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  1. #1
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    Jan 2015
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    Default Extending a deck post

    Hi new to this forum so hopefully I am posting this in the right area. I currently own a Queenslander in Brisbane which is on a sloping block. I have a rear deck attached to the back of the the house(2 really or should I say 2 levels). Part of the deck is exposed to the weather i.e. doesn't have a roof. I am wanting to put a roof over this area in the form of a gable. Had enough of the ongoing maintenance.

    This is where the problems starts. The posts that support the deck currently pass through it and end just above the railing height. The post need to be extended to allow me to build the roof over the top of the deck. The posts are currently 4.4 metres and 4.6 metres in length and both would need approximately 1.3 metres added to get to the correct height.

    Question is would a half lapped scarf joint( not sure if this is the right name) that has been through bolted be ok? Or should I just try to replace the full length of the post( I am trying to avoid this as it would be a PIA).

    Posts are hardwood 100x100.

    Any help/advice would be appreciated.

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  3. #2
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    Woodstock (Cowra)
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    That is a job for a licensed builder ONLY if you value your house insurance and public liability and if something does happen either during or after construction the first thing the insurance company will do is check with the council for the appropriate certificates and who is the licensed builder.
    Sorry, but this is one time that you do need to leave it to the professionals.
    The person who never made a mistake never made anything

    Cheers
    Ray

  4. #3
    Join Date
    Nov 2007
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    melbourne australia
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    Can you get an owner-builder certificate in QLD?

  5. #4
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    Bardon
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    Quote Originally Posted by rwbuild View Post
    That is a job for a licensed builder ONLY if you value your house insurance and public liability and if something does happen either during or after construction the first thing the insurance company will do is check with the council for the appropriate certificates and who is the licensed builder.
    Sorry, but this is one time that you do need to leave it to the professionals.
    Thanks for your concern. I am well aware of the implications in relation to carrying out this type of work DIY as I build the lower (first story of the deck) and had this work fully certified myself. There wasn't any requirement to have BCC(council) approval. This is the same situation for the proposed roof over the deck.

    My problem is that I have had 4 builders look at the work and only 1 quote of $120K to do the work, no one wants to do it or they want to charge ridiculous prices. I have had work carried by "professionals" in the past and have had to rectify shoddy works myself and don't get me started on the certifiers and the general lack of knowledge in regards to building and or Council's requirements.

    All I am asking at this stage is the proposed possible and or safe? Either way I am going to need an owners builder licence and obtain a permit as I did previously for the lower deck. I am asking this before I submit my plans for the appropriate permit, just don't want to waste my time submitting only to have it not approved and have to resubmit.

    Anyway as I said before any help would be appreciated.

  6. #5
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    Nov 2021
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    Sunshine Coast, QLD
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    Without seeing a layout/design it is difficult to give advise, adding to the posts is possible (and is really the easy part) you could just sandwich the post between steel plates or house out the centre of the post to accept one steel plate. However there are other things to consider such as are any of the existing posts in the correct position to support the roof structure layout, do they have the right foundation to take the point loads of this new structure, do the existing 2 levels have enough post bracing (to stop deflection) to accept the roof structure.

  7. #6
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    Nov 2007
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    $120K? Heís taking the pi$$. I donít blame you for DIY.

  8. #7
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    Nov 2017
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    Melbourne
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    Quote Originally Posted by Berger4 View Post
    All I am asking at this stage is the proposed possible and or safe?
    It's possible.

    Whether it meets requirements for wind loading, live loads after the new roof loading and other things that make it safe and not something your insurer will seize upon to deny a claim for property damage or personal injury, or that a prosecutor will identify as grounds for a criminal charge if there is an injury, are very different issues.

