Rule of thumb
![]() |
[edit] Introduction
Rule of thumb is an English phrase that has been in common use since the 17th century. It describes a method of doing things which, although not scientifically verified, is broadly correct although it may not be strictly accurate or reliable in all applications, even though it may have proved successful on past occasions.
It may be that a rule of thumb is eventually proved in science to be correct, although it may still be referred to as a ‘rule of thumb’ – see below.
[edit] Use in construction
Builders of the past would have used rules of thumb in construction. Gothic cathedrals eventually would soar in height as master masons learned through experience to understand certain relationships e.g, the height of a tower in relation to its base and wall thickness; the depth of foundations according to soil conditions, or the diameter and spacing of piers to support the masonry above.
Advancement would typically be through making mistakes - frequently catastrophic - and learning from them. A classic example is the collapse (in 1237) of the main tower at Lincoln Cathedral, and the collapse (1210) of the south-west tower of Chichester cathedral followed in 1635 by the collapse of its north-west tower.
Rules of thumb are still used today by construction professionals as they can give a basis from which a more detailed design may be delivered.
Examples of rules of thumb are:
- The Evans rule, which arose out of a Royal Academy of Engineering paper by Evans et al: the 1:5:200 ratio. This states that if initial building construction costs are ‘one’, over the years ‘five’ will be the operating and maintenance costs, while ‘200’ will be business operating costs.
- Health and Safety Executive (HSE): in assessing noise risks for large, dynamic sites …’as a general rule of thumb, the noise level is probably 80db or more if the noise is intrusive but normal conversation is possible between people 2m apart – comparable to a busy street, a typical vacuum cleaner or a crowded restaurant'.
- BSRIA has a publication called 'Rules of thumb - guidelines for building services (5th Edition) (BG 9/2011)', providing a source of approximate engineering design, environmental performance and project cost-data for building services projects.
- The '45 degree rule' and the '50:50 rule' for determining rights to light.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Great British Energy install solar on school and NHS sites
200 schools and 200 NHS sites to get solar systems, as first project of the newly formed government initiative.
600 million for 60,000 more skilled construction workers
Announced by Treasury ahead of the Spring Statement.
The restoration of the novelist’s birthplace in Eastwood.
Life Critical Fire Safety External Wall System LCFS EWS
Breaking down what is meant by this now often used term.
PAC report on the Remediation of Dangerous Cladding
Recommendations on workforce, transparency, support, insurance, funding, fraud and mismanagement.
New towns, expanded settlements and housing delivery
Modular inquiry asks if new towns and expanded settlements are an effective means of delivering housing.
Building Engineering Business Survey Q1 2025
Survey shows growth remains flat as skill shortages and volatile pricing persist.
Construction contract awards remain buoyant
Infrastructure up but residential struggles.
Home builders call for suspension of Building Safety Levy
HBF with over 100 home builders write to the Chancellor.
CIOB Apprentice of the Year 2024/2025
CIOB names James Monk a quantity surveyor from Cambridge as the winner.
Warm Homes Plan and existing energy bill support policies
Breaking down what existing policies are and what they do.
Treasury responds to sector submission on Warm Homes
Trade associations call on Government to make good on manifesto pledge for the upgrading of 5 million homes.
A tour through Robotic Installation Systems for Elevators, Innovation Labs, MetaCore and PORT tech.
A dynamic brand built for impact stitched into BSRIA’s building fabric.
BS 9991:2024 and the recently published CLC advisory note
Fire safety in the design, management and use of residential buildings. Code of practice.