Underlay
Underlay or underlayment is a term used to describe materials in both flooring and roofing.
[edit] Flooring
Underlay in flooring is material typically made from rubber, sponge, foam, felt, plastic and so on. It serves as a protective layer between the 'unfinished' subfloor and the final floor covering. Depending on the material selected, underlay can help provide thermal and acoustic insulation, reduce impact noise, reduce wear and enhance comfort. It is sometimes advisable to use higher quality underlay in order to avoid the deterioration that can occur with lower quality products that can harden and crumble over time.
Underlay is most commonly used under vinyl flooring, wood flooring and carpet. Some forms of carpet - such as rubber or foam backed carpet - do not require underlay.
[edit] Roofing
Underlay in roofing is material made from rubber, felt, tar paper, synthetic underlayment and other protective substances. As a roofing membrane, the purpose of underlay is to helps to prevent water that has penetrated through or under the roof covering from leaking into the building.
There are non-breathable underlays and breathable underlays based on ventilation requirements of the roof.
NB The 2018 International Residential Code (IRC), published by the International Code Council (ICC) defines underlayment as: ‘One or more layers of felt, sheathing paper, nonbituminous saturated felt, or other approved material over which a roof covering, with a slope of 2 to 12 (17-percent slope) or greater, is applied.’
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
The UK's Modern Industrial Strategy: A 10 year plan
Previous consultation criticism, current key elements and general support with some persisting reservations.
Building Safety Regulator reforms
New roles, new staff and a new fast track service pave the way for a single construction regulator.
Architectural Technologist CPDs and Communications
CIAT CPD… and how you can do it!
Cooling centres and cool spaces
Managing extreme heat in cities by directing the public to places for heat stress relief and water sources.
Winter gardens: A brief history and warm variations
Extending the season with glass in different forms and terms.
Restoring Great Yarmouth's Winter Gardens
Transforming one of the least sustainable constructions imaginable.
Construction Skills Mission Board launch sector drive
Newly formed government and industry collaboration set strategy for recruiting an additional 100,000 construction workers a year.
New Architects Code comes into effect in September 2025
ARB Architects Code of Conduct and Practice available with ongoing consultation regarding guidance.
Welsh Skills Body (Medr) launches ambitious plan
The new skills body brings together funding and regulation of tertiary education and research for the devolved nation.
Paul Gandy FCIOB announced as next CIOB President
Former Tilbury Douglas CEO takes helm.
UK Infrastructure: A 10 Year Strategy. In brief with reactions
With the National Infrastructure and Service Transformation Authority (NISTA).
Ebenezer Howard: inventor of the garden city. Book review.
The Grenfell Tower fire, eight years on
A time to pause and reflect as Dubai tower block fire reported just before anniversary.
Airtightness Topic Guide BSRIA TG 27/2025
Explaining the basics of airtightness, what it is, why it's important, when it's required and how it's carried out.
Construction contract awards hit lowest point of 2025
Plummeting for second consecutive month, intensifying concerns for housing and infrastructure goals.
Understanding Mental Health in the Built Environment 2025
Examining the state of mental health in construction, shedding light on levels of stress, anxiety and depression.
The benefits of engaging with insulation manufacturers
When considering ground floor constructions.
Lighting Industry endorses Blueprint for Electrification
The Lighting Industry Association fully supports the ECA Blueprint as a timely, urgent call to action.