Box Lintels

Box lintels are designed for use within internal masonry solid wall construction, and are available to suit standard, heavy and extra heavy duty loading applications. They are available for 100mm and 140mm wide masonry.

Catnic box lintels can be bought either with or without a toe, depending on the intended application. They’re made from galvanised steel and designed for load-bearing within masonry cavity, internal, and external solid walls.

Choose your best-fit box lintel from the Catnic range below.

Catnic heavy duty box lintel for 100mm interior solid wall

Support & FAQs

Box lintels are structural elements that have been designed for use in external and internal solid walls as well as in some instances with cavity walls. Catnic offers two kinds of box lintels – a rectangular shape internal solid wall box, and an external solid wall box with a toe.

Read more: What are box lintels?

Internal box lintels are used for supporting loads over internal openings in load-bearing walls. These lintels are designed to support masonry, floor, roof, and point loads. Insulated internal box lintels (an option offered by Catnic) can also be used to support the inner leaf in cavity wall constructions.

External solid wall box lintels are used for 200-215 mm exterior solid walls. These lintels are also designed to support masonry, floor, roof, and point loads.

All box lintels can be used over large spans. Catnic offers them in various lengths, with heavy duty boxes reaching a length of 4.8 meters

Box lintels should be fully bedded on bricklaying mortar. In the case of an external solid box lintel, there should be a drip on the lintel toe facing the outside of the building. The lintel should be levelled along the length and width. Floor and roof loads should not be applied until the masonry cures.

Read more: From start to finish: How to install a Catnic lintel

The size of lintel you need is mainly determined by the structural opening span you have to cover, plus an additional 300 mm. This can vary from project to project, meaning accurate measurements are key to a successful installation.

Read more:Lintel size guide: How to specify lintel dimensions

Calculating the load imposed on lintels depends on a variety of factors, including the wall type in which the lintel is installed, and whether floor or roof loads need to be accounted for in addition to masonry loads.

Lintels are primarily designed to support uniformly distributed loads (UDLs), but on occasion, when point loads occur, they also need to be considered. This guide only provides an overview of how the loads on the lintel are established and should not be used as a substitute for obtaining loading calculations directly from the lintel manufacturer or a qualified structural engineer.

  • Book a CPD

    Deepen your understanding of lintel specification with a practical CPD session delivered by our team. Ideal for architects, structural engineers, and specifiers.

    Icons / Long Arrow
    Kingsgrove Housing Development, Wantage, OXFORDSHIRE. February 2021

  • Need help finding a lintel?

    Request FREE Schedule

    Icons / Long Arrow

Download Lintel Whitepaper

Unlock practical, up‑to‑date guidance on modern lintel specification. Three expert whitepapers cover thermal breaks, Part L & Future Homes Standard compliance, and best‑practice lintel design for today’s residential builds, giving you the clarity you need to specify with confidence

Icons / Long Arrow
Note Taking Concept. Smiling young African American woman sitting at desk working on laptop and writing letter in paper notebook, holding pen and looking at screen. Happy millennial female using pc

  • Stainless Steel Lintels

    Icons / Long Arrow
    Stainless steel cavity wall lintel

  • Not sure which lintel you need?

    We offer a FREE scheduling service, simply fill in a few details using our online form to get started, and a member of our Technical team will be in touch.

    Icons / Long Arrow
    Closeup of people examining project blueprint drawings on a desk

  • Lintel Accessories

    Icons / Long Arrow
    Catnic white soffit cladding

  • FREE Webinar

    Boost your expertise with our FREE on-demand Lintel webinar program! Enhance your product knowledge, stay ahead in the industry, and unlock new opportunities!

    Icons / Long Arrow

What our customers think

  • “We have found the thermally broken lintels well-made, easy to work with and durable. Using thermally broken lintels on site has helped us to comply with the Building Regulation Part L requirements in a simple, straightforward manner”

    George Sowerby
    T.G Sowerby Developments Ltd

  • “I recently placed two orders with Catnic and I can honestly say from speaking to the rep Toby, all the way to transport their service and communication regarding the orders was superb!.”

    Dave Daniels
    Travis Perkins PLC

  • "Catnic has always been very quick and prompt in getting back to us when we ask for quotes and any problems we may come across. Very useful and easy to deal with! Excellent!"

    George Atkins
    Turnbull

  • “Catnic is a leader in its field, and the high quality of its TBL is testament to that. The team has been on hand at every stage of this project so far, offering technical support during the planning stages and now into the early stages of installation"

    Matt Taylor
    RBLI

  • "We have been using Catnic Lintels for over 10 years, they are by far the best. A superbly well organised company who offer exemplary service, their lintels are extremely capable and well suited to our high quality homes."

    Chris Dodge
    County and Coast Homes

  • “Catnic worked with our drawings and outlined exactly what we needed - including the structural loading measurements. Catnic is the only manufacturer that provides such a comprehensive scheduling service for free. It really is invaluable."

    Mike Parkinson
    Keyworker Homes

  • "Catnic is able to provide quality products according to the demands of the project at a competitive price"

    Steve Blythe
    Skanska

Video Guides

When selecting a lintel, there are three factors that should be considered to ensure the correct specification: the type of wall construction, the dimensions of the structural opening and the total load on the lintel. In this video, we run you through the lintel selection process.

Catnic thermally broken lintel installation

Once you have chosen the correct lintel for your project, it is crucial that the lintel be installed properly – if it is not, it could lead to serious issues for the building. In this video, we explain the installation considerations for cavity wall lintels.

Builder installed Catnic CG90/100 lintel

Catnic’s Thermally Broken Lintel is the only lintel on the market to provide a complete thermal break between the inner and outer leafs. In this video, we outline the key benefits of Thermally Broken Lintels and explain the installation process.

Catnic TS90/100 lifted into position by builders

Steel lintels, and specifically Catnic's thermally broken lintels, have a significant role to play in reducing thermal bridging and achieving carbon gains. They represent one of the simplest and most economical ways for building fabric to be designed and constructed to help achieve the carbon gains necessary to meet current and future building regulations.

Catnic balcony installation at kingsdown gate

Lintel Resources

Request a Schedule

Which product would you like to request a schedule for?

Get a Free Quote

Which product would you like to get a quote for?

Added to your cart