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Housing - New Build: Best type of Timber Frame????

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  1.  
    • CommentAuthorPugliese
    • CommentTimeOct 19th 2011
     
    If you have read my post on the Newbie forum you will understand that we are inexperienced self builders seeking guidance.

    Plot with full PP has been acquired and house redesigned and currently in with the planners. We have decided on Timber frame but am unsure about the type we should choose. I have narrowed the choice down to:-

    a) 140x38mm with 600mm centres, clad with 9mm OSB 3 sheathing board and Corovin breather paper, 140mm Warmcel 500 Insulation plus 50mm of Celotex to bring the u-value down to 0.16

    or

    b)Warm wall construction of 89x38mm with 400mm centres, clad with 9mm OSB 3 sheathing board made airtight down to 0.6 and breather paper, 100mm rockwall insulation within the frame and 200mm EPS outside bringing u value down to 0.10 and of course super airtight.

    Both are similar cost and I have to say I am drawn to the warm wall construction because of the superior thermal properties, although with this method there is the additional cost of MVHR but that is something we want.

    So I would just like to know what the pros & cons are of each approach.

    Thanks in advance
    • CommentAuthorDarylP
    • CommentTimeOct 19th 2011
     
    .... well,

    We have a client who is building to CfSH Level 3, using timber frame:
    89mm studs at 400 c/cs, insulation between the studs, sheathed with OSB, sealed all round, then 'clad' with 150mm-200mm rigid insulation.
    They are off mains gas, no chance of solar due to overshading from nearby trees.
    We suggested a 'fabric first' approach, and then address the DHW needs with an oil condensing boiler.

    The timber frame is kept within the heated enevlope, enabling good airtightness, and minimising thermal bridging.

    Cheers...:smile:
    • CommentAuthorqeipl
    • CommentTimeOct 19th 2011
     
    b)
    • CommentAuthorPugliese
    • CommentTimeOct 20th 2011
     
    Well so far it would seem a thumbs up for b) but it would be good to have some feedback from anyone who has used either system
  5.  
    Hi Pugliese, I've used the warm stud method in close to 20 houses with good results, you're welcome to drop over to Irl and have a look at some of the finished products?
    • CommentAuthorGreenPaddy
    • CommentTimeOct 20th 2011
     
    Pugliese,

    could you explain to me why the first option including the 50mm kingspan externally would not warrant the use of MVHR but option (b) would? As I understand building regs, it is recommended that alternative forced ventilation is installed where build quality takes the air leakage rate to below 5m3/m2hr (which isn't that great really).

    I built my house with a very similar system to option (a), but would now recommend option (b), due to the moisture permeability of those materials. For me, a well sealed house and MVHR is a no-brainer.

    Regards, GreenPaddy.
    • CommentAuthorTimber
    • CommentTimeOct 20th 2011
     
    Option B looks good to me.

    Bit tired at the moment, but will provide a more thought out response tomorrow.

    The little details will make all the difference. Remember timber need to be kept dry, but also allowed to breathe. Whatever solution MUST keep these aspects in mind.

    A cavity between the cladding and timber frame is also a must (in my opinion).
    • CommentAuthorPugliese
    • CommentTimeOct 21st 2011 edited
     
    Posted By: GreenPaddyPugliese,

    could you explain to me why the first option including the 50mm kingspan externally would not warrant the use of MVHR but option (b) would? As I understand building regs, it is recommended that alternative forced ventilation is installed where build quality takes the air leakage rate to below 5m3/m2hr (which isn't that great really).

    I built my house with a very similar system to option (a), but would now recommend option (b), due to the moisture permeability of those materials. For me, a well sealed house and MVHR is a no-brainer.

    Regards, GreenPaddy.


    Hi GP

    Company offering option a) have been quite evasive when I have asked them to confirm their maximum air leakage rate post construction. I am currently waiting for an answer but all they have confirmed so far is that they will guarantee a pass of the Building Regs Part L 2010 which is, that to pass an air leakage test, a dwelling must achieve an air permeability result of 10 m3/(h.m2) - Might as well leave the window open:bigsmile: hence no requirement for MVHR.

    Regards
    P
    •  
      CommentAuthorDamonHD
    • CommentTimeOct 21st 2011
     
    I thought that the max air leakage came down by half in (Oct?) 2010...

    Rgds

    Damon
    • CommentAuthorTimber
    • CommentTimeOct 21st 2011
     
    ^No. Still 10
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 21st 2011
     
    10m^3.h^-1.m^-2
    So that is 12kg of air per square metre per hour of in real language 12kg.m^-2.h^-1.h^-1.
    Air typically has a SHC of 1.012 kJ.kg^-1.k^-1 (0.000281111kWh.kg^-1.K^-1)

    So my kitchen is currently loosing 0.02 kWh.h^-1 with the window open.
    Oddly enough my fridge has churning out a mean of 0.021kW over the last 17 hours (more of this later).
    • CommentAuthorGreenPaddy
    • CommentTimeOct 21st 2011
     
    ST,

    just to check, have you allowed for the temp diff?

    assuming 0.000281 kWh/kg/K at 1.2kg/m3 at 10m3/m2/h infiltration rate gives 0.00337 kWh/m2/K

    Assume your kitchen is 16m2, and delta T = 15, so 16x15x0.00337 = 0.8kWh

    So perhaps your kitchen is losing 800W of power, even with the window closed?

    To get back to the actual sealing issue for a house, then for a 200m2 house which hits 10m3/m2/h (which some have argued is a rather arbitrary measurement, but at least some yard stick)...

    ...the house could be losing almost 700W for each degree of temp diff to outside, just cause it hasn't been designed and then very importantly assembled well. Mid winter that's 2kW.

    Hope my figures above are correct:confused:

    regards, GreenPaddy.
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 21st 2011
     
    Kitchen is 9.8m^2 and temp difference was 7K

    0.00028*9.8*7=0.0192

    Currently 12 C outside and 19 C inside, window open.

    I often make errors in my arithmetic :shamed:
    • CommentAuthorborpin
    • CommentTimeOct 21st 2011
     
    I'm looking at b) but a 'standard' TF of 95x45 9mm OSB all joints glued and nailed, filled with warmcell, 200mm EPS externally.

    HTH
    • CommentAuthorGreenPaddy
    • CommentTimeOct 23rd 2011
     
    Borpin,

    looking at something similar too, but wondering what has made you choose warmcell frame fill rather than more EPS?

    Regards, GreenPaddy.
    • CommentAuthorborpin
    • CommentTimeOct 23rd 2011
     
    Warmcell instead of more EPS for speed (cutting up EPS) and the warmcell, damp sprayed, will provide additional air tight sealing that can never be achieved with EPS pushed in.

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