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Green Building Bible, Fourth Edition
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    • CommentAuthormarsaday
    • CommentTimeAug 26th 2017
    Ok, it seems i am going to have to build what i want at 9m wide and 3.3m in length (not 4m) to meet this 30sqm rule.

    The BC guy is private, so possibly has a different slant to how the local council would see things. He seemed to think i should just go for 30sqm to avoid all the hassle with the regs.

    If i really want that extra space i suppose i could do the two buildings as someone earlier suggested.

    My room sizes are going to reduce down by about 30cm on each dimension, however. So my usable space is actually going to be 26sqm.
    • CommentAuthorsnyggapa
    • CommentTimeAug 26th 2017
    do check whether the BC limit applies to floor space (habitable) or overall footprint. I don't know, but if it's habitable space then you may be OK on your original dimensions
    • CommentAuthorsnyggapa
    • CommentTimeAug 26th 2017
    update to above. from what I can see


    “floor area” means the aggregate area of every floor in a building or extension, calculated by
    reference to the finished internal faces of the walls enclosing the area, or if at any point there
    is no such wall, by reference to the outermost edge of the floor;

    so as long as you meet this criteria:

    Small detached buildings
    1. A detached single storey building, having a floor area which does not exceed 30m2
    , which
    contains no sleeping accommodation and is a building—
    (a) no point of which is less than one metre from the boundary of its curtilage; or
    (b) which is constructed substantially of non-combustible material.

    where floor area seems to be defined as internal floor area, you should be OK up to 30m2 of internal "floor area", so you can go bigger than 9 x 3.3
    • CommentAuthormarsaday
    • CommentTimeAug 26th 2017
    Ok, thanks i will check with the actual council BC next week.
    • CommentAuthorsnyggapa
    • CommentTimeAug 29th 2017
    and if he disagrees, point him at the legislation above !

    looks firmly like you can have 30m2 of usable floorspace, so build your 9x4 slab and make the walls thick enough to make the floorspace 30m2 :)

    good news is that you can then use thick walls and cheap insulation...
    • CommentAuthormarsaday
    • CommentTimeAug 30th 2017
    Yes it is internal floor space. I was planning on using 125mm timber for the walls. So i will use 100mm rigid insulation in the office bit.
    If you do use 100mm insulation, could you use 75 between and 25 over the studs? Otherwise you have an unmitigated thermal bridge at every stud. That way, if you use foil-backed insulation, you can also just tape the foil as VCL.
    • CommentAuthormarsaday
    • CommentTimeAug 30th 2017
    Possibly, but how much would it really affect the actual feel to the body while you are in there?

    This is going to be an occasional space which will be heated with an electric heater. I am not building it for my own needs, just thinking about the possible resale value of the house as these offices in the garden seem pretty popular.
    • CommentAuthorsnyggapa
    • CommentTimeAug 30th 2017
    if you need the walls thick anyway to get past the 30m2 thing, you could use 200mm of rockwool instead of the rigid insulation. 100 in the studs and 100 over the top. probably cheaper too
    • CommentAuthormarsaday
    • CommentTimeAug 30th 2017
    I think all i could use if soft would be 100 between the studs (in the walls and in the roof section). This insulation in the walls and floors will actually be much cheaper than the rigid, so i will prob go for this.
    '' This insulation in the walls and floors will actually be much cheaper than the rigid, so i will prob go for this.''

    ..and potentially about half as effective in terms of lambda value.

    I see some advantages in quilt or 'fluff' rather than rigid plastic, in timber frame, but 100 quilt between studs will not excite anyone. I would strongly support the idea of a secondary non-load-bearing frame to allow 200 (or more). I realise this building won't be covered by Bldg Regs, but it may still be asked to 'perform', even if it's with a future owner.
    • CommentAuthormarsaday
    • CommentTimeAug 31st 2017
    But it is a big shed, with a little office at one side. The energy requirements are going to be very low. Beefing up the walls will waste the space for storage of tools etc. We put 100 soft fill in new wall extensions, so why isn't it good enough for a barely used shed/office. On cost grounds it will save me a lot.
    IMO go for the 100 soft fill It won't make much difference (i.e. you won't recover the outlay) for an occasionally used office and if life changes you can always add a bit of IWI to the office. For resale value 100 soft fill for most people will class as 'insulated' and I don't think (at the moment) any more will get you any brownie points.
    Posted By: Peter_in_Hungary...if life changes you can always add a bit of IWI to the office. For resale value 100 soft fill for most people will class as 'insulated' and I don't think (at the moment) any more will get you any brownie points.

    If a new situation applies, whoever it applies to can decide on relative priorities & add IWI, or even EWI[1] if they really want to maximise office (or storage) space.

    [1] From the point of view of the office, when it comes to reviewing the internal wall, EWI would just mean adding to the storage side of the partition rather than the office side.
    • CommentAuthormarsaday
    • CommentTimeSep 1st 2017
    I agree Peter. Planning on using ply sheets oiled for the internal finish, so pretty easy to unscrew these and add insulation later if really required.
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