Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



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.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




    •  
      CommentAuthorfostertom
    • CommentTimeJul 21st 2022 edited
     
    Surprising - and pleasing to me: in
    https://mailchi.mp/passivehouseplus/building-a-better-passive-school?e=04983d3d80

    "the airtight layer consists of Medite Smartply OSB3 with careful taping at junctions and between panels"

    My 'standard' construction is:

    pbd & skim
    on studwork/raftering
    with 11mm OSB3 gapfilling glued and screwed (or nailed) externally,
    full filled with blown-in cellulose (Warmcel);
    EPS 'EWI' outboard of the OSB3
    acrylic rendered.

    I have the OSB3 as vapour-breatheable but airtight layer, supplemented by the fair airtightness of the blown-in Warmcel. But the airtightness of OSB3 is widely questioned, as it's not quality-controlled or specified by the manufacturers. I've relied on hearing Regional PH Assessor Peter Warm say "I've never had to fault OSB3 as airtight layer of a PH". Robust, somewhat self-healing airtightness without membranes and tapes.

    When I did the WUFI course in Dublin, a boffin from Coillte (Medite Smartpky) was there and he put me down for an 'expert' consultation panel, as Coillte intended to address this issue. Instead they came out with plastic-coated Propassiv Smartply, which completely missed the point, as the need was for OSB3 quality-controlled to be airtight but vapour open.

    Apart from all that, the article is full of PH buildability tips described competently enough to be technically useful.
    •  
      CommentAuthordjh
    • CommentTimeJul 21st 2022
     
    Err, what? The link is to a reprint (with many duplicated paragraphs - perhaps it had to meet a word count target? :) of a long-ago article from PH+. "This article was originally published in issue 8 of Passive House Plus magazine." - that was back in 2013 or 2014 - I can't see a date on my copy. From memory I think Medite Smartply OSB3 was the previous name before it got rebranded as Smartply Propassiv. There's only that product on their site now, anyway.

    I don't think anybody's ever claimed, let alone proved that 11mm OSB is airtight. The school project specifically talks about taping the joins too, so I'm not sure what your 'no tape' is about.
    • CommentAuthorMike1
    • CommentTimeJul 21st 2022
     
    Posted By: fostertomBut the airtightness of OSB3 is widely questioned, as it's not quality-controlled or specified by the manufacturers.
    That's the key factor - OSB3 may or may not be airtight, depending on the manufacturer.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 21st 2022 edited
     
    Old gems, re-issued to subscribers as 'The Thursday long read', worth reading anyway.

    Propassiv is the coated version of Smartply made by Medite, part of https://www.coillte.ie/about-us/our-story. Shipped from Cork, for S/Central England this foreign import has less 'airmiles' than the UK alternative Scottish Sterlingboard, as well as 'no added formaldehyde' glue, poss because Irish trees already have more natural formaldehyde than Scottish ones.

    Peter Warm and now I see Architype both say that OSB3 has adequate, if not complete, airtightness. Personally I supplement it with blown-in cellulose, belt n braces, and I use gapfilling glue and screw instead of tapes, and around windows expanding tape (Compriband) plus silicone sealant into sized gaps, instead of tapes.
      2011-07-26 021reduced.jpg
    •  
      CommentAuthorfostertom
    • CommentTimeJul 21st 2022
     
    and inside, 0.7mm dryliners' galv flatstrap and angles as noggings
      2011-07-26 040reduced.jpg
    • CommentAuthorborpin
    • CommentTimeJul 22nd 2022
     
    Instead of WarmCell, I'd specify Icynene.

    Have you ever found WarmCell settles, at all (i.e. 5 years later do a TI inspection)?
    •  
      CommentAuthorfostertom
    • CommentTimeJul 22nd 2022
     
    Yes Icynene has some of the same beneficial properties, except no hygroscopicity, which is a big loss.

    It doesn't show above, but we weave galv garden wire in and out of the studs @ 400c/cs; the Warmcel packs around that and doesn't slump. Anyway, if well blown in it shouldn't, as is under slight permanent compression.
    • CommentAuthorborpin
    • CommentTimeJul 31st 2022
     
    Posted By: fostertomhygroscopicity
    I had to look that up!

    Why would you want to insulation to absorb moisture? Part of the attraction of Icynene was that any moisture would just pass through (as I understood the physics of it).
    • CommentAuthorSimonD
    • CommentTime7 days ago
     
    Posted By: borpin
    Posted By: fostertomhygroscopicity
    I had to look that up!

