opinionBy Francis Gichuhi
The cost of a roof is mainly dictated by how much you want it to insulate against sun during hot days while remaining natural and rustic.
To achieve such features, roof manufacturers go to great lengths such as using acrylic paints that contain small sand granules on steel sheets. This enables the steel sheets to appear rough and rustic and also insulate during sunny weather. Unfortunately, to achieve this, the costs are quite high at approximately Sh1,900 per square metre of surface area.
Use of 'green' roofs, whereby live plant material is planted on the roof's surface, will achieve insulation and give good rustic aesthetics at a lower cost. Plants that require no maintenance such as Sedum can be planted to creep on the roof surface.
To increase aesthetics, different varieties with different shades and textures can be planted. This can ensure your roof gives you the insulation and beauty while saving money and helping reduce the Carbon footprint in the atmosphere.
Notable green roofs
Chelsea Football Club Training grounds roof, which was designed by AFL Architects, has a 1,000 square metres surface of Sedum plant. Another notable green roof project is Architect Susanne Zuniga's residence in Portland, USA. The roof has a very low slope, whereby Sedum has been planted and a water-proof membrane used to prevent water from seeping into the house.
It would be interesting to see Kenyans try out these new green roofings to break the monotony from the usual Mabati (corrugated iron sheets), concrete and clay tiles that are a common sight.
Use of soil to aid the Sedum growth increases the total roof weight. Luckily, Sedum requires a very minimal depth of soil to grow, around 100mm deep hence considerably reducing the total overall weight of the roof.
Edible roof gardens
In some instances, edible plants have been planted on roof surfaces. They provide the obvious advantage of food production. Researchers such as Sandy Thai of the University of California have come up with detailed research on edible roof gardens such as the one that can be seen here: http://lda.ucdavis.edu/people/2009/SThai.pdf
In conclusion, green roofing offers more advantages compared to ordinary roofing in terms of superior aesthetics, better insulation and reduced cost of construction. Careful selection of the plants to ensure they are hardy and require minimum watering is important. The more people embrace such green roofs, the more we will reduce the Carbon footprint in the atmosphere.
Gichuhi is principal architect at Nairobi-based consultancy firm A4architect.com Email: firstname.lastname@example.org Website: www.a4architect.com