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Living Roofs

Posted on Mar 12, 2018

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BR18-56

 

A global shift towards a more sustainable future is changing urban development as we know it. When it comes to roofing, are living or green roofs a permanent fixture of the future?

Living roofs are roofs partially or completely covered in vegetation typically found in coastal areas, semi-deserts or dry mountain landscapes.

They must have the correct waterproofing membrane, substrate and drainage layers to support plant life and protect the dwelling from erosion.

Not only do living roofs elevate the aesthetic appeal of the cityscape but they also bring much-needed biodiversity to cities dominated by concrete collages.

According to the International Green Roof Association there are four types of living roof:

EXTENSIVE – a thin layer of soil supporting a mixture of low-growth and drought-tolerant plants.

  • Soil depth of up to 60-200mm
  • Low maintenance
  • Best use = ecological protection layer
  • Ideal plant species: succulents, herbs, mosses, grasses

SEMI-INTENSIVE – a deeper layer of soil that allows for a more diverse mixture of greenery.

  • Soil depth of around 120-250mm
  • Medium maintenance
  • Best use = customised living roof
  • Ideal plant species: shrubs, herbaceous perennials and grasses.

INTENSIVE – a substantial layer of soil supporting a range of plant species including trees and shrubs for a private garden or outdoor living area.

  • Soil depth usually 150-400mm
  • High maintenance
  • Best use = park-like garden or outdoor living area
  • Ideal plant species: lawns, perennials, bushes and trees.

MODULAR-TRAY LIVING ROOFS – pre-vegetated trays of plant life that are placed on roofs and clicked together in a grid (cheapest and easiest option to install, maintain and fix water leaks).

  • Ideal plant species include sedums and native wild flowers.

“Green roofs can protect the waterproof membrane underneath (from UV and wind etcetera),” director of Greenroofs Ltd, Will Thorne, says.

“Overseas, many waterproof membrane companies will extend the warranty period from 20 to 40 years if they are having a green roof.”

Taking into account Canterbury’s geographical positioning, we’ve tallied up the pros and cons of adding a living roof to your next build or renovation:

PROS

  • Mitigate the effects of climate change
  • Produce better air quality through low-carbon cities
  • Create mini eco-systems that grow bird and plant life
  • Excellent waterproofing and water retention solutions
  • Natural thermal insulation = lower electricity bills
  • Little maintenance (some plant species look after themselves)
  • Completely unique and customised layout
  • Softens the aesthetics of concreted urban landscapes by adding colour and texture to roofs
  • Increases the lifespan of a dwelling.

CONS

  • Hard to retrofit (best suited to a new build)
  • Can be more expensive to install and maintain than a typical roof
  • Choice of plant species is subject to practicality and suitability
  • If a leak occurs, it can be difficult to find (unless using modular trays)
  • It can also be difficult to maintain if not choosing self-servicing plants
  • Its full aesthetic appeal can’t be appreciated as much from ground level as from height, like in metropolises with skyscrapers.

Image supplied courtesy of Greenroofs Ltd.

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