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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    •  
      CommentAuthorDamonHD
    • CommentTimeJan 18th 2011
     
    None visible at all in the room where the drylining is.

    Upstairs in the bedrooms, yes, on the windows in the mornings. None visible anywhere else other than the bathroom after a prolonged bath/shower. We ventilate/air such rooms by opening the window for an hour with the rads off and the door shut usually. Running a dehumdifier makes the air noticeably dryer/sharper but does not remove a large amount of moisture (as evidenced by what ends up in the output bucket) and an RH meter never shows what I assume to be outrageous values (ie usually well under 80%).

    Does that answer your question ST?

    Rgds

    Damon
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 18th 2011
     
    Damon
    Yes it does, thanks.
    I don't have any more issue with condensation than you have, and I suspect that the majority of households don't either. Only household that have mould/damp/condensation problems need to do something about it, but then that is a self selecting group and cannot be used as evidence that all households are the same.

    I am thinking about going the MVHR route when I have finally sorted out all the draughts, not that many to go now.
    • CommentAuthorTimber
    • CommentTimeJan 18th 2011
     
    Damon, it might be worth doing some retro-spective condensation risk calcs to see if there might be an issue. How much insulation was between the existing timber studs etc, before the aerogel backed plasterboard was applied?

    Timber
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 18th 2011
     
    Difficult to tell. Between 25mm and 50mm maybe. We simply didn't expect a membrane of any sort, just possibly an insulating quilt of some sort in the void, maybe. And the north and west walls may not be the same as one is brick faced and the other with a mixture of hanging tiles and siding.

    One reason for only doing one room is that there is not very far in any direction for moisture to escape into the existing structure or outside, so while build-up is possible, I hope that I've kept risks to a minimum given my general level of ignorance.

    If I do any more extensive works, eg EWI, I'd get a grown-up in to do the sums.

    (For the moment I'm topping up my loft insulation a bit to take it definitely over 270mm everywhere as this year's minimal improvement effort.)

    Rgds

    Damon
    • CommentAuthorTimber
    • CommentTimeJan 18th 2011
     
    Ok.

    It is interesting to note that timber frame walls havn't really changed much over the years in their principal. They have just got thicker with more insulation.

    The difference in cladding shouldn't effect the timber frame wall bit itself. The cladding, typically has no bearing on the loadbearing timber wall itself.
    •  
      CommentAuthordjh
    • CommentTimeJan 19th 2011
     
    Posted By: TimberIt is interesting to note that timber frame walls havn't really changed much over the years in their principal.

    Though I think they've stopped infilling with wattle and daub now in most parts of the country :bigsmile:
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 19th 2011
     
    Only do to a shortage of cows to provide some of the material...

    Rgds

    Damon
  1.  
    Posted By: DamonHDOnly do to a shortage
    Oh gosh, you're writing "due" in the way it's pronounced in the US: "do".

    Paul in Montreal.
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 19th 2011
     
    Oh bother (as the Cyborgs said when they accidentally assimilated Winnie the Pooh), I'm turning into a Merkan.

    Rgds

    Damon
    • CommentAuthorTimber
    • CommentTimeJan 19th 2011
     
    djh - haha, yes my comment was aimed at 'modern' studwork timber frame buildings.
  2.  
    Posted By: TimberViking - You said "Water Vapour coming from the inside the house can condense on the cold side of the timber frame, the ventilated cavity is necessary to dry this moisture."

    That is sort of correct and wrong at the same time. Condensation shouldn't form on the sheathing on the outside of the timber frame. The vapour control layer on the warm side of the insulation is there to reduce the moisture vapour passage though the wall to a level where condensation won't form.

    The cavity is not there to allow condensation to evaporate, it is there to allow moisture vapour that has safely made it though the wall dissipate to the outside world, rather than condensing on the brickwork cladding.

