When specifying lintels one of the first questions to ask is whether you need prestressed concrete lintels or steel lintels. There are times when you will benefit from specifying concrete lintels, but this post is our top tips about specification in general, but predominantly for steel lintels.
Top Tip 1 – Check your triangulation
If there is 600mm each side of the opening and no obstructions above the opening, then triangulation can be achieved.
One of the biggest factors in the specification of lintels is whether you can reach triangulation above the door or window opening you are looking at. I won’t go into too much detail about triangulation – For the purpose of this post, I will outline the basic theory of triangulation with regards to specifying lintels.
To achieve triangulation, you must have 600mm of brickwork either side of the opening, and no obstructions immediately above the opening. The theory behind this is that if you can achieve triangulation, the load that will bear onto the lintel will be the triangle of masonry plus any other loads like flooring. The triangle is 0.6 x the clear opening.
If you cannot achieve triangulation, for example, you don’t have 600mm either side of the opening, then the lintel will have to bear the load of the full masonry above the opening plus any other loads. This may result in the specification of an HD (heavy duty) lintel at greater expense.
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Top Tip 2 – Look at floor load orientation
The floor joist orientation at the top shows there is no additional impact on the opening. The image at the bottom shows the floor beams impacting the opening which would result in the specification of a different lintel.
Floor load orientation can have a significant effect on loads and point loads on an opening depending on where the floor beams are sitting.
The following diagram shows the impact floor load orientation can have on the load on an opening and hence the lintel required for that opening.
Top Tip 3 – Gain an appreciation of load span tables
Most lintel manufacturers produce thorough lintel load span tables and calculations that architects and engineers can use to specify the correct lintel. A basic understanding of the data and how to interpret it is essential when specifying lintels.
Fortunately, we have a specification team to help clients not only understand the load span table data but to produce full specifications as well – if required.
If you are unsure about the values and data in load span tables you can read our post load span tables: a beginner’s guide.
Top Tip 4 – Understand Load span ratios
As well as load span tables it is worth specifiers having an appreciation of the load span ratios, and what they mean.
The ratios below relate to steel lintels, and the figures are expressed as inner leaf to outer leaf.
- 1:1 – lintels supporting masonry only
- 3:1 – lintels supporting masonry and timber floors
- 5:1 – lintels supporting concrete floors
- 19:1 – lintels for eaves applications
The values on the load span tables should be applied as per the ratios above when considering loads, and lintel selection.
Top Tip 5 – Watch out for stair trimmers
The image on the left shows the stair trimmers having no impact on the opening at the bottom. The image on the right shows a different orientation which would result in a point load on the opening, and probably a different lintel requirement.
The last tip is a bit of a strange one, but something we have learned over the years. Stair trimmers can create point loads on openings which in turn will have an effect on what lintel is specified.
Much like the floor load orientation, the image below demonstrates the impact that stair trimmers can have on openings.
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