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General: Thermal bridges in Walter Segal type builds….

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    • CommentAuthorringi
    • CommentTimeAug 19th 2016
     
    Base on resent discussion, does anyone have a design for a Walter Segal type build (frame on wooden legs, on pad foundation) that removes the thermal bridges from the floor etc?

    Also are there any Walter Segal type builds that have past the passive house certificate?
    • CommentAuthorEd Davies
    • CommentTimeAug 19th 2016 edited
     
    Nobody seemed interested in any thermal bridges through my posts at the building warrant stage so there's nothing in the formal plans to deal with this.

    What I plan to do, though, is measure how much bridging there actually is in practice by measuring the surface temperatures on the posts on the inside of the house at floor level. Assuming there is any noticeable leakage (I think there likely will be) I'll wrap the bottoms of the posts in insulation externally after checking for moisture movement down there. There'll be 400 mm or so of crawl space under the house so just about room for somewhat unpleasant access. I'm thinking 150 mm of EPS boxed in with Panelvent or the like.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 19th 2016
     
    Sounds good. Crudely speaking, you'll be making the timber cols into an insulant 400 'thick' @0.12 conductivity - is that gd enough to match the 'tea cosy' insulation?

    To acheive that, I've found in Therm in analogous situation that the EPS 'boxing in' doesn't have to be that thick - just enough to be say twice as resistive to sideways heat-leak than to heat transmission by the preferred downward route. Any more, diminishing returns. If the 400 isn't enough, it doesn't help to increase the EPS 'boxing-in' thickness.
    • CommentAuthorEd Davies
    • CommentTimeAug 19th 2016 edited
     
    Not really 400 thick as the posts don't reach the ground. Their bottoms are nearly 200 mm above ground level sitting on galvanized steel brackets with a tongue sticking a further 200 mm up the middle of the post. (The steel brackets are on 500 mm concrete pads on or close to solid rock.)

    I'd not want the EPS to touch the ground or the base plate of the bracket in case of wicking of water. It should be dry under there once the house is above it and the sides are boxed in but better to be sure. So there'd be some heat leakage through the vertical steel. Still, the flanges supporting the posts ought to be covered.

    Your comment about limits on the useful amount of sideways resistance match my intuition.

    (PS, for scale, the posts are (145 mm)² and the ledger boards are 220x45 C24 and LVL.)
      dsc01949-small.jpg
    •  
      CommentAuthordjh
    • CommentTimeAug 19th 2016
     
    Posted By: Ed DaviesI'd not want the EPS to touch the ground or the base plate of the bracket in case of wicking of water.

    Think also about insects and small animals and birds.
    • CommentAuthorEd Davies
    • CommentTimeAug 19th 2016
     
    Yep, that's why I'll box in with Panelvent or something, as well as to stop wind blowing in joints.
    •  
      CommentAuthordjh
    • CommentTimeAug 19th 2016
     
    Posted By: Ed DaviesYep, that's why I'll box in with Panelvent or something, as well as to stop wind blowing in joints.

    Panelvent won't stop anything; it's basically just hardboard. I'd be looking at something cement-based or a render layer.
    • CommentAuthorringi
    • CommentTimeAug 19th 2016
     
    If the house is only one module wide, so all posts are within outside walls, what about fixing horizontal 2x2 to the inside of the walls, so providing space to insulation between the posts and the inside?

    Is there any long term reason that the posts in Segal type building have to be fixed to the ground, instead of just resting on the pads?

    Ed,

    How are you going to insulate the floor?

    Looking at the metal brackets going up into your posts, I question if there is any benefit in wrapping them in insulation.

    Why have you got so many metal brackets, rather than bolted joints like http://www.irishvernacular.com/ his design using 3 bits of timber fixed together to make each post, allowing for pockets to fit ledger boards etc look very nice.

