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Beam Size

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  1. #1
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    Default Beam Size

    Hi again Everyone,

    We are doing an extension - basically extending the house back a few meters at ground level. The extension will measure 6.2 meters wide (the width of the current living area).

    The builder we are dealing with advises that we unless we want a 400mm deep beam accross where the extension starts, we will need a post mid way accross the 6.2 meter span.

    We really don't want a post mid way as this will be the middle of the kitchen (the span is 6.2 meters) and 400mm seems like a bloody big beam.

    Are there any other options (i.e steel, double width beams) that would give us 1) no post mid span and 2) a smaller beam?

    Just want to be clear on our options.

    Frog_hopper

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    A Member of the Holy Trinity echnidna's Avatar
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    yer builders right
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    Bob Thomas

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  3. #3
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    Thanks for the reply Echidna - no other options then? (steel, wider beam etc).

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    Diamond Member Barry_White's Avatar
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    Have you got a sketch of what you are trying to have built.
    Regards Bazza

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    The views expressed by the poster are general in nature and any advice should be taken in this vein. The poster accepts no responsibility if this advice is used. When undertaking any work personal professional advice should be sought from suitably qualified persons in the field of work being undertaken.


  5. #5
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    Hi Frog_hopper,

    Assuming a few things here, I would consider making a steel girder type truss and hiding it in the new roof framing if height is a problem. Steel columns hidden in the new walls.

    As Bazza says a sketch would help.
    cheers
    Bill

  6. #6
    That's SIR!!......Not CUR Ivan in Oz's Avatar
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    Quote Originally Posted by billbeee View Post
    Hi Frog_hopper,

    Assuming a few things here, I would consider making a steel girder type truss and hiding it in the new roof framing if height is a problem. Steel columns hidden in the new walls.
    Bill
    Thought about this one while eating tea with the Kidlettes.
    No wonder I got indigestion
    Heavy Duty Roof Truss.

    I'm with you BillBeee
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  7. #7
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    Just saw this post now, i work as a structural drafter so ill be able to advise you on Monday as to the size of your beam.

    Steel is an option with a column at each end. The size of the beam depend on the load its carrying from the roof.
    Where the wall was removed to open up for the extension did you have a gable end roof or pitch roof?
    if its pitched measure the lenthg from the gutter to the ridge and also need to know if its tiled or sheeting.

    or send a pic or sketch


    cheers Marz

  8. #8
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    just wondering if the beam the builder was talking about was F17 hardwood could marz1 work out the rating on timber that was F34 or better. A good piece of mountain grey gum will rate out to F34 yellow box goes better,providing you can source the length beam. This way you could make the beam smaller in dimension.

  9. #9
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    The roof line we are extending is a hip gable (and extension will also have a hip gable, just moved out a few meters). i.e We are extending the gabled end of the roof. It is a tiled roof. I have tried to attach a photo, but get an "Error on page" message. I will try to attach it from work on Monday.

  10. #10
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    Steel would make it smaller, I had that option but I stcuk with the timber because it was easier to work with. You can get pre-cambered manufactured F27 gluelam beams ... but it will still be quite large. Think you'll need steel if you want to get the size right down.

  11. #11
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    I don't mind if the beam is up to about 200mm, maybe 250mm deep. It's just that 400mm will look terrible.

    frog_hopper

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    OK, we have a bit more information, not a gable but a hip.

    The way I read it you want to take out a full end wall and extend on. The engineer might not like that, you may need to leave say a 600 wide section at each side, to provide shear panels. Depends on a few things, people here can advise as much as they like and we all talk round in circles, but the fact is that your local regs and certifiers WILL decide.

    As long as you have a reasonable roof pitch.
    Use multinail roof trusses like in the attached photo.
    The trusses to the right are spanning about 7M.
    Imagine them as over your new walls.

    The trusses on the left joining at right angles with joist hangers, imagine them as your existing roof structure cut at the eaves and joined to the new trusses. Your first new truss may or may not be a double one, that is two nailed together. You may have to connect with bolted brackets through the new truss and your rafter/ceiling joist combos.

