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
A case study and a warning to would-be developers
Creating four dwellings for people to come home to... after half a century of doing this job, why, oh why, is it so difficult?
Reform of the fire engineering profession
Fire Engineers Advisory Panel: Authoritative Statement, reactions and next steps.
Restoration and renewal of the Palace of Westminster
A complex project of cultural significance from full decant to EMI, opportunities and a potential a way forward.
Apprenticeships and the responsibility we share
Perspectives from the CIOB President as National Apprentice Week comes to a close.
The first line of defence against rain, wind and snow.
Building Safety recap January, 2026
What we missed at the end of last year, and at the start of this...
National Apprenticeship Week 2026, 9-15 Feb
Shining a light on the positive impacts for businesses, their apprentices and the wider economy alike.
Applications and benefits of acoustic flooring
From commercial to retail.
From solid to sprung and ribbed to raised.
Strengthening industry collaboration in Hong Kong
Hong Kong Institute of Construction and The Chartered Institute of Building sign Memorandum of Understanding.
A detailed description from the experts at Cornish Lime.
IHBC planning for growth with corporate plan development
Grow with the Institute by volunteering and CP25 consultation.
Connecting ambition and action for designers and specifiers.
Electrical skills gap deepens as apprenticeship starts fall despite surging demand says ECA.
Built environment bodies deepen joint action on EDI
B.E.Inclusive initiative agree next phase of joint equity, diversity and inclusion (EDI) action plan.
Recognising culture as key to sustainable economic growth
Creative UK Provocation paper: Culture as Growth Infrastructure.
Futurebuild and UK Construction Week London Unite
Creating the UK’s Built Environment Super Event and over 25 other key partnerships.
Welsh and Scottish 2026 elections
Manifestos for the built environment for upcoming same May day elections.
Advancing BIM education with a competency framework
“We don’t need people who can just draw in 3D. We need people who can think in data.”