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Reading Span tables and LVL vs Hardwood

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  1. #1
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    Default Reading Span tables and LVL vs Hardwood

    Hi,
    I'm about to start building an extension on to the back of our house. Plans have been drawn up by draftsperson, owner builder course done, just waiting on some engineering drawings for garage that I'm getting included at the same time before submitting to certifiers.

    In the meantime I'm trying to work out what to use for the bearers and joists. I was originally going to use F17 Seasoned hardwood, or some form of LVL (Red Alert maybe). I did a rough budget based on F17 and some span tables I found.

    I've since bought the Seasoned Hardwood F17 Span table supplement and they appear to suggest that no matter what span or size of timber they will need to be two lengths nail laminated.
    i.e. FLW of 2400, RLW 4500, with tiled roof and cont. span of 1900 = 2/120X35 bearers. (and may need to go bigger if I can't find 120X35 easily)

    So I just wanted to check is it normal that no matter what sized F17 hardwood I choose it will need to be two lengths nail laminated together? I'm sure I had older span tables that showed single bearers e.g. 120X70

    On the other hand if I look at LVL's 140X45 seems to be the equivalent so am I better heading down that path as it looks like it could be cheaper due to less timber required.

    Cheers,
    Michael

  2. #2
    Duck Fat - 2K club member SilentButDeadly's Avatar
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    Span tables have moved on as engineers have become more conservative and engineer timber design and spec has improved....that's why you see hardwood span tables getting a bit mad. The tail is wagging the dog.

    First things first...you'll have to use whatever materials are specified by the plans. Period. It is not either or these days.

    Personally...having used both...I'd use the LVL. It is more expensive to purchase on a per metre basis but it is faster and easier to install and since it is an engineered product there aren't the warp/weft & weirdness issues down the track when it comes to fitting floors and ceilings that you can get from hardwood even if you have been meticulous about levels.

    I still like hardwood but then I like a bit of warp and weft too.
    People don't ever seem to realise that doing what's right is no guarantee against misfortune

  3. #3
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    Quote Originally Posted by SilentButDeadly View Post
    First things first...you'll have to use whatever materials are specified by the plans. Period. It is not either or these days.
    Your probably right in most areas but I was able to make changes without submitting new plans. In my case, the plans specified a rafter LVL that was not on a span table and would have needed an engineer to certify (no idea what the draftie was thinking). I used an LVL span table and picked from there. Worked out cheaper on materials as well as not needing engineer. The inspector was totally cool with it. I'm in a rural area and perhaps it's a bit more easy going here.

  4. #4
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    Nah not just rural Su. I change the spec of plans all the time with the designers consent. Subbing pine for lvl's for example or HWD for lvl or the other way round. As long as you run it past the designer and get his written consent there is no drama. A quick check on the hyne program for sizing and a phone call is all it takes generally. To the OP, without punching the numbers, you would probably get a way with 130 x 63 lvl for the bearer. 45 width is too narrow for a bearer IMO so 63 is good. You could even go up to 150 x 63 for some added beef.

  5. #5
    1K Club Member barney118's Avatar
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    download designit Timber Engineering and Design Software from Carter Holt Harvey - DESIGNIT and you can print off your own certificates (if required) most plans have somewhere that the dwg/ building complies with BCA and if you have substituted as an OB then you generally only need certification as per D/A requirements.
    cheers Look out if I have a tape measure in my hand.....I'm upto something

  6. #6
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    If your the owner & builder you can substitute structural materials all you like as long as they are equal or better in strength & durability. At some point you will have to inform the inspector / certifier of the changes for their records, now if your a contractor doing a project then you would have to get permission for any changes to materials, usually this will only be permitted if supply cant be found or savings for the client can be promised. The old 120 X 70 SHWD tables have a clause at the bottom saying the members can be vertically laminated to get the required sizes, so the tables are the same just a bit simplified in one of them.
    regards inter

  7. #7
    Golden Member paddyjoy's Avatar
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    Is it also ok to change the spacing of members? For example if an engineer specifies 170x45 LVL joists at max 450 centres on the drawings, could you substitute 130x63 LVL joists at 300 centres which actually gives a higher capacity and rigidity?

  8. #8
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    Again. The same thing I did when changing the rafters for my mates owner build. The original rafters were spaced at 900 and I changed it to 450 when changing the rafter sizes. This saved a fair bit of work and money as the plasterboard was able to be attached directly to the rafters and didn't need battening out. You need to ask your inspector really.

  9. #9
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    Cheers,
    I was hoping I would be able to substitute some elements.
    e.g. I want to have an L shaped dwarf wall with engaged piers on two sides instead of isolated piers. When talking to my draftsperson she said she will specify isolated piers 230X230 which will be considered minimum requirement and if I go above and beyond then that it is OK. She mentioned that if she were to specify a dwarf wall and when it came time to build and I wanted to save money and reduce to spec to isolated piers it wouldn't be allowed without re-approval.

    Also I guess when you guys mention speaking to inspector that would mean the private certifier and inspector I've engaged for this?

    My plans don't have that much detail on them but I'm assuming that is because I only have a set marked "for checking" at this stage, she still has the plans for DA submission.
    But most parts have comments like roof trusses to manufactures specifications, or timber bearers and floor joists.

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