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Green Building Bible, Fourth Edition
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    • CommentAuthorbardo
    • CommentTimeOct 14th 2019 edited
     
    We are building a straw bale timber frame home. Walls are up and lime rendered then larch clad on outside, Clay plaster on go on inside. The straw walls/timber frame sits on a two sleeve concrete block wall which goes all the way round and then a sleeper wall through the centre. Airbricks are installed every 1.5 metres. Building regs required us to use a plastic DPC over the soil with gravel on top. A french drain was put around the foundation wall and the gravel underfloor is now completely dry. The water table is at least a hundred foot below the earth.

    I'm looking at non celotex insulation options for the suspended timber floor made from 300mm timber ijoists. I am open to either using treated 300mm sheepswool product or a non organic insulation such as rockwool though don't want a syhthetic which off-gasses. I'd like feedback on the following please from experienced builders who have taken the same route successfully. (1) What type of insulation to use and why? (2) what to use at the base of ijoists to support insulation? (note I don't have grills on the airbricks meaning that mice could possibly enter the void underneath). (3) What to use on top of the insulation/ijoists e.g. vapour permeable membrane? (4) we have worked with an electrician to do the first fix and underfloor cables have been put inside 40mm PVC flexible hose as to avoid direct contact with insulation. Is this a good practice? (5) A concern I have is water spillage from above. Any thoughts on this? Cheers!
  1.  
    1.What about cellulose ('Warmcel' - recycled newspaper)? 2. breathable membrane, writing facing the soil. Take a 'tuck' in the membrane at each joist and staple say 25mm to the side of the joist. Are they solid timber or 'I' joists or, better, open web joists? 3. Intelligent membrane. 4. Contact with insulation (except EPS or XPS) is not an issue. Being buried in it is. If your electrician is happyb that no de-rating is required you should be OK. Cable in trunking on the cold side: almost certainly OK. Ditto on warm side, probably OK. Cable in trunking buried between 2 layers of insulation - probably not OK unless the breaker is de-rated. 5. Sorry, no. Don't spill things! It is a tricky one.

    Overall: Tape all the membranes.
    • CommentAuthorbardo
    • CommentTimeOct 14th 2019
     
    Thanks Nick. Cellulose is an interesting option. If there was a spillage I'd be concerned about using recycled newspaper in floor. Using 300mm timber JJI JOISTS.
  2.  
    With a degree of permeability in both membranes the Warmcel would probably cope with a minor spill, and if it's a major flood you've probably got other problems as well!

    I imagine there might be some members here with experience of moist Warmcel…?
    • CommentAuthorbardo
    • CommentTimeOct 15th 2019
     
    What's your view of sheeps wool or rock wool Nick. Why Warmcell?
    •  
      CommentAuthordjh
    • CommentTimeOct 15th 2019
     
    I know some people have used straw bales underfloor as well, and all the cases I read about came to regret it because the straw decayed. I would have the same worry about pretty much anything else organic - they're all potentially subject to damage from one or more of water, water vapour in excess, insects and rodents. So on the list you've offered, I'd go for rockwool. It's generally quite difficult to replace underfloor insulation if there is ever a problem.

    Rather than a membrane at the bottom, I'd be tempted to use a permeable board myself. If they're I-joists the boards can rest on the flanges; if they're solid timber they can be nailed underneath. Either Panelvent or an unglazed hardboard (same thing really I think).

    Whatever you do, you want some way for liquid water (or wine!) to flow through to the ground rather than collect in or above the insulation.

    As Nick says, cable contact is only a problem with polystyrene insulation, but embeddding requires the cable and breaker to be derated AIUI even if the cable is in a conduit. But it's the electrician that has to sign it off, so ask him.
    • CommentAuthorbardo
    • CommentTimeOct 15th 2019
     
    Thanks DJH. Aside from the itching during fitting. I wonder about the thermal performance of rockwool compared to sheepswool. Will rockwall release moisture? has there been any comparison done on this forum?
    • CommentAuthorDarylP
    • CommentTimeOct 15th 2019
     
    "Rockwool" can be significantly better than sheep's wool, and cheaper too....:bigsmile:
    •  
      CommentAuthordjh
    • CommentTimeOct 15th 2019
     
    Posted By: bardoAside from the itching during fitting.

