How to build small deck and pergola?

[martyjames]

Hi

I am wanting to build a small  3m by 3m deck with pergola. The decking material will be composite decking. A landscape architect drew a simple plan for me -see photo below. I would really appreciate help in locating generally stocked items from Bunnings for the build (im in Ashfield, Sydney).

He said to bolt 100mm x 100 mm posts to the small wall at back of yard (see yard pic below). What height would you recommend?

Could you advise with link to best posts to use from Bunnings please. The posts will be painted.

The bearers are drawn as 100 mm x 75 mm - again can you advise with link to best timber to use from Bunnings for these bearers please.

The rafters are shown as 75mm x 50 mm -  can you advise with link to best timber to use from Bunnings for these rafters please.

(if these sizes are not stocked pls advise closest suitabe that is stocked at Bunnings pls)

Regarding the posts at the front of the deck (not bolted to the small wall at the back), they will sit on a slightly sloping concrete slab - what is the best way to "seat them" onto the slab?? (prefer not do dig into slab if possible as there may be a drain there)

What type and size timber would i use to join the top of the posts for the pergola and and cross members?

Many thanks

[JacobZ]

Hi @martyjames,

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

I would suggest that you need to contact your local council to identify what planning and permits, are required for this structure. It is likely that you will require engineered drawings ensuring that your pergola meets the weight bearing capacity and wind load requirement for your area.

I have concerns that the dimensions of timber you have been provided are well under what is required for the spans you are looking to create and the potential wind load that this structure is likely to come under.

The addition of a deck to the structure adds another element that is likely to affect planning requirements.

A professional engineer will be able to guide you on the requirements for your proposed project.

If you have further questions, don't hesitate to ask.

Jacob

[martyjames]

Hi Jacob

Thanks for the reply. I already spoke to council and no approval required under the State Government’s policy for exempt development that is designed for low impact works such as a ground floor deck😁 (by the way, the pergola will not be covered with any roofing material)

Does anyone else have any thoughts? Thanks

[EricL]

Hello @martyjames 

I suggest having a quick look at these guides - How to build a low-level deck by @Adam_W and How to build a low-level deck by @MitchellMc. This will give you an idea of what you need to take into consideration regarding planning your decking frame.

I also suggest looking at this discussion - How to build a basic pergola? by @Ange11. 

Let me try and point you to the materials you've mentioned. The closest product to the 100mm x 100mm post is the 100 x 100mm 2.4m Fence Post Hardwood CCA. The bearer's size are equivalent to 100 x 75mm Post H4 Treated Pine Wet CCA 3.0m.

The rafter size of 70x50 is close to the 70 x 45mm Outdoor Framing H3 Treated Pine 6.0m. For your pergola I suggest using 90 x 45mm Outdoor Framing H3 Treated Pine - 2.4m. I suggest speaking to your landscape architect regarding anchoring the post to the concrete base as that particular question requires a full discussion.

Here are some discussions that might help: 

• How to accurately bolt post anchors to existing concrete pad by @pepsp
   
• How to get a post plumb using a bolt down anchor? by @mh 

Let me call on our experienced members @diy_hausdesigns and @woodenwookie for their recommendations.

If you need further assistance, please let us know.

Eric

[martyjames]

Many thanks Eric

[MitchellMc]

Hi @martyjames,

I just wanted to jump into the discussion to reinforce what my colleague @JacobZ had pointed out. The timber calibres in your design are far from adequate for your project. They do not meet span requirements and, if used, would likely fail and could cause serious injury. 

For example, your rafters at 70 x 50mm cannot span 3000mm. You'd be looking at something closer to 140 x 45mm at the very minimum. The beams (bearers) are also incapable of spanning that gap, especially whilst supporting the rafters.

The design needs to be planned from the ground up with suitable timber. Given this is a multifaceted project where the posts both hold the weight of the pergola and the deck, you really need to have an engineer design the structure for you. 

We'd be more than happy to help you select appropriate timber and point you in the right direction.

Please let me know if you have any questions.

Mitchell

[martyjames]

Ok thanks for your input Mitchell , much appreciated