An issue has been raised when replacing windows that the blockwork inner leaf is missing a lintel.

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The hollow blocks have been in-filled with concrete which makes me believe that this is a ‘cast-it-yourself’ lintel where blocks have been hollowed out, rebar inserted and concrete cast.

Can anyone confirm whether this was a valid construction technique in the 1980s in the UK? If so can you provide more information such as the size and expected quantity of reinforcing bar?

  • $\begingroup$ its a valid technique for making a lintel. I would have expected U shaped blocks instead of the standard block. However they can simply knock out the interior cell walls and lay rebar across, as you have described. The amount of rebar will vary depending on the span of the opening and wall loading. You might be able to verify the presence of rebar with a cover meter. You could also put in some temporary shoring and chip out one of the blocks near the end of the opening to see what reinforcing is there if anything. The next question is, does it extend far enough into the wall. $\endgroup$
    – Forward Ed
    Mar 24, 2021 at 18:28
  • $\begingroup$ A local structural engineer should be able to assist you with this. $\endgroup$
    – Forward Ed
    Mar 24, 2021 at 18:29
  • $\begingroup$ There were plenty of houses built in the 80s in the UK with no lintels at all. If you fit the window frames as you build the walls, the frames acted as a temporary support for the walls until the cement set. If you get any settlement and cracking, the easy fix is to install a steel plate as a lintel. $\endgroup$
    – alephzero
    Mar 25, 2021 at 2:37

1 Answer 1


I have designed cement block beams and lintels, nothing wrong with that. As long as you use limited masonry stresses and longer embedment required for bonding and follow the code.

But this is not that. It seems the cells are not filled and most likely the exposed rebars are badly rusted and split from cement inside the voids.

I would add a proper lintel or header and ignore this.

  • $\begingroup$ Why do you think the cells are not filled? $\endgroup$
    – egg
    Mar 24, 2021 at 20:36
  • $\begingroup$ usually voids float to the top; cement fill the bottom. when you see voids on the bottom of a beam that means you have much larger voids above. $\endgroup$
    – kamran
    Mar 24, 2021 at 20:49

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