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    • CommentAuthorEd Davies
    • CommentTimeFeb 9th 2017
     
    Posted By: cjardcondensation occurs when the air close to a surface holds too much moisture for the temperature that the cooler surface reduces the air to.
    This myth that air “holds” moisture was found to be wrong 200 years ago. Please stop repeating it.

    http://www.ems.psu.edu/~fraser/Bad/BadClouds.html

    Thermal bridges, by definition are warmer than the surrounding unbridged area, because more heat is flowing through them because they're a bridge.
    Only if there's insulation on the outside. If there's a bit more insulation on the inside, why wouldn't they be “by definition” colder than the surrounding unbridged area?
  1.  
    "Did the Thermoblock and Celcon cause you any issues at all during the cutting/laying, and did you suffer any Celcon cracking when the frame was bolted through to them?"

    Had no issues laying the Thermoblocks - same method as any block. Just a lot lighter to move around which made a nice change! As for cutting them, you won't be able to cut them if you hit one of the cement cylinders within the actual block. What I did, was to get a nail to pierce through the EPS to locate the columns to make sure I was not about to blunt my saw!

    I'd probabaly go for an extra wide Thermoblock so that you have extra tolerances once your sole plates go on top. I had to drive to Belgium to get them though as Jewsons screwed me around. I had to courses of celcon blocks on their side (rather than upright) with the extra wide TB on top.

    No issues with chemical fixings - just pre-drill the holes all the way through into the celcon blocks.
  2.  
    Thanks, looks like the way forward for me, I will discuss with my Structural Engineer tomorrow.
    • CommentAuthorringi
    • CommentTimeFeb 10th 2017
     
    I don’t know your roof shape, but if you allowed the ceilings to take up some of the loft space, could you give yourself the option of having the floor a little above ground?

    Also I can’t help thinking that a “passive foundation” with the EPS sitting on top of your slab (or block and beams) may be the best option.

    Shame we can’t hang the walls from the roof and support the roof with internal posts on the insulated floor, and therefore just have EPS below the walls……. (Your Structural Engineer would LOVE to do the calcs for this; most builders would hate building it.)
    • CommentAuthorcjard
    • CommentTimeFeb 10th 2017 edited
     
    Posted By: EdThis myth that air “holds” moisture was found to be wrong 200 years ago. Please stop repeating it.


    You probably don't remember a time when your teacher told you that if you had 2 apples you can't take 3 away. Later, you were told actually you can do negative numbers but you can't take the square root of them.. Later still...

    It's a suitable abstraction, and abstraction is necessary. if we got into the quantum physics of everything all the time, communication would be very tedious..



    Only if there's insulation on the outside. If there's a bit more insulation on the inside, why wouldn't they be “by definition” colder than the surrounding unbridged area?


    They wouldn't be much of a thermal bridge if there was insulation between the warm bit and the bridge, would they?
    • CommentAuthorEd Davies
    • CommentTimeFeb 11th 2017 edited
     
    Something that's weird about this “air holding water” myth continuing to be repeated is that it's actually more complicated than a less inaccurate and misleading explanation: water accumulates on a surface when the surface is sufficiently cool that evaporation is less than condensation.

    No need to invoke tiddly layers of cooled air. No need for quantum physics [¹]. Still works when it's not a flat surface of pure liquid water because it's ice, a salt solution, a concave meniscus in a capillary or a convex surface of a rain drop - just the rate of evaporation is modified by those conditions so the equilibrium vapour pressure is a bit different.

    As to thermal bridges: why would the bridge be warmer than the surrounding materials? Because it's in better thermal contact with the indoor air [²]? But mightn't it also be in better thermal contact with the outdoor air so shouldn't it be cooler, too?

    [¹] First published by John Dalton in 1801 without, not surprisingly, the use of quantum physics though I don't doubt quantum physics comes into it if you dig a bit deeper.

