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General: Breathable flooring, main reason/s?

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  1.  
    • CommentAuthorGareth J
    • CommentTimeMar 9th 2026
     
    A friend has just put down a limecrete floor in a solid stone wall built house. Part of a system with foam glass as an insulation layer underneath.

    I didn't ask him, but what's the advantage over a non breathable setup? Something like DPM, concrete slab, PIR/EPS, top layer/s. His place is all above ground and is a well built house.

    I can see that there are likely lower carbon and non plastic based advantages but from a performance perspective, does the floor need to breath? Is it mitigating potential moisture issues? This might have been covered loads or be completely obvious and I've missed it so apologies in advance!

    The suspensoended floor in my own solid wall cottage needs attention at some point in the future so am keeping half an eye on options. It's complicated by being half dug into the ground around it though.
    •  
      CommentAuthordjh
    • CommentTimeMar 9th 2026
     
    Limecrete with foam glass is popular with straw bale builders on the basis of supposed low impact and as you say, no plastic. (Though we have polypropylene fibres in our lime render :bigsmile: )

    There's no requirement for floors to breathe, but they should resist moisture coming up (foam glass is a capillary break) and allow moisture going down (foam glass). But how far spills get going downwards with a DPM in place is an unknown quantity.

    A French drain around the outside is a good thing to have if your floor is part below ground. With the drain itself below floor level.
  3.  
    The ground below the house is colder than inside the rooms. Moisture vapour migrates to the coldest point it can access and then condenses, like in a dehumidifier. So a breathable floor removes moisture vapour from the house..If this is blocked off with a vapour tight membrane then more mechanical ventilation will be needed to remove moisture vapour instead.

    Conversely, if there is liquid water in the soil, it can wick up through a solid floor by capillary action. This was a reason to have a ventilated suspended floor as a safe route for soil moisture to escape, if the soil isn't naturally dry and well-drained.

    A DPM or capillary break forces any rising water to go sideways rather than upward, so it should ideally continue underneath the walls to the DPC so water isn't directed to rise up inside the walls or skirting area. Obviously this is how new buildings are built but difficult to retrofit. Some recommend that a retrofit DPC should be turned a couple of feet up the inside of the wall.

    As with most old house things, if it's worked ok for a hundred years then it's best not to change it too much, unless there's a reason it isn't working any more! It's possible to insulate between and beneath the joists of a susp floor while keeping it vapour open and breathable, but not if there are existing damp problems.

    As far as I can tell the embodied carbon emissions from commercial NHL lime are much the same as from Portland cement, and foam glass is worse than aggregate.

    Edit to add: Ive been working on a 1970s conc block bathroom extension to 1850s stone house, there are a hodgepodge of different levels and floor types and the floor was below the DPC level and damp. I'm trying out building the floor level up above DPC with 50mm XPS polystyrene insulation (Marmox) and floor tiles which are vapour and capillary closed. Time will tell!
    •  
      CommentAuthorfostertom
    • CommentTimeMar 10th 2026 edited
     
    Nice summary Will.
    Surely, carbon emissions of foam glass shouldn't be compared with aggregate, as it's not an alternative to aggregate (as in concrete), but to dual 'compacted hardcore' (which yes may be aggregate, traditionally broken brick) plus conventional insulation?
  5.  
    Fair point! The emissions from quarry materials come from the truck used to deliver them, so lots depends how far away that is. Glass comes from further away and obvs involves a kiln too. Can be difficult to get any data but eg Steico wood fibre that is trucked from Czechia is surprisingly high CO2 compared to polystyrene shipped from Sweden, because of the weight. Not easy!
    • CommentAuthorGareth J
    • CommentTimeMar 10th 2026
     
    Thanks all, very interesting.

    So, from a purely functional perspective, there is an important advantage, that it reduces risks of pushing groundwater across to walls. That makes sense and I hadn't thought of that.

    My gut feeling though is that, if that is of particular risk, the floor should probably be made/kept suspended and ventilated. Or, with any kind of fall available to outside, the risk could also be mitigated by drainage and gravel below any floor system. It really doesn't feel sensible to expect house ventilation to remove significant quantities of moisture from the ground on top of all the other ventilation it has to do.

    Wrt my own house, it doesn't really work well. I've done my best to french drain externally the below ground bits that have been exposed before but there's a garage on the remaining side and, while the suspended floor and kitchen cupboards keep most damp issues out of sight, the floor void isn't deep enough and the ventilation points numerous enough so the floor is fore sure rotting here and there.

