Bearers and Joists? Or just bearers and decking?

[Mick666]

Hi all,

I'll do my best to be clear - I want to build an entry deck to our new home. The deck will be roughly 1800 wide by 5000 long. The first 2000 of the deck is within the entry alcove at the front door, then proceeds out another 3000 to the front boundary. My little problem is ground clearance - I have roughly 250mm from the bottom of the door to ground (essentially the slab depth) and I want to use 32mm thick decking. So what I thought I would do was use thicker timber for the bearers and not have any joists on top. So I would use ledgers attached to the house with a couple of post in the middle for support in the alcove section with beareres bolted on (the first 2000) and then for the remaining 3000 use a normal amount of stumps with the bearers bolted on in the same fashion. I figured this way I could use 600mm centres for the stumps and using a 200mmx50mm bearer disregard the need for joists.

I have been procrastinating about this project for quite a while because I can't decide how to overcome this issue without leaving out the joists. I suppose I really need someone to tell me either that I'm wrong and that the method I'm proposing will not work and perhaps offer me a better solution or quell my reservations by telling me yep it's all good.

Just to provide all the facts - I love wideboard decking (the 32mm thick variety) so if possible I'd rather not compromise that aspect of the design but everything else is subject to any and all advice. Also I hate trampoline like decks so I want it to be super sturdy as well....geez louise I don't ask for much do I:roll:.

Many, many thanks.

Mick.

[silentC]

Technically, you should have clearance of 400mm between the bottom of your bearers and the ground.

I think your options lie in the paving and or concrete area.

You could perhaps get away with laying a T/P sleeper deck on the ground. I think anything else is asking for termite/woodrot problems.

You definitely wont get something that low to the ground approved by council if you're going to do it by the book.

[silentC]

BTW there's nothing that says you need to use bearers if the joists are capable of spanning the dimensions of your deck. You just need more stumps is all.

[DJ’s Timber]

What about Duragal

[silentC]

There's nothing in the doco I have on Duragal about it but I don't see why it would be any different to the regs for timber framed decks. I'll have to try and find where in the building code it states that decks must be a minimum of 400mm off the ground because I've only ever been told that word of mouth by builders and inspectors.

[silentC]

Apparently it's in BCA Table 3.4.1.2:


Sub-floor Clearance: generally 400mm min. to enable inspection for termites and vermin (refer BCA Table 3.4.1.2)

But in my copy of the NSW Timber Framing Manual it says:


For well drained dry spaces, the minimum clearance between the ground and the lowest floor framing member shall be 200mm or more if access is required for inspections.

Whatever you do, you want to make certain that you're not providing a highway into your house for termites. If your slab is the barrier, then the edge needs to be exposed for at least 75mm.

[Mick666]

Hi all,

thanks for the speedy replies!! Mmmmm, yes clearance is a bit of a problem huh? I just took a quick look at the OneSteel site (sorry, never heard of DurGal before) and am very interested. Do you think that it (or another similar product) would do the job? It would certainly allays my fears regarding clearance and wood rot or moisture issues. How would you attach it to the stumps? Would the piping start to collapse if you tightened the bolts connecting it to the stumps too much? What sort of screw would you use to attach the decking to the steel? Would it be much harder to work with than timber?

Sorry I have a million questions but I really appreciate all your advice.

PS SilentC ..."by the book" - what council don't know (or can't see) won't hurt them:D

[silentC]

All my decks and verandahs are Duragal but they're all much higher than yours will be.

Duragal can be welded or tekscrewed (it's designed to be screwed). For stumps, you use a bit of 90mmx90mm post and the bearer or joist would sit on top of that using one of their post connectors. Decking is nailed to it with twist nails using a coil nailer. They don't recommend screwing decking to it.

You're biggest problem would be to get any of the standard bits in with the headroom you've got. If you used a 75x50 joist, which is all you need for that span, that only leaves you 175mm for the stump. You'd probably just be better off putting a gal stirrup in the footing and sitting your joist straight on top of that.

I still think I'd be looking at pavers or something flat on the ground. I just think it's too low to do with timber.

