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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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    • CommentAuthorArtiglio
    • CommentTimeDec 27th 2020 edited
     
    Good evening

    Me again, thinking ahead i’m looking at the insulation specs that have been suggested to me. Having gone to a company that specialises in breathable systems as i have a mix of solid brick and flint walls with lime mortars, its not surprising the whole spec revolves around would fibre.
    However the roof structure is having a loft conversion and roof makeup is going to be pretty standard.

    Slate, batten, breathable membrane, counter battened, 180mm t&g sarking boards, mix of. 4x2 and 4 x 5 rafters pitched at 65 degrees. Ventilated at low and high level. The cost of wood fibre to get to buiding control requirements is pretty steep and I can get there much cheaper with celotex. I appreciate I’ll lose thermal mass and some sound deadening (added bonus of wood fibre i’m told).
    But will celotex cause any great problems, if needed could I add a top layer of wood fibre and mineral plaster to give a bit of moisture “buffering”.
    I’d much rather spend the money saved doing the masonry walls and suspended floors properly.
    Not trying to skimp rather get best value and make installation easier and quicker.

    Any insights much appreciated.

    Ps, a vapour control layer is allready specified.
    • CommentAuthortony
    • CommentTimeDec 27th 2020
     
    What U-value are you aiming at?

    Best bang for your buck with insulation is glass/rockwool/ecowool containing recycled material but that would increase thickness.

    Do you mean 4x2 and 5x2 rafters?
  1.  
    I would use standard EPS EWI for the walls if you can EWI.
    I have used this on a couple of my houses with stone/rubble walls and I have had no problems.

    If you have to IWI then this can be EPS backed plasterboard (purpose bought or made up on site (cheaper)).

    For the roof I would go for glass or mineral wool as I find it easier to get a good fit between timbers than when using board insulation.
    • CommentAuthorArtiglio
    • CommentTimeDec 27th 2020 edited
     
    Cheers Gents

    No the rafters are a mix of 4x2 and 4x5, its an oast house roof from around 1907. The room sizes are pretty generous and losing a bit of space is not an issue there are already some 4x4 purlins which makes adding the board under the rafters pretty straightforward and no loss of space in practical terms.
    The building is listed and council want a proven breathable system on the masonry walls if i’m to do any insulation, thicknesses in these rooms is a bit more critical and will end up somewhere between 60 and 120 mm. To be frank if I wasn’t doing it for myself i’d likely just insulate the roof spaces and forget the rest, instead,putting the cash into the wow factor for prospective buyers.
    The specs i’ve had suggested bring the insulation levels upto that would be required bty building control in a normal refurb ( though as its listed i could do next to nothing) , however all being well i’m here for the longterm and reasonable levels (ie close to those required by building regs) are where i’m aiming for but there will be more than a few areas where it’ll not be practicable, nothing can be added to the exterior, and some rooms are too small/ odd shaped to make thick iwi work whilst retaining the buildings history.
    Double glazing has been refused outright, so there’ll be secondary glazing where it can be made reasonably unobtrusive.
  2.  
    Posted By: Artiglioits an oast house roof from around 1907.

    Do you have round oast (if so lucky you 'cos the witches and ghosts can't hide in the corners) or is it square built?
    If round then board insulation won't work well and wool type will be needed, if square then the choices are better.
    Have the council defined what they mean by 'breathable'? I can't recall seeing Celotex being described as breathable anywhere.
    Rockwool between battens should work but usually IWI is fitted with a VCL as you say
    Posted By: ArtiglioPs, a vapour control layer is allready specified.

    and this is fitted on the warm side of the insulation to prevent condensation on the inside surface of the wall (but you probably know this already) I just don't see how the required VCL can be fitted but at the same time comply with the Council demand for a 'proven breathable system on the masonry walls
    • CommentAuthorArtiglio
    • CommentTimeDec 28th 2020
     
