Can I use a cavity lintel

[Holywood]

I have bought a heavy duty cavity lintel to comply with the approved plans for insertion of a beam to cover a wide opening we will be cutting into a load bearing wall. It will carry some of the loft joists. A builder who I had in to give me a price for cutting out and installing the beam says that it is the wrong type and that an RSJ is more suitable. He thinks it would not be possible to "slip" the beam in under the jacked up joists as it is for a cavity taking blocks on both "wings" of the lintel.

Should it not be possible to jack the joists up as usual, put in this cavity lintel and then lay a course of block along its length on both "wings" before removing the jacks (after the cement has dried on the blocks)? Would 1 course of blocks on the cavity lintel be enough to spread the weight along the lintel? Would it work if a wall plate was placed over the blocks before the joists were lowered?

Thanks for any help as I can't return the lintel.

[property man]

He is right a RSJ is better also you will need calcs for the steel as you cannot just use any

[Holywood]

Thanks for the reply.

[TheDoctor5]

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