    Rockwool isn't too bad. Wear a disposable overall and take a shower afterwards if you're concerned.

    I wonder about the thermal performance of rockwool compared to sheepswool.

    Well, the specs are published so it's easy enough to check that Daryl isn't telling porkies :bigsmile: :wink:

    Will rockwall release moisture?

    Not sure what you mean here? It doesn't absorb water; it's not hygroscopic. Mostly it's only organic products that are.
    • CommentAuthorGreenPaddy
    • CommentTimeOct 16th 2019
     
    Sheeps wool tends to be around 0.04 lambda, with a "vapour openness" of around 9.

    I mostly specify Knauf earthwool (not a share holder) as it's got recycling as a major component, but mostly as it's not itchy. Compared to sheeps wool, it can have various lambda values as good and often better than sheeps wool, depending which one you choose, has "vapour openness" of 3 or 4, so better than sheeps wool, and is about half the price for the same lambda value. It doesn't grow on trees, or sheeps backs unfortunately. Mice will nest in it, as they will in just about anything, but they don't seem to munch on it. Insects don't much like it, not so for sheeps wool.

    With 300mm JJI's, filled with wool type insulation products, you'd get the following Uvalues...

    wool lambda 0.044 (typical cheap loft roll) = Uval 0.14 W/m2K

    wool lambda 0.04 = Uval 0.13 W/m2K

    wool lambda 0.032 = Uval 0.11 W/m2K

    Wondering why you don't put mesh in the the air vents?

    Are the JJI's all installed? If you deff will not have mesh on vents, then I might be inclined to fix OSB to the underside of the JJI's, if they aren't already fitted.

    What's the gap under the JJI's to solum?

    Is there supporting underbuild to the JJI's mid span, or are they full span?
    • CommentAuthorPetlyn
    • CommentTimeOct 16th 2019
     
    Have you considered using completely inert, fire-proof, rodent and insect proof and therefore non degradable expanded glass as the insulation medium and bringing the floor into the warm envelope by installing the insulation in bead form above a dpm so that it closes off the entire space.

    In Building Regs terms this becomes a floor with a solid substrate not requiring ventilation.

    You then have the confidence that the insulation value is long term and forms a permanent feature of your build.

    The expanded glass beads would be usable in direct contact with cable ducts or trunking without determent and being of pourable or blown form in terms of distribution, would entirely fill awkward cavities.

    We have some remaining from our build if you have an interest in receiving a sample.
    •  
      CommentAuthordjh
    • CommentTimeOct 16th 2019
     
    Posted By: PetlynThe expanded glass beads would be usable in direct contact with cable ducts or trunking without determent

    The cable would still require derating though.
    • CommentAuthorbardo
    • CommentTimeOct 21st 2019
     
    <blockquote><cite>Posted By: Petlyn</cite>Have you considered using completely inert, fire-proof, rodent and insect proof and therefore non degradable expanded glass as the insulation medium and bringing the floor into the warm envelope by installing the insulation in bead form above a dpm so that it closes off the entire space.

    In Building Regs terms this becomes a floor with a solid substrate not requiring ventilation.

    You then have the confidence that the insulation value is long term and forms a permanent feature of your build.

    The expanded glass beads would be usable in direct contact with cable ducts or trunking without determent and being of pourable or blown form in terms of distribution, would entirely fill awkward cavities.

    We have some remaining from our build if you have an interest in receiving a sample.</blockquote>

    Thanks Petlyn, I'd be up for looking at this as a possibility. I wonder about costs for filling both 300mm joists and sub floor void compared to rockwool or sheepswool. Where did you buy yours from?
    • CommentAuthorbardo
    • CommentTimeOct 21st 2019
     
    <blockquote><cite>Posted By: GreenPaddy</cite>Sheeps wool tends to be around 0.04 lambda, with a "vapour openness" of around 9.

