The environmentally-friendly roof (Day 113)

Grass roofed buildingI’ve always been intrigued by buildings with ‘living’ or ‘green roofs’. It’s easy to forget they are not a modern invention. Places like Skara Brae Prehistoric Village in Scotland date back more than 5,000 years and have distinctive roofs using the benefits provided by nature.

Green roofs today are sold on the back of their environmental and economic benefits such as insulation and cooling properties, ability to significantly reduce rainwater run-off from roofs, and their value in promoting biodiversity and habitat in built-up areas. They look very impressive and distinctive too.

I think they are a useful reminder that buildings need to connect more with their environment for good reasons like reducing heating costs and greenhouse gas emissions. In the UK, around 13 per cent of greenhouse gas emissions come from the residential sector.

There is good evidence to suggest that some countries, like the UK, have lost their way with dwelling design considering the amount of money spent on ‘retrofitting’ loft, cavity and other measures in recent years and the UK Government’s current Green Deal initiative.

Our default position now should be to look at buildings not simply as ‘roofs over our heads’ but more active contributors to the issues we face every day.

In this context, it is good to see some students at the University of California who created a roof tile coating that when applied to an average-sized residential roof breaks down the same amount of smog-causing nitrogen oxides per year as a car driven 11,000 miles (18,000 km).

Students at University of California - Riverside

From left, Kawai Tam, Chun-Yu “Jimmy” Liang, Jessica Moncayo, Edwin Rodriguez, Carlos Espinoza, Kelly McCoy, David Cocker and Louis Lancaster (University of California – Riverside)

The students calculated that 21 tons of nitrogen oxides would be eliminated daily if tiles on one million roofs were coated with their titanium dioxide mixture. They also calculated it would cost only about USD$5 for enough titanium dioxide to coat an average-sized residential roof.

The anti-pollution properties of titanium dioxide are well-known and I’ve mentioned these before in previous blogs. What is encouraging is that projects dealing with issues like pollution are prominent in the education of the next generation of chemical engineers.

titanium dioxide coated tiles

The students coated 2 tiles with the titanium dioxide mixture (left). Uncoated tiles appear to the right and a commercially available tile is shown top.

Nitrogen oxides are formed when certain fuels are burned at high temperatures. They react with volatile organic compounds in the presence of sunlight to create smog.

Currently, there are other roofing tiles on the market that help reduce pollution from nitrogen oxides. However, the students focused their studies on collecting data to help quantify the reduction in smog levels.

They found the titanium dioxide coated tiles removed between 88 per cent and 97 per cent of the nitrogen oxides. They also found there wasn’t much of a difference in nitrogen oxide removal when different amounts of the coating were applied, despite one having about 12 times as much titanium dioxide coating – surface area, not the amount of coating, is the important factor.

When you consider the surface area of all the buildings in the world, there is clearly a great opportunity to transform ‘dumb’ buildings into active ones that address issues like pollution control and energy production.

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One thought on “The environmentally-friendly roof (Day 113)

  1. Hot places such as California could learn a lot from the traditional building methods used in the Middle East along with some of the modern ideas that you suggest. However, such cultural exchange is difficult at present.

    When we had our house remodelled we removed the windows on the south side of the house and built a sun shade over the ground floor study to reduce the afternoon solar gain. Our house remains very cool in Summer as a result.

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