    Quote Originally Posted by Berger4 View Post
    Either way I am going to need an owners builder licence and obtain a permit as I did previously for the lower deck. I am asking this before I submit my plans for the appropriate permit, just don't want to waste my time submitting only to have it not approved and have to resubmit.
    I don't want to seem rude or unhelpful but, if you want to be safe both personally (i.e. not successfully sued or prosecuted) and with the building, you'd be a lot better off getting a building designer or engineer or whatever is acceptable in Queensland to design it to the required standards rather than relying on random comments from people on a forum who haven't even been on site and whose expertise might be limited to never having actually built any sort of building, although one of them once did a rather nice dog kennel. Especially as you're trying to get the permit passed on the first attempt. The approving authority is unlikely to be persuaded that your submission should be accepted because, for example, the anonymous member 419 on Woodwork Forums said it would be okay. And your insurer and or the criminal prosecutor certainly won't be persuaded, because they will punish you for any failure to comply with all the relevant building code requirements.

  9. #8
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    Quote Originally Posted by jack620 View Post
    $120K? Heís taking the pi$$. I donít blame you for DIY.
    I think we've all quoted extreme prices on jobs we don't want.

    And then been really pi$$ed off when someone accepts the quote, and suddenly it seems like maybe not such a bad job for the money and tempts us to accept the job, especially if things are a bit slow or there's a gap in our diary for a really bad job at a stupid price.

    This is where temptation should be resisted with all our living being, because we are the only idiot on the planet whose extreme price has come in under the higher extreme prices of others who wanted the job even less than us, assuming that anyone else could actually be bothered quoting on this mammoth loser.

  10. #9
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    Jan 2015
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    Bardon
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    Well that seems to have gone pair shaped fast and has left me with a lot to unpack.

    Let me start with Camelot. Thanks for the advice and different options the 2 plates sounds and would probably look a bit agricultural, the plate in the middle of the post seems like a lot of work(assuming I have the description right?) Only reason I asked about the lap joint is that this join was used on a front smaller deck/porch by a previous builder who constructed a carport along with the deck. Don't ask me why it was done like this(my brain just starts to boil at the thought of it) needless too say things weren't built/put in their right locations as per the Architects plans and needed to be changed after concrete pours etc. Anyway all this was approved by an engineer, the architect and signed off by the certifier. I thought I was being over cautious when I asked about the lap join considering it had already been used on my house, I just wasn't sure if it was kosher.

    Camelot the footings for all of typist are Pryda high wind stirrups all set in grossly over size concrete footings. I know this as I replaced all the footings on the original deck before putting in the second deck. Mind you the original deck was only built approx 15 year previously by a builder and all approved by council(I didn't own the house then) upon investigation by me I found the footings to be what I considered woefully inadequate. I replaced the footings to a recommended design spec from the engineer who was doing the pool at the same time, I then oversized the footings just in case I wanted to do what I am now.

    As for the bracing? yes I believe it does as I added cross bracing into the under side of the deck at the time as again what was there was grossly inadequate I also added in cross battens(not sure fi this is the right term) and vertical hardwood battens to the ends.

    As an aside once the roof is done I am replacing all the joist and decking and will be enclosing each end in with chamferboards to give some privacy/ make a semi open outdoor room.

    419 thanks for the advice. I am willing to to cop whatever the insure does on the chin given that they will more than likely do anything to get out of paying a claim. As for criminal charges I am sure this won't happen as I don't think anyone will get injured.

    As for the design. I feel I am more than up to the task being a Landscape Architect, having ran a landscaping business and worked for local government for the last ten years as a project manager. I am sure I have the skills to research and design the project.

    Again just after some thoughts on the post/lap join. Is it kosher? Would the QBCC find it OK?

    Jeez after all that I wish I had just paid the 120K. Time for a beer(I know its morning and I shouldn't, but I need one after that).

  11. #10
    Join Date
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    TBH, I think extending the posts is the least of the technical issues on this job. How do you intend attaching the new roof the the existing roof or wall?

  12. #11
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    Jun 2010
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    Geelong
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    Bracing is king. We need photos and/or plans/drawings to be able to help

  13. #12
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    Sth Gippsland Vic
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    Quote Originally Posted by Berger4 View Post
    Question is would a half lapped scarf joint( not sure if this is the right name) that has been through bolted be ok? Or should I just try to replace the full length of the post( I am trying to avoid this as it would be a PIA).

