72 BUILD April/May 2009

SUSTAINABILITY CASE STUDY

construction wastereductionIn this urban hamilton house, construction waste reduction was an important part of the sustainable design strategy, from design planning through to demolition. By Roman Jaques, BRANZ Senior Sustainable Building Scientist with Heidi Mardon, Director, The enviroschools Foundation of New Zealand

Addressing construction waste is an often overlooked environmental aspect, usually due to competing economic or practical constraints. Although there

is limited official data, it is thought that, during construction, an average New Zealand home typically generates 2 to 3 large skips (around 22 to 33 m3) of waste material that goes to landfills. This equates to between 19.0 and 28.6 kg/m2 of waste per house.

Planning for better waste management can be divided into three areas: design, construction and demolition.

Start with the design

Aspects of this design that should facilitate good material management over the building’s lifetime included:

a simple design, both in form and in ❚

detailing, that made use of a limited palette of construction materials and fittings, to facilitate salvaging at the end of the building’s life ensuring flexibility in the interior spaces, ❚

so that they can change as the occupants’ needs changeselecting a builder who was keen to include ❚

these waste management goals in their operationsexplicit mention of material waste minimi- ❚

sation intentions within the specification – ReBRI guidelines were referred to, along with eight of its key principles – covering the main aspects of good waste managementincorporation of some recycled and reclaimed ❚

materials, such as rimu from the demolished house, the vanity basins and a bath.

Construction aim to divert 30% waste

During construction planning, the first step was to determine the local markets that existed for the wastes that would be generated and what

other wastes could be diverted with a little extra effort. The target was to ‘divert at least 30% (by volume) of solid waste generated on site that would otherwise have been sent to landfill’. This translates to sending less than 21.3 kg/m2 to landfill over the construction period.

The main contractor supplied labelled recyc-ling bins, and the site foreperson was briefed on the waste strategy. Due to the extra effort required by the main contractor, the clients assisted with the sorting and separation of the waste and were responsible for the monitoring and checking. The dedicated recycling area, with marked recycling drums, moved as the site progressed so it stayed well positioned.

Many things can be recycled

Collecting and recycling all metals, untreated timber (for firewood) and materials for curbside collection (number 1 and 2 plastics, glass, paper and cardboard) was relatively straightforward. Other items diverted from the landfill were:

burnt out tools, appliances and electrical ❚

extension cables (to scrap metal dealers)standard plasterboard off-cuts – those that ❚

didn’t contain protective waxes or fibrous reinforcing (dug into the landscaping to act as a soil conditioner)number 5 plastics, mainly from paint pails ❚

and the special open matrix plastic battens required for the solar wall heater (to Raglan’s Xtreme Waste facility for processing)polyester insulation off-cuts, including its ❚

clear plastic wrapping (delivered back to manufacturer in Auckland for reprocessing into new product)rimu laminated vanity cut-outs (retained for ❚

use as chopping boards) 20 mm polystyrene protection sheets (reused ❚

as insulation, mainly for reducing thermal bridges around steel portal framing)non-treated timber (stored for firewood) ❚

some material excavated during site ❚

establishment (kept on site for landscaping).

Ian Mayes, the local eco Design Advisor, retrieving some burnt-out extension cord (from the waste trailer) for copper recycling.

BUILD April/May 2009 73

Bagged polyester off-cuts from the thermal insulation ready to be sent back for reprocessing into new product.

timber off-cuts were generated that couldn’t be used for firewood.

Not all the subcontractors got the recycling message, but the clients picked up the slack by doing some sorting and separation themselves. however, smarter ways of reminding the subbies about waste reduction and providing more timely feedback to the main contractor on their success towards reaching waste goals could improve this. This feedback needs to be done visually or verbally and ideally carried out weekly as part of an informal site meeting or through a site noticeboard. Next time, smart waste management practices (in the form of tips written alongside or opposite the detailed construction drawings) will be trialled for effectiveness.

Useful resources

There are some useful resources to assist those interested in tackling construction waste. ReBRI (www.rebri.org.nz) is the most comprehensive resource for the New Zealand industry, but level (www.level.org.nz see under ‘material use’) and the Smarterhomes website (see under ‘construction’) are also good.

local knowledge was helpful for this project too. For example, hamilton City Council’s eco Design Advisor Ian Mayes had worked for the award-winning Xtreme Waste facility and was able to provide creative solutions.

A future article will explore in more detail the waste quantities and types generated on site and diverted from landfill.

Before (left) and after (right) shots of two ends of a portal frame, which was covered with 20 mm packing (protection) polystyrene sheets to achieve a thermal break.

good communication during construction with the project manager and the site foreperson was the key to minimising waste.

Future-proofing

More formal ways that careful design could facilitate the ability to easily deconstruct the house at the end of its life to maximise the amount of reuse/recycle materials were also explored. Unfortunately, the clients could not find any useful information for light-weight domestic-style construction that could faciliate easy deconstruction. however, some future-proofing was carried out. As an example, a careful as-built catalogue of the building’s

progress was made. This provides a detailed overview for the next owners for maintenance and means any renovations and additions can be made with a good deal of knowledge and a minimum of rework. This catalogue will become part of the owners’ house manual and stay with the house.

Regular feedback needed

looking back, the quantity of material going to the landfill could have been reduced further. Ideally, untreated Douglas fir would have been good for the internal framing (where appropriate) but the timber merchant found it difficult to source. This meant a lot of (treated)