# Forum Home Renovation Decking  8 x 6m low deck using doubled 90x45 bearers and 90x45 joists face flat- advice pls!

## damian1

Gday, 
Just thought I'd get some advice from the experts on spans etc for the deck I need to build while the missus is on holidays with the kids. Need to build it in three weekends and after work sessions.... 
Deck is 8m x 6m. Building it at ground level straight outside the back door- so limited vertical height to work with, as I dont want to undermine the house foundations. Plan is to use 6m treated pine (H3) lengths for the bearers and then run the joists at 8m (using 2  x 4.2m lengths cut to size). 
I spoke to Mike at  Colli & Sons (big timber supplier here in WA) who reckons he has build decks for 12 years. He recommends; 
doubled 90 x 45 H3 treated pine for the bearers spaced at 1m.  
90 x 45 H3 treated pine for the joists as well, but this time place the timber on its larger side face down  ie the 90 side face down. Spacing at 500mm.  
300mm half stirrups for post supports every 1130 for the bearers. One bag of kwikset concrete for each post. Have the stirrups sticking up out of the ground 75mm for termite clearance. This is a heap of posts to install- 54 to be exact.  
Bolt the bearers to the stirrups using 2 x 210mm galvanised cuphead bolts. Screw the joists to the bearers using 1 x 75mm treated pine bugle screws at each joint.  
decking is currently planned to be 65mm x 19 wide jarrah Smartdeck. It is a secret fixing type system.Apparently much quicker to install than top screwed system and guaranteed spacing between boards. Smartdeck â Beautiful timber that won't cost the earth. Install the secret clips using a nailgun and construction adhesive. 
Using the above plans the total distance from ground to bottom of deck will be about 215mm. This is quite close to the ground I know- but H3 treated pine should be OK with extra wood preservative on all cut ends. Plus it never rains in WA so moisture hopefully not a problem. I could lay builders black plastic to prevent moisture and weeds, but am concerned that I would be creating a dam/duckpond below the deck. 
Thoughts ? Any criticism of the above ? My key concerns are: 
deck bounce- will the bearers and joists as described above permit bounce ? Colli & Sons assure me it will be ROCK SOLID. Doubled 90 x 45 bearers ok - contemplating 140 x 45 but that adds quite a lot of height and cost? Using joists 90mm side down ok ? It will save me 45mm in vertical height. Am I better to dig a little deeper and install the joists the traditional way i.e. on edge ?  
I am thinking reduce the joist spacing to 400m but stick with bearer spacing at 1m (actually 963 using the blocklayer deck calculator program- fantastic site). 
Installing 54 posts will be a lot of digging. I am thinking of hiring a post digger but everyone I have talked reckons its a waste of time. Better to use a post shovel and work up a sweat- that way the holes are where you want them to be and are not 500 x 500 wide. Thoughts ? I'm thinking one bag of kwikset per post is not enough. Likely need 2 or 3 bags per post -  which could mean 100-150 bags of concrete ! Is there a better way ? Maybe I should get all posts installed on the bearers and everything squared up and then get a miniload of premix delivered and pump concrete straight into the 54 holes ? Any idea of cubic metres of concrete I would need - my estimate is about 300x300x300 per post of concrete, which delivers 1.5 cubic metres of concrete for 54 posts. Sound about right ?  Maybe I should round up to 2 cubic metres to be safe. 
Total cost of above is about $5100 for a 48 square metre deck. Seems quite good based on all the pricing I've read on this forum.
All advice appreciated ! 
Cheers 
Damian

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## zaqwsx3

Hi Damian - how did you go with this deck? 
I'm in a similar situation to yourself, where I only have about 200mm height to play with from the ground up to my desired deck height. Did you lay your joists with the 90mm side face down? That's a solution I hadn't heard of before - wondering if anyone has used it successfully before. Would also be interested in the 'bounce' factor, and impact on its load bearing ability given I haven't seen any span tables that factor it in. Total height around 151mm: 
* Deck - 16mm height (65x19)
* Joists - 45mm height (45x90)
* Bearers - 90mm height (90x45) 
Cheers,
Dan

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## shauck

Dan, have you considered getting machinery in and scraping back the ground, sloping it away from the house, so you have more clearance to use 90x45 joists and bearers as they were intended to be used? Even 100mm would be worthwhile. Then use H4 for the bearers at least, if not for all of it. If it was me, I'd be doing a 1 sleeper high retaining edge with redgum sleepers, appropriate drainage and fill the area and put down pavers. Way better longevity. I love decks and building them but when you're that close to ground, unless you can lower the ground level, that's what I'd do. 
Another option is to eliminate bearers altogether and go for a supporting system that sits under each joists at distances that replicate the required span of bearers. All sorts of stuff out there, including the pic below.

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## zaqwsx3

Thanks Shauck.  I haven't looked into getting a digger in to scrape the level lower - was just another cost I was hoping to avoid if at all possible. 
I measured the height again, and I have about 280mm from ground level to the desired deck height.  Another obstacle I have is a silt pit drain that sits near the rear sliding door.  Not hard to lower, just more work though.    
I'm hoping the deck will go from the house out about 8m into the yard, where there's a pool we're restoring.  There's an old deck around the pool at the moment (you can just see part of it in the pic above), although I'm looking to rip this up and replace it to the correct level. 
Bunnings have those concrete footing blocks for about 20 bucks each, and they're 190mm high, but 140mm to where the joist would sit.  Many thanks for the tip. 
cheers,
dan.

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## shauck

280mm is not the worst starting point. Why not just have your bearers 2x90x45 and your joists 90x45 running inline rather than joists on top of bearers. Stirrups (there are various heights available) in concrete instead of posts, to support bearers. joist hangers to attach joists to bearers. That'll give you 170mm clearance to ground level or a little bit less if your decking level is to be less than the house. I'll bet a lot cheaper than the other option. Probably less work too than trying to level each one of those concrete supports. You can dig the holes for the stirrups, attach the bearers to the stirrups, set them up level, square at set distance, etc using props, with stirrups hanging in the holes and fill em up with concrete. Take care not to knock them out of place and double check them before they set.

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## Gaza

Joist 45 mm deep only span 600 IMO no way 1.0mt, 90mm only spans approx 1.3 in mgp10  
Sent from my iPhone using Tapatalk

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## toooldforthis

As said above I would be paving it, but if you really want a deck scrap the soil first so surface water drains away from house and doesn't pool. 
You could also consider doing away with the joists and using 140x45 bearers and box them out (like noggins) and lay the deck on them. You would need to spec out spans, and considering doubling them up, to optimize hole digging - tho in Perth digging holes in sandy soils is pretty easy going. A bag or 1.5 should be enough per stirrup. 
Edit: whoops that was in reply to original post, digging holes in Melbourne is different, but boxed sub structure frame could still be considered.

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## shauck

> You could also consider doing away with the joists and using 140x45 bearers and box them out (like noggins) and lay the deck on them.

  Those would be joists still, not bearers. They'd also be closer to the ground by 50mm. No need to go to that expense or trouble. Just 90x45s for joists and bearers, inline. Cheapest, simplest, and furthest from ground. Clearing the top soil and making sure the ground slopes away from the house (if it doesn't already), is good advise.

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