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My first low level deck - subfloor help.

Hey everyone.

yes sorry - this is "another low level deck post". I have decided to build my own 90x19mm merbau deck at home and have spent way too much time just working out what finished floor height i want it at. I am taking the path of exempt development and as such am working to ensure I have 2400mm clearance between the deck and the underside of the final patio roof.

my deck if 6.9m long (length of house) by 3.6m wide (keeping under the 25m2, 1m from boundaries, within 500 of ground, and eventual patio roof highest point less than 3m from the lowest point of natural ground level. This will result in 2400 ceiling height. My land is not level so top of the deck will range from 200mm above the ground at one point to 500mm above at another.

I looked at span tables and got confuzzled. can anyone help suggest the most economical ledger/bearer/joist/footing sizes & layout?

thanks in advance.

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MitchellMc

Welcome to the Workshop community @qroozn. Many thanks for your question, I'd be happy to start the discussion.

I've taken the liberty of using a calculator to get you fairly close to the mark. The plan is based on using bearers of Treated Pine Outdoor Timber Framing 190 x 45mm, joists of Treated Pine Outdoor Timber Framing 90 x 45mm and posts of Treated Pine H4 Post 90 x 90mm. I've included two different orientations depending on how you want to run your decking boards. There is generally a better visual flow onto the deck if the boards are run perpendicular to the house as in the second plan option.

If you have any further questions or need assistance, please let me know.

Mitchell

qroozn

https://www.workshop.bunnings.com.au/discussion/comment/8801#Comment_8801

Thank you very much For the detail MitchellMC. Definitely more bearers and piers than I had expected. Interesting comment about runnning the boards perpendicular to the house - I had not considered this option.

a question - if I was to run a ledger off the “single veneer brick” currently at the back of the house... would I still need deck piers against that wall?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/66633#Comment_66633

Hi @qroozn,

You could reduce the number of bearers, but that directly affects the dimensions of the joists used. If you were to remove a bearer then we would need to now build the joists from 120 x 45mm increasing the cost. If you remove a bearer and use the 90 x 45mm you will potentially end up with a spongy deck as the joist might flex across the wider span. The same can be said with piers if you remove some you might need to increase the dimensions of the bearers to compensate.

A ledger generally acts as the last row of piers and bearer when abutting to a house.

Mitchell

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