Deck Plan

[adam_2021]

Hi everyone, I would like to build a deck at the back of my house as my first winter project and I am after some help with the design.

The deck would be aligned flush with the house and the measurement would be around 7.6 x 5.4. There is only a couple of hundred mm from the ground up to the floor of the house level, so I was thinking of using four rows (7.6m) of 120x45 or 150x45 bearers at 1.8 spacing and then putting joists in line with those also at 1.8 spacing.

I would have the bearers sit on stirrups concreted in also at 1.8 spacing meaning 20 total.

A few questions to begin.

Is the bearer size and spacing suitable? I can modify the total size somewhat to suit.

What size timber should I plan to use for the joists and noggins if necessary?

Is stirrups at 1.8m also suitable?

Thanks in Advance😊

[MitchellMc]

Welcome to the Bunnings Workshop community @adam_2021. It's fabulous to have you join us and many thanks for your decking questions.

You might like to sketch out your deck plan so our members have a better idea of its layout. I'd also suggest having a read of @Adam_W's guide on How to build a low-level deck.

If you can let us know the height you have to build the deck within, I can advise some suitable timber. Classically, on a deck that is to be built within a couple of hundred millimetres, you'd just use joists connected to the stirrups instead of a joist over bearer system. Those joists would be spaced around 600mm apart.

Online you'll find timber deck span tables that show how far structural timbers can span unsupported. If you're looking to use the maximum span, you'll need to refer to those. There are also deck calculators that let you input your dimensions and they'll show you an appropriate structure.

I look forward to hearing what the height is you have to work within and providing further assistance.

Please let me know if you have questions.

Mitchell

[adam_2021]

Hi @MitchellMc , thank you for the information.

Yes, I was thinking of a single level structure. There is only 200mm to work with from ground to house floor level.The deck is to be a simple rectangular structure 7.5m x around 5m. The 5m side can be adjusted to suit the span of timbers if necessary.I would appreciate any advise on timber size and spans. Thanks, Adam

[MitchellMc]

Hi @adam_2021,

That's not sounding like enough room to do a traditional joist over bearer system. From your 200mm height, 19mm is for the decking and 120mm for the bearer, that only leaves 61mm for the joist and clearance from the ground. Even if the joist is laid on its 45mm side, that only leaves 16mm of clearance from the bearer to the ground. If you're building this over soil, that's not enough room and it will lead to premature rot and decay.

What I'd suggest is that you use Treated Pine Outdoor Timber Framing MGP 10 120 x 45mm at 500mm centres across the width of the deck. So 10 lengths at 7.5m long or 15 lengths at 5m long. The decking is run perpendicular to these timbers. That would give you 61mm clearance under your deck.

You'll need to check some timber span tables online to see how far 120 x 45mm can span. I'd suggest that stirrups every 1000mm would be around the right ballpark.

Mitchell