HSE Health&Safety Executive The effect of adjacent buildings and topographical features on the wind pressure field around buildings Prepared by BRE for the Health and Safety Executive 2003 RESEARCH REPORT 157 HSE Health&Safety Executive The effect of adjacent buildings and topographical features on the wind pressure field around buildings Dr Philippa Westbury, Mr Liam Roche, Dr Bridget Pierce & Mr James Smith BRE Environment Division Bucknalls Lane Garston Watford WD25 9XX This work has been carried out to help develop guidance on siting open flue terminals for natural draught domestic gas boilers. It aims to investigate the effects of adjacent structures and topographica features on wind pressure fields around dwellings, and to identify scenarios where the likelihood of flue maximumpressureexperiencedbyaflueterminal abovea45°pitchroofwasfoundtoexceedthatfor an isolateddwellingbyupto 6o%whenverytall orwidestructures(e.g.embankments)werelocated downwind of the dwelling. The percentage increase was higher for the 30° pitch roof, although absolute pressuresforthe 45°pitch roof weregreater. The greatest increased risk of flue flow reversal was found to occur with a background ventilation strategy rather than when a dominant opening was present, and when the adjacent structure was to roof pressures occurred concurrently with negative wind-induced interior pressures This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy. HSE BOOKS @ Crown copyright 2003 First published 2003 ISBN 0 7176 2750 0 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the prior written permission of the copyright owner. Applications for reproduction should be made in writing to: Licensing Division, Her Majesty's Stationery Office, St Clements House, 2-16 Colegate, Norwich NR3 1BQ or by e-mail to [email protected] ii EXECUTIVE SUMMARY This report describes a programme of wind tunnel testing and computer modelling which has been carried out to investigate the impact of adjacent structures and topographical features on the wind pressure field around dwellings, in order to determine building configurations that could increase the susceptibility of flues to flow reversal. The work is part of a wider programme to investigate the flue performance of open flued, natural draught domestic gas boilers, and to identify any safety implications arising from their increased efficiency which tends to cause greater sensitivity to adverse wind effects. The main objectives of the work are to investigate the effects of height and separation distance of adjacent structures and topographical features on wind pressure fields around dwellings, and to determine the sensitivity of the wind pressure field to additional factors such as dwelling geometry and orientation/geometry of the adjacent building. Furthermore, the work aims to identify scenarios where the likelihood of flue flow reversal is high due to positive pressures acting on the flue terminals and/or negative wind- induced interior pressures. For this part of the work, a combination of wind tunnel testing and computational modelling has been used. The results from this work will help to develop guidance in BS5440 on siting open flue terminals. The results show that, for a ‘standard' domestic dwelling with a 45° pitch roof, the maximum positive pressure on the dwelling roof occurs when an adjacent structure is directly downwind of the dwelling, and the dwelling is immersed in the positive pressure field produced by the downwind structure. The magnitude of the pressure depends on the height and width of the adjacentstructure,andits distancefromthedwelling.Themaximumpress