    I mostly specify Knauf earthwool (not a share holder) as it's got recycling as a major component, but mostly as it's not itchy. Compared to sheeps wool, it can have various lambda values as good and often better than sheeps wool, depending which one you choose, has "vapour openness" of 3 or 4, so better than sheeps wool, and is about half the price for the same lambda value. It doesn't grow on trees, or sheeps backs unfortunately. Mice will nest in it, as they will in just about anything, but they don't seem to munch on it. Insects don't much like it, not so for sheeps wool.

    With 300mm JJI's, filled with wool type insulation products, you'd get the following Uvalues...

    wool lambda 0.044 (typical cheap loft roll) = Uval 0.14 W/m2K

    wool lambda 0.04 = Uval 0.13 W/m2K

    wool lambda 0.032 = Uval 0.11 W/m2K

    Cheers

    Wondering why you don't put mesh in the the air vents?

    Yep goon do that. Good idea.

    Are the JJI's all installed? If you deff will not have mesh on vents, then I might be inclined to fix OSB to the underside of the JJI's, if they aren't already fitted.

    Installed though have wooden flanges so can fix from top if decide to take this route.

    What's the gap under the JJI's to solum?

    400mm

    Is there supporting underbuild to the JJI's mid span, or are they full span?</blockquote>

    Sleeper wall in middle offering extra support.
    • CommentAuthorbardo
    • CommentTimeOct 21st 2019
     
    <blockquote><cite>Posted By: djh</cite><blockquote><cite>Posted By: bardo</cite>Aside from the itching during fitting.</blockquote>
    Rockwool isn't too bad. Wear a disposable overall and take a shower afterwards if you're concerned.

    <blockquote>I wonder about the thermal performance of rockwool compared to sheepswool.</blockquote>
    Well, the specs are published so it's easy enough to check that Daryl isn't telling porkies<img title=":bigsmile:" alt=":bigsmile:" src="/newforum/extensions/Vanillacons/smilies/standard/bigsmile.gif"></img><img title=":wink:" alt=":wink:" src="/newforum/extensions/Vanillacons/smilies/standard/wink.gif"></img>

    <blockquote>Will rockwall release moisture?</blockquote>
    Not sure what you mean here? It doesn't absorb water; it's not hygroscopic. Mostly it's only organic products that are.</blockquote>

    Thanks DJH. btw...n your straw bale home how did you detail the bathroom to reduce and deal with moisture?
    • CommentAuthorPetlyn
    • CommentTimeOct 21st 2019
     
    What overall area do you have to fill in your project? We have a reasonable quantity left over and would be prepared to negotiate a price if you were looking for a quantity - let me have an address and I'll get a sample off to you?

    Glass beads have many advantages over traditional loose-fill insulations from their compressive strength (MPa of 1.2), good thermal conductivity (W/(m-K) 0.0661), they are non-combustible, easy to use as they will pour or blow into any awkward space are therefore much easier to use than wool or board type insulation. They don't absorb large quantities of water (max 15%) and do not settle, degrade or get eaten/used as nesting material for vermin/insects etc unlike EPS.

    We have used glass insulation throughout our build as we believe that money spent now on an insulation that will stand the test of time and in doing a once and for all job, we will not have to worry about what might be eating or living in the floor, walls and roof or whether there is any decrease in performance efficiency.

    I will include a spec sheet with the sample if you would like further info.

    Thanks
    •  
      CommentAuthordjh
    • CommentTimeOct 21st 2019
     
    Posted By: bardobtw...n your straw bale home how did you detail the bathroom to reduce and deal with moisture?

    The showers are placed against internal walls and the walls are covered in XPS-core laminated boards so completely indifferent to and impervious to water. Where there is an external wall forming one wall of a shower enclosure it's just covered in the regular lime plaster and painted with clay paint like every other bit of wall. I did paint the areas within the showers with Stormdry and that seems to help with making any stray water bead up into drops and run off instead of being absorbed by the lime.

