Self leveling deck?

[Bleedin Thumb]

I would like to design a deck around a big old campher laurel in a kids playground. The tree is a real feature so can't be harmed by the construction so the problems are :

1. The roots are everywhere and I wouldn't be able to place posts very deep and I can't attach bearers to the trunk.

2. The posts will lift in an uneven fasion over time so the deck should be designed so it can be easily re-leveled every couple of years.

Give us your thoughts ... no matter how wacky. Just remember it has to be kid safe.

The deck will be about 2.5m wide (radius plus opening size of about 1.5m for the trunk)

[rod1949]

Yep, dig it out, its a noxious weed, make a forture selling the timber.

[silentC]

What about some sort of suspension arrangement with cables from posts beyond the root system?

[journeyman Mick]

BT,
I'd be looking at using screw in anchors as these will minimise impact on the root system. You can get ones you screw in with a bobcat, dingo or mini excavator post hole auger attachment. Over these I would slide a pipe with a cleat to take the bearer and fix by drilling through both and bolting. That way you can always return to level things out.

The other thing I've seen done was on a board walk around a building built on fill on the waterfront. As the ground settled after construction the boardwalk dropped. One end was bolted to a ledger on the building, the other to timber posts. The building stayed put but the posts dropped down with the ground. They knew this would happen and so hadn't checked the bearers into the posts. When the decking got a real cant to it they just jacked it up a section at a time and rebolted it to the posts. The screw in anchors would have less impact than a post, even if it was only fitted in a hole with rammed in backfill.

Mick

[Pricey]

Yep, dig it out, its a noxious weed, make a forture selling the timber.

Hardly an issue for built up locations. Camphor may be a resilient grower, but it is also an excellent shade tree for the right area.

As far as the deck goes i would suggest the use of concrete footings. These will not need to be anymore than about 300 x 300 x 400. They could be finished just above ground level.
Next make some 60x60x3.2 gal box section piers. Weld the ends closed with some 6mm plate and the top should have a hole about 21mm. Make up some 60 x 60 x 6 angle line brackets say 100 long and weld them onto the top of some 20mm threaded rod. Run a nut up the thread with a suitable washer. This rod will slip into the hole in the box section, which is set in the concrete. The plate on the bottom will stop the concrete from entering the box section and reducing the amount of adjustment that is available. While you've got the welder out, weld some scrap onto the lower part of your box section to act as a key for the concreted piers. Now when you initially set up the deck you can use the threaded rod for finely adjusting the levels of bearer and joists.
The length required will be dependant on the height you want versus the expected amount of adjustment you may need.
For example if you made the box section 300 long then made your threaded rod 300 if it was set in the middle you would have about 150 movement up and down roughly.
The sizes i mentioned are only as a guide for the example. And as long as the threads were out of the dirt you could set the piers as low as you wanted.

Hope this may help you.

And yer keep the camphor tree so that i can make something out of it later on

[echnidna]

I'd build it like a boardwalk on bearers laying on the ground so it just floats.

[pawnhead]

H 20mm threaded rod. < snip ><snip> then made your threaded rod 300

I don't like the idea of sitting a deck on some 20mm threaded rod, 300mm long. You'd need something more like a piece of Acrow prop. It would be pretty expensive cutting up Acrow props to use for all your footings though. They'd have to be aluminium Acrows as well, else they'd rust up pretty quickly and be immovable.

Edit: Unipiers are adjustable up to 200mm. Held together with Tek screws. I used them on a job about ten years ago now, and they're much cheaper and less hassle than getting bricks and brickies in.

[Bleedin Thumb]

Thanks for the replies,

Bob, even though your suggestion is easy to construct I recon that it would exacerbate the problem of the roots.

Silent I initially thought of that but decided that the OH&S issues were a mindfield. But the more I think of it - it seems very funky ..a deck with a bit of movement, good for lots of reasons and fun for the kids but... how do you quantify the load bearing capacity of a tree's limb.. its possible to sling off the trunk but still..... lots of issues..for your own home...yes but this is how I earn my living and dead kids ain't good for business.

