Cost considerations often drive choices when building a property, but thinking more broadly from project design to material specification can be worth its weight in gold.
THE BUILDING PROCESS is all about making decisions – hopefully the right decision at the right time based on sound, quantifiable data. However, too often, we look back and wish we had made a different decision or choice.
Too often cost drives choices
The construction industry in New Zealand has traditionally focused on the lowest upfront cost, driven largely by the building owner or developer’s initial cost expectations.
This has led to the specification of materials with the lowest purchase or installation cost as the prime consideration. Meanwhile, the cost of ensuring the component performs over the life of the building is not part of the equation.
Buildings are complex and subject to a wide range of influences. These include the client brief, budget, finance, return on investment, net lettable area, planning rules, site, climatic and environmental conditions, aesthetics, access, durability, height, complexity, safety and so on.
Making the best choice
Conflicts over choices need to be resolved. Common things to consider include:
● whole-of-life cost (LCA) or initial cost
● realistic vs unrealistic client and budget
● views vs sun
● garage location and sun
● wind direction and strength
● benign vs aggressive environment
● low or limited maintenance vs high or regular maintenance
● complexity vs simplicity.
The choices continue when thinking about materials, such as:
● multiple vs single claddings
● pitched or low-slope roofs
● eaves or no eaves
● area of glass vs area of thermally well insulated wall
● double vs single glazing in the northernmost parts of the country
● internal vs external gutters
● the client’s desire for a roof deck, which is a known high-risk element
● standard aluminium window frames vs thermally broken aluminium, PVC or timber
● material performance vs appearance
● serviceability vs minimum durability
● verified material durability, for example, BRANZ Appraisal vs unverified supplier’s assurance
● levels of insulation.
Each of these influences has variances or subtleties that can be exacerbated or moderated by the design. To explain, let’s take some examples.
Life cycle assessment (LCA)
In simple terms, LCA is the selection of a building component, element, material or finish based on the accumulated costs over the expected life of the element or building. These may include initial cost, maintenance costs and ultimately reuse or disposal costs.
Initial cost is simply based on the cost of purchase without considering the costs associated with the use of that element over its life. Often, materials with a higher initial cost have a lower total cost over their life as they may last longer or require less maintenance.
The question of eaves
Eaves are universally recognised as a device that can reduce the weathertightness risk of a wall cladding by deflecting water from the surface. The benefit depends on the eaves width and their height above ground.
However, eaves can have a detrimental effect on metal claddings by reducing washing by rain at the top of the cladding, resulting in areas of wall prone to corrosion.
A new BRANZ research programme has just started investigating the effect of microclimates that may occur due to building detailing such as this.
Form or function
What determines the choice of a particular material over another – is it dictated by the appearance of the material or by its performance?
The desire for a certain appearance may be at odds with the performance of the material within its in-use environment.
View or comfort
When designing the glazed area of the wall, remember that glass is less thermally effective than the adjacent framed wall.
If views are important, does the glass need to be that big? Perhaps the view would be enhanced by the strategic placement of smaller windows. This could result in a more thermally efficient building and a view that is framed to make the space more interesting.
Most New Zealand housing requires double glazing to meet Building Code clause H1 Energy efficiency requirements. In the far north, it is possible to use a tool to show that the building meets the Code requirements with single glazing, but is this worth it? We believe not.
A BRANZ survey of new-home owners highlighted concerns that their new house is not as warm as they thought it might be.
To ensure a good level of performance, go above the minimum. Install higher-performing glazing such as double glazing in the far north and thermally broken aluminium, timber or PVC frames in the south.
Reducing the risk from gutters
Internal gutters may be a convenient solution, but often they aren’t worth the risk. While a gutter integrally formed with a roof membrane has a lower risk associated with it, any failure will result in water within the building.
With metal roofs, irrespective of the gutter lining, there is always the risk that if the gutter blocks or overfills, the water will find its way under the roofing and into the building.
A better choice is to design them out if possible or make them as fail-safe as possible with an oversized drainage and overflow system.
Articles are correct at the time of publication but may have since become outdated.