The granny flat cladding that lasts 25 years in Frankston, and the one that fails in eight
Short answer: fibre cement weatherboard at $95 to $150 per m² supplied and fitted is the right call for most granny flats in Frankston, Karingal, Langwarrin and Carrum Downs. Inside roughly 500 m of Port Phillip Bay, spend the extra $2,000 to $4,000 on AS 3566 Class 4 fixings and a marine coating on any steel. The cheap specification that fails early here is thin unbacked vinyl weatherboard on a west facing wall, and painted pine trim anywhere near the water.
Cladding is about 8 to 12 per cent of a granny flat build, but it decides most of what you will spend on the building over the next twenty years. A 50 m² flat carries roughly 85 to 100 m² of external wall once you allow for the eaves and the gable ends, so the difference between the cheapest and the dearest option on this page is around $25,000 up front, and a repaint cycle that is either six years or twelve.
Cladding compared for Frankston and Peninsula conditions
Rates are 2026 supplied and fitted per square metre of wall, including battens, sarking, flashings and paint or finish where the system needs one. Expected life is to the point where the wall needs replacing, not the point where it needs a repaint.
| Option | Cost per m² fitted | Life in this climate | Maintenance load | Typical warranty | Who it suits |
|---|---|---|---|---|---|
| Vinyl / PVC weatherboard | $80 - $120 | 12 to 18 years, less on a west wall | Wash twice a year, cannot be repainted successfully | Fade and cracking cover, commonly 10 to 20 years, heavily conditional | Tight budgets on sheltered inland blocks only |
| Fibre cement weatherboard | $95 - $150 | 30 years plus with the paint kept up | Repaint at 8 to 12 years, wash yearly | 15 to 25 years on the sheet, conditional on installation to the manual | The default for most Frankston granny flats |
| Prefinished profiled steel | $110 - $170 | 25 to 40 years inland, 15 to 20 years unprotected near the bay | Rinse the salt off twice a year, no painting | Long paint and perforation cover, but conditional on distance from the water | Modern look, bushfire overlay blocks, low upkeep |
| Compressed fibre cement sheet, express joints | $130 - $190 | 30 years plus | Repaint at 8 to 12 years, joint sealant at 10 to 15 | Similar to weatherboard, plus 10 to 20 years on the sealant | Flat modern facades, studios, dual-occupancy fronts |
| Rendered lightweight panel (EPS or AAC) | $150 - $230 | 25 to 35 years | Repaint at 7 to 10 years, patch impact damage promptly | System cover of 10 to 25 years if the whole system is one supplier | Matching a rendered house, best thermal result per dollar |
| Brick veneer | $220 - $320 | 60 years plus | Almost none, repoint at about 30 years | Effectively the life of the building on the brick itself | Permit conditions or a neighbourhood character requirement |
| Cedar or hardwood weatherboard | $220 - $380 | 20 to 30 years oiled, 8 to 12 years neglected near the bay | Oil every 2 to 3 years, more often on the north and west | Cover is on the timber grade only, not on the finish | Owners who want the look and will do the upkeep |
Indicative Frankston and Mornington Peninsula rates for 2026. Wall area, scaffold, access and the number of external corners all move these numbers. Call (03) 9022 1391 for a specification priced against your actual elevations.
What the numbers on the product actually mean
Three ratings do the real work, and only one of them is printed on the cladding itself.
AS 4312 corrosivity category. This standard maps Australia into atmospheric corrosivity zones from C1, very low and inland, up to C5, very high and on the surf coast. Frankston, Seaford and Mornington front a calm bay rather than open surf, so the aggressive band here is much narrower than it is on the ocean side of the Peninsula. As a working rule we treat the first 200 m from the Frankston or Seaford foreshore as severe, 200 m to 1 km as marine, and anything past about 3 km as ordinary suburban. Ask any cladding supplier which category their warranty covers at your address, and get it in writing.
AS 3566 fastener class. This one is stamped on the screw box, and it is the cheapest thing on the whole job to get right. Class 3 is the coastal class, Class 4 is severe marine. A box of Class 4 screws costs $40 to $80 more than the Class 2 screws a hurried installer will already have on the ute. Every rust streak you have ever seen running down a nice new wall in Seaford is a Class 2 screw that should have been a Class 3 or 4.
BAL under AS 3959. If your block sits in a Bushfire Management Overlay, and pockets of Langwarrin, Mt Eliza and the Peninsula hinterland do, the bushfire attack level rules some products out entirely and forces sealed joints, ember mesh and non-combustible cladding. That is a planning and building matter, not a taste one, and it needs to be settled before you fall in love with timber. Our page on Victorian granny flat permit rules sets out which overlays trigger what.
The local conditions that decide it
Frankston’s weather comes off the water from the west and south west. The wall that fails first is almost always the west elevation, and on a granny flat it is usually the one facing the back fence with no eave over it, because the setback was tight. Three things follow from that.
- Eaves are cheaper than cladding. A 450 mm eave costs $60 to $110 per lineal metre and roughly doubles the life of the paint underneath it. On a 9 m west wall that is $540 to $990 spent to protect about $1,200 of paintwork every cycle.
