Wooden Sundeck Constructed in Toti Durban

This wooden sundeck we constructed in Durban was a low-level deck which was barely off ground level. We were taking it flush off the level of the floor in the lounge and extending it outwards into the garden. The grass was not growing properly in this area due to large trees that were creating a large shadow so the client wanted to deck it to eliminate this problem.

The biggest challenge when building a wooden deck near or on ground level is to get a support beam underneath the joists where needed. There are two methods one can use. The first is what I call the cleat and beam system whereby a beam is placed underneath the joists to give them their support. We normally use a 38 x 114 joist and a 50 x 228 beam. One needs to span the 38 x 114 to a maximum of 2m but 1.8 is preferable. So every 1.8m to 2m one needs to slot an under beam below so as to support those joists. Posts should be used every 3m on the 50 x 228 beam. With this spec one can save on timber while still providing adequate support so that the deck is structurally sound.

The problem with this system arises because if you have a 228 beam, plus a 114 joist and then a 19mm deckboard on top of that your total height needed above ground level is 361mm. If the deck is too close to ground it will mean excavating soil to be able to drop that beam down enough to still arrive at the original height of your deck. Although this is quite possible and not that too time consuming, it sometimes results in the main beam sitting in soil or it may come into contact with wet soil over time. One must therefore use at least H4 CCA Treated SA Pine as the beam and in fact that whole substructure should be H4, even though the joists aren’t in contact with soil, to ensure that no rot will occur.

The other method is to create a frame, all in the same plane using 38 x 114 and use no under beam. This will result in the deck only being 133mm in height so that no excavation will be needed in order to bring the deck up to the required height. However now that you don’t have a beam to attach posts to, you will need to attach the posts to the joists and fascia beams. Again this is not a problem, but it will require a few more posts than in the first method as you can only span your 38 x 114 to a max of 2m. Hence more posts, more concrete and more labour in digging holes.

We used the joist and beam system here as we had enough space below to set the beam without having to dig too far into wet soil. So our work was made lighter by not having to dig too many holes.

Once the substructure is up, the deckboards can go down. On this wooden deck we used 19 x 68 balau deckboards. We used two deckboards as a fascia to cover our joists and beams, filled our holes with epoxy, sanded and sealed.

For a free no obligation quote or advice on your deck or other outdoor timber construction please call us on 031 – 762 1795 or use the form below to contact me.

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15 Comments Add yours

  1. espdesign10 says:

    Haha! Then I’ll go with your recommendation of smooth side up! 😉

    I’ve sent you an email with a couple of pics from the weekend’s work..

  2. Edward says:

    This is a most insightful article to a common problem of low decks – thank you very much!

    1. Pleasure Edward, hope you come right there with your deck, give me a shout if you need help. Send some pics when you’re done please. Would like to see how it worked out.

      1. espdesign10 says:

        Thanks Garrick
        Started setting out mine on the weekend.. a lot more work than one imagines!
        By the way.. which size s/steel screws would you recommend using for balua/garapa on SAP substructure?

      2. Hi Edward

        Yes it can sometimes get daunting, but just take your time. It’s easier than it looks.

        I use kalgard coated screws 10 x 60 (shaft size is 5mm, screw head is 10mm). Use a 4mm pilot bit with counter sink all in one so you only need to drill once). The ones you buy from the hardware are not that good. You can get a proper tungsten tip counter sink which will last the job, but they cost about R200-00.

        Stainless is of course better and I would assume the same size but I have never used them. The cost difference is not that much. Having said that, the Kalgard ones come with a 25 year guarantee. The coating is baked on similar to a powder coating so it can”t rub off when the screws in turned in.

      3. espdesign10 says:

        Hi Garrick
        Thanks for your valuable answer.
        Yesterday I found 10 x 60 (5mm shaft) 304 stainless steel screws with Torx head here in East London for 60c each.
        What do the Kalgards look like from the top?

      4. Hi Edward

        The Kalgard screws have a Pozi 2 head. Pozi 2 is good because the are quite strong so you don”t strip the bits as easily. What are you going to seal your deck with?

      5. espdesign10 says:

        Thinking of going with Garapa.. and then leaving it natural.
        Should the s/steel screws also be okay, or would you rather recommend the kalguards?