Pricey, sounds good but I think that you would have to go larger than 20mm rod with a deck that big and laden with kids.

Mick that sound good,makes sense about not notching the bearer in. Infact i probably wouldn't even attach the joists to the bearers.

I think you could build the deck in sections like pieces of a pie and jack up bits as needed and refix the bearer to the correct RL.

If you cross braced the decking and joists so you could liftout sections you could get to the inner bearer to adjust its height too... perhaps a box section arrangement - (egg crate).

Gee's those suspended adjustable cables sure seem the go... how do I cover myself?

[silentC]

How does NPWS get their suspended bridges and other stuff passed?

Come on, you know you want to do it, you'll find a way

[Bleedin Thumb]

Actually Silent I just realise that you suggested posts in your original posting...... not suspended from the tree.....hey thats got merit! infact that's bloody easy!

Now Mick...with your earth anchors..(never used them).. how deep do they need to go, if I went for Silents suspended idea I would suspect that you could get a lifting force on some posts if all the kids congregated on the opposite side of the deck. A screw-in anchor sounds the go.

[Pricey]

Thanks for the replies,
Pricey, sounds good but I think that you would have to go larger than 20mm rod with a deck that big and laden with kids.

I did say that the sizes were only used as an example.

Brand new houses are built with the same principle using 30mm threaded rod. Remember that the rod is vertical with the weight down onto it.

I can take a pic of what i described but used as a house pier if you would like to see it. This is a common method used up here with reactive soils, this process is used because of the ease of re-levelling the floor of a house built in these areas.

I'm not sure if this method is common all over Aus or not. I've only seen it in the Central Qld region.

[pawnhead]

Remember that the rod is vertical with the weight down onto it.

Yeah, but once you get a bit of height to it, lateral support becomes an issue. Mick's idea of a pipe sliding over another one, bolted together, like a Unipier, gives more lateral support.

[silentC]

If you used 90mm Duragal posts, you could use the adjustable pier connectors. They're a 30 or 40mm threaded rod with a bracket on top. I used them for a few bits and pieces here. They only have about 75mm adjustment though.

You still have the problem of a firm footing that isn't going to be disturbed by tree roots.

[joe greiner]

Mick's idea with the ground anchors sounds perfect. I'd suggest the smaller size (about 100mm diameter) so you can turn them by hand for later adjustment. I installed some by hand, using just a stout piece of reo through the pipe tee at the top. I think the total depth was about 600-750mm. You'll need substantial headroom for underdeck adjustment for any option. To reduce buckling length after raising, make the initial installation close to the ground. You may need power equipment for full-depth installation with roots nearby, but un-screwing should be feasible by hand. Make attachment brackets removable, and arranged to engage a bolt through the pipe tee. To raise, prop the deck, disengage the bracket, and un-screw. IIRC, the screw pitch is on the order of about 50mm, so a 180-degree turn would raise it 25mm for re-attachment.

Penetrating the root jungle could be purgatory. Best to defer final design of the framing until after the anchors are in, because you may need to relocate a few. Make sure you have enough room for later swing of the adjusting lever at all locations.

I think I got my anchors at Home Despot (Bunnies equivalent ASFAIK). The type with a pipe tee at the top would probably be easiest to devise the mounting. Another style has an eye (like an eye bolt); attachment detail might be somewhat different. Found some of those at http://www.mcmaster.com/ page 2038 as of today. [Easier to enter "ground anchor" in the search field.] The "holding power" listed is for pullout; compression capacity should be about double.

Obviously, YMMV. See what's available in your neighbourhood, and buy one of each size that looks good for installation and adjustment testing. They're not horribly expensive.

Joe

[journeyman Mick]

Joe,
the screw in piers aren't an off the shelf item around here.

BT,
I'd suggest chasing up a screw pier supplier and seeing what they have. Different diameter piers would have different depth requirements. I guess it would be a toss up between smaller diameter/greater depth and larger diameter/shallower depth. It would depend on whether there was lots of surface roots or they were deeper.

Mick