Jan 16, 2018: Should I Replace My Tile Roof

In our last two Newsletters I’ve talked about why brick veneer houses with tile roofs are such a bad choice for Australia’s climate. To reinforce that point, here’s quote from Harry Seidler (‘famous’ Australian architect) which was written in 1954 and sent to me yesterday by one of our readers.

‘…topping it all there is that inevitable huge and expensive pitched roof structure covered with Marseilles tiles which has absolutely no justification for its existence in this climate. Without insulation, the large body of air above such buildings will heat up in summer and produce highly undesirable conditions inside… Such roofs put all their weight onto the exterior walls and require excessive support. They are wasteful in labour and material…

No clue is given by the exterior of the building as to the local climate. With their complete lack of integrated outdoor living facilities, these buildings are utterly alien to a country with a climate of such small temperature variations as those prevailing in the southeastern part of Australia; a climate which is comparable to that of some Mediterranean countries or of California.’

 

What's wrong with this picture?

What’s wrong with this picture? (Image Source: Trip Advisor)

Now I’m no fan of Harry Seidler, in fact I detest most of his work especially the Blues Point Tower which I think ruins the view up Sydney Harbour past the gorgeous curves of the Opera House and the Harbour Bridge. In the photo above look how the Blues Point Tower seems to be supporting the roadway of the Harbour Bridge. This is one of the most iconic and photographed views in the world and the Blues Point Tower stuffs it up (a bit). Compare the photo above to the photo below where I have (gleefully) taken out the Blues Point Tower.

Isn't that much better?

Isn’t that much better?

Unfortunately here in Australia we have an obsession with ‘Heritage Conservation’ which causes us to preserve things simply because they’re old (or designed by a starchitect with a big name like Harry Seidler) regardless of whether they were ever any good or not. So I doubt we’ll ever be able to enjoy the Opera House and Harbour Bridge without the blight of the Blues Point Tower but I live in hope… and I digress.

The point is that even an architect as egotistical an insensitive as Harry Seidler could tell that tile roofs didn’t make any sense in Australia’s climate, yet today, 64 years after he wrote the quote above, it is still the most common way to roof homes, at least in the southeast. The only difference is that now most new roofs seem to be using very dark or even black tiles which is even more insane because they will absorb even more heat in summer. So we’re going backwards.

As far as I’m concerned, the only roofing material that makes sense for our climate is a light coloured Colorbond like the ‘Shale Grey’ roof we have on the Greeny Flat (as you can see in the photo at the top of this page). But wait, we’re doing a complete energy retrofit of the house next to the Greeny Flat (click here to learn more about that) and it has a dark tile roof…. so what’s the story?

180116 Queen St Roof

Dark tile roof on the house next to the Greeny Flat.

The story is that we are planning to remove all the tiles and replace them with a ‘Shale Grey’ Colorbond roof to match the Greeny Flat and then install solar panels on the new roof. We just haven’t got to that stage of the project yet but here’s a 3D image of how it might look when it’s finished.

180116 New Queen St Roof

3D model of the finished house.

So Should I Replace My Tile Roof?

About a year ago I did an Energy Assessment for a family in Sydney who were having overheating issues in their house. Yesterday I received the following email from Margaret after she had read my last couple of Newsletters.

‘You’ll be pleased to hear that we bought a “new” PHEV towards the end of last year so we are now in the process of getting solar panels installed. We’ve gone with a Space Solar 5.5kW system with micro-inverters. As usual with this type of thing it also raises questions, so we were wondering what your thoughts are on whether our 60 year old terracotta tiles will cope with the mounting of the solar panels. We have factored in that the panels have a 25+ year life so do we bite the bullet now and change to light-coloured colorbond with anticon (ceiling cavity is already insulated to R3.5) to match the back of the house. Have you had any experiences with this type of scenario? The installer says that they check the roof before installing but the last thing we want is to have the roof leak in the future.’

