We’re often asked to explain the cost of CALMFLOOR’s active mass damping solution compared to traditional structural modifications for reducing floor vibrations in existing buildings. Having spent over 30 years dealing with excessive floor vibration problems, I can safely say CALMFLOOR is more cost-effective than any form of structural modification.

Theoretical considerations

The vast majority of existing building floors require vibration reduction because:

  • Existing occupants can’t tolerate the lively floor vibrations caused by nearby foot traffic or the ground-borne vibrations transmitted to the building.
  • New occupants require far lower vibration levels, especially after a change of use, for example, in office-to-lab conversions.

These environments are inevitably referred to as ‘low frequency’ floors, i.e. they’re excited in resonance by human footfall or ground-borne vibration transmission. Typical vibration reduction requirements range from a factor of 2 to 8. Indeed, any good structural dynamics textbook will tell you the most effective way to reduce resonant vibration is to increase floor damping by 2 to 8 times. This is precisely what CALMFLOOR delivers—demonstrably and rather uniquely.

In contrast, any kind of structural modifications that add mass and stiffness to the floor will, theoretically, be much less effective and, crucially, require disproportionately large quantities of structural materials. How much larger? Well, to hit that 2 to 8-times reduction, you’ll need around the equivalent in mass. It then demands even more structural stiffness and strength to support the colossal additional mass that’s spread throughout the building, including its foundations. This overview gives us an idea of the vast quantities of additional materials that are needed. We’ll explore that further in the case study below.

Technical considerations

Floor vibrations don’t occur throughout the entirety of the floor. They’ll be present only in ‘hotspot’ areas, most typically in unpartitioned areas. Areas around supporting walls, lift shafts, stairwell cores, columns, short and stiff beams and non-structural façades attached to the floor and around full-height non-structural partitions don’t vibrate excessively or require vibration control. This is shown in Figure 1, which reveals the majority of this office floor, a proposed office-to-lab conversion, actually satisfies the R<2 criterion.


Figure 1:
A composite steel-concrete office floor structure with spans up to 15m and a total floor area of 3400 m2. The white areas represent lift cores, stairwells and vertical utilities. Figure 1a) shows a floor plan with a contour plot of vibration response factors that indicate the maximum floor vibration has a response factor of R=10.7 (approx. 42,000 mips). There are only seven hotspot areas with R greater than 2 (approx. 8,000 mips) – the target for the lab conversion. The floor area requiring control was clearly less than 25% of the total physical floor area. Figure 1b) shows the locations of the 13 CALMFLOOR units (purple diamonds) needed to fully control this floor to a R<2 limit.

However, practical constructability and structural continuity constraints mean structural modifications can’t be made solely to the vibration hotspot areas. They must be implemented over a far wider floor area, often the whole or vast majority of the physical floor area. Conversely, CALMFLOOR can focus only on the hotspot areas – and is versatile enough to be moved if a change of tenant or floor layout requires it. Figure 1 shows 13 CALMFLOOR units were controlling vibrations over a 3,400m2 floor – that equates to an average of one CALMFLOOR AMD over each 300m2 of the floor area. It’s another key consideration that features in the cost comparison shown below.

Practical considerations

Implementing essential and typically very significant structural modifications causes major disruption. The contractor will demand full possession of the floor structure over many months; while the floor is being reconstructed, it can’t be occupied – that means a loss of revenue to the building owner.

Contrast this with CALMFLOOR. It can be installed in a matter of hours, it causes no disruption and will work with just a flick of a switch – straight out of the box.

This cost of disruption is yet another fundamental consideration that has to be taken into account when assessing the cost of structural modifications. We’ve covered it below.

Financial considerations

The cost of structural modifications is an up-front cost that typically requires capital investment; hence there is an associated cost of providing such capital, namely the interest rates incurred.

An investment in CALMFLOOR active vibration control also has an initial capital cost that’s also associated with interest rates. However, the on-going annual maintenance cost is tax deductible – liken it to the cost of running any other electrical and mechanical equipment in a building. These financial considerations are also covered below.

Case study: CALMFLOOR vs structural modification in a 10-storey office building

While every building is indeed a unique prototype that calls for case-by-case analysis, the most effective way to demonstrate my experience in any cost comparison between CALMFLOOR and a structural modification approach is through a case study. Note, I’ve made rough, but entirely reasonable assumptions in order to achieve a fair like-with-like comparison.

This case study examines a 10-storey office building with a gross floor area of 1,000m² per storey, requiring a fourfold reduction in vibration levels – similar to our example in Figure 1. The structure features composite floors with steel beams supporting a 150mm concrete deck, comprising ten 10×10m floor panels (or bays). The building has a typical façade, column layout and partitioning.

For this analysis, we assume that 70% of the gross floor area falls within vibration ‘hot spots’ and that one CALMFLOOR unit is needed per floor panel, covering 100m² each. These assumptions are deliberately conservative compared to the case in Figure 1, leading to a higher estimated unit count and, consequently, a higher projected cost than would likely be required in practice. This only strengthens the case for CALMFLOOR as the best alternative to any structural modifications.

The structural modifications

To achieve a four-fold reduction in floor vibration, the concrete deck would need to be increased from 150mm to at least 300mm. The cost of additional concrete, reinforcement, formwork, labour and structural strengthening is conservatively estimated at £150/m² though, in practice, it’s likely to be higher.

Assuming seven CALMFLOOR units, each costing £20,000, are required to control 1,000m² of floor space, the cost per square meter would conservatively be £140. In reality, this figure is likely to be lower.

The cost of disruption

This type of major structural modification on a 10-storey, 10,000 m2 building is likely to take at least nine to 15 months – we’ll assume 12 months. This represents a loss of revenue of £600/m2 per year for a typical office space in London. The loss of revenue for a standard lab space in London would be approximately twice that, i.e. £1,200/m2.

The cost of capital and maintenance

At a cost of £150/m², the capital servicing cost for structural modifications, assuming 5% annual interest, is £7.50/m² per year. In comparison, the annual cost for CALMFLOOR is £7/m².

We’ll add additional tax-deductible maintenance cost of £1,000 per unit per year for a CALMFLOOR system. With seven units required for a 1,000m² floor, and accounting for 19% business tax relief, the effective cost is £5.67/m² per year.

The overall cost

Based on these figures, for the entire 10,000m² building over 20 years, the total cost of structural modifications is estimated at £9 million – and are likely to be higher. In comparison, the cost of the CALMFLOOR active vibration control solution is just under £4 million, with the actual cost likely being lower. Over 40 years, these figures rise to £10.5 million and £6.5 million, respectively.

In conclusion, the CALMFLOOR solution is approximately half, or even less, than the cost of a structural modification approach.

If you’d like to know more about the comparative costs of CALMFLOOR active mass damping and structural modification for a project you’re considering, please get in touch and we’ll help you make an informed decision.

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