- Sandy soil moves less, clay moves more. Closer to the foreshore at Frankston and Seaford you are generally in sand, which gives a stable Class A or S site under AS 2870. Inland at Carrum Downs, Skye and parts of Langwarrin you are in reactive clay, often Class M or H. Reactive clay means seasonal movement, and a rigid jointed system such as render over panel will show that movement before a lapped weatherboard will.
- Low lying blocks stay damp. Around the old Carrum Carrum swamp country at Carrum Downs and Seaford the water table sits high and some blocks carry a Special Building Overlay. Cladding needs its bottom edge held clear of splash and finished ground level, and the wall needs a real drainage plan behind it. We cover the ground side of that on backyard drainage for a Frankston granny flat.
Not sure which corrosivity band your block sits in?
Tell us the street and we will tell you what we would specify, and what we would not bother with. Free, no obligation.
The cheap specification that fails early here
The failure we get called to most often is not exotic. It is a thin budget board system fixed straight to the frame with no drained cavity, using Class 2 screws, on a west facing wall with a 300 mm eave or none at all. In the first two summers the boards expand and the joints open. Salt and grit lodge in the open joint. Water gets behind the board on the first hard south westerly and, because there is no cavity, it has nowhere to drain to. Eight years later the bottom two rows are swollen, the screw heads are weeping, and the repair costs more than the original saving of $3,000.
The second failure is trim. Owners specify a good board and then let the builder run finger jointed painted pine for the corners, window reveals and the fascia. Pine trim on a coastal west wall is a five to eight year item. Upgrading to fibre cement or primed hardwood trim on the exposed elevations adds $600 to $1,400 on a typical flat and takes that failure off the table for good.
The third is a missing drainage cavity. A ventilated cavity behind the cladding costs $12 to $22 per m² in battens and labour, so $1,000 to $2,200 on a 50 m² flat. It is the best value line item on the whole external wall and it is the first one a cut price quote deletes, because you cannot see it once the boards are on. If a quote does not say how the wall drains, ask before you sign, and read our guide to comparing granny flat quotes.
What commercial grade and marine grade are worth
Not much, on their own. Neither phrase has a definition in the National Construction Code or in any Australian Standard for wall cladding. Commercial grade usually just means a thicker sheet or a heavier gauge, which may or may not matter on a single storey granny flat that nobody will reverse a forklift into. Marine grade on a fastener does mean something, because AS 3566 gives it a class number. Marine grade on a coating means something only if the supplier will name the corrosivity category and the distance from the water in the warranty document.
The useful test is to ask three questions and write the answers on the quote. Which AS 4312 category is this warranted for at my address? What class are the fasteners to AS 3566? Is the warranty on the product only, or does it include the labour to refit it? A supplier who answers all three without hesitating is selling you a real system. A supplier who says the words premium and marine a lot but will not put a category in writing is selling you a phrase.
What we recommend, and when not to spend the money
For the typical Frankston granny flat, meaning a 45 to 60 m² one or two bedroom flat on a suburban block a kilometre or more from the water, we specify fibre cement weatherboard over a ventilated cavity with Class 3 fasteners, fibre cement trim on the north and west elevations, and a 450 mm eave wherever the setback allows one. On a 50 m² flat that lands at roughly $9,500 to $14,000 of the total build, and it is a 30 year wall.
Within about 500 m of the bay at Frankston, Seaford, Mornington or Mt Martha we keep the same board but move to Class 4 fixings, stainless or hot dip galvanised structural brackets, and either a marine coated steel or a rendered panel on the elevation that takes the weather. That is a $2,000 to $4,000 premium, and it is the difference between a wall you wash and a wall you replace.
Here is the honest constraint. If your block is at Langwarrin, Skye, Carrum Downs or anywhere else more than about 3 km from the water, do not pay a coastal premium. Marine grade fixings, salt rated coatings and stainless brackets are money wasted there, and a builder pushing them on an inland block is padding the quote. Equally, if you are putting up a small non-habitable garden studio rather than a dwelling, painted plywood or a budget board is a perfectly sensible answer and we will say so rather than upsell you. We also do not take on render refresh work on existing houses, so if the cladding question is really about matching a tired main house, get the house quoted separately.
Three related pages worth reading before you lock a specification. Prefab versus built on site changes which claddings are even available to you. The budget granny flat page shows where cladding sits in the three price tiers. And if you are still working out the size, size it in square metres first, because wall area is what you are actually buying. The full itemised list is on our 2026 pricing guide and the ground works sit on Frankston site costs.
Cladding questions we get asked in Frankston
What is the best cladding for a granny flat in Frankston?
Does salt air really affect a granny flat in Frankston?
How much does granny flat cladding cost per square metre?
Is brick veneer worth it on a granny flat?
What does marine grade actually mean?
How often will I have to repaint a granny flat in Frankston?
Get a cladding specification priced for your block
Send us the street and we will come back within one business day with the corrosivity band, the cladding we would specify and a fitted price per square metre.
Want the whole build priced, not just the walls?
Free on-site design consultation across Frankston City and the Mornington Peninsula, with a fixed written quote inside 7 days.