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
Who, or What Does the Building Safety Act Apply To?
From compliance to competence in brief.
Commissioning Responsibilities Framework BG 88/2025
BSRIA guidance on establishing clear roles and responsibilities for commissioning tasks.
An architectural movement to love or hate.
Don’t take British stone for granted
It won’t survive on supplying the heritage sector alone.
The remarkable story of a Highland architect.
The Constructing Excellence Value Toolkit
Driving value-based decision making in construction.
Meet CIOB event in Northern Ireland
Inspiring the next generation of construction talent.
Reasons for using MVHR systems
6 reasons for a whole-house approach to ventilation.
Supplementary Planning Documents, a reminder
As used by the City of London to introduce a Retrofit first policy.
The what, how, why and when of deposit return schemes
Circular economy steps for plastic bottles and cans in England and Northern Ireland draws.
Join forces and share Building Safety knowledge in 2025
Why and how to contribute to the Building Safety Wiki.
Reporting on Payment Practices and Performance Regs
Approved amendment coming into effect 1 March 2025.
A new CIOB TIS on discharging CDM 2015 duties
Practical steps that can be undertaken in the Management of Contractors to discharge the relevant CDM 2015 duties.
Planning for homes by transport hubs
Next steps for infrastructure following the updated NPPF.
Access, history and Ty unnos.
The world’s first publicly funded civic park.
Exploring permitted development rights for change of use
Discussing lesser known classes M, N, P, PA and L.
CIOB Art of Building photo contest 2024 winners
Fresco School by Roman Robroek and Once Upon a Pass by Liam Man.