    In the guest room where's there's a bit of a possibility of more than a few stray drops striking the wall, I mounted a waterproof roller blind on the ceiling and we roll that down to cover the wall before using the shower, then roll it up after a while to allow the wall to breathe.

    There are MVHR extract vents in all the wetrooms of course, and that helps clear any water after a shower.
    • CommentAuthorbardo
    • CommentTimeOct 22nd 2019 edited
     
    Posted By: PetlynOverall areas is approx 115 M2 with an over all depth of about 700mm. I presume that would mean a lot of glass bead?


    Overall areas is approx 115 m2 with an over all depth of about 700mm. I presume that would mean a lot of glass bead? Do you have sufficient to cover the floor area here?
    • CommentAuthorPetlyn
    • CommentTimeOct 22nd 2019
     
    We have a minimum of 30m3 available which, over your square area and allowing for the joists in the space, would give you a depth of 30cm at an insulation value of 0.0661 W/(m-K). At this depth, one would have thought the insulation value itself beneath the floor would be sufficient which would allow the lower part of the void to be backfilled with a cheaper material before introducing the beads in their free-flowing form to fill the irregularities beneath and in between the joists.

    Alternatively, you could consider using more of the beads which we obtained direct from the manufacturer in Europe - we can give you details of our source and as we said, a sample and spec sheet are available for your consideration.

    Our beads at a very attractive price are available at £5000 for 30m3 and to fill the void entirely would seem to be an expensive option. The beads are indestructible and non-compressible and so will give a permanent result, warranting the use of an aggregate, such as pea shingle as the substrate with geotextile to separate?

    The beds are available in normal big-bags holding approx 0.55m3 each and can be moved across a floor easily by two people for siting.

    Hope all this helps.
    • CommentAuthorbardo
    • CommentTimeOct 22nd 2019
     
    Posted By: PetlynWe have a minimum of 30m3 available which, over your square area and allowing for the joists in the space, would give you a depth of 30cm at an insulation value of 0.0661 W/(m-K). At this depth, one would have thought the insulation value itself beneath the floor would be sufficient which would allow the lower part of the void to be backfilled with a cheaper material before introducing the beads in their free-flowing form to fill the irregularities beneath and in between the joists.

    Alternatively, you could consider using more of the beads which we obtained direct from the manufacturer in Europe - we can give you details of our source and as we said, a sample and spec sheet are available for your consideration.

    Our beads at a very attractive price are available at £5000 for 30m3 and to fill the void entirely would seem to be an expensive option. The beads are indestructible and non-compressible and so will give a permanent result, warranting the use of an aggregate, such as pea shingle as the substrate with geotextile to separate?

    The beds are available in normal big-bags holding approx 0.55m3 each and can be moved across a floor easily by two people for siting.

    Hope all this helps.


    Thanks Petlyn, though beyond our budget. Good luck reselling.
    • CommentAuthorGreenPaddy
    • CommentTimeOct 23rd 2019
     
    Ok, so JJI's in place, with 400mm gap to solum...

    If you set say 9mm OSB onto the JJI flanges, then your Uvalues would worsen, to something like;

    wool lambda 0.044 (typical cheap loft roll) = Uval 0.18 W/m2K

    wool lambda 0.04 = Uval 0.17 W/m2K

    wool lambda 0.032 = Uval 0.14 W/m2K

    What about running a foil faced breathable membrane under the JJI's, running perp to the JJI's?

    Start by fixing a timber 25x50 batten to the external block underbuild, at JJI underside height. Staple (and glue) the VPM to that batten, to give a seal to the wall. Then, VPM to first JJI, passing under it, bring the VPM up the vert face of the lower flange and onto the top side of that flange, fold back on itself, staple through the double thickness of VPM onto the top side of the flange, then go back down side of flange, and across to next JJI, passing under it, before repeating.

