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minimum clearance under deck

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  1. #1
    Apprentice (new member)
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    Default minimum clearance under deck

    Hi All,

    I have been reading this forum for a while now getting some good ideas for a 7 x 5.5m deck that I am planning which will require a council building permit.

    I am wondering is there a minimum heigh requirement for a deck to allow for adequate ventilation under the deck. Is this measured to the top or bottom of the decking timber.

    Thanks for all the good advice and pictures on the forum, it is really useful for a novice home handyman

  2. #2
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    Uh. Im not really sure there is such a thing....

    You could prop your joists right on the concrete (as long as there is somewhere for the water to run off - i normally pack them so they are off the ground a few mils) but there is no 'rule' that requires them to be X height off the ground...

  3. #3
    Golden Member GraemeCook's Avatar
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    Besides drainage and ventilation you also need enough space to be able to keep the area clean. A build up of leaves, etc will soon start composting and rotting any wood it is in contact with.

    Cheers

    Graeme

  4. #4
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    My council (Hornsby NSW) requested minimum 400mm clearance between underside of the lowest timber member and the finished ground level for visual inspection of termite barriers in accordance with Parts 3.1.3 and 3.1.4 of the Building Code of Australia and AS3660.1-2000.

    Hope that helps.

    Stewart

  5. #5
    Old Chippy - 4K Club Member
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    Quote Originally Posted by Spider Webb View Post
    My council (Hornsby NSW) requested minimum 400mm clearance between underside of the lowest timber member and the finished ground level for visual inspection of termite barriers in accordance with Parts 3.1.3 and 3.1.4 of the Building Code of Australia and AS3660.1-2000.

    Hope that helps.

    Stewart
    That's not for decks - most of which are Class 10 (BCA) structures. A deck can sit on the ground if need be so long as it is built using the appropriate treated timber ie: H4 or H5 for timber that is contact with the ground. Generally if the deck is close to the ground the edges are closed in so leaves etc do not build up underneath, but shrubs and plantings can do the same job. Ventilation is rarely an issue for any deck - it will have gaps between the boards at the very least.

  6. #6
    Rigid Member UteMad's Avatar
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    That was what i was gunna say.. never had a min height enforced by council for a deck before..

    We go pretty low a lot of the time as people want a 1 step onto deck but more height is better for ventilation of the subfloor

    cheers utemad

  7. #7
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    Quote Originally Posted by Bloss View Post
    That's not for decks - most of which are Class 10 (BCA) structures. A deck can sit on the ground if need be so long as it is built using the appropriate treated timber ie: H4 or H5 for timber that is contact with the ground. Generally if the deck is close to the ground the edges are closed in so leaves etc do not build up underneath, but shrubs and plantings can do the same job. Ventilation is rarely an issue for any deck - it will have gaps between the boards at the very least.
    Hornsby Council has come up with some strange ideas before , but i was just quoting what i had imposed on me in my Construction Certificate - Addition - Deck Extension issued in 2007. It was listed in the Addendum to Specifications under a sub heading of "Frame"
    The BCA was classed as 10b as you stated using BCA 2007.
    The plans had the extended deck on brick piers with a ledger bolted onto the existing brick/concrete decking,
    So has my council got it so wrong ? or possible lack of knowledge from the planning division? or pushing their own barrow?

    Stewart

  8. #8
    Old Chippy - 4K Club Member
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    IMO your council has it wrong, but your problem is fighting 'city hall'. Does your council do its own inspections and certification or do they have you nominate (and pay) your won certifier? If the former then looks like you have a problem, if the latter they will usually allow the construction to proceed according to BCA and if necessary annotate the final certificate of occupancy and use and note the change. Sometime they would annotate a copy of the plan too.

    If it were me I'd build it to comply with BCA and fight them afterwards. If you try to get it changed beforehand it'll take decades . . .

    But it might also be that there was no mention of the type of timber - and that makes a difference. It'd be worth having a chat with your council anyway as it might simply need to have the specs made more clear about use of H3 treated timber for all sub-floor members. The construction can be the same ie: ledger on wall and piers or stirrups for the outer row)s) of bearers, but they could be only 50mm off the ground. First step would be to talk to the council.

  9. #9
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    It was all good, I finished it last year and i had enough clearance without having to change anything with the original plans, but my builder mate had to pull apart his deck and dig out 400mm clearance for council !! Lucky it wasn't of decent size.
    Maybe the type of timber is an issue (wasn't on my plans) but the clearance was for termite barrier inspection not anything to do with type of material used,
    It wasn't a problem for me this time, but next time............? cross that bridge when i get to it.

  10. #10
    Old Chippy - 4K Club Member
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    Quote Originally Posted by Spider Webb View Post
    I
    Maybe the type of timber is an issue (wasn't on my plans) but the clearance was for termite barrier inspection not anything to do with type of material used.
    If the sub-floor timber is H3 or above it is rated as termite-resistant - and no barrier involved on a deck so I'm not quite sure what that as all about. Good you got yours done OK though . . .

  11. #11
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    My council (Nillumbik) also specify the 400 mm for termites if the deck is attached to the house, Freestanding are okay.


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