CASE STUDY - New Apartments Showcase Low Carbon Building Benefits

Building with renewable engineered wood rather than concrete offers a significant win for the environment and the financials, a new case study has revealed.

The study used Clearwater Quays luxury apartments in Christchurch, New Zealand as a test case. Clearwater Quays was constructed as a part of Mid-Rise Wood Construction, a public-private partnership between the Ministry for Primary Industries and Red Stag Investments.

The aim of this $6.75 million programme is to encourage widespread adoption of precision engineered timber in mid-rise building construction. Since its inception in 2018, the programme has assembled a pool of New Zealand professionals experienced in mid-rise wood building design and construction to help share and grow knowledge and expertise with the broader industry.

‘Mid-Rise Wood Construction’ complements the government’s initiatives to encourage high value domestic processing and manufacturing from New Zealand’s plantation forests and deliver a zero-carbon construction sector by designing to increase low carbon materials used in construction. Programme projections suggest if engineered timber is widely adopted, this construction method could save the country $330m annually by 2036.

This extract focuses two sections of the case study:

1. Cost Management and Analysis of the project

2. Environmental Impact Analysis and CO2 Calculator.

Mr Lynch says carbon calculations for the Clearwater building show its timber construction saved 87,400kg of carbon dioxide (CO2), compared with a CO2 release of 952,600kg if it had been built of concrete, and 794,600kg if built of steel and concrete. The $3.37m price to design, develop and construct the apartment block would have been $3.89m for concrete construction or $3.59m for steel and concrete. The calculations include financial impacts of a reduced construction time.

The full Clearwater case study is now freely available for construction professionals (https://midrisewood. co.nz/wpcontent/uploads/2022/09/ Clearwater-Case-Study-V2.4.pdf.). The full case study also includes general considerations, design, construction, and learnings.

The project has been deliberately designed to be open source, with all project information being made available to showcase the advantages of the new building materials and methods.

This case study uses a five-level, luxury, residential apartment building to highlight the holistic benefits of engineered- timber construction compared with a traditional steel and concrete approach.

The Clearwater Quays Apartments has a total floor area of 2,130 m2 (including garages) with two open-plan apartments per level overlooking the lakefront of the prestigious Clearwater development in Christchurch, New Zealand.

Combining cross-laminated timber (CLT), laminated veneer lumber (LVL), glulam and panelised framing timber (e.g., structural insulated panels) creates a cost-effective, fast, resilient, and sustainable system for mid-rise construction. Engineered timber is not only naturally beautiful but also provides a very strong, low carbon and comparably low-cost alternative to steel and concrete. It is easy to transport, relatively light, and has outstanding earthquake and fire resilience.

Cost comparisons for the Clearwater Quays project across three construction methods; concrete, steel, and mass timber, show that on a materials-only basis mass-timber had the highest cost. However, when the development impacts of the shorter construction programme were taken into account, the mass timber options became the least expensive by 6% compared to concrete and steel and 13% compared to the all-concrete option.

In addition to the financial advantage of mass-timber builds, this case study shows environmental benefits that cannot be ignored. For the Clearwater Quays project, the carbon calculator for the mass-timber building was a net negative 87,500 kilograms. If the building were to be built in traditional steel and concrete, it would have resulted in 800,000 kilograms of carbon being released into the atmosphere, and over 950,000 kilograms of carbon if concrete alone had been used.

The Clearwater Quays project was commissioned by a company with an interest in the timber industry. Showcasing timber both structurally and visually was a driving factor of the design brief.

The challenge for Mid-Rise Wood Construction was to maximise opportunities to highlight the aesthetic and structural quality of timber. This goal was achieved by incorporating dramatic, sculptural staircase structures projecting from the southern façade of each residential tower. These curvaceous forms create a counterpoint to the otherwise linear road- facing southern façade.

The spacious entrance lobby was designed to draw people into the building via a large portico structure. The apartment living areas face north with bedrooms and services areas orientated to the south.

The structural frame of each residential tower is entirely timber including CLT panel floors, and a lift featuring light framed timber. The only non-timber elements to the structural system are the concrete slab ground floor, and footings.

The cost of a mass timber build compared to concrete and steel.

Mass-timber building using LVL, glulam and CLT is a relatively new method of construction. In the past decade, the building industry has seen an increase in interest, due to awareness of climate change and the need for sustainability leadership. This type of interest means that most mass-timber builds have been “passion” projects or statement buildings that have been developed to show the possibilities as well as the direct and indirect benefits of this type of building.

