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Fundamentals: Long timber planks

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    • CommentAuthorEd Davies
    • CommentTimeJun 5th 2014
     
    C24 220x45. How long can I get it?

    I imagine 4.2 or 5.4 metre lengths are dead easy - timber merchants will have it to hand. Up to about 7.2 m shouldn't be too difficult. But what about a bit longer - I need about 8.2 m or so lengths? I'm imaging it'd need pre-ordering and there'd be a bit of price premium per metre. Is that right or would it be unobtainium?
  2.  
    special order usually above 7.2
    • CommentAuthorowlman
    • CommentTimeJun 5th 2014
     
    At that length, if straightness is important, IMO rather go for glulam. You may have to compromise on the size though.
    • CommentAuthorEd Davies
    • CommentTimeJun 5th 2014
     
    Ta. Funnily, glulam was my original thought, too. Straightness would be nice, as always, but not absolutely critical as the bottom of the floor structure (OSB3 I'm assuming) and the battens for the floor stick to the bottom and top respectively of shorter joists running between these beams. So long as the joists are straight and attached in a flat plane a few mm each way on these beams shouldn't matter too much.
  5.  
    Could you not just use engineered trusses? Much lighter than such massive beams and will be stronger as well - plus with spaces for routing stuff through. Only issue might be the height.

    Paul in Montreal.
    • CommentAuthorowlman
    • CommentTimeJun 5th 2014
     
    Are they load bearing?
    • CommentAuthorEd Davies
    • CommentTimeJun 5th 2014
     
    Yes, I probably could and without the messing around I've had I probably would. My original (as in, when I'd just bought the land last October) design had glulam beams going the other way with I-beam joists between them.

    My house designer and I then wasted about four or five weeks in late December and a lot of January redesigning and re-redesigning bits to his prejudices. The planning app went in in early Feb and was granted later on in March. Since then we've faffed some more with detailing (debates about sarking and stuff) then he, for reasons totally beyond my comprehension, briefed the SE to start from scratch when I was expecting him to just do detailing. The only thing that stopped me going completely ballistic was that, just before I realized what had happened, I observed that the SE's design was pretty much what I originally-originally had in mind (before I got a bit enamoured with engineered timber towards the end of last summer).

    I've got the SE to change to I-beams for the rafters but the rest is just plain-old timber. I can live with that.

    What I don't want to do is make any more changes now unless they're really absolutely essential. I'm running out of money, patience and summer and just need to get on with it as immediately as the building warrant process allows.

    Height is an issue in the sense that these 220 mm beams are not high enough and will have 145 mm battens on top to allow enough insulation to fit in the floor. The original SE design had an additional row of concrete posts down the middle to support the floor - something none of my designs had. I suggested using deeper beams to get the required strength but he has instead added a few more beams bolted side-by-side (these long beams are the outer pair of those - the inner ones are shorter between posts). I don't know why.
    • CommentAuthorEd Davies
    • CommentTimeJun 5th 2014 edited
     
    Posted By: owlmanAre they load bearing?
    Yes. For the floor including the big thermal store.
    • CommentAuthorborpin
    • CommentTimeJun 5th 2014
     
    Posted By: Ed DaviesHeight is an issue in the sense that these 220 mm beams are not high enough and will have 145 mm battens
    Maybe I'm missing something but why not just use deeper I beams then?

    Are these supported in the middle? I'm guessing so. If so just split them at that point?
    • CommentAuthorEd Davies
    • CommentTimeJun 5th 2014 edited
     
    Posted By: borpin: “Maybe I'm missing something but why not just use deeper I beams then?â€Â

    Funnily, I suggested using deeper beams but was ignored. For reasons given above I'm not going to pursue the matter. I-beams might not be so great though as there are lots of joists hanging off them. I beams are great if you've got a relatively flat load spread across them but once you start adding lots of point loads they finish up with so much blocking you might as well have just found a solid bit of timber to do the job.

    If they'd asked me to expand on my suggestion of deeper beams I'd have suggested 44x304 (stocked in Inverness) or 45x350 (available at a few days notice) glulam. The 350 high would be especially nice as the beams each side of the post could be connected across the top with 18 mm ply, 220x45 joists strung between them with 145x50 battens across and only 3 mm difference to make up somewhere.

    Posted By: borpin: “Are these supported in the middle? I'm guessing so. If so just split them at that point?â€Â

    Yes, supported at the ends and two points in the middle. Have a look at the structure in this blog post and my blog background image:

    http://edavies.me.uk/2013/09/roof-rethink/

    All my and the house designers variations on that theme have had the main beams running east-west in the house between the posts (the south face is one of the sloped roofs, not the gable end as in some solar A-frame designs) as shown on that web page with the joists of various sorts (timber or I-beam) running north-south across the width of the A-frame.

    The SE's design, though has the main beams running north-south so about 1.8 metres from the little stub posts to the main posts then 3.6 metres between the main posts and another 1.8 metres to the stub post on the other side. He then has the joists running east-west in each of the rooms.

    (Two asides: 1) in more recent designs the rafters sit on top of the east west beams on the stub posts rather than hanging off them. 2) Actually, the beam I'm asking about is nearer 7.2 than 8.2 metres - 8.2 metres is the overall width of the house and there's quite a bit of roof overhang. I'll have to measure accurately to see if it's actually not over 7.2 metres - the drawings I have aren't dimensioned in that way.)

    So yes, it would be possible to split this beam. However, it's taking a lot of weight and it's to be bolted to the side of a relatively narrow post so breaking it would need additional bracketing of some sort. Wouldn't want to use steel there as it would create a cold bridge.
    • CommentAuthorborpin
    • CommentTimeJun 6th 2014
     
    So is it the piece of wood across the bottom of the A you are after or the one running the length of the house (EW NS does not really help) :)
    • CommentAuthorEd Davies
    • CommentTimeJun 6th 2014
     
    Borpin, across the bottom of the A.

    If you don't think in terms of EW and NS in the design of a house then perhaps you're doing it wrong? ;-)

    If you've any doubt about my description of the orientation of the house then look at the piccy here:

    http://edavies.me.uk/2014/02/sketch-update/
    • CommentAuthorEd Davies
    • CommentTimeJun 6th 2014
     
    Posted By: Ed DaviesI beams are great if you've got a relatively flat load spread across them but once you start adding lots of point loads they finish up with so much blocking you might as well have just found a solid bit of timber to do the job.
    Having said that I now come across Simpson Strong-Tie:

    The ITB/HITB is an innovative new hanger that eliminates the requirement for backer blocks when supported from an I-joist header.
    Didn't realize you could do that.
    • CommentAuthorborpin
    • CommentTimeJun 6th 2014
     
    Posted By: Ed DaviesIf you don't think in terms of EW and NS in the design of a house then perhaps you're doing it wrong? ;-)
    Doh!

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