7 Ways to Cool Your Roof for a Hotter Climate

In a hotter world, the roof over our heads is our first line of defence

One of my most memorable moments as a young architect was when I took a client outside in the scorching sun with an umbrella.

Here’s how to keep your house cool, I said.

‘Pop’. Up went the umbrella.

Instantly cooler.

I’ve spent a whole career watching consultants leap to the newest tech in the quest to design cooler buildings, usually racing past the simplest, most passive, most affordable, and most effective solutions — like putting up an umbrella. Of course, our buildings can get hot from the air as well (ambient temperature) but the Sun is a guaranteed heat source and we have full control over how much it heats our buildings.

Photo by Tommy Kwak on Unsplash

Adapting our building’s roof is the first line of defence against heat. Here are 7 viable options that might suit you. There’s a lot more scientific detail and building code compliance behind these which I’ll spare you from, so make your own investigations if you’re taking this further.

1. Paint the roof a light colour. A light roof maximises how much of the Sun’s energy is reflected, also known as the Solar Reflectance Index (SRI). Where an SRI of 0 is black and absorbs all energy and 100 is completely reflective, a flatter roof should be at least SRI 64 or better.
2. Install sarking under your roof. This is the reflective foil sheeting you often see used in construction. It’s great at preventing heat from moving through it and also prevents moisture transfer.
3. Install thermal insulation in the roof space. Typically laid over your ceiling structure and easily retrofitted without touching the roof cladding itself.
4. Install a roof vent. These let the hot air out of your roof space. Can be installed as a vent in a gable end or as a spiral vent on the roof. These are highly effective and work harder the hotter it gets. Easy to retrofit.
5. Add solar panels. While solar panels are converting some of the Sun’s energy to green electrons for you they also shade your roof. Lighter roofs also improve solar panel output, so if you do everything above you’ll be making some valuable adaptations.
6. Replace the roof. More common than you might imagine for older housing stock. Use lighter colour roofing, and while you’re at it also install thermal insulation and include solar panels.
7. Install a green roof. I’d consider this the most comprehensive move and for an existing building can often require a new roof structure and drainage system. Some existing buildings can cater for a lightweight green roof. I’ll leave the details of this option for another time, but suffice to say the green roof genre is rapidly growing (sorry). Things get even more interesting when we add solar panels to a green roof — but I’ll save that exciting one for later too.

It goes without saying that any works on or in your roof should be carried out by licensed and capable tradespeople.

I often use the simple matrix below to compare options, ranking each opportunity using cost and adaptive value which is a way of considering how much the adaptation will help cool our home. This one’s just a guide but intuitively considers the up-front cost, energy savings, insurability against climate risk, and re-sale value of your home.

The Adaptive Value Matrix (Digby Hall)

Remember — to retreat from the Sun, the roof is our first line of defence and worth the investment.