New Deck plan - I'm nearly there but i need some help...

[DayDreamer]

The plan:

To build a totally exposed, freestanding deck 6 meters wide, 3.7 meters deep. It will be surrounded on three sides by brick/rendered walls so ventilation will be poor. I have to excavate all soil as the new deck surface will sit flush with the current ground level. 4 meter wide Stairs will rise away from the deck to the top of a retaining wall (approx 700mm higher). See the attached design. The side walls already exist, the retaining wall is still to be built.

For the deck:
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*Three Bearers: 100x75mm in 6meter lengths spaced 1800mm apart, each supported directly by 4 gal stirrups in concrete footings (spaced 1800mm apart). I.e. Bearers to stirrups directly, no vertical posts.

*Fourteen Joists: 100x75mm in 3.7m lengths spaced apart by 450mm.

*280 meters of hardwood Decking: 90x19mm.

*Fasteners: SS square drive 10g type 17 50mm screws.

For the stairs:
---------------
*70 meters of the same decking.
*Fasteners the same as the deck.
*Stringers: No idea at the moment.
*Maybe a ledger board at the top (bolted to a retaining wall that the photo doesn't show).


Help please???:
----------------------
- Should i cut the joists and hang them between the bearers, or sit the joists ontop of the bearers and thus excavate an extra 100mm of soil?

-How much clearance between the ground and the bottom of the bearer? I've read about a minimum 150mm, but I've seen lots of photos where the deck basically touches the ground. However, the poor ventilation (and prior termite problems) might require it.

-How many screws will i need? I'm thinking about 2500?

-Wood Type: Should i go class 1 hardwood for the bearers and joists, or treated pine? I asked the manufacturers about H3 treated LVL and they didn't recommend it for poorly ventilated exposed decks.

- I've no idea how to support the stairs from below. Should the stringers go all the way through the deck to stirrups in concrete or can i have them fixed directly to the final bearer (i.e. by a joist hanger)?

[strangerep]

The plan: [...]

I can't recall if you said you already had a copy of Alan Stains'
construction manual(?). If not, it's essential to get a copy, or some
other comprehensive book. The sizes, etc, are probably different
depending on whether you're using F7 treated pine, or (say) F27 KD
hardwood. But I'll leave it to others with more professional
construction experience to comment on those details.

One other thing: for bearers/joists more than 45mm wide, they
won't be kiln-dried, hence are subject to a lot more shrinkage. That
means you should probably try and go for narrower, deeper beams,
or maybe double-up 45mm kiln-dried pieces side-by-side for the
bearers. Using a deeper piece may be more cost-effective because
if you double the depth, you quadruple the load-bearing capacity.
But if you double the width, you merely double the load-bearing
capacity.

- strangerep.

[billbeee]

Hi
I don't like saying it, but why build a timber deck at all in that position. That's what pavers or stamped concrete is for. A lot cheaper too.
Ventilation is the least of your worries.
What about drainage? Looking at your drawing the thing will flood.

Regards
Bill

[DayDreamer]

Hi
I don't like saying it, but why build a timber deck at all in that position. That's what pavers or stamped concrete is for. A lot cheaper too.
Ventilation is the least of your worries.
What about drainage? Looking at your drawing the thing will flood.

Regards
Bill

Hi Bill. I do understand your point which is why I had planned on having a drain in the excavated area. I guess it's a look and feel thing in the end. My opinion is that a wood deck & stairs will look sensational (atleast i prefer it over pavers/concrete but i am concerned about the practicalities of using timber in such a design. I was going to pick as durable timber as possible, but if you all think that it just wont be good enough then i'll definately heed the advice.

[Yonnee]

If you run 4 bearers @ 1230mm, you'd only need to run 90mm x 45mm. Fair bit cheaper for starters. For the extra cost of an extra bearer, you'd save a fair bit on joists.

I couldn't see a reason why you couldn't run H4 T/pine sleepers as bearers straight onto the level ground and fix them with galv'd spikes.

[DayDreamer]

-How many screws will i need? I'm thinking about 2500?

Actually, having done a recalculation based on 90mm boards, i think i'll only need 1500 screws give or take.

[billbeee]

Day dreamer,
No, no, don't let me put you off, you have obviously worked it out well.

I tend to go for more cost effective designs because most people want that. Also we might get a tad more rain on occasions than you do.

Most of our decks up here are elevated, so I have a different slant on things.
You are getting some good advice in this thread, so I'd say go for it.

Put as much preservative on as you can. On all the timber before fixing.
Good luck with it.
Bill

[strangerep]

I guess it's a look and feel thing in the end. My opinion is that a wood deck & stairs will look sensational (at least i prefer it over pavers/concrete but i am concerned about the practicalities of using timber in such a design. I was going to pick as durable timber as possible[...]

Thinking about it some more, I have to say I agree with BuilderBill's
original concerns. You clearly want something that will be a wonderfully
attractive feature of your property, but any sort of full-exposure exterior
natural-finish timber requires heaps of maintenance. And even then, for a
deck surface, it's rather a losing battle. Even a highly durable timber will
go grey and ugly without maintenance. I think you should explore the
relative costs/tradeoffs of some other non-timber solution.

If I was starting over again, I'd try very hard not to have a timber deck,
but rather investigate tiled solutions. If it's low down near the ground, I'd
lash out and get a reinforced concrete slab and steps with correct fall, etc,
and then tile it. You could put a stunning large central emblem pattern that
would look fantastic. It would keep looking good over time, with very little
maintenance apart from occasional cleaning.

Sometimes the best advice about exterior natural timber is "don't use it".

- strangerep.

[UteMad]

Hi
I don't like saying it, but why build a timber deck at all in that position. That's what pavers or stamped concrete is for. A lot cheaper too.
Ventilation is the least of your worries.
What about drainage? Looking at your drawing the thing will flood.

Regards
Bill

Annoys me too....Not that your not entitled to a deck if you rang for a quote i would tell you if i didn't know you to go find the dearest paver you like pay good money to have it fitted then multiply the quote by 2.5 and thats what a deck so close to the ground will cost.....Most people say something along the lines of "oh i thought decking would be a cheaper way to go" ......Nuf said ..... I saved 2hrs wasted on a customer with no idea...
If you have a direct question PM me as i prefer to offer a direct answer to your question not misguided generalisationss others will copy and get in trouble with....I would prefer you concreted and tiled or concreted and paved you'll get a better finish for your application...As a DIY your in for too many pitfalls that you won't reckognise for a few years when things start to go wrong


cheers Utemad Oh i like smilies tooo all my fave looks

[dazbeer]

Can anyone recommend painting the underside of Kwila decking (on a ground level deck) to increase its lifespan?

[UteMad]

Can anyone recommend painting the underside of Kwila decking (on a ground level deck) to increase its lifespan?

Give the cochroaches each a brush as they run under the deck and feed them to paint it with your crums you drop through the cracks LOL....

You have to do all the way around the board including edges... I am not really a fan i find the bottom is better left to breath and provide as best sub floor ventilation as you can

cheers utemad

[Trav]

I'm with others here. A deck in that location would run seriuous risk of rot etc, and would be a real termite attracter.

Pavers, tiles etc would look equally good in my view and would take heaps less maintenance.

Trav

[DayDreamer]

Hey All;
Thanks for the sound advice. I've decided to heed your wise words and opt for a paved area instead of deck. It's a bit of a personal let down as i really wanted to get stuck into some wood work, but practicality wins in the end.
This is a brilliant forum and has no doubt saved me money and hassles further down the track.

cheers,
DayDreamer.