[pharmaboy2]

Mick,

\firstly for termite's be sure to use gal stirrups out olf the ground, have a decent 5mm gap between each board (good for light under the deck), and leave 10 or 15mm gap between deck and house to make sure any termite bridge can be seen.

As to consruction method, the usual way is to use a beareras a fascia and joist hangers for the joist, so you could use say 90/70 bearer down the 5m side, with 90/45 joist hangers with hardwood joists on the hangers, total depth of 132mm. This however would mean the boards running away from the house instead of across.

You can set it up the other way as well, but you have to be a little more carefulk with your heights as bearers will have decking across the whole thing, so it would also be best if the spacing made that occur entirely over the bearers (so you still have gaps bewteen the boards - it looks kinda funny when one gap has something under it for its entire length.

200mm inspection gap isnt too bad for something only 1800 wide with gaps between boards

[Mick666]

Hi SilentC,

thanks again for the replies. It's not that I'm opposed to pavers and the like it's just that it's a kind of akward space as one side of the entry alcove is lower that the other because the house is on a three step down slab (three different heights). So one side of the alcove is say plenty high enough (because of the step down in the slab) while the other is quite low (as I mentioned like 250mm slab height). So laying concrete or even gravel/sand foundations for pavers is somewhat problematic so I thought a deck would relatively solve the issue. If the 200mm height restriction is the same in Victoria (where I'm located) then I guess I might be able tio manage that...somehow.

Nonetheless, our frame is steel and our house is brick so I'm not overly concerned with termites - especially if I use stirrups as opposed to stumps as you suggest pharmaboy2. So could I just run the bearer/joist across the stirrup and fix through it the same way you would a stump? But I definitely want the boards running parallel to the house rather than perpendicular to it otherwise as you walk toward the front door you will be staring down the gaps the whole way....which seems to look kind of weird and accentuate the gaps as well.

[silentC]

200mm inspection gap isnt too bad for something only 1800 wide with gaps between boards
Make that about 100mm if he uses your method and assuming there's no step from the threshold to the deck.

BTW I set my verandahs up using a fascia beam. The joists are welded to the back of the bearer. Total height plus decking is 170mm (150mm bearer). I still wouldn't put it that close to the ground.

[silentC]

one side of the alcove is say plenty high enough (because of the step down in the slab) while the other is quite low (as I mentioned like 250mm slab height)
In that case you're probably OK because you've got more clearance on the downhill side. I've got one point in mine where it's about 300mm off the ground but it slopes away and I can crawl under and see right up into the corner.

[Mick666]

well... I won't be able to crawl under to look because it will still butt up against the house - it's just the alcove is lower on one side. Can you purchase stirrups with different size housings? That is, that have a different size stirrup to allow for larger or smaller stumps? Or is it pretty much a one size fits all type of product and you just pack or trim according to your needs?

Thanks guys, this is fantastic information....I LOVE THIS SITE!!!!

[silentC]

There are a few different types. You can get a one sided stirrup that only has one flange that will accept any size post. The standard one is made to suit a 90mm post.

[ausdesign]

There are small areas in the Jan Juc / Bells area covered by wildfire management overlays which if your within may impact on the construction.

[Mick666]

Hi SilentC/All,

I just thought of one other question that has occurred to me as I was reading other folks posts regarding low decks (or as I may want to call it if council drop by "walkway"). Is it possible/feasible to forgo posts/stumps all together and just bolt my bearers straight into/onto a one sided stirrup? Up until this week I was all set to buy 100x100 H5 Tp stumps, whack them in and cut them off where necessary with the intention of notching in the bearers but as I sit here I wonder why I can't just bolt the bearers straight on to the stirrup? Provided they were all in the right spot and at the correct level then they should just slot in and I don't have to worry about moisture on timber etc.

Whadayareckon?

Cheers
Mick

[silentC]

I've never built anything that close to the ground but I don't think there's anything that says you have to have stumps. In fact the stirrup would be the stump in that case. I've got a feeling I've seen it done somewhere.

I think if you're going to go down that path, then follow Pharma's advice and leave a gap between your walkway and the house so that you reduce the likelihood of termites bridging and you should be right. It then just becomes a landscaping structure. In fact you've almost convinced me to do a similar thing at our place where I have a similar problem.