Brett Field
A deck bearer can span from about 900 mm to 4,200 mm between posts, depending on its size, its timber and how long the joists it carries are. In Timber Queensland's residential deck table, a double 140 x 45 mm treated pine bearer spans 2,000 mm when it carries joists 1.8 m long, and a double 240 x 45 mm bearer spans 3,400 mm.
Below are sample rows from that table for treated pine and hardwood, how to pick a bearer size, how far apart the posts go, which timber to use, and the Gold Coast rules. These are published figures from Timber Queensland and WoodSolutions, checked on 10 November 2026. They are a guide, not a design for your deck: your engineer or building certifier signs off the real frame.
What is a deck bearer, and how is it different from a joist?
A bearer is the big beam that sits on the posts or stumps, and the joists are the smaller beams that sit on top of the bearers. The decking boards are fixed across the joists. So the load runs from the boards, to the joists, to the bearers, to the posts and footings.
Each one has its own span:
- Bearer span is how far a bearer runs between two posts. It sets how many posts and footings the deck needs.
- Joist span is how far a joist runs between two bearers, or between a bearer and a ledger on the house.
- Joist spacing is the gap between one joist and the next. Timber Queensland sets this at 450 mm maximum for a home deck.
The length of joist a bearer holds up matters a lot. Timber Queensland calls it the floor load width and gives it as the length of joists supported. Longer joists put more deck on each bearer, so the bearer cannot span as far. Our guide to deck joist spacing covers the joists and their own span table.
How far can a deck bearer span?
In treated pine, from 900 mm for a small single bearer carrying long joists, up to 3,400 mm for a double 240 x 45 mm bearer carrying short ones. Here are sample rows from Timber Queensland's Technical Data Sheet 4, Residential Timber Decks, for seasoned treated pine in stress grade F7. "2/" means a double bearer, two pieces side by side.
| Treated pine F7 bearer | Joists 1.8 m long | Joists 2.4 m long | Joists 3.0 m long | Joists 3.6 m long |
|---|---|---|---|---|
| 140 x 45 mm | 1,300 mm | 1,100 mm | 1,000 mm | 900 mm |
| 2/140 x 45 mm | 2,000 mm | 1,700 mm | 1,500 mm | 1,400 mm |
| 2/190 x 45 mm | 2,700 mm | 2,300 mm | 2,100 mm | 1,900 mm |
| 240 x 45 mm | 2,200 mm | 1,900 mm | 1,700 mm | 1,550 mm |
| 2/240 x 45 mm | 3,400 mm | 2,900 mm | 2,600 mm | 2,400 mm |
For these sizes the table gives the same span whether the bearer runs over one span or several. Timber Queensland notes that sizes deeper than 200 mm may not be easy to buy, so check with your timber yard before you design around 240 mm bearers.
The table only holds under its own conditions:
- The bearers carry the deck floor only, not a roof. Any posts holding up a roof must sit directly over the deck supports.
- The decking weighs no more than 20 kg per m2. Tiles over fibre cement need their own design.
- A bearer can overhang its last post by up to 25% of its allowed span, as long as the span behind that post is at least twice the overhang.
WoodSolutions adds that the AS 1684 sizes do not apply to a tiled deck, or one with a spa or hot tub. Those need a structural engineer.
What size bearer does your deck need?
Start with the length of your joists, then pick a bearer that spans the post spacing you want. Bigger bearers mean fewer posts and footings.
Here is an example from the treated pine table. Say your joists are 2.4 m long. A double 140 x 45 mm bearer needs posts no more than 1,700 mm apart. A double 190 x 45 mm bearer stretches that to 2,300 mm. On a 7 m long deck, that is the difference between 6 posts and 5 posts along each bearer (our sum: 7,000 ÷ 1,700 = 4.1, so 5 spans and 6 posts; 7,000 ÷ 2,300 = 3.04, so 4 spans and 5 posts).
