Horizontal beam on top of ceiling joists in loft

[deadfire19]

I'm looking to install new floor joists in my loft between the existing ceiling joists.

There's a beam running the whole length on the loft over the top of all the ceiling joists. It's nailed to every ceiling joist.

The floor joists will be 175mm tall (mounted on 18mm ply) compared to the 100mm tall ceiling joists so I need to get them through this beam.

Does anyone know what the beam is doing structurally in the loft? It's not attached to the structural walls it crosses at all, only to the top of the joists and the rafters on either side of the the 12m span. It must have been part of the original 1930s house construction since it must have been installed before the roof.

I'm hesitant to notch it unless I can figure out what it's for.

Thanks in advance.

 

[A Trowel]

Ceiling binder

 

[deadfire19]

Ceiling binder

Would it be reasonable to support the ceiling underneath the binder from the room below, notch the ceiling binder from underneath and then screw the ceiling binder into the new floor joists?

My understanding is that the binder supports the ceiling joists from sagging.

 

[cdbe]

An Idea of what's going on would help - proper loft conversion the binders would generally be engineered out, some DIY thing requires a bit more thought.

 

[deadfire19]

An Idea of what's going on would help - proper loft conversion the binders would generally be engineered out, some DIY thing requires a bit more thought.

I'm currently re-doing the room below the section of loft in question and wanted to re-do the insulation with PIR. However, I realised this would be a waste if there will be a loft conversion in the future since the PIR would be ripped out since the floor will need proper joists.

That being said, I additionally feel that adding in proper floor joists will allow for heavier storage in that section of loft, since the current ceiling joists are 100*50mm @ 300mm centers spanning 3100mm, which is far below the required size for anything but light loads.

With that in mind I wanted to prepare this section of loft with sufficient floor joists to futureproof it against a future loft conversion.

As I convert the rooms on the first floor the plan was to fix up the corresponding ceiling above. Adding in the floor joists is relatively easy (minus the ceiling binder issue).

My aim was to replicate the method used in this video:

(however, this person did not have the binder issue)

 

[cdbe]

Nothing to stop you replacing the existing joists and removing the binder if you have the ceiling down (you can reuse the timber elsewhere). Just make sure you replicate the old ones fixings to the rafters and joists on the other side. You can drom them a bit lower into the room below to help with headroom in the loft if necessary. Think about where your future staircase will go and consider any necessary trimming joists and don't forget your noggins.