    Given that your ground looks level (and I expect is rather solid) why did you not go for a Viking Homes type “passive foundation” with a “stick timber frame” build?
    • CommentAuthorEd Davies
    • CommentTimeAug 20th 2016
     
    Posted By: ringiIs there any long term reason that the posts in Segal type building have to be fixed to the ground, instead of just resting on the pads?
    My understanding of classic Segal is that they aren't fixed to the ground - just resting on DPM on a concrete pad which is enough above ground level and appropriately sloped that water drains OK. E.g., the Brighton community Segal houses are like that, I think. The idea is partly that once you've cut your beams to the appropriate length to millimetre accuracy you can take out any residual difference by tapping the posts the last mm or so.

    Still, with a slightly aerofoil shaped house on the brow of a hill overlooking the North Sea I'm just as happy to have something stopping the house walking off its pads over the years. Those brackets also contribute to the racking strength, I assume, though the SE wasn't overly communicative about the logic of his design.

    How are you going to insulate the floor?
    Mineral wool fill. Those 220 mm C24/LVL beams are only the bottom part of the floor. There'll be another layer of 145 mm C16 beams above but those can only go on once the roof's done (they fit between edge blocking between the I-beam rafters).

    My preference would have been for a deeper floor in one layer - e.g,, 360 mm or so I-beams but see my remarks about being willing to sack your professional advisers on another thread.

    Looking at the metal brackets going up into your posts, I question if there is any benefit in wrapping them in insulation.
    Yes, there will still be a path through the base part of the bracket but if the flanges under the posts are wrapped I don't think that'll make too much difference.

    Given that your ground looks level (and I expect is rather solid) why did you not go for a Viking Homes type “passive foundation” with a “stick timber frame” build?
    I guess mostly mental inertia: I'd got used to this idea before settling on the particular site and determining its geology. I did actually have a little exchange of email with Seamus about the possibility - if he'd any pet builders around here (i.e., north of the Central Belt) used to his system I might well have switched.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 20th 2016 edited
     
    Nice crystal clear pic Ed - hard to tell if it's real or SketchUp!
    Posted By: Ed Daviesthere will still be a path through the base part of the bracket but if the flanges under the posts are wrapped I don't think that'll make too much difference
    Fraid not - the steel will conduct outside-air/ground coldness right up to their tops as if there were almost bare. The temp gradient starts there.

    Tell me yr email (or anyone else interested) and I'll send the pdf that got an alternative, timber ground floor design idea through the Blbg Insp.
    Posted By: Ed Davieshappy to have something stopping the house walking off its pads over the years
    Ben Law simply rests his poles on the pad top, but holds the whole down by cables from driven-in ground anchors.
    https://www.amazon.co.uk/Roundwood-Timber-Framing-Ben-Law/dp/1856230414/ref=sr_1_1?ie=UTF8&qid=1471694189&sr=8-1&keywords=ben+law+%22roundwood+timber+framing%22
    • CommentAuthorEd Davies
    • CommentTimeAug 20th 2016 edited
     
    Posted By: fostertom: “Tell me yr email (or anyone else interested) and I'll send the pdf that got an alternative, timber ground floor design idea through the Blbg Insp.”

    Bit late now for me, if not for the OP, that picture's about 6 weeks old (though it's a bit depressing how little it's changed since: just most of the rest of the cross beams and beams along the edges). But still:

    https://edavies.me.uk/contact.html

    Hope it's not a huge PDF, though, as I'm still stuck on mobile internet with little hope of getting proper broadband in before I've been living in my current rented house for a month. BT really is a small but significant drag on the UK economy.
    • CommentAuthorEd Davies
    • CommentTimeAug 20th 2016
     
    Thanks Tom. However, that reminds me…

    Posted By: ringiGiven that your ground looks level (and I expect is rather solid) why did you not go for a Viking Homes type “passive foundation” with a “stick timber frame” build?
    The other issue is that a “passive slab” would also have have been quite high out of the ground. Solid rock with a layer of clay on top just doesn't drain - the ground is pretty much permanently saturated so staying above ground level is important.

