Thread: Diagonal Decking Spec - Is this plan right?

Looks good, but I'm no expert. Have you considered using F17 or F27 opposed to MGP10, what height is the deck above ground level?

Why not continue your deck build in one thread opposed to starting new threads and losing continuity .

Originally Posted by Fat Chili

Looks good, but I'm no expert. Have you considered using F17 or F27 opposed to MGP10, what height is the deck above ground level?

Why not continue your deck build in one thread opposed to starting new threads and losing continuity .

Cos when people are scanning the millions of posts on this site, they want to find a post that is specific. My last post was about flooring design in terms of how to lay the top of the deck. Now that I feel that is sorted, I wanted some technical advice as to how to do the diagonals. Seeing that they are two fairly different requirements, I felt a new thread was in order...later is someone wants to know about diagonal decking joins they don't have to trawl through my other posts on what the top could look like. Hope that explains it.

Cheers...

It will work but I would have simplified it a bit, namely have your wall plates extending as bearers past the wall on each side to form a boxed section of bearers and just run a joist on the diagonal to facilitate the joining of deck boards.

Hope that makes sense.

I'll try another way of saying it.- Just run your bearers past the Crn of the house to the end of the deck on the right hand side. On the left side run the bearers 90 deg to the firsts lot joining with a butt joint.

Then run a joist at 45 deg from the crn of the house with the other joists butting into this.

You may be right about having a bearer on the 45 deg but I can't see any structural reason for it, it will just be more work and it doesn't look like people will see under there.

The deck subfloor is only 50mm off the ground?? Is that right ??

I've also never seen any 45 degree joist hangers - they may make them but I've not seen them!

Doog

Originally Posted by Dirty Doogie

The deck subfloor is only 50mm off the ground?? Is that right ??

I've also never seen any 45 degree joist hangers - they may make them but I've not seen them!

Doog

Yeah that's right. Only 50mm gap between the ground and where the bearers will be set on the stirrpus. Reason is that my house has floorboards already and I want to have them the same level. Even to put this in I need to raise my back door a little. I only have between 300-350mm to play with, so with a 190 bearer, 90 joist and 20 flooring, that rounds it out at 300, so I only have 50 left for the gap...that's also why I am using galv stirrups and H3 treated pine as I am paranoid about termites seeing we have found a few around and its Perth, which has a high concentration generally of the little beggers...

As for 45 degree joist hangers, I was thinking of using the normal ones and bending them...not possible?

I'm sure something like this could be used to simplify things - just some ideas for you.

45 degree joist hangers from Pryda - http://www.pryda.com.au/catalog.php?sectionid=20&type=Hangers%20and%20Truss%20Boots&conn=LFSL

Or

Mitek - Gang-Nail - http://www.mii.com/artefact/download.asp?aid=19713

I've used the Mitek products before, when manufacturing pre-nailed wall frames and roof trusses, never had any problems.

Not sure about where you are but when I built our verandahs, we were required to have 400mm clearance between the ground and the bottom of any bearer, unless there was fall away from the highest point.

For the diagonal, I would definiately want two hip joists side by side, perhaps with a gap in the middle. You are never going to get 45 degree butt joins in your decking to look right - the neatest way (I reckon) is to cut in a board perpendicular to the mitred ends after you have laid the deck - so you need a couple of hip joists to make sure you have enough width to nail the ends of your boards plus the filler board. I made mine 50mm wide, which gave me an inch either side to take the ends of the decking.

Mine is steel. I framed it up with a fascia bearer at the front, with the joists butting in to it. At the rear/house side the bearer is under the joists. With a 2m verandah, I didn't need a middle bearer. The hip joists are the same material as the rest of the joists, but you have to check the span because they are spanning further than the rest. There are trimmer joists then that run out perpendicular to the bearers and butt into the sides of the hip joists to maintain the 450mm on centre spacing.

All this is welded up in my job, but you can do the same with Pryda fittings - I've seen it done.

With yours, I would probably run the middle bearers right through, rather than butting in to the hips, and then sit the hips on top.

Hi Chilli,

Well I learn something every day re 45 degree joist hangers. Ta !

WA Decker -- I'm thinking you may have approval problems making a deck without subfloor clearance. Termites would bridge a 50 mm gap in 5 minutes and you wouldnt be able to see them in your situation.

I'm just wondering then if you really need the 50mm gap - put H4 treated bearers straight onto ground on concrete pads. This means that termites can still get into your deck timber. You could get the soil under your deck treated.

