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Home extension, use of 'post anchors' instead of hardwood stumps?

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  1. #1
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    Default Home extension, use of 'post anchors' instead of hardwood stumps?

    Hi all. Long time subscriber, first time posting.

    I am owner-building an extension on a 100+ year old weatherboard house in WA. We will be adding a bath, laundry and snug, and will be doing a timber stumped floor with subfloor.

    Our drawings said that our stumps should be 90x90 wooden posts, or 100x100 RHS, but I am wondering if the 'off the shelf' half stirrup post anchors (as per this link: Type D - Half Stirrup With Leg - Dunnings) are a sufficient replacement for the options originally suggested?

    I've spoken to a few people and am getting some conflicting advice, first that these stirrups are to tie a building down, not hold a floor up, therefore, not suitable.
    But also from a person who should be suitably knowledgeable that these would be fine, as they should bear 10s of tons of direct vertical load and would still do the trick just fine.

    So I turn to you, the very experienced and in the know, to settle the debate before I make a decision that might mean I ruin my build before I start

    Also attached are scans of the drawings I'm working off of (please disregard scribbles).

    As you can see, fairly light timber structure, with a subfloor, which I assume must be how we're getting away with such light bearers (this did pass through the building inspector guys and we do have a permit... so must be okay! )

    Thoughts?

    Can I use those posts or no?

    Attached Thumbnails Attached Thumbnails skm_c25819011616250.jpg   skm_c25819011616260.jpg   skm_c25819011616251.jpg  
    Last edited by phild01; 17th Jan 2019 at 10:55 PM. Reason: topic header refined

  2. #2
    1K Club Member Pulse's Avatar
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    Default Setting out home extension, can I use 'post anchors' instead of hardwood stumps?

    I'd use 100x 100 RHS with plates welded on. You need some bracing which isn't provided by the post anchors. Seperate subfloor bracing might let you use the anchors but RHS is easier I think.
    ====

  3. #3
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    Quote Originally Posted by Canuck View Post
    Hi all. Long time subscriber, first time posting.

    I am owner-building an extension on a 100+ year old weatherboard house in WA. We will be adding a bath, laundry and snug, and will be doing a timber stumped floor with subfloor.

    Our drawings said that our stumps should be 90x90 wooden posts, or 100x100 RHS, but I am wondering if the 'off the shelf' half stirrup post anchors (as per this link: Type D - Half Stirrup With Leg - Dunnings) are a sufficient replacement for the options originally suggested?

    I've spoken to a few people and am getting some conflicting advice, first that these stirrups are to tie a building down, not hold a floor up, therefore, not suitable.
    But also from a person who should be suitably knowledgeable that these would be fine, as they should bear 10s of tons of direct vertical load and would still do the trick just fine.

    So I turn to you, the very experienced and in the know, to settle the debate before I make a decision that might mean I ruin my build before I start

    Also attached are scans of the drawings I'm working off of (please disregard scribbles).

    As you can see, fairly light timber structure, with a subfloor, which I assume must be how we're getting away with such light bearers (this did pass through the building inspector guys and we do have a permit... so must be okay! )

    Thoughts?

    Can I use those posts or no?

    You are proposing an alternative structural method , so you're going to have to provide all the relevant details to the building certifier & an amended plan, it all costs $ before you even start.
    inter

  4. #4
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    interd6, what do you mean 'alternative structural method'?
    Are you referring to the fact that I am proposing something different than the submitted plan?
    Or that this suggestion is just 'not the done thing' and therefore needs additional justification?
    Thanks
    Canuck

  5. #5
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    Thanks Pulse. I actually mulled it over and over and was leaning back again to the 100x100. The fact that the anchors don't really tolerate horizontal shifting was the clincher in my poor sleepless mind It's an old house and everything moves!

  6. #6
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    I would be closing the 600 floor joist spacings to minimum 450 and defintely be doubling the 90x45 bearers up..also I'd be using lvl or hardwood over pine.

    Why use timber stumps, when you will just have to replace them in 10 years.. use steel if concrete stumps are not available over there.

    This seems to be designed to the bare minimum required

  7. #7
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    Quote Originally Posted by Optimus View Post
    This seems to be designed to the bare minimum required
    NSW doesn't seem as swampy as Vic

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    Swampy?

  9. #9
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    Quote Originally Posted by Optimus View Post
    Swampy?
    Soft, seems stumps down there continually need adjustment or replacement, and there seems to be a need to dig really big deep foundation holes.

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    Oh sorry, i was meaning the timber sizes/spans..

  11. #11
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    We are in WA, in a pretty dry area.
    I still don't want to be redoing anything in 10 years time...
    😕

  12. #12
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    Quote Originally Posted by Canuck View Post
    interd6, what do you mean 'alternative structural method'?
    Are you referring to the fact that I am proposing something different than the submitted plan?
    Or that this suggestion is just 'not the done thing' and therefore needs additional justification?
    Thanks
    Canuck
    your proposed changes will only do what the original design will do, with added cost & no benefit. There will be a knock on effect with additional labour costs as under floor access will be restricted for plumbing & possibly electrical work because of the added stump bracing in the way.
    inter

  13. #13
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    In 100 years has the original house been restumped? What did they use?

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    Quote Originally Posted by intertd6 View Post
    your proposed changes will only do what the original design will do, with added cost & no benefit. There will be a knock on effect with additional labour costs as under floor access will be restricted for plumbing & possibly electrical work because of the added stump bracing in the way.
    inter
    Hadn't considered that. Thank you for your input! Helps a lot!

  15. #15
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    Quote Originally Posted by r3nov8or View Post
    In 100 years has the original house been restumped? What did they use?
    No it hasn't. Still original solid timber (jarrah or wandoo stumps, not sure which) direct in ground. We do have to replace or shim several now, so after this extension we will have to look at that and decide what to do.

  16. #16
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    I'd be sorting out the original foundations before adding the extension

  17. #17
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    Quote Originally Posted by r3nov8or View Post
    I'd be sorting out the original foundations before adding the extension
    X2

    A must..

    Use a water level and determine the levels of the original house.. I'd put my house on that after 100 years the stumps will or moved due to rot

  18. #18
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    Quote Originally Posted by Optimus View Post
    X2

    A must..

    Use a water level and determine the levels of the original house.. I'd put my house on that after 100 years the stumps will or moved due to rot
    We are restumping the back wall where the extension joins, and will ensure that is level, and then adjust the original house to match.

    The main house is not too bad for level, actually, especially for 100+ years, and only has a few low/high spots we need to work on. And these seem to be more due to bearers and joists bowing than stumps sinking, remarkably!
    One side of the house had a not-so-handyman-special window put in, with no flashings or anything! The wall and some of the floor and clearly some of the joists/bearers/stumps have been affected. We'll know more once we pull the floor.

    We had to pick our battles, and honestly, getting rid of the asbestos riddled mess that used to be the back room (laundry, bath, toilet) was more important. Gotta pick your battles, right?

    old-back-room.jpg

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