Thread: 1st Post About 1st Deck woohoo

gday jerry

you've got about 80mm to work with, say 20 for the decking boards leaves you 60 for the structure along the edge of the house. there are a number of posts on the forum about building along the ground and i believe the lowest to date was using treated-pine battens 35mm deep, fixed off to the concrete with dynasets.

if you were to use this option across the pavers you would need to pack under the battens or joists with steel, hard plastic, pavers, old cutting discs, fibro, (anything that doesn't compress) - the further out from the house the more packing, unless you wanted your deck to slope as your paved area does.

once over the grass you can dig the square of grass out to the size of a thick paver or a brick to act as a suitable base to spread the load onto the dirt. you would also need to cover the grass with a decent matting to prevent growth getting through. the bunnings woven plastic is just shyte for this, you need the dense felt matting which is a little more exy but when you're not mowing your deck in five years time you'll have forgotten about the extra cost a long time ago

spacings -
- battens at 4-500 depending on how springy you like it;
- packing under the battens (say, 35 - 50 deep) at 3-400 apart. 50 - 75 deep and you could go out to about a metre. 75-90 and you could go out to about 1250 apart.

packing under the battens is the easy part though! don't be afraid to stand on it and bounce up and down. that's how bouncy it will be once it's built. as you are putting them all in place you can hold their spacing by doing the first run along the house with your decking.

r's brynk

You also need to check with your local council. Many have a minimum of 450mm off the ground deck height. (i think for termites ). Not a big problem if its small and free standing but if its attached to the house then its a different story.

Originally Posted by dazzler

You also need to check with your local council. Many have a minimum of 450mm off the ground deck height. (i think for termites ). Not a big problem if its small and free standing but if its attached to the house then its a different story.

You need 400mm for inspection or 150mm for ventilation. If you provide termite protection to the deck and not allow a path into any other structures then 150mm is OK. Check with your council as to the requirements but you could also try some thick sleepers as a base and have a barrier between the sleepers and the joists. For this to work you need to demonstrate that ventilation is not and issue for the timber and their is no path the termites can follow to reach the unprotected timber.

Have you considered a concrete slab? I know it isn't a deck but the deck may not be practical.

Would you consider bedding down sleepers instead of having decking?
Different look though.

Alternatively, have your decking as an "island" with a gap between it and the house, then place a row of paving, sleepers or pebbles to separate it from the house.
Not sure if this needs council approval, but it could be argued that the decking is merely your landscaping choice, and none of the council's business???

good points about termites! the extra run of bricks sounds like a good plan, they would need to be mortared into position so the little buggers have to tunnel over them, however you can't cover any ventilation or weep holes if they exist at this level. alternatively you could make the first two or three runs of board easily removable (less screws, or blocked instead of screwed?, maybe even hinged?, or in sections on their own battens?) so you can inspect where the deck butts up against the house. jerry can you confirm the construction of your existing floor? ie, timber or slab on ground (or other)? are there existing brick vents along the base of the wall where you wish to build? at what level in relation to these are the weep-holes? (they will be the missing vertical mortar joint aka the perpen)

Thanks heaps for the input guys, I really do appreciate it. P.S I went to bunnies to buy that book by Allan stains, still getting my head around the spanning charts, funniest thing so far about them is that they don't seem to change at all when refering to single or continuous on the bearer spacings..

How would you guys tackle a 3m wide span.
I'd prefer to keep the deck seperate from the house if possible, I was actually thinking that I would be able to get away with using 90x45 treated pine eveywhere but I don't think I can span quite that far.. Doubling up on the bearers ofcourse. Cheap but good...would it work

I'm getting confused with load widths as it dscribes them as two half spans over a bearer?? is that the same for a bearer over a post??

I'm starting to think that a bearer only type deck around the side of the house is an option with the least digging invloved.

brynk, to answer your question the house is a typical double brick here in Perth, just like the other 90% of them here. There are no brick vents along the base of the wall

what are your overall dimensions?

when you talk about large spans with bearers you are looking at a minimum depth of around 300, probably more (unless you look at steel). sounds like your house is slab on ground which is good for the ventilation thing. at what height were your weep holes? as you can't cover these either

load-widths are two half spans because if you place a theoretical load at centre span of a member then 1/2 the load will go to one support and the other half to the other. this is why you see 2 load widths centred over a support of the member (ie, a post) - this post has to support two halves of a bearer, one half coming from one way and the other half coming in from the other.

so given this, imagine the last post. this is only supporting 1/2 the load of the posts mid-span. there is a more economical way to do it - reduce your number of supports by taking advantage of a cantilever at each of the ends.

because of your deck-height it is certainly more economical to build a free-standing structure on ground, without concerning about bearers and footings. otherwise you will have to dig the dirt up, only to cover it with a deck. because there is no risk of the structure 'falling over' then you only need to build for durability to ensure your labour isn't wasted in 5 years time

according to some older span tables of mine, continuous span bearer f7 seasoned softwood continous span:
2/290x45 : FLW 1200 span 5000 canti 1500; FLW 2400 span 3600 canti 1000; FLW 4800 span 2500 canti 700;

r's brynk

Originally Posted by brynk

reduce your number of supports by taking advantage of a cantilever at each of the ends.

