What your carport is trying to tell you.
Structures rarely fail without warning. They lean a little, weep a little rust, rattle on a windy night, and put a hairline crack in the slab - usually for two or three years before anything dramatic happens. Here is the ten-minute walk-around, what each sign actually means on Cardinia clay, and what it costs at the cheap end versus the expensive end.
Four things, a spirit level and a torch.
You do not need a builder for the first pass. Four things, and you can check all of them in ten minutes with a spirit level and a torch. A post that is no longer plumb, or a roof line with a visible kink in it, means the footings are moving. Rust weeping from under a screw head means the washer has perished and water has been sitting in the hole. A hairline crack radiating from a post base in the slab means the footing and slab are fighting each other. And daylight visible at a wall flashing means the flashing has lifted. None of those are emergencies this week. All of them get expensive if you leave them two years.
Do it in autumn if you can. That is when Cardinia clay is at its most settled, so anything out of plumb in March is genuinely out of plumb rather than mid-swing.
What each symptom actually means here.
The post is leaning.
In Pakenham it is reactive clay under an under-dug footing, roughly nine times out of ten. Class M clay moves 20 to 40mm seasonally and Class H moves 40 to 60mm, and a shallow 300 to 450mm pad simply rides that movement until the post walks out of plumb. The second cause is water: a downpipe or a roof spitter dumping at the base of a post keeps that patch of clay in a permanent wet-dry cycle and accelerates everything. A leaning post is not cosmetic - it means the load path is off axis and the structure's wind capacity is no longer what the engineer calculated.
Cost: re-routing a downpipe to fix the cause, $280-$650. Cutting out and re-pouring a single pad footing to correct depth, $1,400-$2,600 per post. Rebuilding a carport whose four posts have all walked, $7,000-$11,000. The gap between those numbers is the entire reason to look now.
Rust is weeping from the screw heads.
It depends entirely on where the rust is. Surface rust weeping from around a fastener is the common one and it is fixable - the washer has perished and water sat in the screw hole. Re-screwing solves it. Rust along a cut edge or a drill swarf trail is cosmetic in the short term and worth cleaning off. What is serious is rust blooming from underneath the sheet in a sheltered area that never gets rained on, or rust at a point where a copper, brass or bare galvanised fitting touches the Colorbond - that is galvanic corrosion, it eats through from the contact point, and it voids the coating warranty.
Cost: full re-screw of a single carport roof $380-$850, double $620-$1,100. Replacing sheets that have perforated, $45-$85/m².
It rattles and bangs in the wind.
Yes, worry about this one more than most people do. Noise means movement, and movement in a roof sheet means fasteners have lost clamping force or the purlin spacing was never right for the profile. Under AS/NZS 1170.2 the governing load case for a carport is net uplift, so a roof that is already flexing in a 40km/h breeze has a smaller margin than the engineer designed for when a real spring north-westerly arrives. A rattling roof is a roof telling you it is loosening. Re-screwing a single carport costs $380 to $850 and it is the cheapest structural insurance available.
There is a crack in the slab.
Not necessarily a problem. Fine, straight, evenly-spaced surface cracks are usually shrinkage from the cure and are cosmetic - common on slabs poured in a hot dry Pakenham January. What matters is cracks with a step in them, where one side sits higher than the other, and cracks that radiate out from a post base. Those are differential movement, which means the slab and the footing are moving independently in the reactive clay. Under AS 2870 the slab should be tied to the pad footings on a reactive site. If it was not, that step will keep growing.
Water is staining the wall below the flashing.
The wall flashing where an attached carport meets the house is the most common leak point on any structure we inspect, and it is the one that does collateral damage. Water tracking behind a flashing gets into the fascia, the wall frame and eventually the eaves lining, and by the time you can see the stain inside, the repair is a carpenter's job rather than a roofer's. Cost: new flashing and re-seal, $450-$900. Flashing plus rotted fascia and eaves repair, $2,400-$5,500.
The gutter overflows in heavy rain.
Pakenham gets roughly 800-850mm of rain a year and our winter downpours are genuinely heavy. An overflowing gutter is either blocked - very common under the gums through Beaconsfield Upper and Heritage Springs - or it was undersized for the roof area from day one. Overflow dumps concentrated water at the base of a post, which brings you back to problem number one. The two failures feed each other, which is why we treat guttering as structural rather than as trim.
A 2011 Officer carport, caught early versus caught late.
Same structure, same defect, two different owners. A 6 x 6m attached double flat-roof carport on a 2011 estate home in Officer, Class M clay. The builder ran the downpipe to a spitter that discharged onto the lawn about 400mm from the front-left post.