    The foil should face the solum! That will give a well supported continuous layer, at full JJI depth, not losing the depth of the lower flange. You could actually let the foil VPM droop below the JJI's, by say 100mm, and even put 400mm of the cheap loft roll 44 (Uvalue for that arrangement = 0.12W/mK).

    That's deff how I'd do it, and not just on paper, have done that on a previous project. Remember to fluff up the wool insulation as you install it, so it's got lots of air en-trained in it, and not squashed, as it comes out of the roll.
    • CommentAuthorbardo
    • CommentTimeOct 23rd 2019
     
    Posted By: GreenPaddyOk, so JJI's in place, with 400mm gap to solum...

    If you set say 9mm OSB onto the JJI flanges, then your Uvalues would worsen, to something like;

    wool lambda 0.044 (typical cheap loft roll) = Uval 0.18 W/m2K

    wool lambda 0.04 = Uval 0.17 W/m2K

    wool lambda 0.032 = Uval 0.14 W/m2K

    What about running a foil faced breathable membrane under the JJI's, running perp to the JJI's?

    Start by fixing a timber 25x50 batten to the external block underbuild, at JJI underside height. Staple (and glue) the VPM to that batten, to give a seal to the wall. Then, VPM to first JJI, passing under it, bring the VPM up the vert face of the lower flange and onto the top side of that flange, fold back on itself, staple through the double thickness of VPM onto the top side of the flange, then go back down side of flange, and across to next JJI, passing under it, before repeating.

    The foil should face the solum! That will give a well supported continuous layer, at full JJI depth, not losing the depth of the lower flange. You could actually let the foil VPM droop below the JJI's, by say 100mm, and even put 400mm of the cheap loft roll 44 (Uvalue for that arrangement = 0.12W/mK).

    That's deff how I'd do it, and not just on paper, have done that on a previous project. Remember to fluff up the wool insulation as you install it, so it's got lots of air en-trained in it, and not squashed, as it comes out of the roll.


    Hi Green Paddy and thanks for your thoughts. Very good of you to take the time. I've now screwed mesh over the airbricks and will render around later. That should stop the mice, though I can't be a 100%. As for accessing the underneath of the boards not really possible to get underneath the i joists. If I did use 9mm OSB what difference does the extra 0.03 make to performance in real terms? i.e., the difference between no OSB with a Uval 0.11 W/m2K and using 9mm OSB with a Uval 0.14 W/m2K.
    • CommentAuthorGreenPaddy
    • CommentTimeOct 24th 2019
     
    The obvious answer is about 20%, but you're not asking that of course. All things being equal, I would go for the best Uvalue I could sensibly get. Usually cost or available depth sets the "sensible" limit, though Passiv Huas empirical data suggests something around 0.15 is a "sensible" limit. I go a bit below that, where possible, as passiv solar gain here in the Highlands can be a scarce commodity.

    They are both good values (0.11 and 0.14), but here's the thing, the cost of the cheap loft roll 44 is much less than the reduction in thermal properties.

    Comparing 100mm depth per m2 - loft roll44 = £2, rafterroll32 = £8

    You could install the 400mm depth of LR44 (sitting in the VPM hammock) for much much cheaper than the 255mm depth of RR32 sitting on the OSB board, or indeed say 125mm rigid insul board.

    Or slice it this way... say target Uvalue of 0.13 ish, the costs for full thickness of insulating material for each m2 of your floor would be in the order of;

    - LR44 £8

    - RR32 £24

    - rigid PUR/PIR £20

    So to the question of OSB mouse barrier. I'd take the large savings over the chance of the odd mouse, making itself at home. Pays your money, makes your choice. As usual, there isn't a RIGHT answer, you've got to set your own position on the specturm.
    • CommentAuthorbardo
    • CommentTimeOct 24th 2019
     
    Thanks Paddy,

    So let's say we don't use the OSB and instead go for either scaffolding mesh or a membrane how would you suggest we fix for a lasting secure insulation base. If a membrane, would it need to be a vapour check type such as intello or a breather membrane such as solidex?

