Custom Deck - Joist Requirements

6 Apr 2015
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United Kingdom
Hello, just joined, I have a decking I am building for someone and trying to keep it low budget but obviously I need it to hold a decent amount of weight.

The decking is slightly raised to cover some existing patio steps that are alongside a conservatory and have a patio flooring.

I have designed it for the posts to stand on the patio as it is completely level with a gradient running to one edge for water flow and the decking will follow suit to this.

I have done some modelling of the joist and supports, and advice on this would be appreciated?

I am an electrical/electronic/pneumatic/hydraulic engineer so this really is not my fortay but if you need help with anything else let me know.

This design uses 4"x4" posts and 6"x2" beams. Is this overkill as the decking will be sitting maximum 375mm above the patio.

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I presume that does not include hand rails etc? We have presumed PP wont be an issue as a conservatory has already been installed and its privately owned and I have let them know about this.

Thank you.

EDIT: Tell a lie, I changed the design to knock out the step it is covering so it does not exceed 300mm anyway so it won't be an issue as long as it does not include hand rails. Conformation on this?
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There are a billion topics already on this if you use the search engine but if the decking will be no more than 300mm above [natural] ground level and will not breach the other criteria then you should be fine.

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