    My friend is very happy with his new setup and feels the living environment is greatly improved. Damp and musty smells have gone. Sounds a really positive experience, if a little more expensive than a more conventional floor that may have achieved similar.
    • CommentAuthorsgt_woulds
    • CommentTimeMar 10th 2026
     
    STEICO does not have any mills in the Czech Republic, all woodfibre insulataion manufactured for import to the UK is manufactured in Czarnkow, Poland.

    I question your claim regarding CO2. I'm guessing this does not include production of the materials?


    Polystyrene should include ALL emissions:

    - extracting the oil,
    - shipping to refinery, (on tankers using bunker fuel)
    - shipping (on tankers using bunker fuel), to sweden,
    - trucking to the manufacturer,
    - production,
    - then trucking the finished product to port,
    - where it is shipped on ferries or container ships (on low grade fuel and ineficient engines) over to the UK,
    - a lorry takes it to the distribution centre or final customer.


    STEICO by contrast:

    - Timber is transported by lorry from within 200 miles of the mill (all timber is sourced from within Poland)

    - Production uses waste timber for combined heat and power + solar for around 60% of the energy requirements - the rest comes from the Polish grid (which admitadly is not the greenest but is improving).

    - 100% of the timber is used either in the product or for biomass. I'm not sure if that is true with crude oil used in plastic production?

    - Finished products are shipped by lorry overland to the nearest port (usually in France). There is some container shipping but it is a statistical blip

    - Ferry to UK

    - Lorry to distribution centre or final customer


    Transporting insulation to the UK is never the best with regards to emissions , but the main motorway routes through Germany, Belguim, France are starting to be be electrified (pantograph I think) so it is hoped that Hybrid lorries can be introduced within the next 5 years
  8.  
    Insulation manufacturers have to work all that out for you and declare it in their EPD. They have to spit it into categories of A1-A3 raw materials supply chain through to manufacturing, A5 assembly, and C2-C3 disposal

    Steico's EPD declares 310kgCO2eq per m³, mostly from heat used in manufacturing, and with net off of CO2 bound up in the timber and released at end of life

    Typical EPDs for polystyrene declare 50kgCO2 per m³ for raw materials and manufacturing and another 70kg if incinerated at end of life or 0 if landfilled


    Should convert m3 into insulation value but they're both similar in this case.


    The EPDs don't include transport to your site, you have to add that

    Dunno where I got Czechia from sorry (possibly another wood fibre I was using?) but Poland is further away.

    1m³ x 1700km x 110g/t-km x 0.25t/m³ = 40kg CO2 per M3 of wood fibre by truck


    1m³ x 2000km x 15g/t-km x 0.02t/M3 = 1kg CO2 per M3 of polystyrene by ship from Sweden



    Was surprising to me, but polystyrene has lower lifecycle emissions than wood fibre.

    Is because you need a lot more kg of wood fibre than of polystyrene for the same effect.

    Doesn't mean either are necessarily the wrong material, I'm actually fitting some wood fibre this afternoon (Gutex from Germany!)


    Edit to add: some bio insulation vendors claim their product has no CO2 release because they take credit for CO2 absorbed by the growing plants but not for CO2 released at end of life. To their credit Steico make both these numbers clear in their EPD. They presume that the end of life wood fibre will be burned in a power station and used to make electricity, which is perhaps optimistic, better than being landfilled and degrading into methane.
    •  
      CommentAuthordjh
    • CommentTimeMar 10th 2026
     
    Here in Suffolk nothing is sent to landfill, we are told. Everything is incinerated. Not sure I really believe that, but given we're not the most forward-thinking bears in the world, why do other areas still use landfill?
    •  
      CommentAuthorfostertom
    • CommentTimeMar 10th 2026
     
    I'm all for landfilling plastics (any liquors suitably contained), against incineration. Sometime soon we'll be glad to quarry stockpiled hydrocarbons.
    •  
      CommentAuthordjh
    • CommentTimeMar 11th 2026
     
    Posted By: fostertomI'm all for landfilling plastics (any liquors suitably contained), against incineration. Sometime soon we'll be glad to quarry stockpiled hydrocarbons.
    Plastics should be recycled! They are here. Not landfilled or incinerated. But if you were to landfill them with a view to 'mining' them how would you sort them out so the chemistries matched?
    • CommentAuthorsgt_woulds
    • CommentTimeMar 11th 2026
     
    Most plastic in the UK is not recycled. The majority of the material we send for 'recycling' is actualy sent on to an incinerator.