I wouldn't advise cantilevers on decks unless necessary. The span tables are set up with load widths assuming that the other side of the member is supported. In terms of the member loaded the load will be roughly the same but the member that is cantilevered will not be covered in those tables.

If the member is not supported at both ends then the unsupported edge will deflect much more and may make the deck feel bouncy.

I think if you are going to use the timber deck option I would get a series ex railway sleepers (hardwood) you see in bunnings. Dig them into a series of trenches. At the spacing required for the decking to span. Making sure that you have "trimmers" at the edges and thus making a box (lay the ones closest to the house far enough away from the brickwork to see down there).
Then use some sort of metal ties or brackets to link the brickwork and the sleepers and get a termite protection company to lay some kordon sheet or termicide as a barrier. Then lay the decking on top. You will not need inspection due to the fact that you have provided a barrier for the termites. If they say you need ventilation then leave gaps between the trimmer sleepers along the 10m length.

Not the most cost effective but it will work and it complies with the BCA as an alternate solution.

Brynk, my overall dimensions are 3m wide by 10m long. I'm not sure what you meant by the following, "because of your deck-height it is certainly more economical to build a free-standing structure on ground, without concerning about bearers and footings" especially that last bit about the bearers and footings. Did yu mjean that since it is all low lying it will reduce the cost of posts/stumps/concrete??

Brynk, you also asked about weep holes. The house brickwork doesn't have any at all. The only drama is the fact that the house has a couple of full length windows on the proposed decking side so it needs to be kept low i.e. sliding door level or a little lower

I don't mind puting three posts/ stirrups down to span the bearers, i'm just looking to have it done in the smallest possible member so I can save on height and keep it as low as possible.

Does anyone think that having a bearer supported on three stirrups is the way to go across the width?? bearer material being 2x 90x45 stitched together spanning 1500 continuous. Joists consisting of 90x45 f7 seasoned pine again over the top of the bearers spanning 1300 continuous. At least that way i'm keeping my heights down from the paved area to 180 overall + the decking board thickness on top. I could get the deck a little lower by taking some of the earth away aswell???

Is it more economical to lay the boards along the width or the length, i'm gonna go with width as material seems to be cheaper in the shorter lengths ayy. I guess it all depends on how much you need to spend on supporting it one way or the other way, I just don't know which way is better or if anything above I have thought of makes much sence...

DvdHntr, lol got any good DVD's....
I understood the cantilever idea a bit, I don't think i'll go that way, if I was to cantilever it prob be wouldn't be more than a 200mm..Maybe thatway I can use less posts.. or at least make sure that the construction will be slightly underspan making it strong as there would be no future plans to have roof going over it, maybe just a sail or two..

Maybe its cheaper to ledger of the house and use some 150x100 bearers that way i'm only using two posts per bearer and pissing in my span, running the joists between the bearers to save on height?? Is this idea have any merit???

Once again thank you so much guys for the input, it's actually better to brainstorm like this as it helps me learn and get my head around things...so cheers 'n' beers to all.

J.

i can't disagree that canti's feel springy - this is definately the case., and would be even more noticable on a softwood or less-dense hardwood. the timber framing code (AS1684) and the associated span tables do cover canti's in their provisions. can't speak for the staines decking book though, as i have never read it.

sorry yes i should clarify - it will be more economical for you to place the structure on the ground without bearers & under-ground footings. your deck height is 80-odd mm's at the lowest point near the house. i'm guessing it gets to around twice/ three times that three metres away from the house? you can use brick piers in accordance with the footing code, closer than the points of maximum span on your joists - according to my (slightly outdated) continuous span seasoned f7 softwood joists 90x45 at 450 centres: max span 1700.

this plus the decking height brings it in at nominally 110mm above the pavers just outside your door. for the joist run against the house you could use a 90x45 laid flat (45+20 = 65 above the ground). the savings from not using bearers would cover the costs for a treatment as dvdhntr describes. here is a light read for your enjoyment!

Protection for whole-of-house timbers from subterranean termites

r's brynk

Originally Posted by brynk

the savings from not using bearers would cover the costs for a treatment as dvdhntr describes.

Unless it is floating in the air there needs to be either a termite barrier, treated timber or hardwood with less than 20% sapwood.

Hi brynk,
Care to summarise the light read for us .

Doc.

brynk,

The ground level is flat as a tack so 3m's away from the house is just as flat as right next to the house.

Structure on the ground without bearers??, wouldn't everything rott quicker or are you still refering to the sleeper idea stated previously. your not saying it's ok to lay the joist directly over the grass are ya..

Brynk, i'm also a little confused about quote"for the joist run against the house you could use a 90x45 laid flat (45+20 = 65 above the ground)" are you refering to the part of paving I have and just running joist over the pavers with some anchors??

All I want is to get my construction as low as possible without digging if possible in a economical fashion, If I have to dig a bit I will...

Does my bearer deck Idea have any merit??

or you guys reckon its still cheaper to run all 90x45 profiles rather than 150x50bearers with joists in between.

Doc,

light read alright, havn't looked at it yet the number of pages scared me

You may be best off pouring a concrete slab and gluing the decking to the top. No termite issues.