      6. Stainless are the best of course. You should counter sink about 5mm and then screw the screw right in and fill with a clear epoxy mixed with fine sawdust to match the colour. Then grind off with a 36 grit pad with a rubber backign pad on teh grinder. Then sand to get rid of scratch marks using a 40 grit on a rotext sander or similar. This as opposed to leaving your screw head exposed or set at the surface of the board. By leaving it exposed will allow water to get into the counter sink hole and any rot will start at that point. It”s more work, but well worth the effort. Be sure to use clear epoxy, not the grey or white stuff.

        w.r.t. sealing or not sealing. Garapa, or balau for that matter, won’t rot any quicker if left unsealed. Both will turn grey form UV, so it makes sense to use the cheaper board then as they will both look the same and provided you get quality timber both will last as long as each other. Not sealing it may result in checking more quickly or small fissures opening up in the timber over the years which can act as water traps. If you do seal stick to only oil based, zero wax content preservatives. Woodoc make one called Deck Dressing (not Deck Sealer).or Timberlife Satin Wood Base 28. Please don’t use anything that will dry on the surface.

        Check your prices too between 19 x 68 boards and 19 x 90 boards. The latter are normally more per square metre. Be careful of red balau, it comes in good quality and bad quality. the bad stuff splits and is much less dense so will rot more quickly. Yellow balau is good and very cost effective.

        Search this blog for maintenance and you will find some articles on that as well as the last article on reducing rot in wooden decks.

      7. espdesign10 says:

        Thanks for your detailed response – I have be reading through your blog extensively – there’s a wealth of information you’ve put together here!

        Think I am going to go with Garapa 19×90 – can get it for R36/m incl.
        Then I will probably leave it natural, or as you suggest use the Woodoc Deck Dressing.

        As for the screws – think I’ll go with the s/steel 10×60’s – does one put two screws at every intersection – i.e. every 450mm?

      8. Hi Edward

        I normally use the 68mm board, but I would put 2 screws on each joist and on the ends. You can get away with putting two screws on the ends of the deck board only and then one on each joist in the middle of the board on alternate shoulders (if that makes sense). But the little extra effort and time by putting two on each shoulder all the way down the board will help in ensuring that the board has less chance of cupping over time. Don”t put one in the middle the 90mm boards of course have a grater tendency to cup.

        Good luck shout whenever you want and if you want you can write an article which you can post to this blog.

      9. espdesign10 says:

        Hi Garrick

        Sorry I haven’t replied in a while (been having lots of problems this side!).
        One of which, I got the Garapa planks delivered to my place today, but instead of being smooth both sides (as ordered) – they delivered ribbed one side, smooth the other.

        Does it make a difference? Is there typically a ‘superior side’ and an ‘inferior side’? Or can I just put the ribbed side down and have the smooth side up?

        Otherwise, I will rather go with your recommendation and use two screws per intersection, especially on the 90mm width.

        Regards
        Edward

      10. Howzit Edward

        Grooves up so that the water can escape quicker between joist and deck boards. This will slow down any degradation caused by rot. It is fallacy that grooves provide more traction as a non slip surface. In fact grooves up will cause the deck to be more slippery. Wood is not slippery by nature. It is the stuff such as dirt, algae etc. on the wood that makes wood appear to be slippery. So grooves up will collect lot more junk and make it slippery. Also with grooves up you can never sand it if you have to and also you can’t fill the screw holes with epoxy as you can’t sand it flat so the water will then sit in the screw holes and rot the board. Grooves up makes it much harder to clean ones deck. I also read a comment once about grooves up actually being more slippery due to less surface area on your shoe. So there’s it, grooves are good and they must go down. Plus they look horrible up.

        On a lighter note, the best comment I have heard about the argument of grooves up or down is that it has to be grooves up because once your deck is finished and you celebrate it with a few mates and a few beers and end up having too many beers and pass out on the deck, with grooves up you will wake up the next morning with lines on your cheek and everyone will know that you passed out on the deck. So grooves down, then no-one will know you passed out on the deck….:)) Do you have any pics yet? You can inbox me info@thewoodjoint.co.za.

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