Low-level deck that needs to support tons of weight

Adog

Hi Brain trust,

I’m going to be building a low deck on this concrete slab so bearers and joists same level. It measures approx. 5160 x 4260. I have approx. 150mm from concrete to top of deck to fall in line with sliding door frame

I’m thinking of using:

Galvanised brackets 

90 x 45mm H3 pine so I’ve got room for adjustment and levelling 

into concrete

M10/M8  75mm coach screws bracket to joists/ bearers

I will be running the decking long ways (Specrite Merbau Decking)

My challenge:

My significant other has decided she loves a outdoor concrete table 2m long x .900 wide (145kg!)

Concrete bench seat 1.6m long x .400mm wide (60kg!)

Can fit maybe 8 around the table (8 x approx. 80-90kg) although this will hardly ever happen outside of christmas time

145+60+ (8 pax x 90kg average person weight) = 925kg

My question is, is this doable with the products I’m using and also how should I strengthen the frame? Spacings? Doubling up bearers/ joists etc?

The table will be sitting in the middle of the deck so will I have only strengthen this area only?

This is a large deck and i am trying to do it the smartest way with as little punishment to my hip pocket as possible.

Any and all help much appreciated.

Thanks in advance 

MitchellMc

Welcome to the Bunnings Workshop community @Adog. It's wonderful to have you join us, and many thanks for your question on deck construction.

A standard raised deck built to code is designed to hold around 200kg per square metre. For your deck, the simplest solution would likely be to double up the joists where the table will be sitting and space them so the legs can sit upon them instead of the decking boards. If you are happy to have the table in one location, it will be a simple matter of having joists underneath the legs and then a bracket or, even better, a Builders Edge 25-40mm Pedestal Foot Minifoot directly under the legs. That will transfer the table's weight into the pedestal feet and the ground instead of the structure. The pedestal feet can hold up to 200kg per foot.

I've put together a rendering below to illustrate how you could reinforce the area. I'd suggest the best option might be to build the deck normally and then add in the additional joists and supports in the area where the table makes contact. As mentioned, you'll want the feet above the joists and not in between them.

Please let me know if you have any questions.

Mitchell