What timber to use for floating deck under a pergola?

[Zog]

My house has a pergola that was already here when I bought the house. the floor of the pergola is really badly done pavers. I plan to build a deck over the pavers. There appears to be a bewildering number of choices of wood for decking and joists. Can anyone suggest types and sizes ? I don't want to spend a fortune, as long as it doesn't start to rot in a few years. I'm open to modular panelling if that is an economical choice. I'm planning on using the 50 mm adjustable support footings from Bunnings. My only woodworking experience is shelves, coffee tables and a desk. It will be about 40m2. It's a bit messy in the photos because of other work I've been doing. The original pavers have been laid directly onto the ground.

[Akanksha]

Hello @Zog,

Great to see you make your first post! Hope you've been finding the site a handy resource for your D.I.Y. projects. 

This is an exciting project which I'm sure our resident D.I.Y. expert @EricL will be happy to assist with once he's back on the site later today. Let me also tag some of our ever-helpful members @pepsp, @DIY4Knuckleheds, @diy_hausdesigns and @Tara86 to see if they have any thoughts.

In the meantime, would you be able to provide photos of your pergola and the pavers so our members have a better idea of your project and can suggest some timber options that are more suitable for your requirements and space?

If you haven't already, I recommend reading the following guides by experienced renovator @Adam_W: How to select decking timber and How to choose the right timber for the job.

You may also find this Bunnings guide useful: Which timber to use for decking?

Hope this helps. Please keep us updated as this project progresses. We'd love to see the final result.

Akanksha

[Zog]

Thanks for your reply. I've added some photos.

[EricL]

Hello @Zog 

Welcome to the Bunnings Workshop community. It's marvellous to have you join us, and thank you for sharing your question about building a low-level duck under your pergola.

What a fantastic project to be undertaking, I suggest starting by having a look at these guides - How to build a low-level deck by @Adam_W and How to build a deck by @MitchellMc. These guides should provide you with ideas on how to start planning your decking frame.

It's good to hear that you've seen the pedestal footings at the store. These provide excellent support and are adjustable in height. The common sizes used for timber decking frames are 140mm x 45mm, 90mm x 45mm and 70mm x 45mm. But before you begin choosing materials, I propose drawing a plan with either pen and paper or your favourite rendering software. 

I recommend thinking about its size and shape. Will you be making it a complex frame, or will you keep it a simple square? By making your plan you'll be able to determine how much timber you'll need, the number of fittings necessary and the number of footings you'll be putting in.

I also recommend having a look at the Bunnings video guide on how to build a deck: 

• 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 don't wish to overload you with information, I suggest starting with a plan and proceeding from there. Once you've drawn up a decking frame, I recommend sharing it with the community and any questions that you might have.

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

Eric

[pepsp]

Hi there @Zog 

Sounds like a great project to keep you busy! I built a low level deck a couple of years ago using the Builders Edge big foot XL pedestal feet for the part of the deck that was over concrete. This was combined with stirrups concreted into the ground for the part over grass.

I used H3 treated pine for the bearers and joists, and the actual decking boards are spotted gum. Treated pine would be your cheapest option for wooden decking, and also the shortest lifespan depending on how it's maintained. There are obviously trade off's you make with the different material choices, like cost, how it looks, longevity of the material especially for locations that are very close to the ground (poorly ventilated), not under cover or are by a pool, maintenance requirements. As I understand it mod wood style products are more expensive than timber but don't need to be stained every few years, so it ends up being a capital cost vs maintenance cost issue. When I was choosing materials I spent a fair bit of time researching options to understand these trade off's.

Here's a link to a bunnings article that gives a staring point. But I did a lot more research with various websites and companies before i made my decision https://www.bunnings.com.au/diy-advice/building-construction/decking/which-timber-to-use-for-decking 

In terms of sizing the bearers and joists, definitely spend the time on a proper plan which includes your footings and framing layout.  Also, consider things like height off the ground (e.g. is the area attached to the house and does it need to line up to the floor level of the house)? The pedestal feet I used came with a specification to help get the right spacing of floor joists and feet. From memory I settled on 140 x 45mm bearers/joists.

For a low level deck there's also information out there about how to space your boards to give you a reasonable life before replacement. If you have the option to raise the deck a bit off the ground then the timber will probably last longer.

You also mentioned that the deck area is 40m2. That's about twice the size of mine. I kept it rectangular to reduce complexity (like you I'd never built a deck before) and the size was below council regulations for when you need to get a certifier involved. Cost was somewhere in the order of $3k-$3.5k in 2020. Looking at your photos you have a more complex shape to contend with and it's obviously much bigger. 

Hope this helps. Good luck with the project!

[Zog]

Hey @pepsp Thanks for that advice. The pergola is hexagon shaped but I'm going to make the deck rectangular to reduce the complexity and to cover the gravelled area (or weed farm as I call it). I was planning to use the Deko 250x150x150 concrete foundation blocks for the sections on the soil/grass. It will be at floor level but not actually connected to the house which means council approval not needed here. I'm thinking at this stage I'll probably go with pine because of the size and prices have gone up since 2020, but I'll do more research yet.

[Zog]

Thanks @EricL , I'll check out those links. I haven't drawn up a plan yet as I won't be doing this until the end of the year and I've only just started the planning.