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General: Hempblock - has anyone tried?

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  1.  
    • CommentAuthorminisaurus
    • CommentTimeApr 11th 2026
     
    I thought these ones looked interesting: https://uk.hempblockinternational.com/ - load bearing, no mortar needed, insulation, noise reduction & presumably pretty green.

    Has anyone experience of them? The positives are many, but what are the negatives? price I guess
    • CommentAuthortony
    • CommentTime6 days ago
     
    I dislike the notion (philosophy) of combining structure with insulation believing it to be a mistake.

    Compromises are made as result where it is better not to compromise
    •  
      CommentAuthorfostertom
    • CommentTime6 days ago
     
    How exactly do you find that structural insulation forces compromises?
  4.  
    If we are talking about PUR SIPs then I agree, but I cannot see a downside with hemp blocks.

    They are fire proof, insulating, and structural. The HBI products are brilliant although I wish there was a way to avoid the concrete columns and lintels. Timber pegs (like the old JÖ BLOX system) and LVL lintels would be a better alternative for me.

    The HBI interlocking system is brilliant. If they can get the prices similar to concrete blocks I cannot see any reason for mass housebuilders to specify anything else. I wish this had been available for my extension build.
  5.  
    This particular product is being sold as an infill material with a proprietary steel or RC frame system, so is not treated as load bearing per se. Though it looks ok for dividing walls without needing the frame.

    The thermal properties are good, U=0.2, but not quite good enough to meet England/Scotland building regs, so will need a little extra insulation layering. Maybe a cork plaster layer would be enough? Not clear if the thermal bridging of the steel frame is included in their thermal figures.

    The concern for me is the "16% cement" used to binder the hemp which is not great for CO2, ideally a non structural infill material wouldn't be using cement. And ofc the steel or RC frame isn't helping.

    It irritates me when it's sold as 'natural cement' or 'traditional cement'. It's still cement.

    https://hempblockaustralia.com/wp-content/uploads/2024/11/HBI_TechnicalDetails_LB300_Performance.pdf
  6.  
    As I understand it the 'RC frames' are poured into cavities in specific blocks (as with cinder block construction), with a poured ring beam at eaves height to tie it all together.

    This is the part that I'd prefer to replace with LVL and timber pegging. The blocks themselves are structural, but need reinforcing for lateral movement

    I agree that the inclusion of any cement in the blocks is not ideal, (from talking to them a while back I think this was a decisiuon based on the poor availability of alternatives as well as the structural requirements) but we mustn't let perfection blind us to better products.

    This system takes 5-10 minutes to asseble per m2 of wall and removes the need for mortar. Cement use will be vastly reduced over a conventional brick/block cavity wall.

    It doesn't even need to be finished externally if you can justify the look of the raw blocks.
    •  
      CommentAuthordjh
    • CommentTime5 days ago edited
     
    Posted By: WillInAberdeenIt irritates me when it's sold as 'natural cement' or 'traditional cement'. It's still cement.
    It's Prompt Natural Cement, I believe: "Composed solely of natural argillaceous limestone fired at low temperatures".

    Sounds like an impure version of hydraulic lime (extra silicates). Still uses a lot of energy to make it.
  8.  
    Yes, that's the stuff. When it is fired at many hundreds of degrees (the "low temperature" claim!) the calcium carbonate limestone gives off CO2, to make quicklime.

    However then the lime bonds with the silicate and aluminate impurities (the argillaceous bit) and with water, to form a quick setting hydraulic cement.

    So the bonded-away calcium cannot subsequently re absorb its CO2 emissions, which is the claimed advantage of air-setting limes.

    So, CO2 is emitted from firing the kiln and more CO2 is irreversibly emitted from decarbonating the limestone. It may be 'traditional cement' but it's far from being green!



    The cement content of the hemp block product is much the same as Thermalite style blocks, which I suppose fit into the same market, although worse insulation and water performance. Clay bricks don't emit process CO2 during firing, but do use mortar mix that contains slightly more cement 25% than the blocks do 15-20%, but not a lot different.

    Ideally we'd move away from bricks/blocks of any kind - the volume builders round me are using factory timber kits and just wrapping them with decorative masonry that is not load bearing - with a little nudge from building regs they could happily swap that for lower-cement outer skin materials.
    •  
      CommentAuthordjh
    • CommentTime4 days ago
     
    Posted By: WillInAberdeenIdeally we'd move away from bricks/blocks of any kind
    Agreed. It seems a weird fascination to me.
  10.  
    I'd agree if we had a workforce that was capable of building a TF kit and applying multiple membranes and critical taping and sealing properly. Anyone who has worked on a building site knows this is not the case.

    Let alone the follow on trades that just cut through willy nilly.

