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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    Building a small office within a business unit

    Walls are made from 4x2 2.4m c24 studs at 400 centres and noggins, with a 4x2 sole plate anchored to the slab. Wall plate is 4x2 with an extra on top so essentially 4x4

    Roof joists will be 6x2 at 400 centres for the ceiling and above office light storage with a span of just 2.4m. One end of joists will be attached to 6x2 timber secured to concrete beam with resin and anchors. The other end will need to be fixed to the timber frame wall.

    Do these just sit on top of the 2 layers of 4x2 and then use a restraint or can I use a joist hanger so the bottom of the joist will sit 2" below the top of the studs?

    Do the walls need to be boarded with OSB for strength? If so what size? 18mm? 22mm? 12mm? As it's an office space within a unit I was thinking of PB inside and OSB on the outside with 100mm PIR in-between. Any other detail you can think of?

    Any diagrams or links would be appreciated

    As I'm looking at it now the walls are up I'm wondering if I should have looked at sips panels instead.
    Sounds very robust for an internal cabin. C24 stud at 400cntrs. I build house extensions with C16 at 600cntrs.

    The OSB sheathing is for racking. You won't have wind loading, and I'm guessing it's got corners and not massively long sides. Put what you want on the walls.

    Rest the ceiling joists on the wall headbinder, so you get the full 2.4m ceiling height, cheek nail and use truss clips too if you feel so inclined. Or you can joist hanger, and have the ceiling height a bit less.

    Personally, I'd put earthwool between studs, and rigid board over the outside, then plasterbrd over that. Leaves the inside stud void capable of tacking services. I'm guessing you don't need to worry about a VCL, or a VPM for that matter.
    Excellent tips there. I thought it may be overkill

    Excuse the ignorance but if the studs are 2.4 and the sole plate is 100 X 50, two top plates so another 100mm height.... Therefore ceiling height if joists rest on top will be 2.55m?

    I won't need any vcl I wouldn't think but as the unit itself is unheated I'd need to minimise any thermal losses into space. Currently have a heat pump in the main office. This will be coming off the main room. I was thinking a simple method of a small fan to circulate warmer sure into this room from the main room
    Usually the studs would be cut at say 2250, so u/side of ceiling timber is 2450 (sole plate, bottom runner, top runner, headbinder, all nominally 50mm, though usually 45mm if regularised treated.

    Then brandering (battening with 25x50) plus ceiling plasterbrd brings it down to say 2415, which is perfect height for 2400 plasterbrd sheets, with a small gap to the floor (damp/spillages). If the wall is more than for a 2400 board, then you have waste going to say a 2800 sheet, plus the time cutting. If you ply line it, check the ply dims are sometimes 1220x2440, so have to start ripping down the sheets to match the stud cntrs.

    Depending on the heat loss, it may be adequate just to circulate the warmed air from the main heated space. I'd want a recirc fan anyway I think, to bring some "fresher" air into the smaller area. Worst case, and it's a not quite warm enough, add a small elect panel heater. If it doesn't lose much heat, you won't have the elect heater on very much. You might even find friends or relatives have on old elect fan heater knocking about in the attic. Use that for the hopefully few periods when the gain from the main area is not quite enough.
    Excellent advice, many thanks
    I'm only going to insulate in between the studs, so 100mm lift insulation up to the job? Pb on the inside, trapped 3 and jointed and then just 11mm OSB outside to prevent anything knocking through or marking
    • CommentAuthorGreenPaddy
    • CommentTimeNov 11th 2021
    "up to the job?" - that depends what the job is.

    What level of heat loss is acceptable to you?
    What's the temp diff across the wall (ie. is the area on the outside of these walls going to be very cold?) If it's inside an enclosed space, is that enclosed space heated in any way?

    I'm a bit lost as you started talking about SIP's panels, which would likely have PUR at lambda 0.021 ish, but now suggesting loft roll at likely lambda 0.044 W/mK.

    Check out the cost comparison of say cement board for the outside versus OSB. Locally OSB has gone from £8 a sheet to nearly £30.
    I'd like to learn a bit more about timber framing, savvy good resources?

    Cement board sounds good, but I thought OSB was specifically for strength?
    • CommentAuthorGreenPaddy
    • CommentTimeNov 12th 2021
    I can't honestly say I know the racking capabilities of cement board, but I'd be surprised if it wasn't as good if not better than OSB. But this is an internal partition wall, and not a long run(?) so racking isn't an issue.

    OSB would be the norm of course for any timber frame sheathing, but at the ludicrous cost escalation of the last 6 months, alternatives might well be considered. Cement/render bord gives the robust surface you mentioned, but will also finish much better than OSB, which even when painted, still looks like wheatabix (other cereal foods are available:bigsmile:)
    No it's not an internal partition wall it's essentially load bearing external wall but within a storage unit
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