Porous
The word ‘porous’ refers to materials that include voids through which liquids or gasses may pass. Porosity is the volume of such voids relative to the overall volume of the material.
The SuDS Manual (C753), published by CIRIA in 2015 defines porosity as ‘The percentage of the bulk volume of a rock or soil that is occupied by voids, whether isolated or connected.’
A porous surface is: ‘A surface that infiltrates water to the sub-base across the entire surface of the material forming the surface, for example grass and gravel surfaces, porous concrete and porous asphalt.’
Porous asphalt is: ‘An asphalt material used to make pavement layers pervious, with open voids to allow water to pass through (previously known as pervious macadam).’
A porous pavement is: ‘A permeable surface that allows water to infiltrate across the entire surface material through voids that are integral to the pavement.’
NB Technical paper 35: Moisture measurement in the historic environment, published by Historic Environment Scotland in 2021, defines porosity as: ‘A measure of the total amount of void space in a material, usually expressed as a percentage (%).’
Assessing risks in insulation retrofits using hygrothermal software tools, Heat and moisture transport in internally insulated stone walls, by Joseph Little, Calina Ferraro and Beñat Arregi, published by Historic Environment Scotland in 2015, defines porosity as the: ‘Fraction of airspace within a material, often expressed as cubic metres of air per cubic metre of material (m3/m3) or a percentage of the total volume which is composed of air.’
[edit] Related articles on Designing Buildings
Featured articles and news
Homes England creates largest housing-led site in the North
Successful, 34 hectare land acquisition with the residential allocation now completed.
Scottish apprenticeship training proposals
General support although better accountability and transparency is sought.
The history of building regulations
A story of belated action in response to crisis.
Moisture, fire safety and emerging trends in living walls
How wet is your wall?
Current policy explained and newly published consultation by the UK and Welsh Governments.
British architecture 1919–39. Book review.
Conservation of listed prefabs in Moseley.
Energy industry calls for urgent reform.
Heritage staff wellbeing at work survey.
A five minute introduction.
50th Golden anniversary ECA Edmundson apprentice award
Showcasing the very best electrotechnical and engineering services for half a century.
Welsh government consults on HRBs and reg changes
Seeking feedback on a new regulatory regime and a broad range of issues.
CIOB Client Guide (2nd edition) March 2025
Free download covering statutory dutyholder roles under the Building Safety Act and much more.
Minister quizzed, as responsibility transfers to MHCLG and BSR publishes new building control guidance.
UK environmental regulations reform 2025
Amid wider new approaches to ensure regulators and regulation support growth.
BSRIA Statutory Compliance Inspection Checklist
BG80/2025 now significantly updated to include requirements related to important changes in legislation.