How do I know if my roof needs a replacement of just a roof repair?

One of the most common questions I am asked as I go around looking at roofs around Sydney is:

“Should I repair or replace?”

A roof repair is usually a shorter term option whilst a roof replacement is more of a lifetime choice. There are always exceptions to this rule – and some roof repairs can offer quite long term service.

Sometimes, it is not the roof that is the problem, but the guttering (usually box gutters) or the roof flashings. . And there are the situations where future home improvements are planned and a roof repair is a good ‘bridging’ option. So, this question is quite valid for most home owners.

Using the picture (above) of a typical Sydney roof as an example, the metal skillion roof is in a very advanced state of rust. It is quite obviously a candidate for replacement. Any repair work done on this rusty roof has a very short service life because another spot elsewhere would fail … Add up the cost of all the repairs and still having to do a roof replacement very soon, it is cheaper to just forget the repair option and go straight for a roof replacement now.

The tile roof in the picture is a good example of when repair is a very viable option. The tiled roof valleys may need replacement if they are rusty and the ridge capping may need re-pointing. A repair job on the tile roof should provide another 20 years of good service before any further expenditure is required.

Slate roofs are a slightly different story. I do not do slate roofs because it is an area that I do not carry enough expertise on. In Sydney, slate roof work is best carried out by someone like Heath (a slate specialist) at Westwood Roofing. Slate roofs can be expensive (and difficult) to repair. They are also expensive to replace with new slate – although a colorbond roof replacement for a slate roof is a very good (and cheaper) alternative.

Roofs in Sydney have fairly long lives. 40 to 50 years is typical – and when an enquiry comes through about a 20 year old roof that the owner thinks may need a roof replacement, it calls for some further questioning. A 20 year old roof is a ‘young’ roof.

The reduced serviceability of a Sydney roof points to an installation problem.  Typical examples are:

    • Tile roofs laid too flat:  Sarking under the tiles channel the leaks to the gutter and the house owner has no indication that there are leaks. Over time, the roof battens rot and the sarking deteriorate. Then the roof tiles drop – usually putting a tear in the sarking and suddenly the roof starts leaking…


  • Excessive discharge over tiled roofs:  A downpipe spreader from an upstairs roof, a long valley discharging over tiles and an open ended gutter are typical situations when  roof tiles are inundated with stormwater. The laps leak and eventually rot the battens and sarking.
  • Box gutters with ponding problems:  Installing zincalume box gutters instead of colorbond, together with water ponding issues (due to inadequate falls) can lead to premature failure.
  • Electrolysis due to Incompatible flashing materials: The most common flashing fault is laying lead over a zincalume metal roof. See the  two video below for a better explanation:
  • Failure at joints: The joints at the roof flashings can fail over time. This happens with long lengths of flashings that have large resultant thermal movements that shear off the pop rivets and tear the sealant joints. End laps on roof sheeting can corrode prematurely – especially if the sealant is not positioned correctly.
  • Tree leaves:  These can create damp environments that promote corrosion. So, if leaves get trapped under roof flashings or in gutters – there will be early rust.

So, should you repair or replace your roof?

My first priority when I get onto a roof is to see if the roof can be ‘saved’ by doing effective roof repairs that can add many years to the life of the roof. Some roofs that I see scream Roof Replacement at me. And this is usually the correct option.