    Posts are hardwood 100x100.
    My thinking is half lapped or scarf joints holding a roof up isn't good enough . Even if it worked. They would look like a bit of a hinge point. And side pressure on the bolts into the wood would compress the wood over time with movement getting worse.

    I reckon a good way of extending them would be to do some metal work and slide 1.3 + overlap say 900 = 2.2 Steel hollow section posts over the 100 x 100 timber posts. 100 x 100 comes in 3, 4, 5, 6 and 9mm wall thickness. If you used 100 x 100 x 3 mm steel ( Or thicker) and shaved your hardwood posts down 3mm each side so its 94 x 94 . Then slide the steel over gluing it on with an industrial Poly glue . Then screws or bolts going through in a couple of points. The posts blend in and I don't think could be done better. Add steel U brackets up top to take a timber roof.
    A bit overkill maybe but overkill is what it needs.

    edit. You would want your timber posts to be nice and dry as well . Even over dry like at the end of a hot summer before fitting the steel would be better.

  14. #13
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    Quote Originally Posted by jack620 View Post
    TBH, I think extending the posts is the least of the technical issues on this job. How do you intend attaching the new roof the the existing roof or wall?
    Hi Jack. Yes I agree that extending the post is the least of my worries. Without getting out pen and paper(if I was still working I would probably jump into CAD or use Sketchup, in my own time of course). The deck is a funny L shape with the upright part of the L running along the full width of the back of the house and the foot/toe??? of the L poking out. The bit attached to the back of the house is already attached with the roof essentially an extensions of the house roof, that is the rafters come out of the house and the deck rafters have been attached to this. Hopefully that makes sense.

    The foot/toe?? part of the deck is uncovered, originally I was going to just do a fly over roof for this part but it was decided(wife) that this would not be aesthetically pleasing(I tend to agree but was just looking for the easy way out). Essentially I want to do a gable for this part running back to the house, for this I would need to run a ridge beam back into the roof of the house connecting to the hip approximately less than 50cm into the roof, then build the gable and extend all the purlins of the house roof out one side and make a valley on the other until it meets the inside corner of the L then run purlins over the new trusses. Not what I would consider very technical just a lot of work at heights.

    With all the time in the world on my hands, recently retired. The trouble with finding a builder in QLD(not sure what it is like in other states) I decided I would take it on myself. Idiot I know.

    Hope that all makes sense.

  15. #14
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    Nov 2021
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    Just a little about me, I owned a Tier 3 construction company, so not really an house basher, but I have converted large buildings into Apartments and done a few Refurbishments/Extensions over the years, out of my 4 children only one followed me into the building game and she has her Masters Degree in Architecture.

    With the background you have I don't see why you should have a problem doing the works (or at least supervising the trades) regarding the posts you could just do a 50/50 half lap joint (like you suggested) with the post being in compression you only really need to deal with twist or buckling and therefore adding a steel plate might be better, this is a detail a structural engineer can design.

    Like jack620 mentioned you are going to have to deal with abutting to your existing roof, you mentioned a Gable End so depending on your layout this might mean adding one or two valleys which work better on steeper pitched roofs. If the layout is not too complicated then getting a Structural Engineer to do some details/calculations shouldn't cost too much and they will be needed for your Council Application.

    Good Luck with your proposed project

  16. #15
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    Quote Originally Posted by Berger4 View Post
    As for the design. I feel I am more than up to the task being a Landscape Architect, having ran a landscaping business and worked for local government for the last ten years as a project manager. I am sure I have the skills to research and design the project.
    That changes my attitude. I was concerned that you didn't have sufficient understanding of the task and were at risk of doing a bodgie job.

    I was thinking of a more primitive version of auscab's suggestion for a steel outer reinforcing box, but auscab's suggestion is much neater.

    Alternatively, depending upon cost, rather than thinning the posts where the reinforcing box goes you might be able to get steel boxes made to fit your current and scarfed post in their standard dimensions and fit them full length from the deck to the roof supports so that they become the outer faces of the posts without any visible joints. Use recessed bolts on the scarf joint to allow the box to slide over.

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