You can see here how bad the rust was under the eaves. This wasn't visible from above or in the roof space. The top end of the iron is almost entirely gone and was the source of a slow leak that was causing damage to the ceilings and damp problems.
It can be tempting to keep patching up old iron roofs. Replacing old lead-head nails, wire-brushing off any rust and rust-proofing patches. And if you’ve read Olly Newland’s books, even using a bit of canvas soaked in paint to plug holes! However, at some point, the risk of a major leak of a roof in the neighbour’s garden will become too great to ignore any longer and you’ll have to suck it up and get quotes to completely replace the whole thing.
I was recently faced with this dilemma and so with great trepidation, I climbed up into the roof space to see how bad the damage was. To my great relief, there was hardly any rust at all, just one or two pieces that could use replacing. Great, I thought! However, when I got a roofer to come and quote on the repair, he took one look from the street and said “That’ll need replacing”. “Suuure”, I thought. However, when I explained how good it looked from underneath, he showed me a few ways to check if my old iron roof needed replacing.
While most of a roof can look ok from on top and even underneath, these visible areas aren’t the most vulnerable parts. The ends of the iron and where it’s pierced with nails are what you need to check And these aren’t visible without close inspection.
Hidden Roof Damage
- When on top of your roof, hold the head of your hammer in your hand and bang along the ridges with the rubber handle. If a cascade of rust falls out (Like it did on my roof!), then you have rust under the ridges that is not visible from inside the roof because it’s hidden behind the supporting timber.
- From on the ground, shine a strong torch (Not one of the crappy $10 ones from the DIY shops) up between the guttering and the fascia. This will show up any rust on the ends of the iron that won’t be visible from on top of the roof.
- Walk along the nail lines and check how secure the nails are. If you have a roof like I had, lead head nails will roll down into the gutter exposing rusting nail holes and giving away where the previous owner had siliconed the lead heads in place where nails had already rusted out. Don’t do dodgy silicone repairs!
- If you have a chimney, check the back flashing. That’s the flashing on the uphill side of the roof where rain may pool and debris tends to get stuck. There may be hidden rust here too.
- If you have an older roof that doesn’t use the full-length long run iron, check where the top sheet overlaps with the bottom sheet. Wind can drive water up into the gap and rust out both sheets, creating a nice soft rusty patch that will absorb and slowly leech moisture into your roof space.
When a roof is on it's last legs, the rust can run along the entirely length of the eaves while still looking in good shape from inside the roof.
Other things to check on your roof
- Check all the lead seals on the ridges, vent pipes from the hot water cylinder and toilet. These can get torn by people walking on the roof or just fall apart from old-age.
- Lead will also react with Zincalume roofs, so make sure that they’re not in contact if replacing a roof. Use coloursteel.
- You should also make sure that your hot water cylinder isn’t overflowing. Not only will this cost money but copper will react with a zincalume roof, causing further damage.\
- Painted iron should not overlap unpainted iron as water flowing off the painted surface to the unpainted creates a reaction causing corrosion.
In short, sometimes it’s better to bite the bullet and replace the whole thign rather than to try and repair damage that is hidden and througout the roof. The risk of greater damage to the roof structure or internal walls and ceilings of the house is significant. The cost would also be considerable. Not just in repair but in possible lost rent from the tenant leaving!
Thanks to John Duff Roofing Whangarei for help with my re-roof and this article.
