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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentTimeFeb 24th 2018
    Posted By: TimSmallA typical green roof maybe

    Yes, but that's an inverted construction. I'm interested by what you meant by a non-inverted version and its problems.

    I only ever put poly on top of insulation, then concrete.

    Yes, I think this is the right way to do it, but is contrary to most PIR board manufacturer instructions

    The clue may be in that paper you linked to, which stated that insulation outside the DPM cannot be counted for thermal purposes in German law. So only people building for themselves, who cared about the actual result rather than ticking boxes and earning dollars would build the sensible way. As to why the Germans have that rule, if they do, I have no idea. (or rather I can see that insulation below DPM in a floor may have an unpredictable insulation value, but AFAICT, the alternative is worse.
    • CommentAuthorandyman99
    • CommentTimeFeb 28th 2018 edited
    The screed is now removed. The exposed slab appears very even, although it slopes slightly front to back. It is a minimum of 75mm below the finished OSB3 floor but more like 95mm at the window end.

    Interestingly, our solicitor has no sent us a number of documents, including the original plans for the extensions. The construction notes for the solid floors were as follows:

    “Solid ground floors to consist of 50 cement screed on 100 concrete slab on dpm of Visqueen 1000 polythene sheeting 150 hardcore with sand blinding. Dpm to be paid continuous with dpc in walls.”

    The slab sits on concrete strip foundations.

    The perimeter is 3.5m x 4m, with 2 external boundaries.

    This will be a walk-way from the front door (proposed) into the house. So just looking for final ideas on how to proceed.
    • CommentAuthortony
    • CommentTimeFeb 28th 2018 edited
    I reckon 50mm eps (pir is an alternative) 10mm pir perimeter insulation to outside walls, try to cut sreaight down under the patio door and do perimeter insulation there too to top of floating floor. This could be 22 chipboard but I would use 25 or 28mm t&g ply, with vb on top of the insulation.
    • CommentAuthorandyman99
    • CommentTimeFeb 28th 2018
    What about the slope (20mm) on the slab? Would it be worth trying to level this in some way?
    Tricky. Had you lost the slope in the screed, or was your exg finished floor 20mm out? If the latter, then you can probably live with a floating floor that's 20mm out. If the former, you probably cannot!
    • CommentAuthorandyman99
    • CommentTimeFeb 28th 2018 edited
    The screed increased in thickness towards the window, to account for the slab being out.
    • CommentAuthortony
    • CommentTimeFeb 28th 2018
    Sorry missed that, definitely level it up, use thicker insulation as you get nearer the window with near dry mix sand and cement under to make the top level and flat.
    • CommentAuthorandyman99
    • CommentTimeMar 1st 2018
    Tony, did you suggest ply since it can be obtained in greater thicknesses? I already have used OSB3 for the rest of the floor but it is 18mm. I was intending carrying this through to the floating area. This would also allow greater insulation thicknesses, but if you think thicker ply would be better I hunt for some of that.
    • CommentAuthortony
    • CommentTimeMar 1st 2018
    Might be easier to carry on with 18mm chipboard then —. I like the idea of thicker insulation always
    • CommentTimeMar 1st 2018
    Posted By: tonyMight be easier to carry on with 18mm chipboard then

    You mean OSB presumably?
    • CommentAuthorandyman99
    • CommentTimeMar 1st 2018
    Yes 18mm OSB is what I've been using. I find the T&G is so much easier to handle. I have ordered some 50mm and 25mm Jablite EPS, I'm hoping I can go from 50 to 75 more gradually with the 2 depths and some dry mix underneath. Not exactly sure how yet, but I've got a bit of spare to experiment with.
    • CommentAuthorandyman99
    • CommentTimeMar 29th 2018
    Fitting the floating floor was delayed whilst we continued to debate the final floor plan. We've now finalised the layout and I'm ready to have a go. Just wondering again about levelling, would using a self levelling compound be an alternative method to a dry mix? I have a bit of a phobia of dry mixes, when ever I've used them they've failed to work for me. Obviously I've never tried this before so will give it a go if its considered the best approach. There's about a 20mm fall over 3.5m.
    • CommentAuthortony
    • CommentTimeMar 29th 2018
    That will work out very expensive with self levelling compounds but possible, you can mix on sharp sand to bulk them up. Work out volume and calculate no of bags and costs.

    I would use dry mix, slightly damp actually sharp sand to cement 8:1 use ant powder generously round the edge above and below insulation, star tip that
    • CommentAuthorandyman99
    • CommentTimeMar 30th 2018 edited
    Posted By: tonyuse ant powder generously round the edge above and below insulation

    I have seen ants around the front window where there appears to be a couple of missing rows of bricks, the slab came right to the outside brickwork at this point, so I will rectify this. This window will also be replaced, the sliding window at the front doesn't look right to me and this will require the brickwork to be raised again at a later point.
    One other thing, this new floating floor and the already insulated suspended floor are now going to be one space. It will almost certainly have a wood/laminate covering. Should I try to run the OSB continuously as if one floor, or keep the 2 floor spaces separate? Just worried there may be some movement at the join between suspended and floating
    • CommentAuthortony
    • CommentTimeMar 30th 2018
    One floor
    • CommentAuthorandyman99
    • CommentTimeMar 30th 2018
    And ...

