Using catnic lintel with existing timber lintel

2 Mar 2019
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United Kingdom

I had dormers installed over year and half ago. The windows on the middle floor beneath the new floor are 2 metres wide.

3 to 4 joist of the new floor are sat on wall plate which is above window lintels.

The load is only on the inner leaf however the wooden lintels are solid and cover both leafs.

Is a bit of a faff getting removing and getting concrete lintels in now.

I have thought of another method which is to use a Single leaf catnic lintel only on internal side with the wooden lintel in place.

World this work? It has a swl of 10kn which seems equivalent to concrete lintels.

The wooden lintels are in good order with little difflection but with new floor Im not sure
Last edited:
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1.5years ago. Not signed off yet as I'm doing other work.
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How big (width x depth) are the timber lintels over the windows? And how long are the floor joists which sit on the lintels?
Hi. The timber is 3 inches thick and depth is 1 foot.

The joists span 3.9 metres on one side and 3.7 on the other.

Thanks IMG_20210830_105530.jpg
Is your arrangement something like this....?


  • 2021-08-30_143157.pdf
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Almost but I have dormers too. The back dormer is sat the inner leaf. The front one is sat on an rsj.
If the back dormer is sitting over the wall plate, and you have clad the dormer with plywood or OSB, then the dormer itself will act as a deep beam across the window opening and the 12" x 3" will effectively only be supporting the floor joists, which it should be able to do without undue deflection.

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