Protecting a Coastal Home From Salt Corrosion
Living near the beach is good for the soul and hard on the house. Salt carried on the breeze settles on every surface, and moisture keeps it working. Over time it attacks roofing, fixings, gutters, steel posts and anything else made of metal. A bit of planning and some regular cleaning will slow it right down.
Most corrosion damage happens slowly and out of sight. By the time rust stains show on a wall or a fixing fails, the problem may have been building for years. Knowing how exposed your home is, and where salt collects, helps you spend maintenance time where it counts. Here is how to go about it.
How far salt reaches inland
Distance from the water is the biggest factor. A WA Government technical guideline on corrosion protection quotes Australian Standard AS 4312, which says airborne salt causes the most damage to infrastructure in Australia. For Perth, the same guideline warns that corrosive conditions can reach up to several kilometres inland. So a home a few streets back from the beach is not automatically in the clear.
The National Construction Code housing provisions group locations into low, medium, high and very high environments for metal sheet roofing. Very high typically extends up to 200 metres inland from breaking surf, and the band within 100 metres is the harshest. The code notes it is found on the beachfront in regions of rough seas and surf beaches. High typically applies more than 200 metres from breaking surf, or within 50 metres of sheltered bays.
Medium typically covers sites more than 1 km from breaking surf, or more than 50 metres from sheltered bays. Low is typical of remote inland areas, or sites more than 1 km from sheltered bays. Where conditions on a site vary, the code says to design for the most severe environment. That is a sensible rule for owners choosing replacement materials too.
Where salt does the most damage
Rain is actually a friend of coastal metal. It washes salt off exposed surfaces before it can build up. The trouble spots are the sheltered places the rain never reaches. The WA guideline notes that corrosion speeds up on surfaces that rain doesn’t wash clean, where salts and pollutants can build up.
Check these areas first when you walk around the house. One roofing steel maker’s maintenance guide calls them unwashed areas and names several of them. Common examples include the following.
- Fascias and wall cladding under the eaves
- The underside of eave gutters
- Garage doors
- The underside of carport and patio roofs
- The underside of any horizontal steel surface
Washing salt off the house
Regular washing is the simplest way to slow corrosion in those sheltered areas. For its coated and prepainted roofing steel, a major roofing steel maker recommends washing unwashed areas at least every six months. In coastal areas where marine salt spray is prevalent, it suggests every three months. The same guide suggests washing gutters when the windows are cleaned, which makes it easy to fold into an existing routine.
The method is gentle. Use a mild solution of pure soap or non abrasive dish detergent in warm water. Wash with a sponge, soft cloth or soft nylon brush and rinse well with fresh water straight away. Avoid abrasive or solvent cleaners, and avoid hard, mineral rich ground water. Check your local water restrictions before you start.
Fixings, posts and mixed metals
Small parts deserve close attention. The same maintenance guide says to inspect fasteners regularly. It suggests replacing any fasteners showing signs of red rust. When fixings are replaced, the NCC housing provisions say they must be a compatible metal to the roof.
Mixing metals is another trap. The NCC requires metal roofing and the materials in contact with it, such as fasteners, flashings and cappings, to be compatible with each other. It bans lead materials upstream of aluminium and zinc coated materials. It also bans copper materials upstream of galvanised coatings.
Steel posts under raised homes need a look too. The NSW Government’s advice on corrosion protection of steel posts covers class 1a buildings in coastal areas of eastern Australia. It says a significant number were built on steel posts without due regard for how corrosive the location was. It lists problems such as early and costly restumping, cracked bathroom tiles and doors needing refitting. If you notice those signs in an older coastal home, have the posts checked.
For new work, NSW certifiers must work out the corrosivity category of the site, with reference to AS 4312. Where steel is cut, the builder must repair the cut edges to the original standard of protection. Owners can ask about this during a build, especially for posts and other structural steel.
Painted surfaces, windows and fittings
Paint acts as a barrier, so once it fails the metal or timber beneath is exposed. The WA guideline notes that painting over hot dip galvanised steel in sheltered areas can greatly extend its life. Flaking or bubbling paint on a coastal home is worth fixing early. Our article on peeling paint explains how painters deal with it.
Windows and window coverings take salt too. If you are weighing up new coverings, think about how each material will handle sea air and how easy it is to wipe down. Our look at PVC plantation shutters covers the cost side of that decision. The same thinking applies to balustrades, gates and glass pool fencing, where hinges and fittings sit out in the weather all year.
Unit blocks and shared property
In a strata building, many of these surfaces are common property. Roofs, balcony rails and car park steel are often looked after by the owners corporation rather than individual owners. A planned schedule stops washing and inspections from being forgotten. Our guide to a coastal unit block maintenance plan sets out how to put one together.
Frequently asked questions
How close to the beach does salt corrosion become a problem?
The NCC housing provisions treat sites typically within 200 metres of breaking surf as a very high environment, with the first 100 metres the harshest. Salt still travels well beyond that. A WA Government guideline warns that in Perth, corrosive conditions can reach several kilometres inland.
How often should I wash the outside of a coastal home?
For its coated and prepainted roofing steel, a major roofing steel maker recommends washing sheltered, unwashed areas at least every six months. It suggests every three months in coastal areas with regular salt spray. Use mild soapy water and rinse with fresh water.
Can I mix different metals on my roof?
Only if they are compatible. The NCC housing provisions require metal roofing, fasteners, flashings and cappings to be compatible with each other. Lead can’t be used upstream of aluminium and zinc coated materials, and copper can’t be used upstream of galvanised coatings.
What are the signs of corroded steel posts under a house?
Look for rust, damaged coatings and unrepaired cut ends on the posts. The NSW Government also links poor post protection to cracked tiles, damaged wet area membranes and doors needing refitting. A building inspector or structural engineer can assess the posts properly.
