommentTimeJun 18th 2017
    Also consider your floor covering. If you want tiles, concrete is the way to go.
    Also consider your heating. If you want UFH, concrete is the way to go.
    Posted By: marsadayI have to dig out 370mm depth and then fill back up again.
    Hi Tim, Fill it up with 270mm of EPS (Polysterene) and 100mm of concrete with UF heating, put a plastic sheet in the middle of the EPS if your BC officer wishes.
    • CommentAuthormarsaday
    • CommentTimeJun 18th 2017
    I need to do a 150mm hard core base first according to BC

    So add 270mm insulation and 100mm concrete means a fair bit of hardcore / insulation.

    Am leaning to a wood floor as this will be the easiest option seeing as i am doing all the work. Lifting in wooden joists as opposed to 10-15 Tonnes of material is a lot easier. I am not doing UFH and i am planning on using oak floorboards, so the wooden floor system wins hands down now i have my head around it.

    I have also costed the wood floor as being 50% cheaper as well. That doesn't include the oak flooring though, but i am having this with either system, so not relevant in the calcs.
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