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  1. #1
    Join Date
    Jan 2006
    Location
    Melbourne
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    38

    Question subfloor joist timber type

    I'm replacing rotten hardwood joists and wall (sill) plates in a 1940's double brick house. The original red gum wall plates rested on a bed of mortar on a step in the internal brick walls and have rotted away in parts. The joists are hardwood and have rotted where they sit on the wall plate. The floor is 108x19mm tasi oak T&G.

    I was advised to stick with hardwood but don't know what specs it should have. 90x45 F17 KD (Tasi oak?) easily meets the stress grade (the joist spans are 1.4m) but I've been told its durability class 3 and so unsuitable for sub floor joists. (even if they're not in contact with the ground!) I was intending to use it for both the joists and wall plates (sitting on standard 0.5mm plastic damp coursewall ). If it is unsuitable what should I be using for each? I have to bolt the new joists to the existing joists. Why should this preclude using treated pine?

    Any advice is much appreciated.

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  3. #2
    Join Date
    Jan 2005
    Location
    Canberra
    Posts
    265

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    Tassie Oak no good for floor joists, jesus christ what's the world coming to
    hmm, prob be a sin to waste it on that anyway...

    Just use the plain'ol 100*50 mixed hardwood that's available in your area. Only concern I'd have is shrinkage with using green timber in your situation, so I'd hunt around 2nd hand building material places for some pre-loved 4*2's.

  4. #3
    Join Date
    Aug 2003
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    .
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    10,482

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    Get some KD hardwood, most prolly it will be Vic Ash.
    Most renos, extension subfloors are done with it.

    As long as you get the dampcourse done right the KD will last for ever.

    Al

  5. #4
    Join Date
    Dec 2007
    Location
    Chipping Norton, Sydney
    Posts
    4

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    I've found that my subfloor joists need replacing as well.
    My cavity double brick house was built in the 1970s and the floor is sitting on brick piers with ant caps. I'm guessing that the existing bearers/joists are hardwood but I don't know.

    This is my first home and it needed some serious fixing.

    I've just gone under the floor (clearance of about 700mm), tapped on the beams and joists with a hammer and measured out the lengths that need replacing. I then rushed out to buy H3 treated pine from Bunnies but then SWMBO asked if the pine is sturdy enough to be used there.

    Ozwinner, where would one get "KD hardwood" from, and what is "KD"?

    Rscho, what did you end up using? I hope you're still party to these forums.

    I was just gonna cut to size the 2.4m treated pine (remembering to seal the cut ends, with what, I'll have to ask Bunnies again) and bang them in alongside the rotting/-ed joists. Bang them in because our nice blackbutt hardwood floor has been laid and finished for about 2 years now. (It was decided to lay it straight onto the original floorboards that previously had carpet on top of them - extra floor insulation, we figured.)

    Dad-out-law and I have already done just this on a few joists in the kitchen already because there must've been a massive leak from an old dishwasher. So I know how hard it is to insert joists into the subfloor. Come to think of it, I'll ask dad what timber we used for that, but your suggestions would be helpful, too.

    Sorry for the slurry of thoughts, this is my first post after all.

    PS I've also got a question about bowing of the beams and tying them down to the piers in a separate thread.

  6. #5
    Join Date
    Feb 2003
    Location
    Garvoc VIC AUSTRALIA
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    11,464

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    How close are the joists to the ground?
    Regards, Bob Thomas

    www.wombatsawmill.com

  7. #6
    Join Date
    Dec 2007
    Location
    Chipping Norton, Sydney
    Posts
    4

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    Quote Originally Posted by echnidna View Post
    How close are the joists to the ground?
    About 600mm off the ground.

  8. #7
    Join Date
    Oct 2007
    Location
    Sydney, Australia
    Posts
    173

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    Based on the product code on your docket, someone at Bunnings should be able to tell you if the H3 you bought, is graded structural or not.

    KD is "Kiln Dried".

    What makes you certain that the beams need replacing/supplementing? How good is your subfloor ventilation?

    Cheers, Adam.