For hardwood, here are sample rows for unseasoned timber in stress grade F14, from the same Timber Queensland table. "Continuous" means one bearer runs unbroken over two or more spans, which helps the bigger double sizes.
| Hardwood F14 bearer | Joists 2.4 m, single span | Joists 2.4 m, continuous | Joists 3.6 m, single span | Joists 3.6 m, continuous |
|---|---|---|---|---|
| 100 x 75 mm | 1,400 mm | 1,400 mm | 1,100 mm | 1,100 mm |
| 150 x 75 mm | 2,200 mm | 2,200 mm | 1,800 mm | 1,800 mm |
| 2/150 x 50 mm | 2,600 mm | 2,700 mm | 2,200 mm | 2,200 mm |
| 200 x 75 mm | 2,900 mm | 2,900 mm | 2,400 mm | 2,400 mm |
| 2/200 x 50 mm | 3,400 mm | 3,600 mm | 3,000 mm | 3,000 mm |
Double bearers have their own rules. Timber Queensland says seasoned double bearers can be spaced apart or nailed together. Unseasoned double bearers must be spaced, with solid timber blocks bolted between them at mid-span. For any size or grade not in the table, it points to AS 1684, the Australian Standard for timber framing, or an engineer.
How far apart should deck posts or stumps be?
The posts along each bearer go no further apart than that bearer's span from the table. The rows of posts, one row under each bearer, go no further apart than the joist span.
So the two tables work together. Pick the joist size first, which sets how far apart the bearers can be. Then pick the bearer size, which sets how far apart the posts can be along it.
A few post rules from Timber Queensland and WoodSolutions:
- Stirrups. Timber posts should sit in hot dipped galvanised steel stirrups set in concrete, with at least 75 mm between the concrete and the bottom of the post as a termite inspection zone. Our guide to deck footings covers the concrete side.
- Post size. WoodSolutions says posts usually start at 88 mm, and the deck can be no higher above the ground than 15 times the post's face width. So an 88 mm post suits a deck up to about 1,320 mm high (our sum).
- Joining bearers to posts. Bearers sit on post caps or brackets, or are housed into the post and fixed with two 12 mm bolts.
- Against the house. A ledger at least 90 x 45 mm is fixed to the house frame with 12 mm galvanised bolts or coach screws, no more than 600 mm apart. Timber Queensland warns that brick veneer may not be strong enough, so the deck may need its own posts and bracing.
Once the frame is set out, our free decking calculator counts the boards, joists and screws.
Which timber should you use for deck bearers?
H3 treated pine, cypress or an above ground durability Class 1 hardwood, for a bearer kept off the ground. That is Timber Queensland's rule for deck framing above ground. Hardwood with sapwood in it must be treated too.
Anything closer to the ground needs more. Timber Queensland asks for H5 treatment for framing on the ground and for posts set in it, or an in-ground durability Class 1 hardwood for posts. Our guide to H3 versus H4 treated pine explains the classes.
Stress grade decides the span, which is why the table is split by grade. WoodSolutions says treated pine is mostly sold as F7, unseasoned hardwood as F11 or F14, and seasoned hardwood as F17 or F27. It also says bearers and joists should be long, continuous lengths over at least three supports where possible, with any joins in a bearer made over a post.
Near the beach, the steel matters as much as the timber. The QBCC says that within 1 km of a surf coast is a sea spray zone, and that treated timber can speed up rust on metal brackets. Its article on corrosion protection for joist hangers and connectors says standard Z275 galvanised steel suits inside use only. WoodSolutions' domestic deck design guide says fixings within 1 km of the coast, or within 1 m of a pool edge, must be stainless steel.
Do you need approval or an engineer for your deck?
Most new decks on the Gold Coast need building approval, and some need an engineer as well. The City of Gold Coast says a new timber deck is likely to need approval from a private building certifier. It lists decks under 10 m2 and less than 1 m high as not needing one, if they meet the building rules.
You need an engineer when the deck falls outside the tables. WoodSolutions says that means a commercial deck, or one that takes heavier loads such as tiles, a spa or hot tub. A roof on the deck, or a span or size not in the table, also needs AS 1684 or an engineer's design.
Once it is built, keep an eye on it. The Queensland Government says to inspect your deck at least once a year: check bearers and joists for warping or cracking, look for rot or spongy timber, and check fixings and post brackets for rust.
We build timber and composite decks across the Gold Coast, including pool decks, deck stairs and landings, and we repair old deck frames. You get a timeline with the proposal, before any work starts. See our deck building page.
Where do these spans come from?
Checked on 10 November 2026: Timber Queensland Technical Data Sheet 4, Residential Timber Decks (revised March 2014), Table 3 for bearers and its notes on posts, fixings and ledgers; WoodSolutions Technical Design Guide 21, Domestic Timber Deck Design (revised October 2020); the QBCC article on corrosion protection for joist hangers and other connectors (July 2020); the City of Gold Coast's page on whether your building works need approval (undated); and the Queensland Government's page on inspecting decks and balconies (July 2026). The post count and post height sums are ours. We will check these spans again every three months.
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