    The reasons are complex and based on a number of factors, but as a small example:

    -The market for recycled plastics is very small so there is not enough incentive to invest in recycling

    -recycled plastic is more expensive than virgin plastic

    -recycled plastic is less durable than virgin plastic More impuraties, broken chemical bonds, etc

    -most plastic sent for recycling is rejected due to contamination (food waste, other materials mixed in, etc) and there isn't enough manpower or machinery available to seperate and grade it

    -flexible plastics, (plastic bags, clingfilm, pallet shrink wraps, etc) need very specialised and highly maintained machinery in order to be recycled. Machinery that handles hard plastics get gummed up when flexible plastic is mixed in. Even where machinery is available to handle flexible waste (not many plants in the UK) it needs constant attention and cleaning to prevent stoppages.


    Our Extended Producer Responsibilities (packaging) Regulation was intended to ease the funding strain for recycling, but it has collapsed in the first year as it costs more to run the recycling in this country than they can claim back from the manufacturers. They'd based it on selling recycled plastic, but it is so much cheaper to buy feedstock from China that no-one wants it.

    I'm with Tom, storing it for wlater is a better option than burning it, but where could we possible keep it all without a team of Wall-E robots building rubbish mountains...?
    •  
      CommentAuthorfostertom
    • CommentTimeMar 11th 2026
     
    The last point, I regretfully agree with.
    •  
      CommentAuthordjh
    • CommentTimeMar 11th 2026
     
    That description doesn't seem to match what it says on https://www.suffolkrecycling.org.uk/recycling-composting/recycling-at-home/where-recycling-goes Are they lying?
  15.  
    I’ve used some recycled plastic battens on the current barn conversion project, they did smell very “foody†to the extent that my dog (albeit hard of thinking) ate the swarf from cutting on the chop saw.
  16.  
    Other items that I have bought in the past (grass pave mats) sold as recycled have seemed like virgin plastic.
  17.  
    Could perhaps be the difference between post-consumer recycled plastic and post-industrial process.
    • CommentAuthorsgt_woulds
    • CommentTimeMar 12th 2026
     
    In the UK, in addition to the pEPR (Extended Producer Responsibility (packaging), tax (which covers recycling for all materials), we also have the Plastic Packaging Tax (PPT), that requires all plastic to have a minimum of 30% recycled content to avoid taxation.

    This used to allow firms to count Post Industrial (re-using offcuts) as part of that 30%, but that has now been changed to PCR only. Not that there are any checks on recycled content other than a tick box...

    We have discovered that for some products, anything more than 10% PCR plastic reduces the shelf-life and cannot adequately protect our natural fibre products. PCR breaks down more quickly when exposed to the sun and although shrunk to the products it slowly opens up allowing more moisture and handling damage to occur.

    So honest firms that properly declare their recycled content end up paying more tax.

    Others just carry on regardless, tick a box knowing that the OPSS & the Environment Agency are vastly understaffed and will never check.
    • CommentAuthorsgt_woulds
    • CommentTimeMar 12th 2026
     
    @ Dominic Cooney - I'd be very worried about using PCR plastic battens due to the creep.

    Perhaps this is less of an issue under tiles as they won't be exposed to UK, but they will still get hot.

    As an example, most park benches made of 'plastic wood' go droopy after a few years of exposure and loading.

    I looked at using PCR timbers for my SIPs sole plates to reduce the cold bridge in this area, but none of the suppliars could provide evidence of long term structural performance.
    •  
      CommentAuthorfostertom
    • CommentTimeMar 12th 2026
     
    "they won't be exposed to UK" - As Ghandi said, "That would be a good idea".
  21.  
    I didn't use them as roof tile battens, I only used them as spacers to maintain a cavity between the existing concrete blockwork and our internal Steico-Joist timber frame insulated shell.

    They would be far too bendy for roof tile battens, almost comedy bendy!
  22.  
    @DJH/FT - as I understand it the 'nothing landfilled' claim is refering to household waste.

    Rubble from demolished buildings is not usually incinerated as it mostly doesn't burn without supplementary fuel. To some extent the timber and steel can be picked out and clean masonry can be crushed for reuse as aggregate which is all good, but otherwise it's a mixed/contaminated waste so in landfill.

    Where sheet insulation has been fixed to masonry and rendered over, seems unlikely that those layers will be carefully removed from each other at demolition so each material can be reused or burned in a power station- the whole wall-insulation-render assembly is unfortunately going to be landfill ISTM.

    Hopefully by then we won't still have thermal power stations anyway!
    • CommentAuthorArtiglio
    • CommentTimeMar 12th 2026
     
    We had/have zero to landfill claims from my council, but that ( at the time i was told about it) meant that once the metal and glass had been removed along with any clean and easily sorted paper/ card, the remainder was bailed and loaded into the “walking floor†style of lorry and transported to germany and scandinavian countries where it was burnt in waste to power plants.

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