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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorbardo
    • CommentTimeFeb 6th 2019 edited
     
    We are self building a low impact home with a suspended timber floor. We are on heavy clay and no bedrock and are building a 400mm high plinth wall around the perimeter with air bricks set every 1800mm to provide sufficient airflow to and from the void underneath the home. We are based in west Wales and it rains a lot here especially in the winter. The void underneath the house will be exposed to the elements for a month or so and with the blockwork I've realised that we may have a swimming pool on the leveled ground in the interim. I wonder how others cope with this situation? And It's too late and not ideal to use piers as an alternative. Also this given, when should the plastic DPM layer go on underneath? Presumably this will only compound matters.
    •  
      CommentAuthordjh
    • CommentTimeFeb 7th 2019
     
    Leave some weep holes between the blocks/bricks? Or drill some holes if it's already built. Maybe a sleeve pipe through the holes if required.
    • CommentAuthorgyrogear
    • CommentTimeFeb 7th 2019 edited
     
    FWIW, if this is going to be a crawlspace, then IMHO 400mm seems very minimal for future access, in which case you might consider digging access galleries or refuges or even a sump while there is still time...

    However, your building code is certainly different from mine, which demands 600mm height minimum, and 0.6 sq. metres of access.

    If on the other hand it is a construction void, you will not have future access for checking your joists or adding extra insulation.

    (without wanting to appear overtly intrusive, what is your floor insulation plan ?).

    I inherited an 800mm unfinished concrete CS, that is twice the height of yours... When I discovered the actual heat-losses through the floor-above and decided to insulate it, I discovered it was a lot of work... even with years of caving (and cave-digging) experience not to mention a (once) slender frame... (?)
    :shamed:

    You might try running a Topic Search for "suspended timber floor"...

    Otherwise, here is a good read:
    https://www.sciencedirect.com/science/article/pii/S0378778817311350

    Good luck

    gg
    • CommentAuthortony
    • CommentTimeFeb 7th 2019
     
    How much insulation will there be in the floor? And how will this join to insulation in the walls, will partition walls bridge your thermal envelope?

    Dpc is neither here nor there under concrete obersite

    What do sleeperbwalls sit on?
    • CommentAuthorbardo
    • CommentTimeFeb 7th 2019
     
    Posted By: gyrogearFWIW, if this is going to be a crawlspace, then IMHO 400mm seems very minimal for future access, in which case you might consider digging access galleries or refuges or even a sump while there is still time...

    However, your building code is certainly different from mine, which demands 600mm height minimum, and 0.6 sq. metres of access.

    If on the other hand it is a construction void, you will not have future access for checking your joists or adding extra insulation.

    (without wanting to appear overtly intrusive, what is your floor insulation plan ?).

    I inherited an 800mm unfinished concrete CS, that is twice the height of yours... When I discovered the actual heat-losses through the floor-above and decided to insulate it, I discovered it was a lot of work... even with years of caving (and cave-digging) experience not to mention a (once) slender frame... (?)
    :shamed:" alt=":shamed:" src="http:///newforum/extensions/Vanillacons/smilies/standard/shamed.gif" >

    You might try running a Topic Search for "suspended timber floor"...

    Otherwise, here is a good read:
    https://www.sciencedirect.com/science/article/pii/S0378778817311350

    Good luck

    gg


    The perimeter wall goes all the way round so no crawl space.
    • CommentAuthorbardo
    • CommentTimeFeb 7th 2019 edited
     
    Posted By: tonyHow much insulation will there be in the floor? And how will this join to insulation in the walls, will partition walls bridge your thermal envelope?

    Dpc is neither here nor there under concrete obersite

    What do sleeperbwalls sit on?


    Trench is 900mm deep with 300 mm of concrete poured in base then twin skin blockwork on top.
    300 mm of treated sheepswool insulation laid within steico i joists. These are fixed to a timber box beam which sits on top of the plinth wall (with DPC laid inbetween).

    There is no concrete oversite.
    • CommentAuthorbardo
    • CommentTimeFeb 7th 2019 edited
     
    Posted By: bardo
    Posted By: tonyHow much insulation will there be in the floor? And how will this join to insulation in the walls, will partition walls bridge your thermal envelope?

    Dpc is neither here nor there under concrete obersite

    What do sleeperbwalls sit on?




    Trench is 900mm deep with 300 mm of concrete poured in base then twin skin blockwork on top.
    300 mm of treated sheepswool insulation laid within steico i joists. These are fixed to an insulated timber box beam which sits on top of the plinth wall (DPC laid in between).

    There is no concrete oversite.
    • CommentAuthorbardo
    • CommentTimeFeb 7th 2019
     
    Posted By: djhLeave some weep holes between the blocks/bricks? Or drill some holes if it's already built. Maybe a sleeve pipe through the holes if required.


    That's an interesting idea. Not built yet. Concern is providing access to rodents. I suppose if the holes are small enough then no problem.
    •  
      CommentAuthordjh
    • CommentTimeFeb 7th 2019
     
    I would put steel mesh in front of a fine insect mesh to keep out critters of all kinds. It may be there are pre-made components that are suitable. I know very little about bricks and blocks.
  1.  
    bardo - Is it too late to go for a well insulated solid floor, either concrete or limecrete. Insulation is easy, no worries about ventilation or rot in the future and works better with UFH if you are going that way.
    • CommentAuthorgyrogear
    • CommentTimeFeb 7th 2019
     
    Posted By: Peter_in_Hungarygo for a well insulated solid floor, either concrete or limecrete


    +1 for PIH !

    Although OP *did* say "a low-impact home"...

    Guess the "impact" bit is summarized by need to compare the grey-energy balance of cutting down trees to make joists, thus removing CO2-absorption possibilities, versus use of concrete that creates C02, versus the energy balance of the future heating system, modulated by the benefits of mass versus the grey-energy balance of plastic insulation etc. etc.

    gg
    •  
      CommentAuthordjh
    • CommentTimeFeb 7th 2019
     
    I agree with PiH and would go for a passive slab foundation. Indeed I did! Our clay & trees are such that we needed foundations twice as deep as you. A raft requires half the depth of strip foundations, so you'd have a sensible depth of insulation with ground level floors or thereabouts. I looked at a suspended timber floor using piles but the cost and complexity made it a non-starter as far as I was concerned. A passive slab is so much simpler and more reliable and provides useful thermal mass.

    But I was not thinking as deeply about 'low-impact'. I don't think concrete is as bad as it is sometimes made out, especially given its expected lifetime, and I have an active aversion to sheeps wool in particular after reading and seeing some horror stories. So I was willing to put up with the sin of concrete, EPS and steel.
    •  
      CommentAuthordjh
    • CommentTimeFeb 7th 2019
     
    Posted By: gyrogearenergy balance of cutting down trees to make joists, thus removing CO2-absorption possibilities

    Actually cutting down trees absorbs *more* CO2 rather than less, provided it is managed properly and replacements are planted.
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