Eco Priority Guide: External Shading Devices

 

Overview

Shading devices are regularly exposed to sun and weather, therefore their main eco-priority is life-cycle issues, in particular durability and maintenance requirements. Depending on what type (if any) of additional finish is suitable and its maintenance requirements, the life-cycle costs of external shading devices can be high.

Aluminium and stainless steel are high durability, low maintenance materials but are also high in embodied energy and greenhouse emissions. Careful life-cycle assessment should be undertaken of alternatives, such as timber or fabric, before engaging whole façade aluminium or stainless steel.  

In the case of aluminium and stainless steel shading devices, the improved durability may not justify the increased greenhouse gas emissions generated from the production of these materials. Other materials, such as unfinished recycled hardwood, represent a more appropriate choice of external shading device (see for example the City of Melbourne Council House 2) as this application is non-essential, accessible and maintainable. See glossary entry for more information on Appropriate Durability.

Residentially, many shade devices are custom built during construction and are likely to be made of easily fabricated materials such as fibre cement (sheet, louvres and lattice), colorbond, aluminium and timber. If added by the homeowner they are more likely to be fabric awnings, roller shutters or aluminium louvres.

Commercially (and in multi-unit developments), external shade devices have been in decline due to the increased use of smart glass. This is creating significant problems in the industry as glass tower occupants are suffering radiant heat stress. This situation can best be avoided using external sunshades. See Smart Glazing Selection Eco Priority Guide for further information (coming soon).

 

Eco-Priorities

The following issues relate to both potential positive and negative issues associated with each product class:

Commercial

Priority Order	Fabric PTFE coated Fibre-glass	Fabric Acrylic fluoro-carbon treated	Stainless Steel	Fibre Cement, epoxy coated	Concrete precast	Alpolic- Alumin on resin core	Glass, coated
1	Durability	Durability+	Durability+	Durability+	Durability+	Durability	Durability+
2	GHG+	GHG	GHG	GHG	GHG	GHG	GHG
3	Resource	Resource	Toxics	Toxics	Resources	Resource+	Resources+
4	Toxics	Toxics	Resources	Resources			Thermal
Issues of concern?*	Minor			Minor Possible Bio- diversity

+ Denotes issue has positive outcomes

* Issues that are high-concern and are an eco-design basis for not using the product.

Residential

Priority Order	Fabric Canvas cotton and polyester	Softw’d W’board incl Ply	Fibre Cement uncompr’d	Alumin Awning powder coated, roller or fixed	Alumin Louvres powder coated
1	Durability	Durability	Durability+	Durability+	Durability+
2	Bio- diversity	Bio- diversity	GHG+	GHG	GHG
3	Resource (water)	Toxics if preserved	Resources	Toxics	Toxics
4	GHG+	GHG+	Bio- diversity	Resource+	Resource+
Issues of concern?*	Yes Bio-diversity	Yes Bio-diversity	Possible Bio- diversity

+ Denotes issue has positive outcomes

* Issues that are high-concern and are an eco-design basis for not using the product.

 

Making a Decision

Commentary

Designing shading that is both correct and relevant to the aspect and plane (i.e. orientation and whether shading is vertical and horizontal), is the most important issue with external shading. If the design is not correct, the shade will be inefficient at best, and/or useless at worst. Size and angle of blades needs to be designed according to solar altitude and azimuth angles at critical times of the year. If in doubt how this is achieved, consult fundamental texts (e.g. Phillips 1999), or a passive solar specialist.

Some recent experiences in one of Australia’s iconic new green development precincts has demonstrated that avoiding the use of external shading and opting for tinted ‘high performance’ glass has lead to major heat discomfort for building occupants. Once the sun shines on the glass, it heats up, re-radiating the absorbed heat into the internal spaces and increasing the mean radiant temperature.  While there are a variety of shading options, from double envelopes to conventional shading, that will combat the problem, the industry is in the process of learning the hard way that there is ultimately no substitute for external shading, particularly in hot climates (although ecospecifier has had reports of legal actions in Melbourne about this issue).

