decking advice

Hi Everyone.

Going to spend December re-building my deck and have a whole bunch of question. mainly to check im correct in all the research ive done in coming up with the dimensions.

Firstly before I begin. the house is on the hawkesbury river no more than 5 meters from the water (near brookln) so salt water is an issue.

I am planning on using Hardwood throughout. Merbau for Deck and handrails, and Seasoned Hardwood for posts, bearers, joists and ledger. As far as the grade goes I start to get confused here. I have been using the 'Timber Queensland Technical Data Sheet 4' to help work out my spans and technical requirements. Am i correct in assuming that 'seasoned' timber is stronger and therefore going to give me more span than 'unseasoned' ie. if i rate everything off the 'Unseasoned Hardwood, F14' i would be safe in using this as my base for seasoned hardwood at F14.

Now that I have that out of the way, the deck in question is 5m by 3.6m the 5m run is parralel to the house. I will bolt a 150x50 length @ 5m onto the wall.

The bearers will be 2 x 200x50 lengths bolted to 3 posts (100x100) that will be cemented 600mm into the ground.

I will then hang joist brackets onto the ledger and run my joists 3.6m in a cantelivered fashion over the bearers. The bearers will sit at 3m leaving an overhang of 600mm.

The rest is no problem. I just would like clarification that I am making the structure sound enough. The overall height of the deck is 900mm at the house and then approx 1000mm at the 3m mark.



below is an image to help calrify my undertaking.

Thanks for any help someone can give me

Dave

150*38 f14 unseasoned joists at 450 centres will span 3100 plus 900 overhang.
150*50 f14 unseasoned joists at 450 centres will span 3400 plus 1000 overhang.
These are for decks over 1000 above g/l.

This information is intended to provide general information only.
It does not purport to be a comprehensive advice. No responsibility is accepted by AusDesign for the accuracy or omission of any statement, opinion, or information in this statement and readers should rely on their own enquiries in making any decisions touching their own interests.- it's a sad world

thanks for the reply Peter.

for slight 'overengineering' ill go the 150*50 for the joists.

Will then, the 100x100 F17 posts with 2 200x50s f17 bearers bolted to them 'partially housed' be adequate to support the above span. Ill have three posts bolted to stirups set in at least 600mm of concrete.

the entire deck is 5x3.6m so 18sqm.

Also, are stirups a better way to go over cemeting the posts directly into the ground for longevity?

regards, and thanks for the help

dave

according to hyne, a florr load width of 2.4 and span of 1.5m (going off your picture can be done in f17 vic ash 200/50 - but thats at the edge of design limit, so 2 side by side will do the job well. If housing in, make it partial with bolts, and also make sure you paint thoroughly the housings and cuts, as the open grain facing up is the easiest place for rot to start.

foorings always depend on soil type as much as anything - if its easier I'd err on the side of bigger - not something that ever happens to me - I'm always using a jack hammer to dig holes round my place.

Your much better off going with 150 x 50. If you use 38mm there is a chance the wood might split because of all the nails you bang right down the middle of it. As for f14 vs f17 they are bothe as strong as each other. F17 is just appearance grade which looks a bit nicer. Usually used for posts or 250 x 50 stair material.
As for stirrups, i have never understood concreting the posts straight in the ground. Doesnt matter if they are treated they will still rot or have termite infestation over time. Much better to use stirrups and keep all timber above ground.

sol, posts in the ground provide more lateral stability than stirrups, especially for non braced decks - stirups really only take downward load. Also, hot dipped gal stirups will also fail over a number of decades once the leaf litter and soil gets around them - so apart from 316 ss - things have limited life.

Quality treated pine should last almost indefinately in ground, is well installed (gravel base - concreted in with above ground finish) - I've removed koppers logs installed as retainers with no backfill, holding clay soil, 1.5m from a wharf timber (300*300) that was destroyed by termites with zero rot or damage - the logs were installed in 1975 and have been damp most of the time - so timber can last if its treated appropriately it would seem.

surely stirrups of the attatched image kind cemented in at least 450mm into a 600mm concrete base would give pretty good lateral support?

What about diameter of the concrete base is 300mm to much or little?

cheers

um, 300mm in with those sort of stirupps most certainly will provide lateral support - tghe most common stirups howver are single 25mm gal pipe between the base and the top - that bit been weak as, not to mention the typical 2 25mm coach bolt! - your piccy however is a more substantial bit of gear.

300 round and 600 deep is all I'd do, but if its slushy soil, I'd be on the safe side and bigger - especially if your not mixing the concrete by hand! Having done 6 600mm deep posts this weekend - I really really really wish I could of got a wheelbarrow to them and a mini mix!!!! - experience is not the most fun way to learn........

Just got the quote from the timber. ouch, hardwood aint cheap. The guy at the store is suggesting I use F11 (blackbut or equiv) for the bearers and joists to help bring price down, Personally Im not fussed on the look of the joists or bearers so id say sure but the strength is the only thing that concerns me.

will F11 unseasoned (150x50) span 3000mm with a 600mm overhang? spaced 450mm over 200x50 double bearers of the same F11??

He also suggested Hyspan? Any thoughts..

Regards

dave

From the span tables AS 1684.2 :

For F11 unseasoned N4 wind Cat

150x50 at 450mm centers
Single Span : Span of 3200mm and Cantilever of 900mm
Continuous Span: Span of 3700mm and Canitlever of 1000mm

Not sure what your FLW so cant comment on the bearers.

Cheers
Purse

When it comes to your decking itself, check out local auctions. I did my deck recently and got 550LM of mixed hardwood for $1.80/LM and the mixed colours look sensational. Im not suggesting you go down the mixed colour look, but just to check with local auctions. Most of the good ones have the catalogues online so you can check from week to week til they have something you like. Most hardwoods run over the $4.00 mark and with the amount I needed I saved a packet. As for the rest of it, I just used treated pine and painted it. Good luck. Its a great project with great rewards at the end.