    Its a square oast.Managed to get the cowl up before xmas, it’s been in the way for months since i finished it. More than a few delays getting the oast stripped and reslated and then finding someone to do the leadwork. Apologies the earlier explanation was a bit confused, the roof structure is/will be ventilated (min 50mm air gap ventilation at low and high level) and so in that area there is no need for the insulation itself to be breathable, the breathability is required in respect of the masonry walls, the suspended ground floors and eventually the ground floor in what was the barn the oast is attached to.
    •  
      CommentAuthordjh
    • CommentTimeDec 28th 2020
     
    Just to throw another suggestion in - have you considered warmcel? You might be able to use it both for the walls and the roof.
  3.  
    Posted By: Artigliothe roof structure is/will be ventilated (min 50mm air gap ventilation at low and high level) and so in that area there is no need for the insulation itself to be breathable, the breathability is required in respect of the masonry walls,

    OK roof sorted - How do you get breathability on the masonry walls if as is usual you put a VCL on the warm side of the insulation? Never mind Celotex, Kingspan or other XPS as the insulation.
    •  
      CommentAuthordjh
    • CommentTimeDec 28th 2020
     
    Posted By: Peter_in_HungaryOK roof sorted - How do you get breathability on the masonry walls if as is usual you put a VCL on the warm side of the insulation? Never mind Celotex, Kingspan or other XPS as the insulation.

    (a) use a moisture-buffering insulation, such as woodfibre or Warmcel
    (b) use a variable permeability VCL such as Intello
    • CommentAuthorArtiglio
    • CommentTimeDec 28th 2020 edited
     
    As per djh , the masonry spec is using woodfibre bonded internally and finished with naumit plasters, no vcl in these areas, though a breathable water repellant treatment has been recommended for the outside surfaces, apparently its not noticeable once dried ( if thats the route i take a test area will be done first), expect its similar to a “masonry water repellant” i used on some old weathered chimney stacks i repaired /repointed, 4 years on they look fine.
    Suspended floors at ground level are another area to look at, designer would prefer to backfill and use asome sort of foam glass based system. The underfloor voids are currently poorly ventilated (older end has no ventilation but a 30” void under the joists, though floor has been replaced at some point as old timbers had rotted away, in newer end (1930’s void is only 7” but does have some ventilation) everything seems sound.
  4.  
    + another 1 for wood-fibre. Just spending my 'Christmas Holiday' preparing for the next round. Must just say again how easy Baumit plasters are to use - the only thing you really have to get used to is the speed - everything's a lot slower than 'pink'. Just off to mix some more!
    •  
      CommentAuthordjh
    • CommentTimeDec 29th 2020
     
    Posted By: Artiglioa breathable water repellant treatment has been recommended for the outside surfaces, apparently its not noticeable once dried

    I can vouch for that. I used some on the clay-paint-on-lime-plaster in our showers and it works.
    • CommentAuthorkristeva
    • CommentTimeJan 1st 2021
     
    Posted By: djh
    Posted By: Artiglioa breathable water repellant treatment has been recommended for the outside surfaces, apparently its not noticeable once dried

    I can vouch for that. I used some on the clay-paint-on-lime-plaster in our showers and it works.


    Which make is this. I'd be interested in that when I do my bathroom
    • CommentAuthorkristeva
    • CommentTimeJan 1st 2021
     
    Posted By: ArtiglioSuspended floors at ground level are another area to look at, designer would prefer to backfill and use asome sort of foam glass based system. The underfloor voids are currently poorly ventilated (older end has no ventilation but a 30” void under the joists, though floor has been replaced at some point as old timbers had rotted away, in newer end (1930’s void is only 7” but does have some ventilation) everything seems sound.


    The biggest problem with insulating a suspended floor is the belly ache of getting all the floorboards up. If your floors aren't original I guess that's not such a problem. I've only got a few of my boards up and even though it was necessary it felt like total vandalism. I was as careful as I could be and I hated every moment of it.
    •  
      CommentAuthordjh
    • CommentTimeJan 1st 2021
     
    Posted By: kristevaWhich make is this.

    You mean the water repellant? - Stormdry. The paint was Earthborn.
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