Building taller in Ireland - a benchmarking exercise

As part of the Linesight ‘Building Taller’ report, released in October 2019, we conducted a benchmarking exercise in order to provide a meaningful cost analysis. 

The benchmarking exercise was based on relevant data taken from a sample of 500,000sq.m. of commercial project experience, and 15,000 residential units on which Linesight is currently providing cost consultancy services. 

This benchmarking information is used to present cost comparisons across a number of buildings, where Linesight has provided cost consultancy under their separate distinct use, between commercial and residential. 

We would note that the results of the benchmarking exercise demonstrate that differences unique to each project exist, and there is variety in terms of shape, size and design. 

However, where similarities in terms of design are identified, the results of the benchmarking pinpoint the changes in the elemental costs that are commonplace to the project. This is demonstrated in the following charts.  

Figure 3 compares the elemental shell and core, and CAT A costs over a number of commercial buildings that were benchmarked. The graphs track the buildings in their varying heights, from low-rise to taller buildings, and validate the introduction of new elemental costs (sprinkler) and the increase in the predominant elements (structure, façade, etc.) as the building height increases. The percentage increment in costs is also displayed at the top of each bar to provide clarity as to the overall cost increase.  

As per the commercial graph in Figure 3, Figure 4 tracks the buildings in their varying heights from low-rise to taller residential buildings, with the percentage increment in costs to provide clarity as to the overall cost increase.  

Understanding cost drivers

To further determine the rise in costs due to the increase in the height of buildings, the following considerations, in addition to the waterfall charts on the following page, outline the point at which costs and design change as we start developing from a low-rise building into a taller structure. The increase in costs can be demarcated by the following:

1. Preliminaries – increase in heavier plant and equipment, working restrictions, welfare facilities distributed further up the building as work progresses, and health and safety measures
2. Structural increases – enhanced cores, to deal with structural and service requirements and occupation requirements, as well as increasing the number of fire escapes for evacuation strategies. Additional structural enhancements will be required to deal with loadings (lateral and vertical)
3. Façade – higher costs are due to increased aesthetics, less efficient wall-to-floor ratios due to slenderness, additional performance requirements, wind loadings, control of solar gain and façade maintenance measures
4. Sprinklers – the requirement for various sprinkler systems 
5. Services – further cost to boost water supplies, pressurise heating and introduce interstitial plant floors
6.  Balconies (residential) – expensive solutions, such as recessed balconies and winter gardens are introduced
7. Lifts – additional number of lifts, and the speed of the lifts begin to increase also

The waterfall charts on the following page for both commercial and residential developments display the demarcation in terms of the costs under the headings outlined above.