    Why would you want to insulation to absorb moisture? Part of the attraction of Icynene was that any moisture would just pass through (as I understood the physics of it).


    It has a capillary function that passes additional moisture throught the wall, but probably more importantly it buffers moisture, absorbing moisture peaks and releasing it slowly back out to the atmosphere. This reduces moisture problems found in highly airtight buildings and also reduces the required ventilation rates (although this has not come to be included in Building Regs for ventilation yet - if it ever will).
    • CommentAuthorMike1
    • CommentTime7 days ago edited
     
    Posted By: borpin[hygroscopicity]...
    Why would you want insulation to absorb moisture?

    You want a material that can adsorb moisture (take in water in it's gaseous state) rather than absorbing it (soak up liquid water) - and desorb it (reverse the process), as many natural insulation products do. In other words, as Simon mentions, it buffers moisture vapour.

    The benefits are that this:
    - reduces the risk of condensation (by reducing the build-up of moisture at the interface of the insulation and a colder surface, where condensation tends to occur).
    - Improves thermal comfort (keeps the air within a comfortable relative humidity range for longer)
    - improves air quality (at <40% RH viruses are present in the air for longer, respiratory infections are more likely, and the skin, nose & throat can become irritated; at >60% bacteria and mould thrive)
    - tends to reduce heating and cooling requirements (adsorption of moisture releases heat, desorption takes heat, though research into quantifying this in buildings still seems to be limited)
    •  
      CommentAuthorfostertom
    • CommentTime5 days ago edited
     
    Posted By: Mike1You want a material that can adsorb moisture (take in water in it's gaseous state) rather than absorbing it (soak up liquid water) - and desorb it (reverse the process)
    Is that quite right? Isn't it that many 'natural' materials (like sheep wool) have little sacs which absorb and hold liquid water within, but don't feel 'wet' without? I can't see any insulant holding lots of water as gas, unless compressing it (explosive!). Non-'natural' materials don't have such complex form. The one non-'natural' material which displays hygroscopicity, unfired clay, works a different way to similar effect - can anyone explain?

    PS can't get my head around adsorb vs absorb!
    •  
      CommentAuthordjh
    • CommentTime5 days ago edited
     
    • CommentAuthorMike1
    • CommentTime5 days ago edited
     
    Posted By: fostertomIsn't it that many 'natural' materials (like sheep wool) have little sacs which absorb and hold liquid water within, but don't feel 'wet' without?
    That's a common simplification. My understanding is that moisture is adsorbed by the cell walls (keritin in the case of wool, cellulose in plant fibres) at the molecular level and held there principally by Van der Waals forces. However the fibres continue to repel water droplets, so the spaces between them retain air and it remains thermally insulating.

    Posted By: fostertomThe one non-'natural' material which displays hygroscopicity, unfired clay, works a different way to similar effect - can anyone explain
    The physical structure of clay is very different - mineral platelets rather than organic cells - and it tends to readily become plastic in the presence of water, while taking much longer to dry. For RH buffering you want a material that can readily adsorb and desorb moisture, not just one that's hygroscopic.

    However, to turn this full-circle, I'd be fairly sure that adsorption is the process at play when clay is used - as fuller's earth - in the fulling (cleaning) of wool before it's turned into products such as insulation. It's certainly used for adsorbing heavy metals from water.

    Posted By: fostertomcan't get my head around adsorb vs absorb
    It's not good for the dyslexic either :)
  1.  
    aBsorb = a liquid or gas fills up the pore volumes in a different solid or liquid

    aDsorb = a liquid or gas sticks onto the surface of a different solid

    Both happen more in porous materials, which have larger pore volumes and larger surface areas, eg dead wood can absorb and adsorb water into its little tubes.

    Adsorption is more interesting because the surface properties of the solid can be tuned to adsorb specific liquids or gasses, and release them again at useful moments.

    Nature might have done the tuning already, EG wood can absorb/release water vapour in response to the Relative humidity (instead of the Absolute humidity) which gives it useful RH buffering and wicking properties.

    Synthetic materials can also be tuned, eg those little sachets of silica gel can adsorb moisture and release it again when heated slightly.


    Clay is like sand, only the grains are smaller. The spaces inbetween the grains can absorb and adsorb liquids and gases. Likewise concrete, plaster(board), lime mortar all buffer humidity to some extent.
    •  
      CommentAuthordjh
    • CommentTime5 days ago edited
     
    Posted By: Mike1The physical structure of clay is very different - mineral platelets rather than organic cells - and it tends to readily become plastic in the presence of water, while taking much longer to dry. For RH buffering you want a material that can readily adsorb and desorb moisture, not just one that's hygroscopic.
    According to https://www.conservationphysics.org/wallbuff/wallbuff.html

    "The best common buffer materials are wood, cut across the grain, and unfired clay brick. A specially designed lightweight clay made from bentonite mixed with perlite gives an excellent performance.

