A deck can look fine from above while a post underneath has lost most of its strength at the base. Posts carry the whole load, and they are the part of the frame closest to the ground and the water, which is why they rot first. A rotten post is the one deck repair that should not wait for the summer.
This post covers how to test a post, how it is repaired, and when the number of bad posts means the repair has become a rebuild.
How to test a post
Get under the deck with a torch and a screwdriver. On a sloping block, many Illawarra decks have a metre or more of clearance underneath, so you can usually see the posts properly.
Press the screwdriver into the base of each post, especially anywhere timber meets the ground or stays damp. Sound timber pushes back. If the tip sinks in like it is going into cheese, the post is rotting from the bottom up. A bit of grey on the surface is just weathering and means nothing. Soft, punky or crumbling timber at a structural post is a different matter.
Check the bearers too, especially any that sit low to wet ground or in a spot where water sheets off the house and pools. Our deck repair signs post walks through the whole deck, from the boards to the handrail.
Why posts rot at the bottom
Water sits where timber meets soil or a damp surface. A post rammed into or sitting near the ground, rather than standing on a proper stirrup, is the number one reason decks fail around here. The bad ones turn up in the same places: the shaded south side, under a planter box and beside a downpipe.
That matters for the repair. If the cause is not fixed, the next post along rots the same way. A downpipe discharging onto the footing, a planter holding water against timber or a post buried in soil all have to change as part of the job.
Three ways a rotten post is fixed
Sister a new post alongside. A new post is fixed beside the old one and carries the load, which suits a post that has rotted at the base but is otherwise in place.
Lift and repack onto a stirrup. The post is lifted and set onto a galvanised stirrup so the timber sits up off the dirt. This fixes the cause, which is timber in contact with the ground, as well as the damage.
Replace the post and the bearer. Where the bearer sitting on the post has gone soft as well, it is replaced along with the post. This is more involved than swapping boards, because the deck has to come apart to get at it and the fixings underneath usually need doing at the same time.
A single rotten post caught early is a far smaller bill than a deck that has started to lean.
When balustrade posts are involved
Grab the handrail and give it a proper push. If it moves, or you hear a creak where it bolts down, the post it is fixed to may have rotted at the base, or the fixing may have pulled through softened timber. That is a rebuild of that section, not a tighten.
In NSW, if a deck sits more than a metre off the ground, the balustrade has to be at least a metre high with gaps no wider than 125mm. Many older Illawarra decks predate that standard or have sagged below it, so a post repair is a sensible time to bring the rail up to it.
When it stops being a post repair
If more than one or two posts are rotten at the base, or the bearers have gone soft over a run of the frame rather than in one spot, the job is no longer a repair. You would be replacing the structure and keeping the old boards on top, which rarely makes sense once it is added up. At that point a straight rebuild, priced by the square metre, usually costs about the same as the repair and leaves a deck that is not a patch job. Our deck repair cost guide covers where that line sits, and restore or replace a deck explains how to judge it.
Licence and contract
Deck work worth more than $5,000 in labour and materials needs a licensed contractor and a written contract in NSW, and it is worth asking for a written quote on smaller jobs as well. The NSW Government explains who needs a licence and how to check one on its contractor licence check page.
Getting a post looked at
A fixed quote only means something once someone has been under the deck and looked at the posts. Our deck repairs work covers everything from a few boards to frame work. Ring Dave on 0414 007 351 or send the details through the contact page, and we will come out, get under the deck and tell you what it needs.
Common questions
- How do you tell if a deck post is rotten?
- Press a screwdriver into the base of the post, where the timber meets the ground or stays damp. Sound timber pushes back. If the tip sinks in easily, or the wood is soft, punky or crumbling, the post is rotting from the bottom up. Surface greying alone is only weathering.
- Can a rotten deck post be repaired without rebuilding the deck?
- Usually, if only one or two posts are affected. A carpenter can sister a new post alongside the old one, or lift the deck and repack the post onto a galvanised stirrup so it sits off the dirt, and replace any bearer that has gone soft. If many posts or a long run of bearers are soft, the frame is the problem and a rebuild is usually the better outcome.
- Is a rotten deck post dangerous?
- It can be. Posts carry the load of the deck and the people on it, and balustrade posts take a sideways push as well. A post that has gone soft at the base should be looked at before the deck is used by a crowd, and a loose balustrade is the most dangerous single fault on a deck.
- Why do deck posts rot at the bottom?
- Water sits where the timber meets soil or a damp surface. A post set in or near the ground, rather than standing on a proper stirrup, is the main reason decks fail around the Illawarra. The shaded south side, spots under planter boxes and areas beside downpipes are the usual places.
Want a hand with this at your place? Get a free quote or call 0414 007 351.
