Lintel for a 3600mm bifold

23 Jun 2018
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United Kingdom

I'm working on a single storey extension which has a 3600mm bifold door to be fitted in a 100mm cavity wall.

The weight on the lintel will be:
1 course block (up to wall plate)
50mm x 150mm joists boarded and felted. The one side of joists will be on hangers fixed to the original build, the other will sit on the new wall plate.

I've been looking at a few lintels and unsure which size will work with an acceptable deflection. I dont want the lintel to bow as the doors will not be able to open or close.

I'm considering SK90 or the heavier duty HDK90 or extra heavy duty by catnic

There are other options such as an rsj with a 6mm plate welded to the bottom, but unsure if this is the usual practice for this situation.

Does anyone know if these Keystone's are suitable as I'm hearing different thinks from the resellers.
Last edited:
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Yes its common practice to use a beam with a plate welded to the underside as a lintel, mainly on larger spans where deflection is critical and the length required is bigger than the standard lintel sizes available.

You should be fine with the heavy duty keystone lintel, the load on the lintel isn't particularly big and you'd be well within the load capacity in their span tables.

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