Lintel size guide: How to specify lintel dimensions

After recognising the importance of lintels to structural integrity and safety, you may well wonder what the best choice is for your project. It can be a difficult decision, given the wide variety of lintels in different styles and sizes.

Thankfully you can count on Catnic, as we highlight the availability of lintels in different lengths and dimensions in this guide.

As you may know, lintels are designed to support the loads above windows, doors, and other building openings. You must choose the right lintel type, length and safe working load to support the loads and prevent structural failures

Having introduced the first steel lintel to the construction industry in 1969, Catnic now offers a variety of lintels for the cavity walls, timber frame, as well as external and internal solid walls. We present the most common choices here.

Cavity Wall Lintels

Pictured: Heavy Duty Steel Lintel - TH110/100

Cavity wall lintels are designed for masonry walls, with the outer and inner leaves separated by an air cavity. This is the most common construction method in the UK, with structural support being vital for each masonry leaf. Such support is commonly provided by a one-piece lintel, with a toe that extends to the outer and inner leaf.

As with other varieties, the correct choice of cavity wall lintel will depend on the wall's build-up, the opening's size, and the load-bearing requirement.

Cavity wall lintel dimensions

With that said, Catnic offers cavity wall lintels in lengths ranging from 750 mm to 4800 mm, providing the desirable blend of durability, performance, and cost-effectiveness.

Internal Solid Wall Box lintels

Pictured: Heavy Duty Steel Lintel – BHD100

Internal Solid wall box lintels are designed for structural support above internal wall openings. Made from galvanised steel with duplex corrosion protection, these lintels are suitable for masonry, floor, roof, and point loads.

Internal Solid wall box lintel dimensions

Internal solid wall box lintels are offered in a range of standard lengths from 750mm to 3000 mm in increments of 150 mm at lengths up , and at lengths from 3300 mm to 4800 mm in 300mm increments (including 4575mm, but excluding 4500mm).

External Solid Wall Box lintels

Pictured: Standard Duty Steel Lintel – CN71A

Designed to support loads above openings in external solid walls, box lintels are made from galvanised steel with duplex corrosion protective layer, offering structural performance and durability. They also can be used as closed cavity lintels in traditional cavity walls.

External Solid Wall Box lintel lengths

External Solid Wall Box lintels are available in a range of lengths from 900 mm to 3000 mm in 150mm increments and from 3300 to 4800mm in 300mm increments (including 4575mm, but excluding 4500mm).

The first step in establishing the correct type and length of lintel will be to identify the wall construction. For instance, for the external cavity wall you will need to know the thickness of the outer leaf, cavity, and inner leaf.

Next, you’ll have to measure the width of the structural opening, with a bearing of 150 mm being allowed at each end. So, for a structural opening of 1500 mm, the correct lintel length is 1800 mm.

Finally, you’ll have to work out the weight of the load requiring support. You must account for the masonry, roof load (truss/attic), floor load (joists/slabs), and any live loads as well as point loads (if these occur). You also need to consider the ratio between the outer and inner leaf.

For more help calculating lintel load, consult our guide: How do you calculate lintel load?

With over 100 lintels suitable for a variety of interior and exterior applications, we’re confident of fulfilling your project needs. Manufacturing lintels to order, we also offer different grades of stainless steel for enhanced durability.

After identifying the wall construction and loading conditions, you can use Catnic’s product selector to narrow down the choice of suitably sized lintels. We also provide essential technical details, such as the SWL for each standard length, across the Catnic lintel range.

Striving for complete satisfaction, we encourage you to get in touch with any further enquiries relating to the lintel specification and load calculations for your project.