  9. #8
    Join Date
    Sep 2007
    Location
    Sydney
    Age
    61
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    152

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    I am doing an extension right now, the bearers we used were 90 x 63 LVL and the joists were 90 X 45 LVL. Both treated to resist termites.
    They were light, straight, consistant in size and easy to work with although a fraction more expensive than new hardwood.
    I would recommend them to anyone.
    Cheers

    Alan M

    My Daughter's food blog www.spicyicecream.com.au

  10. #9
    Join Date
    Dec 2007
    Location
    Chipping Norton, Sydney
    Posts
    4

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    Quote Originally Posted by addo View Post
    Based on the product code on your docket, someone at Bunnings should be able to tell you if the H3 you bought, is graded structural or not.

    KD is "Kiln Dried".

    What makes you certain that the beams need replacing/supplementing? How good is your subfloor ventilation?

    Cheers, Adam.
    Thanks for the KD tip, Adam.

    [Note to self: search in FAQ for list of acronyms, such as "LVL"]

    Where I stated "beams", I'd meant bearers. The bearers are good, it's only the joists that are rotted. The hammer-banging gives out a hollow sound from the rotted joists but a solid sound from the good timber (I'm guessing). I'm assuming that bearers are the wider 90x60 and the joists are 90x50 (although "Capital-B" only sells 90x45).

    Where the timber is giving off the hollow sound, I tested the wood by driving a pointy punch (awl?) into it to see if the wood can be penetrated. I'm replacing those where the wood gave way easily and crumbles, and is brittle and flakes like a "Cadbury Flake".

    One of the joists I'm looking to replace runs the length of the wall, it's the one sitting against the outside wall. That's about 4.5m to do. This particular wall has a crack from the window sill that shows for 50cm above floor level (& averaging 1cm wide in the render) and continues down into the subfloor all the way to the ground, but this is another story that's long enough for another thread. (Suffice to say we've had quotes from underpinning guys and it's gonna be around $6k to underpin and lift 4-6 stumps.)

    As for the ventilation, my bro-in-law was surprised that the inner wall had gaps made for vent-bricks but the outer wall didn't. So he knocked out the required bricks from the outer wall in line with the ready-made inner wall gaps, so that air could flow through. I've bought the vent-bricks and they're sitting in place but I haven't mortared them in yet - it'll be my first mortar job.

    Anyway, this master bedroom came with a dual-fan single-brick subfloor vent that's solar-powered. It's hard to describe the moisture content in the subfloor unless there's some kind of reference scale I could relate to. One of the underpinning guys who went under said that it was as normal as any other place. The "inspector" who did the pre-purchase building inspection noted that there was no subfloor access except to the first room that's accessed via the internal garage, but I suspect he got some "pokies money" to ignore the gap leading from this room to the rest of the house's subfloor; because otherwise he would've been able to report on these rotted joists all over the house. Here's a TIP: always be there for the building inspection so that the inspector doesn't succumb to the vendor's temptations.

    Well, sorry for ranting, and thanks for reading and enquiring.

    Everyone's collective knowledge and experience is soothing for me.

    -Mark

  11. #10
    Join Date
    Oct 2007
    Location
    Sydney, Australia
    Posts
    173

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    Have a chat to Uretek before you commit to any regular underpinning. Their method is very quick and almost non-invasive. One of the unfortunate aspects of shrinkage in clay is that (from my experience) it never comes back fully.

    Anyway - sounds as though you're on top of the vent thing - it's also important not to obstruct the external venting with too much greenery or landscaping.

    90×45, 100×50 are pretty much the same thing; the wood starts rough sawn (RS) at the maximum spec, and is finished at the smaller one - then it's known as DAR (Dressed All Round) - another term you may see on invoices or quotes.

    Crumbly wood can also be lyctid damage. See the two thumbnails for actual episodes of each (not photos cribbed from the 'net). It could be possible that the entire length of timber has a characteristic that will ultimately cause it to fail... In any case, supplementing that joist against the wall will be a barrel of fun!

    If this is the same room with seriously bowed joists, I would think hard about renewing the floor there. Not what you wanted to hear, but worth pondering.

    Regards, Adam.

  12. #11
    Join Date
    Oct 2007
    Location
    Seven Hills, NSW
    Posts
    205

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    Blackbutt is good for durability

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