I would not be too concerned with the ability of the old tiles to ‘cope with’ the solar panels. Solar systems are installed on tile roofs all the time. But should they replace their tiles with Colorbond? This is a very good question and they are asking it at the right time (i.e. BEFORE they install solar on their roof). Personally I would be inclined to do what they suggest and replace the tile roof with a light-coloured Colorbond over an anticon blanket. Anticon stands for ‘anti-condensation’ and is a foil-faced sarking product lined with R1.5 fibreglass insulation. It is installed insulation-side up so that the insulation is in contact with the underside of the corrugated metal. This prevents condensation forming (hence the name) and also greatly reduces the amount of heat transfer from the metal into the roof cavity. If they were building a new house I would say there is no question… this is the way to go (if they have an attic but if it’s a raked (cathedral) ceiling then I’d recommend SIPS panels. Click here to read why.)

However on an old house there are other things to consider. The main one is cost. While the Colorbond+anticon is the ideal solution it is a very expensive change to make to a house. We are going to do it on the house next door and we expect it to last for the next 75-100 years so we think it’s worth it. But it’s a hard pill to swallow when the tile roof we have is functioning reasonably well, it keeps the rain out and, in our cooler climate, we don’t have an overheating issue. In Margaret’s case there is an even stronger argument for replacing the roof because they live in a hotter place and they do have an overheating problem. But there are a few other things to consider.

  1. Ventilation – the better ventilated the roof cavity, the cooler it will stay in summer and the dryer it will stay in winter. Attic ventilation is extremely important regardless of the type of roof you have. Older tile roofs typically don’t have sarking under the tiles so they tend to be pretty well ventilated via all the holes between the tiles. Both tile and Colorbond roofs with sarking tend to be poorly ventilated and so do hip roofs, i.e. sloping up on all sides like a pyramid, (e.g. the house in the image above) which is why we have installed a lot of vents in the eaves of the house we’re retrofitting (click here for more on that). Whirlybirds or solar-powered fans are good ways to add ventilation to roof cavities. So, whether you can afford to replace your tiles with Colorbond or not, adding more ventilation to the attic space is a good way to help keep it cool and is very important for keeping it dry and free from mould or rot.
  2. Roof Paint – If you can’t afford to install a light-coloured Colorbond roof another option is to apply a light-coloured paint to your existing tile roof. This is a much less expensive option that can significantly reduce the heat gain through the roof. There are even specially formulated ‘Cool Roof’ paints that have heat-reflective properties which can make dramatic reductions to heat buildup in roof cavities.
  3. Shading from solar panels – another thing to keep in mind is that, if you are planning to install a large array of solar panels on your roof (which Margaret is), those solar panels will actually shade a fair portion of your roof and help to keep the roof cavity cooler as well.

So, the answer to Margaret’s question is, if they can afford it and you want to do the best job for the long term, I would recommend replacing the tile roof with light-coloured Colorbond + anticon. If not then look into having the tile roof painted with a light-coloured ‘Cool Roof’ paint before installing the solar panels and the panels will also help to shade the roof and keep the house cool. But either way remember that good attic ventilation is extremely important.

4 comments to Jan 16, 2018: Should I Replace My Tile Roof

  • Mark

    I love the good old corrugated iron, or nowadays Zincalume. I’m assuming it’s performance is alright as it should be reasonably reflective (although it does get less shiny over time)?

    • admin

      Thanks Mark, the fact is that both zincalume and galvanised iron absorb a LOT more heat than a light-coloured Colorbond. It seems counter-intuitive since they look like they’d reflect a lot of heat but, even when they’re new they soak up the heat and it only gets worse as they get older and less reflective. This is why I recommend light-coloured Colorbond and not Zincalume or galvanised. It’s also the reason why the Greeny Flat has gal on the walls but not on the roof.

  • Nick

    Is there any value in having a layer of plywood under the tin like they seem to in the states?

    • admin

      Nick, thanks for the question. The main reason they do that in the states is because they typically use an awful roofing product called ‘Asphalt Shingles’ that can only be laid on a plywood roof. These are a fiberglass mat impregnated with asphalt and they typically only last about 15 years before the roof has to be redone. Terrible idea. A plywood roof deck does also provide excellent bracing strength to the roof but, if you’re using corrugated metal it’s really not worth the added (and considerable) expense.

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