What joist support for low level deck?

[Bolton]

Hi, I’m about to start a low level deck with posts and bearers. I have a few questions. 

1. How far apart should the posts be on the external bearers and is it ok to fix with bolts and not notched. 

2. For the joists, do I have an internal bearer of simply support the direct joist with posts ?

Thanks in advance. Im hoping to use 120mm bearers. 

[JacobZ]

Hi @Bolton,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Would it be possible to get a few additional details such as the dimensions of the deck? Some photos of the area might also assist our members to offer you more specific advice. Let me know if you need a hand uploading images, I'm more than happy to help.

The overall size of the deck will determine whether you need to seek council approval for the construction of the deck. Generally, anything over 10 square metres requires council approval, but it is important to enquire with your local council for confirmation of this.

The distance between the posts will be determined by the size of the bearer. All decks should be designed with the use of a bearer and joist span table such as these joist and bearer tables from Hyne Timber. The minimum advisable size of H3 Pine, a very common deck framing timber, is 140x35 which can span no more than 1200mm between posts. With each size increase, the span distance increases, so the specifics of your deck will determine what timber you need to use. 

I would also advise that all connections between bearers and posts are notched out. This is because if a bearer is attached to the post with no support from underneath, the entire load from above is placed on the bolts going through the bearer and post. While it may hold up to begin with, it puts increased pressure on these bolts, which over time can potentially succumb to the stress. With a notch in the post, the bearer is supported from underneath, transferring the load from above down into the posts and subsequently down into the ground. It is always worth notching your posts.

The joists can be attached to the bearers at the same height, or internally, with the use of joist hangers of a suitable size and a suitable screw such as the Pryda Timber Connector Screws. The use of this hardware means your joists will not need to be supported by posts, rather it is supported by the bearer and its connection to the posts.

With a few more details, I am happy to assist further, but this should give you some idea of where to start.

Jacob

[Bolton]

 

Here are the 2 frame sizes. It’ll be joist hangers as it’s a low level deck very close to the ground. I will put joists every 450mm and they will span from top to bottom on the picture as the actual deck boards will be horizontal along the 7.1 m edge. 

[EricL]

Hello @Bolton 

Just to add to Jacob's excellent advice, I suggest having a quick look at these guides - How to build a low-level deck by @Adam_W and How to build a deck by @MitchellMc. This will give you a good idea of what you need to take into consideration when planning your decking frame.

A photo of the area will give our members a better idea of the terrain and we can make recommendations regarding footings. 

Here is a link to ideas and inspiration:  Top 10 most popular deck projects.

I also recommend watching the Bunnings deck building guide:

• How to plan out your deck
   
• How to set out a deck
   
• How to install stumps
   
• How to install bearers
   
• How to install joists
   
• How to lay decking
   
• How to add a step to your deck.

I propose drawing your decking plan on paper and sharing it with the community. I also recommend posting any other questions you might have about your deck framing plans.

If you have any other questions we can help with, please let us know.

Eric

[Bolton]

Thank you Eric however this does not answer my original question of how many stumps are needed around the outside and how do I support the joists on the inside or is the joist span ok ?

[MitchellMc]

Hi @Bolton,

As @JacobZ mentioned, you'll need a stump at least every 1200mm around your perimeter bearers if using 140 x 35mm timber. As with the bearers, your joists will need to be supported over their span, but the span between supports is dictated by the calibre of joists you use. What size joist do you intend to use? Say it's 90 x 45mm; you'd need to support them no more than every 1000mm.

You'll need around 27 stumps for the external bearers on the first plan and about 18 on the second.

Please let me know if you have questions.

Mitchell

[Bolton]

Hi @MitchellMc Mitchell, yes I’ll be using 90x45mm and adding noggins. Would they need a stump every 1000mm across all joists ? Thanks

[MitchellMc]

Unfortunately, they will @Bolton. You'd use bearers to span under them all on a higher deck, providing support. However, on a low-level deck, you'd typically need to support them with individual stumps, or you might like to use adjustable pedestal feet on pavers. Check out this step-by-step guide where I use them: How to build a deck. Not only are the feet a good way to support the joists, but as they are height adjustable, they're a fantastic way to level the deck.

Mitchell

[Bolton]

I think that’s what I will do. Posts on the outside and internal feet under paver. I’ve already sloped, weed mat and gravelled underneath so I’ll lay the paver on that packed in. 

[MitchellMc]

Sounds like a good solution, @Bolton.

Keep us updated, and reach out again if you have further questions.

Mitchell