    [²] Assuming we're talking about the case where indoors is warmer.
    •  
      CommentAuthordjh
    • CommentTimeFeb 11th 2017
     
    Posted By: Ed DaviesAs to thermal bridges: why would the bridge be warmer than the surrounding materials? Because it's in better thermal contact with the indoor air [²]? But mightn't it also be in better thermal contact with the outdoor air so shouldn't it be cooler, too?

    Thermal bridges aren't usually caused because the thermal contact with the air is better. In fact the same heat transfer coefficient is usually used for each surface. The indoor one is 0.13 m²K/W and the outdoor one is 0.04 m²K/W. The indoor resistance is greater because still air is assumed, whilst the outdoor figure assumes moving air.

    Think about windows as an example. A single-glazed thermal bridge is cold on the inside, commonly forming condensation, and warm on the outside, as seen in thermal photos. A triple-glazed not-so-much-of-a thermal bridge is cold on the outside and sometimes has condensation there, whilst being warmer on the inside.

    Thermal bridges are bridges because their resistance is less. They are colder on the inside because the fixed resistance of the air layer is a greater proportion of the total resistance and warmer on the outside for the same reason. Insulating them on the outside makes their outside surface even warmer as Caius says.

    Rot on a soleplate is more likely due to a greater concentration of water at the bottom of the wall, IMHO.
    • CommentAuthorEd Davies
    • CommentTimeFeb 11th 2017
     
    Yes, I realise the surface resistances are likely to be the same for the bridge and the insulation. I did wonder whether to go into the different thermal resistance of the inside (still air) surface and the outdoor (windy) surface but decided it would be a distraction. It would, though, tend to make the bridge colder than the insulation absent other considerations.

    However, my point was that the middle of a bridge such as a joist, stud or sole plate is both in better thermal contact with the indoor air (which CJard assumes makes it necessarily warmer) and outdoor air (which he doesn't seem to think would make it cooler) than the middle of the insulation between the bits of wood or whatever.
    •  
      CommentAuthordjh
    • CommentTimeFeb 11th 2017
     
    There's no such notion as the bridge having a single temperature, only specific locations in the bridge. I believe that Tony is worried about condensation and rot on the outside surface of the bridge and that is what we are discussing. However, that surface is warmer for a bridge than for an insulated piece of wall. Temperatures in the middle are pretty much irrelevant, only the surfaces are important.
    • CommentAuthorEd Davies
    • CommentTimeFeb 11th 2017
     
    I didn't suggest any notion of a bridge having a single temperature.

    The actual surface layers (first few mm) are likely to be reasonably well ventilated so water's not likely to accumulate there long term; it'll likely dry out every few days. Inboard of that the bridge material could easily be a bit cooler than the adjacent insulation depending on the construction. That's likely if there's any insulation across the whole wall on the inside.
    • CommentAuthorEd Davies
    • CommentTimeFeb 11th 2017 edited
     
    Indoor air 20 °C, outdoor 0 °C. Wall buildup inside to out: 25 mm PUR (λ = 0.025 W/m·K), 250 mm of timber studs/joists/rafter/sole plate/whatever (λ = 0.120 W/m ·K) with mineral wool (λ = 0.038 W/m·K) between.

    Modelling the timber and mineral wool as 245 mm and 5 mm to get an “instrumentation point” I calculate the temperature 5 mm inboard in the mineral wool is 0.34722… °C whereas in the timber it's a fraction cooler at 0.270270… °C.

    (Edit to add: that's just for two simple 2D parallel calculations. In the real world there'd be 3D heat flows (sideways between the mineral wool and the timber) but still it indicates a tendency for the cold bridge to be colder in a fairly critical area in a moderately realistic buildup.)
    •  
      CommentAuthordjh
    • CommentTimeFeb 11th 2017
     
    We're clearly talking at cross purposes, but I don't understand what you're trying to say well enough to see whether it makes sense.

    The rules inside timber are completely different. We are talking about surface temperatures.

