Carterton Indoor Pool Cost Estimate
After completing the initial concept design process and costing out the various project elements, the cost estimates for rebuilding the Carterton Indoor Pool based have come in significantly higher than the business case estimate of $1.8M.
The estimates were reviewed by the aquatic design specialist, building sub-committee and project working group during December 2024. This brief summarises the analysis behind the estimate and some associated questions.
Summary
The main reasons for the cost increase are underappreciation of the low build quality of the existing facility, insufficient allowance for site issues and cost escalation since the previous estimates.
Aquatic facilities are typically expensive to build, and can be expensive to operate and maintain if not built well. The updated cost per m2 is similar to comparable projects. Option 1 (compliant) will be more affordable but is NOT recommended because it will be challenging to run and maintain the facility. A Spaceframe shed option remains more attractive than a Sprung structure despite the cost increases.
Some allowance has been made in the estimates for further cost increases as well as adequate professional fees to fund the detailed design and construction oversight. There is potential through donated materials, donated products and donated labour to reduce the amount of fund-raising required.
Option assessment
Three options were developed to show the relative cost of critical vs. non-critical elements, taking into account levels of funding challenge. The options range from strict compliance at the low end to industry standard at the high end. Option 1, while compliant, is assessed as unsuitable due to poor performance, increased running costs, and risks to facility durability and maintenance. Option 2, while still below industry standard and not able to perform reliably at peak times will be relatively easy to operate and relatively affordable to build and run. Option 3 will provide a facility to industry standard with good durability and will be the easiest and cheapest to operate and maintain.
Estimate caveat
Every effort has been made to provide accurate estimates within the design budget and volunteer availability. Scope, specifications and costs have been peer-reviewed informally. The estimates are based directly on (Options 2 and 3) as they have been technically drawn and specified, whereas Option 1 has been reverse-engineered. Estimation accuracy is also reliant on our building partners who have donated their estimates at no charge.
Technical reports
Further detail about the facility and project options is available in a number of detailed technical reports, commencing from 2018. Copies of these reports are can be supplied on request. For further information please contact: cartertonindoorpoolproject@gmail.com.
How much has the cost estimate risen?
The business case in September 2022 estimated $1.80M, including fees and contingency, compared with the latest estimate of $3.18M. This is an increase of $1.38M or 77%. (This estimate excludes GST, as it is intended that GST will be claimed back as a charitable expense.)
What has driven this increase?
A summary of the main cost elements is included in the Appendix at the end of this brief. There have been three general areas of cost increase: (1) low build standard of the original pool, (2) site issues not previously allowed for, and (3) cost escalation (i.e. inflation).
The original shed, floor and internal rooms were built by volunteers with donated materials to standards that barely met the regulatory standards at the time. (Whereas, the pool tank was constructed by a contracted builder.) That shed build quality is well below the current regulatory and industry standards. Most comparable projects involve school or public pools built to higher design and construction standards (usually standards set by the former Ministry of Works). Some of the issues this has created for the rebuild are: suspected areas of poor infill material under the floor, structural weaknesses in the pool tank walls, inadequate floor drainage, low-lying floor, poor sewer connection, inadequate balance tank, inadequate disposal of filter backwash waste outflow, and below-standard change, toilet and shower spaces.
Site investigations since the business case have discovered a number of challenges and as-built deficiencies. Rebuild projects (of which this is one) are typically more expensive than comparable green fields projects because of site issues. While the business case estimate included a contingency of $216,750, the estimated cost of the works not allowed for is now $418,783. Those overlooked elements include: firewall, shed footings, acoustic ceiling tiles, power transformer, external plant area, backwash detention tank, replacement balance tank, second soakage pit, reforming the floor at the southern end, tank crack repair, replacement of pool stairs, aquatic lift, floor drains, dedicated fire exit, sewer pump chamber, and replacement hot water cylinder.
The final cost issue is that construction costs have escalated significantly over the life of this project. The business case used a mix of estimates from the feasibility study (2020), Greendale Pool rebuild project (2020) and a quote from Sprung (2022). Construction costs rose significantly following the recent pandemic, with the Statistics NZ index of the capital cost for commercial building construction increasing 29.6% since mid 2020 (and 12.3% since mid 2022). This represents an escalation in cost from $1.8M to $2.3M (or an increase of $532,474). In comparison, the business case contingency allowance was 14% or $216,750. (Cost escalation from mid 2020 to the planned design-build tendering in early 2024 was 27.8%, or an increase of $500,754.)