Caught at year 6 - post 8mm out of plumb:
- Re-route the downpipe to the legal point of discharge under AS/NZS 3500.3: $480
- Re-level and re-pack the post base, re-tension the tie-down: $420
- Total: $900. Structure is fine and will see out its 30-40 years.
Caught at year 13 - post 60mm out, slab stepped 15mm:
- Prop the structure, cut out and re-pour two pad footings to 1100mm: $3,800
- Cut out and re-pour the cracked slab section, tied to the new footings: $1,900
- Re-align the frame, replace two distorted roof sheets, re-screw: $1,650
- Re-route the downpipe - the $480 job that would have prevented all of the above: $480
- Total: $7,830 - against $7,000-$11,000 to simply rebuild it new, which is why some of these end up as rebuilds.
One downpipe. Seven years of not looking. That is the whole page in a single example. Estate-specific detail is on the Officer page, and if the damage came from a storm rather than from time, read storm damage and insurance before you touch anything.
The three that are not a "next month" job.
- A post visibly out of plumb by more than about 20mm. The load path is off axis. Do not wait for spring winds.
- Any roof sheet that has lifted at a fastener, even slightly. One lifted sheet in a north-westerly peels the rest like a tin lid.
- A step of more than about 10mm in the slab at a post base. The footing is moving independently. Everything above it is being asked questions it was not designed for.
Everything else on this page is a maintenance conversation rather than a structural one, and the practical schedule for staying ahead of it is on our Cardinia maintenance guide. If you are weighing up whether the structure has another decade in it at all, how long a carport lasts covers the repair-versus-replace line, and the profile trade-offs that affect maintenance load are on gable vs flat roof. The Pakenham page covers what we see across the three different eras of housing stock here.
Frequently asked questions.
What are the early warning signs a carport is failing?
Four things, and you can check all of them in ten minutes with a spirit level and a torch. A post that is no longer plumb, or a roof line with a visible kink in it, means the footings are moving. Rust weeping from under a screw head means the washer has perished and water has been sitting in the hole. A hairline crack radiating from a post base in the slab means the footing and slab are fighting each other. And daylight visible at a wall flashing means the flashing has lifted. None of those are emergencies this week. All of them get expensive if you leave them two years.
Why is my carport post leaning?
In Pakenham it is reactive clay under an under-dug footing, roughly nine times out of ten. Class M clay moves 20 to 40mm seasonally and Class H moves 40 to 60mm, and a shallow 300 to 450mm pad simply rides that movement until the post walks out of plumb. The second cause is water: a downpipe or a roof spitter dumping at the base of a post keeps that patch of clay in a permanent wet-dry cycle and accelerates everything. A leaning post is not cosmetic - it means the load path is off axis and the structure's wind capacity is no longer what the engineer calculated.
Is rust on a carport roof serious?
It depends entirely on where it is. Surface rust weeping from around a fastener is the common one and it is fixable - the washer has perished and water sat in the screw hole. Re-screwing solves it. Rust along a cut edge or a drill swarf trail is cosmetic in the short term and worth cleaning off. What is serious is rust blooming from underneath the sheet in a sheltered area that never gets rained on, or rust at a point where a copper, brass or bare galvanised fitting touches the Colorbond - that is galvanic corrosion, it eats through from the contact point, and it voids the coating warranty.
My carport roof rattles and bangs in the wind. Should I worry?
Yes, more than most people do. Noise means movement, and movement in a roof sheet means fasteners have lost clamping force or the purlin spacing was never right for the profile. Under AS/NZS 1170.2 the governing load case for a carport is net uplift, so a roof that is already flexing in a 40km/h breeze has a smaller margin than the engineer designed for when a real spring north-westerly arrives. A rattling roof is a roof telling you it is loosening. Re-screwing a single carport costs $380 to $850 and it is the cheapest structural insurance available.
There is a crack in my carport slab. Does that mean it is failing?
Not necessarily. Fine, straight, evenly-spaced surface cracks are usually shrinkage from the cure and are cosmetic - common on slabs poured in a hot dry Pakenham January. What matters is cracks with a step in them, where one side sits higher than the other, and cracks that radiate out from a post base. Those are differential movement, which means the slab and the footing are moving independently in the reactive clay. Under AS 2870 the slab should be tied to the pad footings on a reactive site. If it was not, that step will keep growing.
Free inspections across the Shire.
Seen one of these on yours?
We will check the posts, the footings, the fasteners and the flashings and tell you honestly whether it is a $480 job or a $7,800 one. Free, written, no obligation.