Which is best? White roofs, green roofs, brown roofs or black roofs?

An article in the San Francisco Business Times in January 2014 described some research that suggests that white roofs are superior to green roofs when it comes to saving money.

The research was carried out at the Lawrence Berkeley National Laboratory.

Results showed that a simple white roof reflects 3 times as much sunlight as a green roof. By absorbing less energy from the sun, the roof stays cooler than a standard black roof and therefore doesn't heat the building up.  The cost of creating a white roof is less than the cost of creating a green roof and therefore, according to the researchers, a white roof offers better value for money.

In this blog post we compare and contrast different types of eco-roof to help you decide which is the best option for you.

What are all these different types of roof?

sedum roof

A well maintained green roof  pictured in early summer

Just as there is more than one way to design your living room, there are a myriad of different types of roof.  Thatched, tiled, slated, shingled, asphalt, EPDM, fibre glass, vegetated.....the list goes on.

Broadly speaking, a flat roof will fall into one of four categories; green, white, black or brown.

What is a green roof?

A green roof is what we call a roof, deck or terrace that has an intentionally planted layer of vegetation on it.

The green roof build up sits on top of conventional waterproofing.  It consists of a drainage layer, growing medium and then a layer of plants.

Depending on how strong the building is, the depth of growing medium and the type of planting can vary considerably.

Benefits of a green roof include insulation against heat, cold and noise, rainwater management, creation of wildlife habitat and help improving air quality.

What is a white roof?

white roofWhen a roof is treated with light reflecting material, it is known as a white roof.  It works on the principal that light colours, particularly white, are very poor at absorbing light energy from the sun.  Just as white clothes keep us cooler in summer time, white roofs help keep a building cool on hot days.

Research has shown that white roofs are cheaper to build than green roofs and are just as effective at reducing the need for air conditioning inside a building.

white roof: pic from www.daisygreenmagazine.co.uk

What is a black roof?

This is easy - a black roof is one with standard waterproofing but no reflective coating and no vegetated layer.  It has no particular advantages over any green, white or brown roofs apart from availability, cheapness and familiarity.

What is a brown roof?

brown roofA brown roof is similar to a green roof in many ways.  Certainly green and brown roofs have similar benefits.

Typically, building a brown roof involves using growing media and seeds that are sourced from the site – or very close by it.  The idea is to recreate local habitat on top of the building.

Compared to green roofs, brown roofs are typically around £10 to £12 per square meter cheaper to install. However, it is worth remembering that it takes around three years for a brown roof to establish itself. During this time, they require a considerable amount of maintenance compared to green roofs and so will cost more in this initial period. Once the brown roof has matured though, it becomes fairly self-sufficient and maintenance is kept to a minimum.

Brown roof: picture from www.urbanhabitats.org 

Which type of roof is the most Eco friendly?

Economically, white roofs have been proven to give the best return on investment over a 50 year period IN THE USA.  To my knowledge, there has been no equivalent research done in the UK where weather conditions tend to be very different.

However, as Nanny Brown used to tell me, money isn’t everything.

Table 1 compares at the eco-friendly features of different types of roof

 

White roof

Green Roof

Brown Roof

Black Roof

Summer cooling

Yes

Yes

Yes

No

Winter insulation

No

Yes

Yes

No

Rainwater management

No

Yes

Yes

No

Improves air quality

No

Yes

Yes

No

Wildlife habitat

No

Yes

Yes

No

Extends life of waterproofing (less waste to landfill)

No

Yes

Yes

No

Instant greening (for aesthetic and biodiversity

No

Yes

No

No

score

1/7

7/7

6/7

0/7

 

Here we see that black roofs are a no-no in terms of eco-friendliness.  Their only redeeming quality is that if they are on a suitable building they can be retrofitted with a green or brown roof when budget allows.

White roofs, at least for the UK climate are a partial compromise and will probably save money on air conditioning but do not benefit air quality or biodiversity.

Brown roofs and green roofs are the most eco-friendly by far. 

Where can I learn more about designing and building a green roof?

green roof design guideEnviromat have created a downloadable document entitled “Designing for Maintenance”.

Designing for Maintenance discusses the factors involved in creating a living green roof.  The document explains how to minimise the cost and maximise the benefits of a green roof by choosing the right build up for the building and by implementing a suitable maintenance regime.

The document is free and can be downloaded from www.enviromat.co.uk/green-roof-design-guide

Or, contact Q Lawns on 01842 828266 for more information

Download Designing for Maintenance