    Mind you, brick and block walls can be ruined by uncaring idiots too! That's perhaps a little unfair of me - modern 'brickies' are just techicians now rather than apprenticed craftsmen. There is a scanfdal brewing about badly built walls using inadequate ties and the wrong mortars. only a matter of time until someone is killed.

    But it would be hard for even the most disinterested Great British Builder to mess up laying the HBI system.

    And importantly for house completion targets, it would be considerably quicker to build.

    A quick AI search (I don't trust it but I haven't the time to properly look!) says that the cement content of thermalite is 25+% and around 16% for the hemp blocks. Plus savings from mortar free joints.

    Also, no facing bricks required for the HBI system. Does anyone build thermalite block with external render finish?

    In the UK, the HBI system would need an EWI - direct rendered woodfibre would be my preference - but I contend that it would still be a better fit with the skill set of our GB Builders and the mass house building companies than TF.
  11.  
    Mmm the Thermalite EPD says 15-16.3% cement, but who are we to argue with AI!

    Something like 80% + of houses in Scotland are timber frame kits, it's grown in the last decades, it really is possible to get people to build them well. The logic of building in a factory rather than out in the snow is more 'in your face'! Building regs are a bit tighter too, every individual house on a development is airtightness tested so less forgiveness if you mess up the membrane.
    •  
      CommentAuthorfostertom
    • CommentTime3 days ago edited
     
    That last is an unexpected biggie, for ensuring actual usefulness of new additions to the national housing stock. As well as checking every house, it would seem to discourage reliance on those last-minute shortlived bodge-measures by which developers scrape their one-in-three (is it?) sample house over the airtightness line.
  13.  
    Every day is a school day - hadn't realised Scott Reg's changed 3 years ago to make ALL new builds requiring air test.

    For anyone wanting some background info on heatloss, thermal bridging, interstitial condensation, psi values, construction detailing etc, etc, this is the link to the Scottish Regs 2025 (2026 due out shortly), and go to secion 6 apendicies 6B onwards. Not saying it's perfect, but will answer a lot of the questions that appear on GBF.

    The Scottish Regs (I find) are so much clearer and more informative than the English version (I'm not Scottish . :smile:), written to help rather than by a laywer.
    • CommentAuthorMike1
    • CommentTime2 days ago
     
    Posted By: minisaurusHas anyone experience of them?

    I've not used them myself, but have seen them (from the site boundary) being used in France and it looks an interesting system to me.

    They're a rebrand of the French Biosys product (https://www.solution-biosys.fr/), which has the French equivalent of an BBA Certificate (https://www.solution-biosys.fr/actualites/le-bloc-de-beton-de-chanvre-biosys-bce-obtient-un-avis-technique) for two-storey houses, though they've been used much higher than that with an independent structural frame. External lime render forms the airtightness layer.

    They do contain cement but 84% of the volume is hemp, which does absorb a good deal of CO2. Overall they've been assessed at 0.89 kg.CO2/m² of blockwork.
  15.  
    @WillIn Aberdeen - That is great news, and no surprise as ever to hear that Scotland is ahead of the game!

    I will apologise and rephrase my standard maledictive derogative to 'Great English Builder' :-)


    I have attended far too many sites where we worked in 'the airtight' plot and were forbidden to make any penetrations - at least until the blower test was completed...

    Then it was a freeforall for all trades, who seemed to compete at making the biggest holes, as soon as they packed the door blower away.

    Best one was a Bloor homes site, where the second the blower test was recorded (I'm being literal), a chap cut a 600mm hole for an open chimney vent for a centerpiece hanging fire in the living room.


    I spoke to the air tester at the time - he was just standing there open mouthed. He was completeing 3-6 tests a day and aparently it was common for there to be a line of trades - with drills and saws poised - queing outside each plot nagging him to finish. Even though he knew that the air tests were being rendered useless, he wasn't allowed to change anything or add notes after the test results were recorded.

    The sort of typical tick-box culture that is endemic in the 'English' building sector.


    I still think that a blockwork system will hide less horrors (and be easier to fix), than a timber frame reliant on multiple membranes to ensure integrity.

    Espescially as the standard TF in the UK (including Scotland) is built 'back-to-front', with external racking boards forming a vapour restrictive layer being overly reliant on badly installed VCL.
  16.  
    'The logic of building in a factory rather than out in the snow is more 'in your face'!'


    This would be fine, if the TF was then assembled with the same care as they were manufactured.

    We work with a 'Kit House' company. Every piece of timber is machine cut to a tolerence of less than 1mm, and each part is engraved with location ID. If the plans came with service penetration locations these are pre-cut also.

    They use LVL and I-joists so there is no shrinkage warping to worry about.

    They provid full plans detailing the location of every piece of timber and an ID chart. They even provide all the brackets, nails & screws to fit the frame togester


    Every week they recieve calls from 'builders' asking them to advise on repairs to damaged or compromised timbers that have been butchered on site...

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