    As for condensation in roofs, there should be eaves vents that provide ventillation air into the roof. This air transports moisture vapour away from the roof back to the outside. All roofs (except TRUE warm roofs) require ventillation between the insulation and roof covering. Timber

    Many vapour control layers fitted in older houses don't stop much vapour because they weren't fitted well.
    If Damon has no cracks or holes in his plasterboard wall, then the amount of vapour coming coming through the wall by diffusion is minimal, (less than 1% of what gets through a 1cm hole). Pumping the cavity and externally insulating the wall warms the timber frame up so you can treat it like an unventilated warm roof.
    Saying that water vapour coming through a wall doesn't condense on the outer sheating board or on the external wall is like saying that vapour never condenses on the timbers of cold roofs that are ventilated in cold weather.
    • CommentAuthormattwprice
    • CommentTimeMay 19th 2012
     
    In a similar but different vein, I have found my 1930's wall construction to be largely rough coat render externally over a brick external leaf. Internal leaf is a mix of brick and clinker with approximately a 20mm cavity. The two leaves are tied with headers across the cavity. I suspect that the cavity may have quite a few snots effectively bridging it. It seems to me that the cavity at 20mm will be too small to have insulation pumped into it. Equally it will be impossible to pump concrete into it to close the cavity prior to what I would like to do which is external wall insulation. I am now thinking that I may just be in the unfortunate position of not being able to effectively insulate it unless I do so internally and having just totally renovated (yes stupidly without thoughts beyond 'I will insulate externally at a later date when I can afford it'.. I had other things on my mind like the birth of my first child and gf currently residing at the other end of the country till i can get the house finished!) the house I am unwilling to now insulate internally. I am now thinking of leaving the walls as they are, (I have removed the ground floor joists due to wood worm and insulated and installed UFH over a new ground bearing slab. The loft will for now have 400mm GF between and over the new 200mm joists I installed ready for a subsequent loft conversion) and just accepting the house will never be as good as I would like it. Instead I may build a new smallish passive house standard adjacent to this one before selling both and building or buying and renovating a different property afterwards.. UNLESS... Anyone has any bright ideas? I really would like to insulate externally and think I can get maybe up to 150mm EPS on the walls without fouling the gutters. I'm just concerned about that cavity!
    • CommentAuthorborpin
    • CommentTimeMay 19th 2012
     
    Posted By: TimberIt is interesting to note that timber frame walls havn't really changed much over the years in their principal. They have just got thicker with more insulation.
    I think this is actually one of the problems. No one has attempted to extend the TF principle. I was keen on a TF with external insulation so that it breathed in, but would have had a hard time getting it past the BCO without a cavity between the TF and the insulation which defeats the object! I'm going instead for a light steel frame with external insulation; to all intents and purposes the same but steel instead of timber. No internal VCL just breathe.

    Damon, If you have any sort of internal VCL I suggest that you have a risk of trapping moisture; a new build would be a different matter. I doubt you can do this, but how about being really radical and taking down the brickwork and putting up a breathing insulation (fibre board?) and then external render with a cavity below the render?
    •  
      CommentAuthorDamonHD
    • CommentTimeMay 19th 2012
     
    There is still the void between the brickwork and the timber frame, plus I have only taken the new VCL to the ceiling/floor: there is still the ability for moisture to migrate out between floors and to the loft I hope. But yes, I might have done things differently in the light of more information, and if we continue with our IWI I will try doubly hard to ensure that moisture can escape outwards and the (new) VCL is well toward the warm side.

    Just had Ed Davey round for tea discussing difficulties of TF IWI and solid wall IWI/EWI this afternoon, as it happens! B^>

    Rgds

    Damon
    • CommentAuthorTimber
    • CommentTimeMay 19th 2012 edited
     
    Posted By: borpin
    Posted By: TimberIt is interesting to note that timber frame walls havn't really changed much over the years in their principal. They have just got thicker with more insulation.
    I think this is actually one of the problems. No one has attempted to extend the TF principle. I was keen on a TF with external insulation so that it breathed in, but would have had a hard time getting it past the BCO without a cavity between the TF and the insulation which defeats the object! I'm going instead for a light steel frame with external insulation; to all intents and purposes the same but steel instead of timber. No internal VCL just breathe.

    Damon, If you have any sort of internal VCL I suggest that you have a risk of trapping moisture; a new build would be a different matter. I doubt you can do this, but how about being really radical and taking down the brickwork and putting up a breathing insulation (fibre board?) and then external render with a cavity below the render?


    Things are moving forwards. See the 5th Edition of Timber Frame Construction by TRADA. TRADA are also going to publish a 'modern/alternative methods of timber construction'. Both of these try to take timber frame to the next level, wilst maintaining known good practise for durability of timber.