For shading devices containing timber, third-party certified products with chain of custody, e.g. Forest Stewardship Council (FSC), should be preferenced. The fibre in FC sheet, plywood and treated boards is now generally softwood sourced from plantations in various countries. It is generally not sourced from Forest Stewardship Council (FSC) timber. Hardwood plywood from overseas should not be used without FSC Chain of Custody certification due to the high likelihood of it being sourced from Asian or South American rainforests, or remnant African forests.

 

Decision-Making Checklist

1. Does a thing have to be made or used? If so, does it create a net benefit?
2. Fate: Start with the end in mind. If the product is not reusable, fully biodegradable or highly recyclable at the end of life, or facilitating these activities, its not sustainable.
3. Energy: What will the product’s likely net energy balance be over its life? Will it save more energy than it uses?
4. Durability: Does the product embody an appropriate level of durability for its accessibility, criticality and maintenance profile?
5. Biodiversity: Is there a chance that the product has had a negative impact on biodiversity? Erosion of biodiversity is a one-way street.
6. Toxicity: Is the product toxic and or persistent in the environment at any stage in its life cycle? If so, don’t use it.
7. Resources: Does the product use rare resources/ create a net negative flow of resources (e.g. poor maintainability/ high maintenance requirements)
8. Is the product socially sustainable?
9. Does the product, or its use, contribute to delivering synergy benefits in other building systems?

Source: Adapted from Andrew Walker Morison

 

Quick Guide

Aluminium fixed louvres – extruded 0.6mm powdercoated, virgin alumin
For Inexpensive Durable Lightweight Recyclable Potentially reusable	Against High embodied energy Largely virgin materials
Aluminium elliptical louvres –extruded, powdercoated, virgin alumin
For Durable Lightweight Recyclable Potentially reusable Operable	Against High embodied energy Largely virgin materials
Fabric – Fluorocarbon polymer coated fibreglass
For High durability & tensile strength Self cleaning Translucent Flexible & suitable for tensile structures – minimising structural support requirements Fire resistant	Against High embodied energy Toxic emissions related to fluorocarbons Not recyclable or reusable Non-biodegradable Non renewable, petrochemical base Toxic emissions due to embodied energy associated atmospheric emissions Largely virgin materials
Fabric–Acrylic,  fluorocarbon treated
For Medium durability and strength Moderately self cleaning Flexible Inexpensive	Against Moderate embodied energy Toxic emissions related to fluorocarbons Not recyclable or reusable Non-biodegradable Non renewable, petrochemical base Largely virgin materials
Stainless Steel
For Highest durability of all materials Lowest maintenance Highly recyclable and as high value material, likely to be recycled	Against Not likely to be reusable without remelting and reforming High embodied energy Heavy metal, rare and non-renewable content Toxic emissions due to embodied energy associated atmospheric emissions Largely virgin materials
Fibre cement – Epoxy or polyurethane coated, compressed 9-20mm
For Moderate embodied energy overall Stable surface Plantation based fibre sources	Against High embodied energy oil based coating/s Non FSC certified cellulose Not recyclable – not re-useable if adhered to substrate or fixings Likely VOC emissions from coating Not easily maintained Largely virgin materials
Precast Concrete – 75mm blade
For Highly durable Can be used without additional finish High strength and large span minimises need for intermediate support structure	Against High embodied energy Heavy to support Susceptible to concrete cancer if reinforcing not properly installed Largely virgin materials
Hardwood – Recycled
For Lowest embodied energy of materials without considering maintenance requirements High durability grade timber selection will minimise maintenance Most sustainable source of timber Natural timber aesthetic	Against Semi-durable without paint but maximum durability requires painting, therefore high maintenance if coated otherwise will require replacement within lifespan of building Susceptible to insect attack Flammable

 

Further Information

For more detailed information on this topic subscribers@ecospecifier.ae

 

References

Indoor Environmental Quality with Radiant Based Heating and Cooling. Accessed 23rd Feb 2006, at www.healthyheating.com

Lawson, W.L., (1995), Building Materials Energy and the Environment, RAIA, Canberra.

Olgay, V., (1965), Design with Climate, Princeton University Press, New Jersey.

Phillips, R.O., (1999) Sunshine and Shade in Australia, CSIRO Publishing, Melbourne.