How to build a low profile deck?

Question

Hi, I need to build a low profile deck with hight of 300-350mm, already tried use Bunnings deck planner.

I have couple questons here, hope someone can help please!

* As it is a low deck, what type of sub structure would recmmend?  [Joists on the top of bearers] or [using joist hanger to let joist and bearer at the same level]?
* What type of Post Structure would you suggest? 
* May I use 140x45mm bearer and 90x45mm joists?

JacobZ · Answer

Hi @AndyY123,

You should be fine using the stirrups embedded into concrete.

140x45mm bearers work well and you can choose whether to use the same for your joists, or use 90x45mm for your joists, but the design would change slightly, just make sure you are aware of the different span capacities of these timbers. Span capacities can be found in the Hyne Deck Joist Span Tables.

Outside of our Decking Planner, I use Sketchup for designing decks. It is a free to use 3D rendering tool that is relatively easy to learn.

If you have a play and see what you come up with, I can certainly have a look and offer advice. If you'd like, I could also knock up a quick design for you, just let me know and I'll be happy to help.

I look forward to hearing back from you and helping you out along the way.

Jacob

AndyY123 · Answer

Hi, Jacob

Thank you very much for the suggestions!

Instead of using H4 treated Post, may I use Pryda 300x90mm M10 Full Stirrup Post Anchor? Cast into concrete?

i might choose 140x45mm bearer and 900x45mm joists, do you have recommend design tools? i want to draw up the frame and seek more advices.

Thank you

Andy

JacobZ · Answer

Hi @AndyY123,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

You might like to start by having a quick read through some of the following articles -

* How to understand deck components
* How to understand deck span tables
* How to build a low-level deck.

Assuming the 300-350mm height you've mentioned is to the top of the decking boards, then having a single tiered frame, using joist hangers to attach the joists to bearers, is a much better choice. If you were to use a two-tiered frame, using 140x45 bearers and 90x45 joists, with decking boards that are 19mm thick, you would have approximately 50-100mm of clearance beneath the bearers. If you used a single tiered setup, you would have approximately 140-190mm beneath them. Maximising the clearance beneath the deck allows for better airflow, which means any moisture beneath the deck will dry out quicker, which long term, is definitely worthwhile.

If you use a single tiered frame, where you have 140-190mm of clearance beneath the deck, then you have a few different options. Personally, I would use H4 Treated Posts, either 90x90mm or 100x100mm depending on availability in your area and concrete them directly into the ground. You could also use TuffBlocks with these same posts if you are looking to avoid concreting.

The design shown above will allow you to use 140x45 bearers and 90x45 joists in line with the relevant bearer span table and joist span table. You just need to ensure that the bearers are supported every 1400mm along their full length. This means 4 posts per 3200mm bearer.

In saying this, if you were to use 140x45 joists, which are capable of spanning 2600mm between bearers, you can remove a bearer from the centre of the deck. This means you could reduce the number of posts and considerably reduce the number of joist hangers required.

Let me know what you think and if you'd like some assistance with any additional design work, please let me know. I would be happy to assist.

Jacob