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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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    Has anyone heard of problems with filling underfloor voids with polybeads or even offcuts from eps EWI boards? Ive read a few of the other threads regarding this and most seem to say that it is a worthwhile exercise. Could it create problems with damp and rot as the ventilation will be removed?
    It would solve the common issue with small crawlspaces under suspended floors.
    • CommentAuthortony
    • CommentTimeFeb 3rd 2019
    I have see a very clever guy overseas do it to dozen homes without problems 5 to 10 years ago

    I have tried to apply for a grant to develop the idea

    The theory goes like this, when the pvp is higher indoors than outdoors moisture moves from indoors to outdoors including into the soil/ ground under the house.

    Therefore it won’t get damp or cause rot

    If there is a void it should be ventilated, where there is no longer void it is a grey area or volume.

    I would unhesitatingly do it to all of them

    Research problems needed on ground gas including radon, smelly ground, interaction with pvc covered electric cables, gas safety issues, fire hazards.

    I have a lot of info on this as I got a long way down the line

    I also have a blower gun and will help you do it

    • CommentTimeFeb 3rd 2019
    Agree. Water vapour will (should be allowed to) migrate freely down thro the floor structure, which will remain at pretty much room temperature. Way below that, under a thickness of permeable full-fill insulation, will be the cold subsoil (and even colder surrounding foundation/walls). That's where the water vapour may condense, safely far from the warm floor structure, acting as a kind of dehumidifier for the whole volume.

    By contrast, with void space instead of full-fill insulation, the void may well be full of saturated air, which may condense on the floor structure. Attempting to dissipate that air, standard recommendatuion is for copious through-ventilation, but in Spring and Autumn may well be importing air with even higher vapour content.

    Before thinking of this, essential to ensure that there's no liquid water penetration into the void, via walls or up through the subsoil. And that the floor structure is sound, not rotten. One belt and braces way is to surround the building with a french drain down to bottom of foundation level, which intercepts any horizontal groundwater flow incl from pooling rainwater, and lowers the water table locally. So there's no liquid water, above subsoil level, to penetrate the void. Also cures rising damp.
    So, in essence, it's very doable?! Especially if the ground beneath appears to be dry beneath. And I presume it's imperative to fully fill to ensure the dew point is some distance away form joists.
    Tony, you would blow it in from outside, as apposed to lifting floor boards and filling from above? Im looking for a solution where crawlspace is low and also, hopefully, a cheaper method than lifting the entire floor?
    I know it's been done with foamglas, but that is an expensive way of doing the same thing.
    Mice would love to live in that..!

    The inside of the exterior walls is going to attract the condensation during winter, as they will be much less permeable than the insulation, and are colder than the ground, and are no longer ventilated. Could this be a problem for the ends of the floor joists if these are built into the wall?

    Would you need to break out any concrete oversite layer on top of the soil, as this would attract condensation but restrict drainage?
    interesting additions. It's hypothetical at the minute. I had someone enquire about floor insulation and they baulked at the disruption and cost. I'm hoping that this might be a more straightforward option.
    I'm not sure what the ground make up is, but I'd presume it would just be bare ground, given the age and type of properties around me.
    would the size of "bead" have an affect. I have bags and bags of EPS offcuts from an EWI install, do these need to be granulated down to a few mm or could they be larger?
    • CommentTimeFeb 3rd 2019 edited
    Ideal would be to lay 150mm EPS boards vertically against the foundation wall outside face, within the french drain trench, from bottom of found up to just below external GL. That wd keep the found walls and joist ends warm. Of course if you're doing EWI, those EPS boards wd be continuous with, part of, the EWI. Super tea-cosy!

    This assumnes you've got founds 750 deep or more - if it's an old building with shallow founds, then instead of vertical EPS boards, place that insulation as a horizontal bed of Leca 300mm thick x 900 wide, topped with topsoil over geotextile, a horizontal 'skirt' of insulation also serving as the french drain 'sharp clean aggregate' soak-down medium.
    • CommentAuthortony
    • CommentTimeFeb 4th 2019
    It does not matter even a little bit if the ground is wet, it can even have puddles lying on it.

    The only problem with flooding or deep water would be the buoyancy
    Thanks for the replies, this is very helpful. I'll let you know how I get on. I need to find a willing guinea pig now...
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