    "The best performer of the commonly used building materials is cellular concrete. Nearly all other building materials have a negligible buffering effect at moderate relative humidity."
    •  
      CommentAuthordjh
    • CommentTime5 days ago
     
    Posted By: WillInAberdeenClay is like sand, only the grains are smaller. The spaces inbetween the grains can absorb and adsorb liquids and gases.
    No, clay is like mike1 said, lots of platelets. Sand is three-dimensional grains.

    Likewise concrete, plaster(board), lime mortar all buffer humidity to some extent.
    Not particularly true. Concrete yes; the rest no. See the conservation physics link I posted.
  2.  
    For absorption and adsorption, clay works like sand, only with finer grains. The water coats the surface of the grains and sticks them loosely together. The size of the grains is important because that determines their surface area per kg. The shape of the grains doesn't make as much difference to their surface area, as most natural clays are not feathery or spongey (unlike say aerogel, or the foam-glass based "clay" described in the link above).

    AIUI the definitive experiments on moisture buffering were done by the Fraunhofer institute. They found that adding hygroscopic cellulose insulation behind plaster showed little improvement, compared to the plaster alone, for daily humidity changes repeated over several weeks. This was because the plaster is directly exposed to the room air and has enough buffering capacity to absorb daily humidity swings . The insulation layer's hygroscopic properties (or otherwise) might only be relevant for longer term buffering such as winter/summer.

    Edit dug out one of their papers. They also found that uncoated T&G pine cladding was a better buffer than plaster, but woolen textiles were no better. www.ibp.fraunhofer.de/content/dam/ibp/en/documents/oeVB_eng_3_tcm1021-30995.pdf
    • CommentAuthorSimonD
    • CommentTime5 days ago edited
     
    I'm quite partial to the principles of house building design as described by the Conservation Physics site. Indeed that's the approach I took in designing my house. I do, however, think some of its conclusions have been superseded by more recent research into moisture buffering materials.

    So, I'll just jump in here to suggest that the moisture buffering abilities of the materials is down to pore structure. I'll also suggest that following more recent research the moisture buffering performance of clay might not be as superior as suggested. I've linked to the below paper before. See page 48 for sorption isotherm curves, but will quote a couple of things:

    "Clay and lime presented mainly macro-pores, which have an average diameter of around
    125 nm. Gypsum also had macro-pores of a significant bigger size (365 nm average),
    but it also presented micro-pores, as shown in Fig. 3-2b. Gypsum plasterboard had a
    more accentuate micro-pores presence and a significantly higher average pore diameter
    (631 nm) than standard gypsum. Overall, the gypsum and plasterboard showed a
    significant higher pore volume than clay and lime. Due to the more complex pore
    structure of gypsum and plasterboard, both vapour and liquid transport take place
    into the materials, when exposed to a RH and vapour pressure gradient, while in clay
    and lime only vapour transport occurs. Water vapour transport can take place in
    the macro-pores and its driving potential is the water vapour pressure, whilst liquid
    transport takes place in the micro pores, where the driving force can either be the
    relative humidity and the capillary pressure."

    "Hygric properties and moisture buffering capacity of coatings (clay, lime, gypsum and
    plasterboard and hemp-lime) were determined experimentally. Density, porosity,
    water vapour permeability, sorption capacity and thermal conductivity were measured
    and compared with moisture buffering, calculated performing the NORDTEST
    procedure in a climatic chamber. The laboratory test showed gypsum stored and
    released more humidity than the other materials, due to the presence of micro-pores,
    and the consequent activation of liquid transport together with the water vapour
    transport in the macro-pores. A direct correlation between moisture buffering and
    hygric properties was found, which highlighted a significant correlation between
    porosity and the dynamic sorption capacity."

    "When temperature and RH vary simultaneously, the response of the materials showed
    that moisture buffering performances were effected by temperature, but clay and
    gypsum responded differently to the variable environmental condition, due to their
    different pore structure. Gypsum with its complex pore structure, increased its
    moisture buffering, due to the higher impact of temperature on liquid transport. The
    RH and temperature gradient activated capillary transport and surface diffusion,
    when gypsum was subjected to simultaneous square wave variation. On the contrary,
    the moisture buffering capacity of clay was reduced probably due the combined effect
    of the saturation of macro-pores at high RH and impact of low temperature on the
    hygric properties."

