Building Use: Residential

Typology/Structural Form: Multi-storey - Steel braced frames (ground level) & plasterboard / plywood lined frames (upper levels)

  • Snapshot
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Low to medium-height multi-storey residential structures are increasing in popularity in New Zealand. A very good example of this is the recently opened Christchurch City Mission Stage 1 building Whakaora Kāinga, for transitional housing.  

This build is a very good example of hybrid design and construction where using cross laminated timber (CLT) upper floors and stairs instead of concrete results in a really efficient and lower embodied carbon dioxide solution. Additional benefits that come as a result of using CLT also include lower total building mass and a consequent reduction in foundation capacity and cost.

Easy Gains

In this case study “snapshot”, the typical concrete floor is swapped out for CLT. CLT for floors and stair systems is recognised as a very efficient use of the material. CLT walls are also a good option for internal structural walls for apartments, student accommodation and aged-care buildings, but in this snapshot, the CLT application is just in the floors and stairs. 

The key benefits of swapping concrete for CLT in the floors and stairs are: 

  • Faster installation - A CLT floor on each level was fully laid in 2-3 hours 
    • A concrete floor would take at least a week to install the permanent formwork base, temporary formwork sides, reinforcement steel and concrete placing 
  • Faster job progression - A concrete floor would then require 28 days of curing time 
  • Cost - significant preliminary and general time-related cost savings are achieved due to faster construction 
  • Lower weight - the concrete floor is 100,000 kgs heavier than the CLT floor system in this example.  This enables a lower-cost foundation design and build 

Results Summary

Over the two upper floors, there is a circa $6k saving using the CLT option whilst also achieving a;  

  • 59% reduction in embodied carbon dioxide 
  • 49% reduction in weight 
  • 8 weeks of programme time savings, enabling earlier building access and occupation 

Assumptions (for CLT option include); 

  • Cost savings for 8-week programme reduction 
  • Cost saving for a lighter foundation 
  • Cost additions for acoustic floor system (SounDown™) 
  • Cost additions for premium on GIB Fyreline® to underside of CLT

History / Project Brief

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