I must take issue with Davis Langdon Mott Green Wall on its cost model (BSJ 12/05) and the assertion that accurate floor levelling is an advantage of machine-room-less lifts.

That is purely a function of the drive system and has been around since the advent of the variable speed AC drive 30 or so years ago.

Architects may be going overboard for machine-room-less lifts as they don't have to find space for a machine room, but then they will not have to cure a fault in the control module located at the top of the well, by the machine, when the car is stuck at the bottom.

Another advantage becomes clear when the safety gear operates with the car just below the top landing. I'll settle for a conventional machine room every time.

Peter Lorton CEng, MIEE, FCIBSE, FSLL

Davis Langdon Mott Green Wall responds:

Sorry if we misled Mr Lorton and other readers. We did not intend to imply that accurate floor levelling could only be achieved by machine-room-less lifts, but rather that they are associated with this performance through their modern drive systems. We agree that these lifts do present certain operational difficulties, but the market suggests that, within their performance range, the advantages outweigh the disadvantages.

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Building Sustainable Design