Thin webbed joists
|
| This thin webbed joist was made from strength graded timber and oriented strand boards (OSBs). |
Contents |
[edit] Introduction
Engineered wood products and an introduction to timber structural systems, published by the Structural Timber Association, defines a thin webbed joist as: ‘an engineered wood product (EWP) manufactured with flanges made from softwood or laminated veneer lumber (LVL) with glued, thin webs generally made from oriented strand boards (OSBs), fibreboard or plywood. Thin webbed joists can be used to resist either flexural or axial loads or a combination of both.’
[edit] Characteristics
Thin webbed joists are also known as I-joists (or I joists) due to the “I” shape of their cross section.
|
| This cross section illustrates the "I" shape associated with the name, I-joist. |
I-joists are relatively light and have significant strength in relation to their size. They are also generally believed to be easier to handle and are less likely than equivalent solid timber sections to become misshapen or to split.
The Code of Practice for Engineered Wood Products published by the Engineered Wood Products Committee of the UK Timber Frame Association, states that I-joists “are made using a continuous process in lengths up to 20m and are cut to the desired length either in a factory prior to delivery or on site. The flanges have a pre-formed rout into which the bevelled web section is glued using an adhesive that has been approved for structural purposes (meaning they should either comply with Type I specification as defined in BS EN 301 or should be an equivalent strength and durability as verified by independent third party assessment and certification).’
Service runs for mechanical and electrical infrastructure can sometimes be installed in conjuntion with I-joists and can help reduce the likelihood of squeaky floors.
They can be used with several applications, including:
- Floor and roof joists (however, open web joists also known as metal web joists are sometimes preferred over thin webbed joists for these applications).
- Formwork.
- Ceilings.
- Loadbearing studs.
- Cladding support.
- Prefabricated cassette floors.
[edit] Related articles on Designing Buildings
- Engineered wood rim board.
- Joist.
- Metal web joists.
- Timber post and beam construction.
- Timber engineered structural frames.
- Types of flooring.
[edit] External resources
- Engineered Wood Products Committee, UK Timber Frame Association, The Code of Practice for Engineered Wood Products.
- Structural Timber Association, Engineered wood products and an introduction to timber structural systems.
Featured articles and news
We're expanding our collaborative mission by launching DB Intelligence, an exclusive market research advisory panel. Built environment professionals can now get paid to share their expertise on industry trends, products and services.
Panel members receive direct financial incentives for participating in research projects like short surveys, 1-2-1 interviews and focus groups. Register today to shape the future of the construction sector.
Planning condition discharge in England and Wales
A brief exoplanation from a building compliance expert, with further links.
Overheating guidance and tools for building designers
Guidance for dealing with element of building fabric control that have increasing importance.
Shading for housing, a design guide
From the Good Homes Alliance and British Blind and Shutter Association.
UK Standard Skills Classification (SSC)
A shared framework for describing skills needs.
Social media ban consultation comes to close
CIOB urges UK Government to consider social media’s role in careers guidance in ban debate.
The latest of eight Skills England apprenticeship units
The addition of battery manufacturing welcomed by ECA with a warning about the risks of fast-tracked apprenticeship units.
Building Control Independent Panel final report
A precis of a key report led by Dame Hackitt with full recommendations and link to the government response.
Building Safety recap April, 2026
A short and longer run-through of the month, with links to further information and sources.
CIAT May 2026 briefing.
From medieval scribes to modern word art.
ECA welcomes crackdown on late payment and push for clean energy, whilst CIOB seek fixed cladding removal timeframes.
Cyber Security in the Built Environment
Protecting projects, data, and digital assets: A CIOB Academy TIS.
Managing competence in the built environment
ITFG publishes new industry guide on how to meet the ICC principles.
The UK's campaign to reduce noise pollution: Mythbusting, articles and topic guides.