In terms of domestic water pipe sizing, the industry is in a period of transition. Reliability questions are being raised about the traditional demand assessment system based on the LU (loading unit) method that was introduced to the UK in 1965. This was prior to the advent of water efficiency considerations, when washing habits were very different, and when mixer taps and automatic white goods where uncommon in dwellings.
Based on empirical data from live buildings, and also considering alternative design methods used in similar European countries, the growing consensus is that the UK LU system will significantly over–estimate the peak simultaneous design flow in multi-residential buildings. This TB provides interim best practice guidance for assessing domestic water demand for pipe sizing in various applications, that can be used until such time as further research is completed (e.g. LUNA1) and/or new design standards have been published.
This technical bulletin has been written by Brian Whorlow BA (Hons) IEng FCIPHE, who is honorary Chair of the LUNA group.
About the author
Summary of key items for consideration
What is the origin of UK loading units?
Inherent loading unit problems
Design methods for multiple residential buildings
Design methods within single dwellings
Design methods for commercial buildings
Design methods for congested applications
Author: Brian Whorlow (Honorary Chair of the LUNA group)
See also the Loading Unit Normalisation Assessment research report An assessment of the validity of the loading units method for sizing domestic hot and cold water services, published jointly by the Chartered Institution of Building Services Engineers, the Chartered Institute of Plumbing and Heating Engineering and Heriot Watt University, which is available here.
First edition: December 2016
Second edition: April 2020
The second edition contains no substantial change to text or technical content.