What Size Timber Do You Need For Deck Framing

Choosing the right stock for a new deck starts with span, footing depth and the timber size for deck posts, because a post that is too light can throw the whole frame out. Auswood Timber & Hardware Pty Ltd helps homeowners, renovators and tradies across Clyde, Clyde North and the wider South-East Melbourne area sort that out before materials are loaded. Speak with our team before you order, and you will avoid costly guesswork on site.

Choosing The Right Timber Sizes Matters

Bearers carry joists and pass weight down to posts, so their depth matters as much as their width. Get the right deck bearer dimensions. On many backyard decks, 140 x 45 mm treated pine works for shorter spans, yet 190 x 45 mm is common once spans stretch or roof loads get added. Span tables and the intended use of the deck decide the final call. A small platform for a couple of chairs is one thing, but a broad entertaining area with a barbecue, outdoor kitchen and ten people needs heavier stock under it.

Posts, Bearers and Joists Each Have a Job

Joists set the feel of the floor underfoot, so always get the best timber for deck joists. Since springy boards usually point back to light framing or joists spaced too far apart. Common sizes are 90 x 45 mm and 140 x 45 mm, with the larger section often used where spans are longer, or boards run on a diagonal. Treated pine is the usual pick for value and availability, yet hardwood can suit exposed sites where extra density and wear matter. Straight lengths save time when you start fixing boards, because a bowed joist can show up across the whole deck surface.

Posts, Spans and Site Conditions

The right timber size for deck posts depends on height above ground, bearer layout and wind exposure. A low deck close to the soil may suit 90 x 90 mm posts, but taller decks or decks carrying steps, screens, or a roof often move to 100 x 100 mm or heavier. Footing depth matters too, since softer ground in newer estates around Clyde can shift after wet weather. If the posts sit true and the footings are solid, the rest of the frame is much easier to set out and keep square.

Spacing, Board Thickness and Code Checks

Board thickness changes joist spacing, and this is where plenty of owner-builders come unstuck. A 19 mm board will usually need tighter centres than a 22 mm board, especially with composite products. When people ask about the best timber for deck joists, the answer sits in the span table as much as the species list. Local code requirements, board direction and the load you expect on the deck all shape the right choice, so measuring spans before you buy is time well spent and usually saves a second trip to the yard.

Common Sizing Mistakes

A common mistake is buying what looks right at the yard without checking span tables first. Another is mixing sections through the frame, which can leave the deck twisted and harder to board. Some people also pack out uneven footings with scraps instead of resetting levels, and that shortcut shows up later as movement, squeaks and crooked lines. Getting the frame square at the start saves rework once the boards and balustrade go on.

Ask Us About Deck Framing Timber Sizes

Need a straight answer on deck bearer dimensions before you start? Call 03 8732 0735  or contact us online to get the right timber list for your site.