Replacing a herringbone struct to make space

[Sparrowhawk]

2m from one wall of the 100 year old ground floor ceiling (3.4m joist span, 7.25m front to back) there's some massive timber herringbone structs, made from chunky timber (like this picture)

 

I need to get 3-4 MVHR ducts through here and that isn't happening with this in place.

 

Am I okay to remove it and replace with multiple timber/metal bars at the top and bottom, not crossed? I had a look for a metal box section to insert, or a meccano style angle girder contraption to build but couldn't find any.

 

I've seen the metal X-bracing which are thinner but prob won't leave enough space, plus without taking out part of the lath and plaster ceiling I don't see a way to fit them to the underside of the joists.

 

 

[ProDave]

That is an old and very common way of bracing the joists to stop them twisting.  More commonly done with solid noggins now.

 

Why not replace with solid noggins with large round holes drilled in them for the mvhr ducts to pass through?

[saveasteading]

If you took these out, the bottom of the joists might rotate and be understrength. 

So stop that happening with a stud across the bottom, timber or steel.

You could do the same at the top to save the floor doing the work.

Work out how much space you need and size to allow it.

 

[Sparrowhawk]

38 minutes ago, ProDave said:

Why not replace with solid noggins with large round holes drilled in them for the mvhr ducts to pass through?

 

Good idea, solid noggins would help with strength. I can fit 3 90mm or Flat 51 ducts through (it's actually nearer 33cm wide, but I lowballed here):

or even 4 Flat 51:

 

Cut multiple of these out of 1 inch timber and insert them back to back or spaced apart?

 

I should have been clearer that all ducts need to pass through a single joist-joist gap, thanks to a significantly larger trimmer round the chimney breast than expected (there's a trimmer, then a second trimmer or a row of solid noggins 18 inches out).

Edited August 23 by Sparrowhawk

[Sparrowhawk]

The location of the struct is beyond the wall at the top left of this photo (under the floor in the next room's doorway) but this is where I was today. The joists usually run vertical (in relation to this photo) so I was caught out by the extra row of horizontal ones beyond the fire hearth - I thought that would be the last row. At least they don't run under where the drill is; that massive joist is the end of the horizontal stuff.

 

And yes, at the bottom of photo in the entrance to the extension, the builders left it open to the cavity. Which explains some of the draughts.

Edited August 23 by Sparrowhawk