    In addition and regarding VCL, please make use that the thought of VCL doesn't bring up the though of a sealed plastic bad. VCLs are so much more than that. I really truely hope that 'people' understand the VCL in a lot more detail.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 19th 2012
     
    Any special discounts going? I am sure they have an educational budget and they will get some feedback pretty rapidly from here :wink:
    • CommentAuthorborpin
    • CommentTimeMay 20th 2012
     
    The current design actually encourages IWI on a TF as a VCL inside and a breathable membrane out is how they are designed. My argument for new TF is that the breathing should be done inwards - no VCL and insulation external to the frame (and inside it).
    • CommentAuthorborpin
    • CommentTimeMay 20th 2012
     
    Posted By: TimberThings are moving forwards. See the 5th Edition of Timber Frame Construction by TRADA. TRADA are also going to publish a 'modern/alternative methods of timber construction'. Both of these try to take timber frame to the next level, wilst maintaining known good practise for durability of timber.
    In summary, what are they proposing? Thicker frames or mounting insulation Internally or externally? Thicker frames are pointless (from a construction point of view) and use more timber resources.
    Posted By: TimberIn addition and regarding VCL, please make use that the thought of VCL doesn't bring up the though of a sealed plastic bad. VCLs are so much more than that. I really truely hope that 'people' understand the VCL in a lot more detail.
    Teach us then.....
    • CommentAuthorEd Davies
    • CommentTimeMay 20th 2012
     
    Posted By: borpinI'm going instead for a light steel frame with external insulation; to all intents and purposes the same but steel instead of timber. No internal VCL just breathe.

    I don't like the use of the word “breathe” like this but, other than that, fine.

    My argument for new TF is that the breathing should be done inwards - no VCL and insulation external to the frame (and inside it).

    What do you mean by “breathing...inwards”? Do you mean that any moisture which comes to be in the wall leaves via the inside of the house rather than outwards into the big wide world? If so, how would that work in a UK climate?
    • CommentAuthorDarylP
    • CommentTimeMay 20th 2012
     
    ... clad/wrap the TF (and external insulation) in VCL on the outside. This can be in the form of an air barrier as well to provide air tightness?
    You then keep the TF at room temps/humidity, thus mitigating any interstitial condensation issues.

    We have used this detail on a TF dwelling that had wall U-value of 0.1, and the next one will be around 0.08 we hope....

    Cheers...:smile:
    • CommentAuthorTimber
    • CommentTimeMay 20th 2012 edited
     
    Posted By: DarylP... clad/wrap the TF (and external insulation) in VCL on the outside. This can be in the form of an air barrier as well to provide air tightness?
    You then keep the TF at room temps/humidity, thus mitigating any interstitial condensation issues.

    Cheers...:smile:" alt=":smile:" src="http:///forum114/extensions/Vanillacons/smilies/standard/smile.gif" >


    Urm, receipe for disaster!!

    The VCL needs to be on the warm side of the insulation, not the cold side. Keeping the timber frame warm is a good idea though. True warm wall construction is a good thing (if done correctly).
    • CommentAuthorTimber
    • CommentTimeMay 20th 2012
     
    Posted By: borpin
    Posted By: TimberThings are moving forwards. See the 5th Edition of Timber Frame Construction by TRADA. TRADA are also going to publish a 'modern/alternative methods of timber construction'. Both of these try to take timber frame to the next level, wilst maintaining known good practise for durability of timber.
    In summary, what are they proposing? Thicker frames or mounting insulation Internally or externally? Thicker frames are pointless (from a construction point of view) and use more timber resources.
    Posted By: TimberIn addition and regarding VCL, please make use that the thought of VCL doesn't bring up the though of a sealed plastic bad. VCLs are so much more than that. I really truely hope that 'people' understand the VCL in a lot more detail.
    Teach us then.....


    In the 5th Edition, there is an insulated service void on the inside of the standard timber frame. This allows two things to be done. Firstly you can fit more insulation in there (getting down to about 0.16 W/m2K depending on insulation specs) and secondly it means that the VCL (which is also acting as an air barrier) remains un-broken by service penetrations. If you install the battens forming the internal service void horizontally, you reduce the repeat thermal bridging down to node points only.

    As for teaching... I just would like people to think of Air barriers and VCLs separately, and not to think plastic bag the moment either of them are mentioned. Granted, in a lot of cases the VCL and Air Barrier are the same sheet of plastic, but other times they are different layers and materials other than plastic, e.g. reverse wall construction.