How does the cost estimate compare to similar projects?
The latest project cost (Option 2) is $4,696/m2, compared with the business case rate of about $2,944/m2. An estimate from Holmes Construction (2022) of $3.6M was $5,584/m2 and the Kings’ Swim School Project (a Sprung structure on a new site in Christchurch completed in 2021) was $4,500/m2. The cost of the new Pahiatua Pool (also a Sprung structure) has risen from an estimate of $4M to a tendered contract of $7.2M (80% increase). The Green Family Taradale Pool rebuild in 2020 cost $1.3M for a new shed and HVAC[1] system, but that excludes replacement of the reticulation and filtration system which is currently underway.
Why are aquatic facilities expensive to build and maintain?
Aquatic facilities face issues that other indoor sports facilities do not. In addition to managing the pool water temperature and water quality, a viable facility must manage the air temperature, humidity and chloramine levels inside the building. Metal corrosion can result if this is not achieved and such a system is expensive. The facility enclosure requires a high insulation rating and this can make glazing expensive, or increase the requirement for artificial lighting. The hard interior surfaces and pool surface amplify noise levels which in turn requires an expensive acoustic control medium. The metal structure also requires passive protection measures to ensure longevity, including painted coatings and raised footings to counter the challenges from ground moisture and splash zones.
What are the design scope options for managing costs?
Three building scope options have been considered to investigate the potential range of costs. Option 1 is NOT recommended because of the maintenance and running cost challenges.
What are the practical implications of staging the construction or retrofitting some elements?
There is potential to defer the purchase and installation of some components to reduce the immediate need for project funds. All elements of Option 3 could be retrofitted to Option 2. Retrofitting the glazing and floor coating would require closing the pool for about two months.
Is the Spaceframe structure still more attractive than the Sprung structure?
The feasibility study in 2020 suggested the suitability of an imported Sprung aluminium-arch-and-tensioned-fabric enclosure due to its light-weight materials, high corrosion resistance, adequate insulation rating and high translucence. Sprung has proven more economic than conventional steel or laminated timber structures for recent new builds and greenfields sites. Lower cost, NZ-made tensioned fabric structures are unsuitable because they lack insulation. NZ-made steel and timber structures are the most common solution but these are expensive. The option to import a cheaper Spaceframe building structure arose in late 2023. Spaceframe and Sprung have comparable durability and maintenance performance when the cladding and structure are assessed for whole-of-life challenges and costs. The main challenge for a Sprung structure on our site is the 8m building height as this would require an 8m firewall and may also require resource consent. While Sprung admits more natural light it however provides less usable internal volume. On balance, the Spaceframe option remains more attractive and the primary reasons for cost increases are not related to the choice of shed structure (refer to the Appendix below).
What is the potential for further cost increases?
The construction cost could increase further during design, however the latest estimate includes some allowance for contingency (3%) and escalation (2%) to mitigate those risks.
What are the main design and construction risks and how will they be managed?
There are some foreseeable risks for the detailed design stage. Experienced aquatic facility designers are in limited supply and the cost savings offered by the Spaceframe option are dependent on utilising CREATE Ltd for the detailed design. The cost estimate allows for the market rate for design services.
The large number of contractors and suppliers involved in this project will require an increased level of supervision and management, which may challenge our volunteer capacity. An allowance has been made for professional project management and construction management support.
The construction cost could increase further if there is a problem with the supply of the Spaceframe shed or insulated panel roofing and cladding. There is little that can be done to mitigate this risk.
What is the potential amount of donated labour and materials that will reduce the amount of cash funding required?
There is substantial potential for reducing the cash cost of the project through donations. These could be in the form of supplier-donated stock, private donations for allocated building elements (e.g. walls panels, roof panels, ceiling panels, doors and windows) or donated labour. A very rough estimate of potential donations is $1M.
What does the expenditure plan look like for the new cost estimate?
A key factor affecting the construction programme is that construction cannot commence until the council summer pool closes in late March 2026. An indicative plan, assuming Option 2, would look like this (with Option 3 retrofitting at a subsequent stage):
