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General: Breathable floor with VCL - any point

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    I have a friend with an old stone house. Minimum founds. and of course no DPC.

    As bought it has concrete floors.

    An 'eco friendly' architect is recommending removing the concrete floors and replacing them with something vapour open. There are no problems with the walls or plastering despite concrete floors for about 50 years.

    Their plan is to replace the floors as recommended and then they want to put down engineered wood or click fit flooring (budget dependant) However all the instructions for the various flooring require a VCL under the flooring otherwise the guarantee is void.

    Question - is it worth digging out the floors for something breathable only to put a VCL under the engineered wood or click fit flooring?
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      CommentAuthordjh
    • CommentTimeJun 30th 2024 edited
     
    It doesn't seem to make much sense to me. Concrete is vapour open as far as I know. You'll certainly want a VCL or DPM underneath a wood or click fit floor on concrete. Bamboo might be OK without, I think. Otherwise, rush mats or some forms of carpet etc.

    I could understand if the ground is wet and the concrete was damp as a result, but that doesn't sound like the case. Although then I'd think a capillary break would be more important than breathability.

    I'd think the first thing would be to question the architect as to the basis of his recommendation.
  3.  
    The architect said that the concrete floors would push moisture into the walls so should be removed and replaced with something that allowed moisture to escape other than in to the walls but I would have thought putting a VCL on top would would also push moisture into the walls (if it was going to happen anyway)
    • CommentAuthorowlman
    • CommentTimeJun 30th 2024
     
    Could he simply use a liquid DPM on the existing concrete. Then re-surface or even lay a decoupling tile matting with thin screed/ tile cement on top to provide a clean dry surface to float or even glue down engineered flooring. Unconventional but could work OK.
    Schluter decoupling matting usually requires sticking down but I once used a similar German product that was a floating mat, which was screeded on top. The advantage being it allowed movement between the substrate and the finished flooring. I'll try and dig out details. I tiled on top but I see no reason why you couldn't float or even glue down wood flooring.
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      CommentAuthordjh
    • CommentTimeJun 30th 2024
     
    Posted By: Peter_in_HungaryThe architect said that the concrete floors would push moisture into the walls so should be removed and replaced with something that allowed moisture to escape other than in to the walls
    I think his thought process is flawed/confused and should be challenged.
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    The architect is recommending removing the concrete floors due to the detrimental effect on the walls e.g.damp rising up the plaster. Surely removing the concrete only to replace it with a DPC would be a waste of time and funds.

    Apart from the architect not liking concrete floors in stone/rubble buildings there is nothing wrong (unserviceable) about the floors.

    Do I recall people here removing concrete floors to replace with limecrete for permeability reasons? Hence would it make any sense to put a DPC on top?
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    We put a Limecrete floor (all system materials provided by Ty-Mawr IIRC) into a solid stone walled cottage renovation, but the existing floor was a mix of stone flags and engineering bricks on sand/lime mortar straight onto the ground. We dug out to allow for LECA as insulation, no DPC just geotextile between the layers, original floor went back down along with UFH pipes in lime screed.
    If the existing floor is concrete with no damp issues in the floor or walls, then removing the concrete only to replace it with a DPC would be a waste of time and funds. Unless they want more insulation in the floor, but that is a different story with a load of other considerations.
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      CommentAuthordjh
    • CommentTimeJun 30th 2024
     
    If the floor has been there for 50 years and there's no evidence so far of rising damp, then is there any reason to suspect any in the future? Has the moisture in the walls been measured?

    Limecrete floors are permeable, just as concrete floors are. Limecrete is typically laid on something like leca balls or foamed glass pieces for insulation, and they also have the feature of providing a capillary break. But unless the ground underneath is dry, there can still be vapour flow. Hence the likes of rush mat flooring to keep things vapour open.

    Incidentally, it occurs to me that a concrete floor is not normally flat enough to put hard (rigid) flooring directly on it. It would probably need levelling first.
  9.  
    The floors are flat with the majority with terrazzo tiles so a layer of xps (perhaps 2 -5 cm) should suffice.

    With the floor there for 50 years with no problems in the walls my option would be 'if it aint broke - don't fix it'
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      CommentAuthorfostertom
    • CommentTimeJul 1st 2024
     
    It always puzzles me that the usual thinking, rules and objectives for walls, roofs etc aren't applied to floors. Why don't we install internal VCL in floors (other than for a sort-of different reason under wood flooring, as above) and vapour permeable materials outboard of (i.e. below) that? Or if like me you question the idea of internal VCLs generally, then leave it out. Either way, treat the floor no different in principle than a wall. In the past I've installed a grid of leaky pipes, cross vented to outside, under a floor, equiv of an external vented cavity behind wall cladding, with the DPM below that. Or cross-vented the cavity beneath a raised timber floor.
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      CommentAuthordjh
    • CommentTimeJul 1st 2024
     
    Posted By: fostertomIt always puzzles me that the usual thinking, rules and objectives for walls, roofs etc aren't applied to floors. Why don't we install internal VCL in floors (other than for a sort-of different reason under wood flooring, as above) and vapour permeable materials outboard of (i.e. below) that?
    Because a floor is different to a wall, because the ground is wet. The air is not (in the same way).

    I have straw bales in my walls and am happy with that. I would be happy with them in my roof as well, but there's no way I would use them as floor insulation. There are too many cases where people have tried and then the bales rot.
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      CommentAuthorfostertom
    • CommentTimeJul 1st 2024
     
    Not necessarily - you could be on top of a mound of gravel. Assuming wet, I included a DPM, or cavity under a raised floor. Reply doesn't address the point raised.
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      CommentAuthordjh
    • CommentTimeJul 1st 2024
     
    Sorry forgot to mention the other source of water - indoor flood or spills.

    Posted By: fostertomNot necessarily - you could be on top of a mound of gravel.
    In the very special case of having a natural capillary break under your house, I'm sure that floors could be treated specially - viz the same as walls :bigsmile:

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