    With the design to improve air tightness, I am seeing more and more architects just wrapping everything in plastic for no good reason. Very bad from a timber durability point of view.
    • CommentAuthorEd Davies
    • CommentTimeMay 20th 2012 edited
     
    Posted By: DarylP... clad/wrap the TF (and external insulation) in VCL on the outside. This can be in the form of an air barrier as well to provide air tightness?
    You then keep the TF at room temps/humidity, thus mitigating any interstitial condensation issues.

    Posted By: TimberUrm, receipe for disaster!!

    My thought, too. The air in the outer part of the insulation, next to the VCL, is close to outdoor air temperatures but near indoor absolute humidity (strictly, partial pressure of water vapour). Why would anybody think that condensation wouldn't happen there?
    • CommentAuthorDarylP
    • CommentTimeMay 20th 2012
     
    .. the outer layer insulation is Celotex XR4100. Hardfixed to the OSB sheathing.
    The dewpoint analysis showed no issues.
    What level of water vapour can migrate through the OSB and foil faced PIR, do you think?

    Cheers...:confused:
    • CommentAuthorTimber
    • CommentTimeMay 20th 2012
     
    Not much, but you still DO NOT put a vapour impermiable membrane on the cold side of the insulation.
    • CommentAuthorDarylP
    • CommentTimeMay 20th 2012
     
    ... it isn't... the Celotex 'inside' foil-face forms the vapour impermeable layer, and it is on the inside of 100mm PIR.

    The Celotex sheets are butted together and glued, then taped.
    It is this detail that is the crux, get it wrong and you will run the risk of condensation forming inside the TF. However if you are on top of site detailing, and keep gaps between sheets to a minimum, the results should be good.

    I hope to have some real-world figures in a years time....after a year of occupancy!

    Cheers...:smile:
    • CommentAuthorEd Davies
    • CommentTimeMay 20th 2012 edited
     
    Posted By: DarylP... it isn't... the Celotex 'inside' foil-face forms the vapour impermeable layer, and it is on the inside of 100mm PIR.

    Ah, so you were fibbing; the VCL is on the inside. Fine.

    I think inside-to-out timber frame/VCL/insulation is a great scheme, as you say, keeping the TF in warm, and that's what I plan.
    • CommentAuthorborpin
    • CommentTimeMay 20th 2012
     
    Posted By: Ed Davies
    Posted By: DarylP... it isn't... the Celotex 'inside' foil-face forms the vapour impermeable layer, and it is on the inside of 100mm PIR.

    Ah, so you were fibbing; the VCL is on the inside. Fine.
    No the celotex (foil faced PIR is outside the frame. This is sealed so effectively forms an air and vapour barrier. As it is PIR there is no air that can hold moisture (so nothing to condense). The inside of the PIR must be thick enough to ensure that there is no risk of condensation on this face. Inside is the TF which is warm enough so that any moisture will not condense and the air will be circulated by the MVHR to reduce the RH.

    So no VCL in it's traditional form.
    • CommentAuthorborpin
    • CommentTimeMay 20th 2012
     
    Posted By: DarylP... clad/wrap the TF (and external insulation) in VCL on the outside. This can be in the form of an air barrier as well to provide air tightness? You then keep the TF at room temps/humidity, thus mitigating any interstitial condensation issues.
    Really interested. What did you need to do to convince the BCO? Did you put a 'breathable' membrane on the outside of the TF? I was considering this along with Icynene between the studs of the TF.
    • CommentAuthorTimber
    • CommentTimeMay 20th 2012
     
    Borpin - still not good, and still need clarrification of the VCL and what 'inside' means.

    Remember VCL and warm side of insulation (not structure). In a true warm wall you could construct standard timber frame wall (38x89mm studs sheathed outside with 9mm OSB3. Then on the OUTSIDE of the OSB install a polythene air and vapour conrol layer. Lap, tape and seal all joints. Then fix rigid (foil faced or not) insulation to the outside of that then cavity and cladding.

    By only gluing and taping the outside of the joints, you still have a layer on the outside of the insulation with a higher moisture vapour resistance than that on the inside. If you put any insulation between the studs in the timber frame, it *may* make things worse.

    I am not saying there will 100% be problems with your proposed system, but it does fly in the face of convention.
   
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