The construction of many bespoke mass timber buildings has involved a steep learning curve for the industry. Most buildings have been architecturally and structurally different and built to stand out as exemplar projects so extracting meaningful cost data from such projects can result in a wide range of information.

Using such data can result in invalid comparisons with traditional construction methods, and many projects have defaulted to traditional builds due to this lack of validity.

More recently, the costs of mass-timber builds have been affected by increased industry experience, methodology developments, refined prefabrication techniques and greater competition among suppliers. These factors, combined with more accurate cost estimation software, better understanding of both programme savings and capital return durations, have resulted in more informed cost comparisons.

Increasing both the quality and type of information available to developers will continue to increase the uptake in mass timber builds.

ESTIMATION METHODOLOGY

At the outset of this project, the quantity-surveying team built a ‘digital twin’ cost model for the Clearwater Quays development. (A digital twin in construction, engineering, and architecture is a dynamic, up-to-date replica of a physical asset or set of assets).

The structural engineer developed alternative designs to sufficient detail for the construction manager to be able to estimate the build programme time and for the QS to be able to price the structure and foundations and estimate the cost implications of the time saving from constructing in mass timber.

Building digital twin models for the structures was the next best option to constructing these on site. Within these models, design elements were incorporated that would be associated with these build methodologies.

For example, CLT floors would require acoustic cradle and batten flooring where concrete floors would not. Mass timber-builds would typically have lighter foundations than other methodologies.

The various approaches and considerations of structure, acoustics and fire across each design were addressed and incorporated into the cost estimates.

Utilising a building information modelling (BIM) / virtual design and construction (VDC) approach increases accuracy and allows cost findings to be communicated in a language that clients and design teams understand. All elements are quickly interchangeable and can be fed back into build budgets. Back and forth discussions with the engineer refined these structures and increased the accuracy of cost estimation.

To fully understand any cost comparisons, here must also be a consideration of intangible inputs within the comparisons. Often such inputs are overlooked or there is simply not enough knowledge or expertise to inform feasibility investigations/comparisons.

These are:

• reduced construction durations

• development cost - market risk

• development cost - carrying costs

• development cost - completion settlement.

Typically, the longer it takes to deliver the project, the higher the non-productive costs are. This is true for the construction programme but is also relevant to the developer’s capital investment and financing.

To put it simply, the longer it takes to complete the project the longer it will take the developer to return capital investment. It leads to longer finance carrying durations, increased risk, and can delay further opportunities to invest in the next project.

FINDINGS

Utilising the above digital methodology has enabled a more robust and detailed cost estimation to be developed than could previously be completed without physically constructing each design.

The results of these feasibility investigations are valid at the time of this case study (September 2021). Since September 2020 the cost of concrete and steel has increased relative to mass timber materials, improving the cost advantages of mass timber. The chart below contains typical cost-data comparisons for different types of construction materials.

Comparisons for the Clearwater Quays project across the three construction methods examined show that on a materials-only basis the mass timber had the highest cost. However, once Preliminary and General were factored in, all- concrete options were the most expensive.

When the development impacts of the shorter construction programme were taken into account, the mass timber options became the least expensive by 6% compared to concrete and steel and 13% compared to the all-concrete option.

The development items are made up of the following being applied to each week saved or delayed:

• Market Risk – adverse property market move risk of 5%/year on a $18m value development

• Carrying cost impact – carry cost of $3m land, design/consent fees $2m and head office overheads $1m. Total $6m at 5%.

• Completion settlement/redeploy profit – Assume developer redeploys $2.7 (15%) profit in their next development worth $6.75m at 15% profit in the next year.

It is important to note that development costs will be subject to the developers’ own financing model, capital and investment structure, and contractual exposure to market risk. The referenced figures are based on internal calculation for this project provided by Clearwater Development Ltd.

The length of time it takes to build a mass timber build compared to concrete and steel, and where savings can be made.

Every project has different infrastructures and demands on programme deliverables. Preliminary and General items will usually include project costs that will not physically be left on site, e.g., professional supervision, site fencing, utility costs, insurance etc. On a typical medium sized contract of $10m, expectation would be for a $30,000 monthly average spend on preliminary and general.

For this project, the Clearwater Quay’s construction manager developed alternative delivery programmes for steel and concrete and full concrete structures and compared these with the known mass-timber programme. (It is worth noting here that the construction manager’s background and experience prior to this project had been in traditional building methods, and no allowance was made within the mass-timber programme for efficiencies associated with the learning curve required or lessons and skills attained).