Or you could rake out the soil surface down to 100 mm and spread bluestone or gravel.

What sort of soil is under the proposed deck area? If it is heavy stuff that stays moist I think you might get problems with the tongue and groove decking you plan using. This is becuase the air under the deck will stay moister than the air above, possibly causing differential timber moisture content. You may get some bad smells coming up also if the soil is heavy.

Here on the QLD coast we have termites everywhere and sandy soil if not pure sand. For very low decks the bearers and or joists go straight onto the sand with concrete pads or sleeper blocks under them and we use treated pine decking. There has to a be a 50 mm gap between any decking and house structures though. If you could apply the same technique to your situation the fancy angles and corners you propose would be so easy. No joist hangers, no stirrups needed.

OK I'm full of crazy ideas LOL

Doog

Originally Posted by Dirty Doogie

WA Decker -- I'm thinking you may have approval problems making a deck without subfloor clearance. Termites would bridge a 50 mm gap in 5 minutes and you wouldnt be able to see them in your situation.

I'm just wondering then if you really need the 50mm gap - put H4 treated bearers straight onto ground on concrete pads. This means that termites can still get into your deck timber. You could get the soil under your deck treated.
Doog

Mmm. That could be an idea. The only thing is that I am trying to get my outside deck to matchup exactly to my inside flooring so I am restricted in terms of exact height. I will check the cost of H4 pine bearers though as 28 stirrups and footings costs time and money. I know people may say I need a 50 drop between inside and out with the decking. The area I am decking is protected by a colourbond patio the whole way around so there is only maybe 1/2 metre at the end around 5 metres from the door that gets any spray from the wet. Also its Sept now and the rain will stop in Perth soon. Seriously, we may get a few days a month, but we really only get rain from June to Aug in any real amounts.

I saw a mate put one treated pine joist as his base and then just put joists going the whole way along his deck. Looks ok-ish now but I reckon its a good way to atract the evil termites. The joists were all wet as well as they ended where a roof with no gutter ended as well...

We had termites around about 3 months ago right where I am putting this deck, about a metre from the house, so I know they are definately around (lucky they weren't in the house - we got it checked and sprayed.) The only reason they came though is that I set up a mini seedling and cutting retic spray on some old wood seats and a metal sheet - basically a welcome sign for termites.

If I use concrete footings, galv stirrups, H3 beares and joists and hardwood Jarrah decking, I am thinking that's a hard road for any termite to tread...but I could also get the ground sprayed beforehand prehaps to make sure...I will also repaint any cuts with stuff that deters termites as well...

Are you thinking that this still may not be enough? Its all about minimising the risk of them and save spending a heap on metal substructure which I priced at $7000 for my 72sq mtr deck as opposed to around $1700-2000 for H3 MGP10 Pine.

Originally Posted by Dirty Doogie

What sort of soil is under the proposed deck area?
Doog

It is sand - apart from close to the river, in Perth there is only sand - we even call black sand soil cos we don't know any better - sad hey? That's why my composting bin comes in so handy for my garden - great stuff!
It rained really hard here for the last couple of months (for Perth). And it hasn't rained for about two weeks. The ground is already super dry and sandy - its like a massive sieve (siv?) here - water just doesn't hold. The place where the decking is going is even worse as it didn't get any rain - great stuff for stable footings things just don't shift with a base like that (as opposed to clay).

Hi WA,

In my opinion , even with the ground treated against termites it would still be a bit risky. I notice in your plan that the joists are attached to a wall ledger - this gives termies a highway straight to the house walls , should they get through the other impediments.

Remember that it will be a nice dark still spot with fairly stable temperature under the low deck and termites just love these conditions.

I would suggest then that the deck is completely physically detached from any part of the house - separated by at least a 35 mm gap so you can look down and see if they try bridging the deck to the house. In practise this would mean running another set of bearers next to the house walls and have your joists overhang 75/100 mm on the house side but still 35 mm away from walls.

The theory here being that if the termites really want to get onto or into your deck they cant go anywhere else without detection.

You may also want to consider that once the deck is in it will be impossible to check if termites are getting into the house via the existing house stumps (not sure what your house is made of) or up slab sides on that part of the house.

I'd ring a termite guy and ask his advice on this and get a guestimate of the cost to treat the area.

I hope you're not getting too dejected with the deck idea by now.

Doog