    The paper does look at performance of woodfibre board in the test room.

    It's clear from this phd dissertation that the moisture buffering performance of the materials is not just intrinsic but also depends on outdoor humidity as well as indoor temperature and humidity patterns of variations.

    Please don't shoot the messenger, but I do encourage a read: https://researchportal.bath.ac.uk/en/studentTheses/understanding-moisture-buffering-effects-in-the-indoor-environmen
    •  
      CommentAuthorfostertom
    • CommentTime5 days ago
     
    Good stuff - thanks v much. Some revision of rules-of-thumb happening here.
    •  
      CommentAuthordjh
    • CommentTime5 days ago
     
    "Repulsive electrostatic forces also control the long-range swelling of clays in water.
    Most naturally occurring clays are composed of lamellar aluminosilicate sheets about 1 to
    2 nm thick whose surfaces dissociate in water giving off Na þ , K þ , and Ca 2þ ions, and when
    placed in water they can swell to more than 10 times their original volume (Norrish, 1954).
    The swelling of clays is, however, a complex matter and also involves other forces at
    surface separations below about 3 nm (van Olphen, 1977; Pashley and Quirk, 1984;
    Kjellander et al., 1988a, b; Quirk, 1994)."

    ... from the Israelachvili book I linked to. The sheet-like structure of clay is fundamental to how it behaves.

    Clay swells in water. Sand does not. Clay buffers moisture. Sand does not.

    Even the well-known gardening test to distinguish clay soils from sand etc uses the different behaviour to work.
  3.  
    Whoa, chill out! Take a holiday, go to the beach!

    The very best sand for sandcastles is damp, and it will hold itself in intricate shapes because of the "electrostatic forces" (sic) between the layers of water adsorbed onto the grains. Dry sand just slumps, as does too-wet sand where the pores are filled with absorbed water.

    Sand swells when it absorbs water. If you look down at your bare feet walking on a wet beach, they are surrounded by a ring of dry sand, because when you compress the sand vertically, the previously interlocked grains rearrange to occupy more space horizontally. This helps the sand swell more and absorb more intergranular water. If you move your foot up and down repeatedly, the sand absorbs so much water it 'liquifies' - this is a hazard to buildings in earthquake zones.

    It's fortunate that sand can buffer water by ab/adsorbtion because very many people draw their drinking water from sandstone aquifers, although sometimes that causes shrinkage. Concrete wouldn't work without the sand buffering the water that is required to remineralise the cement.

    Clay does the same things, only more so, because it has finer grains (I may have mentioned that) and so each kg of clay contains many more m³ of adsorption surface.

    Gardeners will tell us that it's not only the total ad/absorption capacity that matters (clay is good), it's also the ability to move water in and out quickly (sand is good). Mix them together for happy plants.

    Enjoy the holidays :bigsmile:
    •  
      CommentAuthordjh
    • CommentTime4 days ago
     
    Let's go back to the beginning
    Posted By: djh
    Posted By: WillInAberdeenClay is like sand, only the grains are smaller. The spaces inbetween the grains can absorb and adsorb liquids and gases.
    No, clay is like mike1 said, lots of platelets. Sand is three-dimensional grains.
    We still haven't managed to convince you of that apparently so here's some pictures of various types of sand:
    https://smallpond.ca/jim/sand/micrographs/
    and here's some of clay:
    https://ceramicsweb.org/micrographs.html

    As you rightly say, clay particles are a lot smaller but do you really still insist that they are similar?

    And then right at the end you say:
    Posted By: WillInAberdeenClay does the same things, only more so, because it has finer grains (I may have mentioned that) and so each kg of clay contains many more m³ of adsorption surface
    So these 'same things' are why building regs have the same regulations about building on clay and on sand, right? Oh wait, they don't! They treat them completely differently because sand and clay behave completely differently. And you even confirm that yourself:
    Gardeners will tell us that it's not only the total ad/absorption capacity that matters (clay is good), it's also the ability to move water in and out quickly (sand is good). Mix them together for happy plants.

    Clay holds water. Sand drains well. Same behaviour, obviously.

    Take a lump of clay. Roll it flat. Do the same with a lump of sand. Good luck with that. Leave them to dry for a week. Pick up the sheets of clay and sand. Again good luck with that. Put them in a kiln and heat to about 1000°C. Take out the clay tile and the heap of loose sand. Sand and clay behave the same. Only in your dreams.
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press