Name for a beam made of metal and wood

Metal web joists.

Standard fitment in all new houses. Much stiffer and stronger so less of those creaky chipboard floors that 70's houses suffer from.

The 22mm chipboard or t&g plywood flooring is glued on all four sides and also glued onto the top section of the beam.

When the glue has set, they cut a hole where the stairs pass through.

Makes first fit electrics a lot easier, because there are no holes to drill. I-beam versions where the web is OSB usually have knockouts in the correct places.

Metal web joints. Thanks all for that.

So if most (all?) residential new builds use MWJ (as known to its friends) as a base for ceiling plasterboard and floor ply, can they be used for loft extensions where they are fixed to the walls slightly above existing ceili ng joists? The lightness, and sufficient (?) strength in comparison to "ste els" would in my uninformed position, make MWJ the ideal base for the floor in a loft extension. Or do they have shortcomings that prohibit their use in loft extensions?

Thanks.

Don't see why not. If you are not securing the loft extension joists to the existing ceiling ones, I think you need to ensure they don't deflect and touch the ceiling plasterboard.

It's not standard fitment in all new homes.

It ought to be as it makes my job easier.

Oh yea - an unliftable floor.

I know what else doesn't squeak and is nice and stiff:

I don't see why they cannot be used in a loft conversion.