    Regarding a vapour barrier, in that I already have a DPM below the slab

    Jablite EPS
    Dry Mix

    I'm thinking that it might not be a good idea to add another one above the insulation?
    • CommentAuthortony
    • CommentTimeMar 30th 2018
    Need a vb on the warm side of the insulation, either on the eps or on the chipboard
    • CommentAuthorandyman99
    • CommentTimeApr 7th 2018
    Would it be best to glue the T&G OSB over the floating floor? I haven't been glueing them over the suspended part, but obviously the screwing down holds the individual boards in place and there is always a chance that it may need to come up at some time in the future.

    I think the boards may tend to separate over the suspended part even though the mass does seem to help solidify the whole thing along with the fact that the other end is effectively tied. If this floor did need to come up, it would have to be for a fairly serious reason. There is nothing under this part, except for some electric cables that are ducted around the perimeter.

    I have to say it seems to be working better than I feared it might, I was particularly worried about the levels where the 2 floor types joined, but so far it feels quite solid.
      floating floor.JPG
    • CommentAuthortony
    • CommentTimeApr 7th 2018
    Oh good, definitely glue the floating floor, I know people who glue over joists too, I don’t except on engineered joists.

    Foaming wood glue is nice, glue the ends too.
    • CommentAuthorandyman99
    • CommentTimeNov 10th 2018
    I'm at the stage of adding the floor insulation/boarding in the new extension and want to use the same floating floor approach as discussed above. I only have about 120mm depth, so with 18mm OSB, that leaves just 100mm for insulation. The external perimeter is 20 m and the area 47 m2, so I dont think I can use EPS here. Celotex has been recommended, my normal building supplier seems to have Xtratherm. All seem very expensive, are there any other options? Do I need any further vapour barriers with this construction. (sub-base - DPM - Slab -Insulation - OSB)

    Thanks Andy
    • CommentAuthortony
    • CommentTimeNov 10th 2018 edited
    Eps is an option, grey/platinum would work, thin pir perimeter insulation and definitely a vapour barrier on top of the insulation
    ''The external perimeter is 20 m and the area 47 m2, so I dont think I can use EPS here.''

    I think you can. Perimeter/area ratio is 0.425

    A 'ready reckoner' will give you an approximate 'base case' U value for a given P/A ratio.

    In your case the base case U is about 0.65W/m2K.

    1/0.65 gives you the base-case R value, of around 1.538m2K/W

    R value of 100mm gEPS is 3.125m2K/W (given a lambda value of 0.031W/mK).

    1.538+3.125 = total R = 4.663m2K/W (note I have not included surface resistances or the board - this *is* quick and dirty!)

    1/4.663 = U = 0.2144W/m2K. Part L1B requires 0.25W/m2K.



    More 'bobbly', but overall much nicer than PIR. Looking at moving over to it a lot more.
    • CommentAuthorandyman99
    • CommentTimeNov 11th 2018
    Good news, I had been considering standard EPS rather than the graphite. The extension floor is much flatter than the refurbished parts so should be more straightforward. Many thanks for responses

    I haven't bought 100mm gEPS lately, but 150 was under £15 (+ VAT) /m2, with discount on larger orders. That does not compare too badly with £39.78 + VAT from a mail-order 'shed' for 100mm PIR 1200 x 2400 = 2.88m2, so 39.78/2.88 = £13.81/m2 (therefore 100 gEPS probably cheaper, although it is never as simple as price /150mm x 100mm), although you get an R value of 4.54M2K/W for 100mm PIR and only 3.125 for 100mm gEPS.

    However if you are looking for a bit of a 'plastic but 'nicer'' feeling, you may go for gEPS if depth allows. More breathable than foil-faced PIR, less noxious fumes (it appears - I have no proof ) - released on cutting.

    Still have not got chapter and verse on pollutants released in fire for each material. There was a good session on plastic insulation and fire at the AECB convention, so I need to find the transcript.
    >> R value of 4.54M2K/W for 100mm PIR and only 3.125 for 100mm gEPS.

    When we looked into it, the extra insulation value of 100mm PIR saved about £1/year extra energy per sheet, compared to graphite EPS. So over the lifetime of the building it was definitely better value to max out the insulation value and go for the PIR than the EPS.

    The fire issue seems to me to be a red herring, I would be a goner to the carbon monoxide and heat from the burning timber, long before the fire burned through the OSB layer into the insulation.
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