    Posted By: Ed DaviesModelling the timber and mineral wool as 245 mm and 5 mm to get an “instrumentation point” I calculate the temperature 5 mm inboard in the mineral wool is 0.34722… °C whereas in the timber it's a fraction cooler at 0.270270… °C.

    I don't think you've allowed for the surface resistances. I make the outside surface temp of the timber warmer than the rockwool.

    Incidentally, if you're bothering with PUR on the inside for some reason, then what about the plasterboard, VCL, OSB, breather etc etc? Why 245 mm, the frame is 140 mm?
    • CommentAuthorEd Davies
    • CommentTimeFeb 11th 2017
     
    Posted By: djhI don't think you've allowed for the surface resistances.
    Good point, forgot those.

    Incidentally, if you're bothering with PUR on the inside for some reason, then what about the plasterboard, VCL, OSB, breather etc etc? Why 245 mm, the frame is 140 mm?
    I was just responding to cjard's “by definition” comment about cold bridges being warmer without going back and re-reading the earlier bits of the thread. Still, the OP's drawing on the first page has (by coincidence) got 25 mm of insulation on the inside. Plus a battened service void behind the plasterboard which would add about the same again. Breather and VLC won't affect the thermal conditions much.

    Redoing with BS EN ISO 6946 surface resistances (inside 0.13 and outside 0.04 m²·K/W) and with 140 mm thickness I too make the outside surface of the timber warmer than the mineral wool (0.3424 °C vs 0.1648 °C). However 5 mm into the structure it's reversed: the mineral wool is 0.7069 °C whereas the timber's only 0.6990 °C).

    That's a tiny difference and in reality 2D and 3D heat flows would reduce it further. Still, I think it's probably not a good idea to assume that cold bridges are necessarily warming than the adjacent insulation.
    •  
      CommentAuthordjh
    • CommentTimeFeb 11th 2017
     
    5 mm inside a solid capillary structure like timber it's pointless just computing temperatures. It's more helpful to compute surface temperatures and drying/wetting periods. Those are what the limited data use to categorize the risk of decay.

    Clearly any additional insulation either interior to or exterior to the timber is going to change the profile. But it is well known that exterior insulation is beneficial whilst interior insulation increases risk, so I'm still not clear what point you are trying to make. In the neutral (no extra insulation layers) case, then the temperature in the centre will be equal (offset slightly because of the different surface resistances). Outboard of the centre, the bridge will be warmer, inboard it will be colder.
  3.  
    Hi everyone,
    I've recently started looking into the sphere of vertical gardening as part of my work or my "Green Building" project.
    Does any one in the forum have experience in this sphere or in building vertical gardens for villas?

    What are the costs? What kind of insulation is needed?
    Are there any leading brands?
    do we need to order some special supplies?
    Thank you in advance for your kind replies, as always.
    Have a great week!
    •  
      CommentAuthordjh
    • CommentTime4 days ago
     
    @zgreentouch, Probably best to delete your question here and just keep it in your New build planning &heating options thread, or better yet delete it there as well and start a new topic with a more informative title. Asking the same question in multiple places just confuses things.

    You can 'delete' your post by editing it and replacing the text with a full stop or with the word 'deleted' for example.
    • CommentAuthorcjard
    • CommentTime3 days ago edited
     
    Peter-Green, please don't perpetuate zgreentouch's mistake/lack of forum etiquette with his thread hijack

    @djh, you can "delete" a post by whispering it to yourself
  4.  
    Thank you, djh, you're absolutely right. I read the comment here, and I posted my question here by mistake. I'm sending my question as a new post under "Housing-New Build". Thank you.

    Peter-Green, thank you very much for your quick response. I'll post this comment anew, and if you don't mind I will also send you some questions privately.
    Thank you again for calling my attention to this, and for the answer.
    • CommentAuthorPeter-Green
    • CommentTime2 days ago edited
     
    cjard, thank you for your comment, I have deleted my message and post it to new conversation on this topic.
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