    Tom's designs with LECA deep into the ground seem great but really need a small caveat that they won't work in this sort of case. We've discussed this before. My strategy has been to stay above the water table (ground level) for all except the concrete pads.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 20th 2016 edited
     
    Ah (again) if your water table's regularly above say half way up the perimeter trench then it wd carry away too much of the subsoil-stored heat. Apart from that (conclusive), nothing below the floor joists (or maybe the sleeper ground beams) minds getting wet.

    In case anyone wonders what we're talking about, here's a blurry jpg - if you'd like the original pdf, tell me your email address.
      rethought.JPG
    • CommentAuthorringi
    • CommentTimeAug 20th 2016
     
    If the post are not fixed to the ground, could a block like Thermoblocks (marmox) be used under the posts?
    • CommentAuthorringi
    • CommentTimeAug 20th 2016
     
    Posted By: Ed Davies
    Posted By: ringiGiven that your ground looks level (and I expect is rather solid) why did you not go for a Viking Homes type “passive foundation” with a “stick timber frame” build?
    The other issue is that a “passive slab” would also have have been quite high out of the ground. Solid rock with a layer of clay on top just doesn't drain - the ground is pretty much permanently saturated so staying above ground level is important


    Even if you build a wall to retain the compacted MOT1 to above ground height, then put the EPS etc on top, I expect the resulting floor height would not have been much higher then what you are getting. However it may have been costly.

    However your issues with the water table and flooding do tend to point towards building on some type of legs.
    • CommentAuthorringi
    • CommentTimeAug 20th 2016
     
    Posted By: Ed DaviesMineral wool fill. Those 220 mm C24/LVL beams are only the bottom part of the floor. There'll be another layer of 145 mm C16 beams above but those can only go on once the roof's done (they fit between edge blocking between the I-beam rafters).


    Are you putting the 2nd layer of beams at right angles to the first, so as to reduce cold bridges?

    What are you putting below the first layer of breams to hold the mineral wool and how will you fit it given the limited working height?

    Your floor being so deep does help with the thermal bridge from the posts, as there is a lot of wood for the heat to get thought before it gets out.
    • CommentAuthorEd Davies
    • CommentTimeAug 20th 2016
     
    Posted By: ringiAre you putting the 2nd layer of beams at right angles to the first, so as to reduce cold bridges?
    Yes. The beams in the pictures will have joists of the same depth between them then the 145x45 C16 upper joists go across the house so are parallel with those beams but at right angles to most of the lower joists they sit on.

    What are you putting below the first layer of breams to hold the mineral wool and how will you fit it given the limited working height?
    Thanks for taking an interest; when I've asked for suggestions on here before nobody has replied at all. Current plan is sarking boards, just like the roof. With windproofing membrane on top, just like roof (except it's underneath for the roof :wink:). Clamping and nailing them shouldn't be too difficult with the roughly 400 mm height available though probably easier with a nail gun than a hammer.

    Your floor being so deep does help with the thermal bridge from the posts, as there is a lot of wood for the heat to get thought before it gets out.
    Yes, I'm hoping that should make the problem fairly limited.
    • CommentAuthorringi
    • CommentTimeAug 20th 2016
     
    What about just using OSB3 or PLY should be less work then fitting sarking boards?

    I am starting to think that spray on flexible insulation is the best airtightness solution for onsite timber frame builds, as it can be sprayed on after you have got the building water tight, so personally I would cost using it instead of the mineral wool, or using 50mm of it to cover all the sheathing boards and their joints to the timber frame.
    • CommentAuthorEd Davies
    • CommentTimeAug 21st 2016
     
    Posted By: ringiWhat about just using OSB3 or PLY should be less work then fitting sarking boards?
    Sarking boards can be nailed on standing up (bending over a bit) whereas larger sheets would need crawling underneath. Also, I really like the idea of something that''ll drain/vent very reliably in the case of water leaks. It wants to be reasonably airtight but definitely not watertight.