    The trusses to the left (running away from the camera) will be say 5 or 6 new trusses of diminishing length sat on your existing roof framing and strapped to it.

    This way you will be able to pull down the end wall (after the new roof is attached) or most of it, and have an uninterrupted ceiling line.

    Heaps of times clients have said things like 'Is it possible to.."?
    My standard answer was usually "Off course it is, anythings possible". The trick is finding a cost effective way to do it.

    My basic philosophy when building an add on like this is "make it look like it grew there". There's no way that a new house would have either a 400 deep beam or a column, so why use one now.
    Otherwise if you can't do that, make absolutely no attempt to match up, make statement that it is completely different.

    Cheers
    Bill
    Attached Thumbnails Attached Thumbnails def-12.jpg  

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    Here is a picture of where the extension will go - 4 to 5 meters out from the end of the hip.
    Attached Thumbnails Attached Thumbnails hip-gable-extended-out.jpg  

  14. #14
    Oink! Oink! pawnhead's Avatar
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    If it's a lintel supporting a tiled roof and ceiling in a normal wind N3 area, and the load width is 6 metres, then a 250UB31.4 will span 6.2 metres.
    That's an I shaped beam with a nominal depth of 250mm and a weight of 31.4kg/m.

    Span tables.

    edit: The 'load width' would be half the distance from the beam back to the next supporting wall. If it is supporting the roof on both sides of the beam (which it would be in your case), then it would be half of both distances combined.
    You'd need some decent columns transferring the loads to the footings as well. If you're removing a lot of wall then bracing may be an issue as well. An engineer would have to certify it, and he may even want new footings under the columns.
    Last edited by pawnhead; 17th Dec 2007 at 11:50 AM. Reason: clar.
    Cheers, John

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  15. #15
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    Timber beams in f17 usually come in 5.4m lengths max.
    hybeam glue laminated beam can come in much longer lengths and are stronger than f17.
    a Hybeam works out o be 2/360X45 at 6.4m max.
    or 400X45 at 7m max.

    steel beam worked out to be 200ub 25.4

    Its not really holding much roof load, i calculated a roof load width of 1.5metres. your new extension i assume will be trussed with the trusses spanning the shortest length which wont trnsfer much load at all to that beam, its only there really to support your existing roof i assumed the worst case it would be conventional framing.
    Cheers Marz

  16. #16
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    As mentioned in a previous post it is more than likely that a girder truss could be designed to span the distance to support the existing and the new roof loads. You will probably need crosswalls at max 9m centres for wall bracing. Do a sketch plan and talk to a truss mob. I see jobs like that every day. You just need to use joist hangers or triple grips to attach the existing cieling joists and rafters to the new girder truss.

  17. #17
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    Yea a truss manufacturer could advise you you if they can design a girder truss to take the load, all you would need is double stud at each end of the girder truss but depends on the cost of design over using a beam.

    cheers

  18. #18
    Oink! Oink! pawnhead's Avatar
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    Quote Originally Posted by marz1 View Post
    steel beam worked out to be 200ub 25.4

    Its not really holding much roof load, i calculated a roof load width of 1.5metres. your new extension i assume will be trussed with the trusses spanning the shortest length which wont trnsfer much load at all to that beam, its only there really to support your existing roof i assumed the worst case it would be conventional framing.
    Cheers Marz
    Conventional framing on the existing house would be a best case scenario. If it were a trussed roof spanning onto the wall he plans to remove, then the roof load would be half of the entire width of the house. That could easily be six metres, but you can't tell by looking at that photo.

    Hyspans are much cheaper than Hybeams last time I checked.
    Cheers, John

    Short Stack (my son's band)


  19. #19
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    Sorry for the delayed reply - just wanted to say thanks to everyone for their input and help - greatly appreciated. I will let you know how I go with things in due course.

    Frog_hopper

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