The results of the comparison show that the mass-timber build had a programme saving of 2.5 months. These 2.5 months were saved during what would have been the critical frame-installation process where costs exceeded the average $30k spend and were closer to $70k. Theoretically, savings during this period would have been $175k when compared with an alternative build method.

Less time on site has many positive benefits in addition to the financial benefits discussed above. Using mass timber construction for the Clearwater Quays project has reduced disruption to neighbouring properties and generated interest that has resulted in positive engagement with the local community.

Contractors working on site have noted the positive effects of a cleaner site and floors, reduced construction risk and an enclosed weathered environment earlier in the programme.

In summary, mass-timber builds can be cost effective when compared with other construction method, but many factors need consideration to ensure comparisons are fair.

DESIGN AND ARCHITECTURE

The most sustainable aspect of the building is the carbon sink of the building’s structure.

The living spaces are heated via reverse cycle heat pumps, negating the need for a central heating system. Natural ventilation has been used for cooling in lieu of an artificial system and trickle vents were also introduced to provide make- up air (with acoustic baffles to control exterior noise).

Low-E glass was originally to be used just for the bay windows as these have the greatest potential for overheating, but following an upgrade from the glass supplier, all windows will now be double-glazed. Low E. Solar panels will supply the electricity demand to the majority of the common area (lobby and stairwell).

ENVIRONMENTAL BENEFITS

The Clearwater Quays project promotes environmental benefits in several different processes. These include:

Carbon

The processes of manufacturing building materials such as concrete and steel produce far more carbon than mass timber. In fact, there is more carbon already efficiently and safely stored within the timber material than produced during manufacture.

Mass timber is a carbon-negative material so using it results in carbon being extracted from the atmosphere and stored in the building material. That carbon storage can off-set the impact from other materials used in the building process, such as steel fixings, cladding systems, and foundations.

Wastage

Lean construction and minimal waste is synonymous with off-site construction. The core structure of the Clearwater Quays Apartments can be categorised into three main elements: (1) CLT floors replace concrete and steel floors; (2) structural steel is replaced with LVL columns and beams to support these floors; and (3) there are the panelised / prefabricated timber frames. These components have all been manufactured off site in controlled manufacturing environments that utilise technology to control and minimise wastage, which substantially reduced on-site waste output.

The Clearwater Quays site was striving to be as close to zero-waste as practicable with all material being sorted before leaving the site. Materials that could be recycled were diverted to the correct facilities.

The use of a QS 3D BIM cost model added significant value in this area. The model not only replicated the construction build and every element, it also accurately quantified every piece of timber, every bolt and tape etc. The model contained information on material specifications, such as sheet sizes, timber supply lengths etc so was able to provide accurate order quantities by unit supply and could produce cutting lists for trades. This process provided key site performance information that encouraged efficient material ordering and use on site.

Traffic

Most heavy traffic on site was generated from the movement of material. The biggest saving to time and cost of a mass-timber build is through the use of CLT floors, but this has other positive benefits too. Construction of a concrete suspended floor requires delivery and installation of several individual elements.

These include steel decks, timber formwork, steel reinforcing, and of course concrete. All this requires multiple truck deliveries arriving and moving on site. A typical CLT floor level at Clearwater Quays can be delivered to site and installed in less than one day.

CARBON CALCULATION

As discussed above, alternative design methodologies were completed for concrete and steel construction. Using BIM 5D Cost modelling technology, the QS team explored various build options and demonstrated some significant findings regarding carbon footprints.

The metadata now stored in the 3D geometry is typically used for cost calculation, but also contains embodied carbon data. Carbon calculation is becoming a major consideration in building projects and can now be automated allowing for quicker and more flexible comparisons across build options.

The results allow the client to understand the environmental impacts of their materials choices in conjunction with cost data allowing for more informed decision making.

This system has been refined in house and automated for completing carbon calculation assessment at feasibility/concept design stage. The models can be generated quickly by focusing on the variable core structures only, while the advanced parametric capability allows for quick conversion to the alternative material choice.

Live data feedback with referenceable 3D-model information allows for in-depth analysis of different building and elemental options, which facilitates identifying and understanding the sweet spots between cost and carbon results in cost effective sustainable buildings.

For the Clearwater Quays project, the carbon calculation for the mass timber building was net negative 87,500 kilograms. If the building were to be built in traditional steel and concrete, it would have resulted in 800,000 kilograms of carbon being released into the atmosphere, and over 950,000 kilograms of carbon if concrete alone had been used.

Article published and written by Built Environment Economist - Australia and New Zealand.

Download the article online: Built Environment Economist - Australia and New Zealand March 2023 by Australian Institute of Quantity Surveyors - Issuu