    There'll be a proper airtightness layer on top (poly sheet between the top layer of joists and the floor deck (22 mm chipboard)) which would be watertight and sufficiently close to the house warmth that any water that pools there would dry out quickly but I don't want to rely on that to keep the colder parts of the structure dry.
  20.  
    ''What are you putting below the first layer of breams...''?

    I don't know. No doubt I'll come up with some had(d) oc(k) solution (sorry!)
  21.  
    Hi Ed, I'd consider pumping the void beneath the floor fully with EPS beads, this would reduce cold bridging through the posts and increase the temperature where the insulation meets the ground. I'd also consider putting a 500mm deep land drain around the house to lower the water table.
    • CommentAuthorringi
    • CommentTimeAug 21st 2016 edited
     
    Ed, I expect that your windproofing membrane would stop water draining out, but I had not thought about being able to put most of the sarking boards on standing up.

    Viking House, How does the u-value and cost of EPS beads compare with mineral wool?

    If I understand correctly you are saying to fill ALL the space above ground with them, hence removing the ventilation from under the floor, what makes this a save option that BC and mortgage survey will agree to?
  23.  
    Posted By: ringiVH, How does the u-value and cost of EPS beads compare with mineral wool?
    When you take for fitting costs they're both about the same price.
    Posted By: ringiIf I understand correctly you are saying to fill ALL the space above ground with them, hence removing the ventilation from under the floor, what makes this a save option that BC and mortgage survey will agree to?
    A simple CRA(Condensation Risk Analysis) shows that insulating outside a timber structure (like a Cold Roof) moves the condensation risk away from the structure. When I fully filled the void beneath the floor of my 1850's redbrick house the temperature of the soil beneath the insulation increased to 14 degrees in mid winter, I've successfully done this in over 50 renovations without issues.
    10mm of insulation stapled onto the outside of a roof rafter reduces the condensation risk by 90%.
    Build your house airtight and there will be no moisture present beneath your floor to condense.
    There's never been a proven incidence of structural decay in a building resulting from water vapour diffusion, so worry about air leakage not diffusion!

    If you're satisfied my suggestion has merit, then talk to your lender and BC officer, if it becomes too much of a struggle to get it over the line you can always revert to plan A, its up to you! If you want me to call somebody on your behalf I'm willing to do so but I am quite busy.
    • CommentAuthorEd Davies
    • CommentTimeAug 24th 2016 edited
     
    Posted By: fostertomCrudely speaking, you'll be making the timber cols into an insulant 400 'thick' @0.12 conductivity - is that gd enough to match the 'tea cosy' insulation?
    Got round to doing this calculation:

    There are 7 “columns” of two of these posts in the house (including the ones in the gable between the house and the porch/greenhouse) but the ones in the gables at both ends can be neglected because they're on the outside of significant amounts of insulation so there's 10 such posts to worry about. Each is 0.145 m square so the total area is 0.21025 m².

    Each post goes through 145 + 220 mm of floor insulation and also 22 mm of chipboard subfloor and the 18 mm sarking board below. Call it 400 mm for round numbers. Using Tom's conductivity of 0.12 W/m·K that's a U-value of 0.12 * 0.4 = 0.3 W/m²·K.

    That's neglecting the insulating value of the wood above and below the floor. The insulation of the wood below is probably worth neglecting as the steel tongue of the bracket comes so close to the bottom of the floor anyway. But also many of the posts will be buried to some extent in internal walls so have a certain amount of extra insulation above.

    Multiplying the U-value by the area gives a heat-loss coefficient of 0.3 * 0.21025 = 0.063075 W/K.

    The 2009/2013 HDD to 20 °C for Wick was 4374 K·day. My site's a little higher and a little bit more exposed so it'd be conservative to use 4500 K·day. Multiplying by 24 h/day to get K.h and by the heat-loss coefficient gives a total heat loss of 6812 Wh/year.