    Posted By: GreenPaddyThe obvious answer is about 20%, but you're not asking that of course. All things being equal, I would go for the best Uvalue I could sensibly get. Usually cost or available depth sets the "sensible" limit, though Passiv Huas empirical data suggests something around 0.15 is a "sensible" limit. I go a bit below that, where possible, as passiv solar gain here in the Highlands can be a scarce commodity.

    They are both good values (0.11 and 0.14), but here's the thing, the cost of the cheap loft roll 44 is much less than the reduction in thermal properties.

    Comparing 100mm depth per m2 - loft roll44 = £2, rafterroll32 = £8

    You could install the 400mm depth of LR44 (sitting in the VPM hammock) for much much cheaper than the 255mm depth of RR32 sitting on the OSB board, or indeed say 125mm rigid insul board.

    Or slice it this way... say target Uvalue of 0.13 ish, the costs for full thickness of insulating material for each m2 of your floor would be in the order of;

    - LR44 £8

    - RR32 £24

    - rigid PUR/PIR £20

    So to the question of OSB mouse barrier. I'd take the large savings over the chance of the odd mouse, making itself at home. Pays your money, makes your choice. As usual, there isn't a RIGHT answer, you've got to set your own position on the specturm.
    • CommentAuthorGreenPaddy
    • CommentTimeOct 24th 2019
     
    Hi Bardo,

    cut from an earlier message above...
    -------------------------------------
    What about running a foil faced breathable membrane under the JJI's, running perp to the JJI's?

    Start by fixing a timber 25x50 batten to the external block underbuild, at JJI underside height. Staple (and glue) the VPM to that batten, to give a seal to the wall. Then, VPM to first JJI, passing under it, bring the VPM up the vert face of the lower flange and onto the top side of that flange, fold back on itself, staple through the double thickness of VPM onto the top side of the flange, then go back down side of flange, and across to next JJI, passing under it, before repeating.

    The foil should face the solum! That will give a well supported continuous layer, at full JJI depth, not losing the depth of the lower flange. You could actually let the foil VPM droop below the JJI's, by say 100mm, and even put 400mm of the cheap loft roll 44 (Uvalue for that arrangement = 0.12W/mK).

    That's deff how I'd do it, and not just on paper, have done that on a previous project. Remember to fluff up the wool insulation as you install it, so it's got lots of air en-trained in it, and not squashed, as it comes out of the roll.
    --------------------------------------------

    The foil faced vapour permeable membrane should be around £2/m2, but see what your local merchant has. You don't NEED to use foil faced, but it's a bit tougher, and enhances the Uvalue a little. Also, there is the possibility of getting some condensation on the outer surface, when the strange weather occurrence of very cold for several days, then much milder damp weather, so the foil face gives a slightly more water repellent surface.

    You could just get the cheapest house wrap VPM, at 50p/m2. I don't use netting, as I feel a continuous layer is better, not least in reducing wind washing, but it's not wrong.

    I would lay a vapour check on the top of the JJI's, before fixing the flooring, to improve air tightness, but don't ask the question on here, as you'll get lots of different equally well argued reasons. Make the floor air tight in what ever way you see fit (PU glue on every board edge etc) is a must. You've a breathable house, so continue that through the floor, into the void, and show that on your drawings so the BSO can confirm he's happy with that approach.
    •  
      CommentAuthordjh
    • CommentTimeOct 24th 2019
     
    Posted By: GreenPaddyStaple (and glue) the VPM to that batten, to give a seal to the wall.

    +1 to all you say above, GP. Could you glue the VPM to the wall and then put the batten over it to clamp it in place? That would give a more robust airtight solution I think.
    • CommentAuthorGreenPaddy
    • CommentTimeOct 25th 2019
     
    DJH - yes, had been thinking it's a bit fiddly to get the membrane on the wall, then fix batten, but on other situations I've fixed the membrane to the loose batten, then silicone/adhesive to the membrane face, and then fix the whole sandwich to the wall (wall, silicone, membrane, batten)
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