    An hour's worth of sunshine on the PV.

    Starting my design again knowing that the top surface of the concrete pads and the hardcore actually stays drained (water pools briefly after heavy rain but doesn't seep back in from the surrounding ground) I might well be tempted by a scheme such as VH suggests: built on posts on steel brackets on concrete pads, box in the sides then fill the lot with EPS beads. That answers Ringi's original question nicely. And also saves worrying about what to make the bottom of the floor out of.

    You could even start with a layer of LECA up to the bottom of the floor then have EPS above. Would that need a membrane between?

    However, if I was starting with that design I'd make the whole floor structure a lot thinner. E.g., keep my 220 mm main joists but skip the 145 mm “counter-joists” above and drop the main joists down to 300 or 250 mm above ground level.
  25.  
    Posted By: Ed DaviesStarting my design again knowing that the top surface of the concrete pads and the hardcore actually stays drained (water pools briefly after heavy rain but doesn't seep back in from the surrounding ground) I might well be tempted by a scheme such as VH suggests: built on posts on steel brackets on concrete pads, box in the sides then fill the lot with EPS beads. That answers Ringi's original question nicely. And also saves worrying about what to make the bottom of the floor out of.
    Maybe box in the sides with EPS sheets then Cement board externally, totally wrapping the external posts in insulation?

    Posted By: Ed DaviesYou could even start with a layer of LECA up to the bottom of the floor then have EPS above. Would that need a membrane between?
    When I looked at Leca for delivery to Ireland it was more expensive per m3 and a worse insulator (0.50W/m2.K vs 0.35W/m.K). It takes up moisture from the ground by capillary action, to avoid this the manufacturers have coated it with silicone.
    EPS beads on the other hand are waterproof and resistant to capillary pull.
    • CommentAuthorringi
    • CommentTimeAug 24th 2016
     
    Ed Davies,

    What build up are you using on your walls?

    Do your large posts/beams with the strong metal brackets provide all the racking resistance the building needs?
    • CommentAuthorEd Davies
    • CommentTimeAug 24th 2016 edited
     
    Not much walls - it's an A-frame so mostly roof. Still, gable walls inside to out will be plasterboard or timber; 90 mm PUR, poly sheet, 235 mm timber I-beams with mineral wool between, OSB, solar warm air collector (on the east gable)/breather membrane; ventilated gap, timber cladding on the west gable (which mostly faces on to the porch/greenhouse).

    Roof is pretty similar except sarking boards instead of the OSB and profiled steel on top above ventilated gap.

    Yes, to racking: there's nothing else explicitly providing racking resistance per engineer's specification though I expect the roof and internals will provide some was well.
    •  
      CommentAuthordjh
    • CommentTimeAug 25th 2016
     
    Posted By: Ed DaviesYou could even start with a layer of LECA up to the bottom of the floor then have EPS above. Would that need a membrane between?

    Leca isn't a capillary break, FWIW. Technopor or some types of perlite are (but not common perlite).

    Yes, to racking: there's nothing else explicitly providing racking resistance per engineer's specification though I expect the roof and internals will provide some was well.

    Isn't the OSB part of the racking resistance? Racking is perhaps another reason to consider sheets on the roof instead of boards, though I suppose the design is done and signed off so not a worry.
    • CommentAuthorEd Davies
    • CommentTimeAug 25th 2016
     
    Interesting about Leca not being intrinsically a capillary break - I have to admit that I thought that that was part of the point of it.
  30.  
    When I first looked at full filling beneath a timber floor with EPS bead a few years ago I carried out some crude tests. I filled a 4 inch pipe with EPS bead (glued) and drilled a line of 5mm holes 10mm apart along the length of the pipe. I pushed blotting paper pieces into the holes and covered them with Gaffa tape. Then I stood the pipe into a basin of water, the water in the pipe rose 2-4mm at the most.

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