Best way to shorten a joist?

[Sparrowhawk]

I have a first floor joist that runs 6cm away from the wall, joist size approx 7 x 2 inches. It's 30-34cm from this joist to the next (working on screw holes), and then 40cm spacing for the rest.

 

I'd like to get my MVHR ducting through here. Is it feasible to shorten the joist by 0.5m and if so what's the best way to fix it?

 

 

I looked for joist hangers that would fix to a parallel wall but found none. Bolts and packing?

 

Edited October 20 by Sparrowhawk

[Russell griffiths]

If it’s one duct then why not just drill the hole and put it through the joist. 
appropriate reinforcement to the joist will be needed. 
presuming 90mm duct. 

[MortarThePoint]

You could cut the joist short and use a trimmer between the neighbouring joist and a face fix hanger on the wall. You'd need to check the wall is OK with the extra load though.

[Onoff]

I'd put a 7" deep steel plate either side of the joist. Nuts and bolts to attach to the joist. Big hole for the duct in each plate. Use a bfo hole saw in the plate hole as a guide to go through the joist. 

 

Could resin anchor into the adjacent wall as well. 

[Sparrowhawk]

1 hour ago, Russell griffiths said:

If it’s one duct then why not just drill the hole and put it through the joist. 
appropriate reinforcement to the joist will be needed. 
presuming 90mm duct. 

It's 3x 90mm ducts I need to get through (and then core drill through the cavity wall to get into the original part of the house). I'm thinking that three would take too much out of the joist to reinforce it? I may be able to reduce it to 2 and take one another route, but that causes other problems...

 

1 hour ago, MortarThePoint said:

You could cut the joist short and use a trimmer between the neighbouring joist and a face fix hanger on the wall. You'd need to check the wall is OK with the extra load though.

 

I like this idea, though the trimmer goes across where I need to run the 3 ducts up before bending right to go through where I've removed the joist Is a metal web joist open enough to get 3x90mm through in a 34cm length?

 

The wall should be okay with the extra load, it's a 1998-built cavity wall, mounting onto the external leaf. The render will need hacking off but is concrete block behind that.

 

43 minutes ago, Onoff said:

I'd put a 7" deep steel plate either side of the joist. Nuts and bolts to attach to the joist. Big hole for the duct in each plate. Use a bfo hole saw in the plate hole as a guide to go through the joist.

 

That could work so long as it can be bolted. The ones I've seen need screws both sides, and there's no way I can insert those in the 6cm gap!

 

45 minutes ago, Onoff said:

Could resin anchor into the adjacent wall as well. 

 

This sounds the easiest way but I know nothing about it. This is like having bolts glued into the wall?

 

If all else fails I could lift the floor above and have the joist replaced with a web joist, but as it's our bedroom I'd be in serious trouble so anything that avoids that is good. Lifting a corner is fine, dismantling the room not so much...

[Sparrowhawk]

As ever BuildHub comes up with excellent previous threads to educate me on resin anchors:

 

[Onoff]

9 hours ago, Sparrowhawk said:

That could work so long as it can be bolted. The ones I've seen need screws both sides, and there's no way I can insert those in the 6cm gap!

 

That's why I was suggesting nuts and bolts. You'll fit the nuts and washers down the 6cm gap. 

 

[Onoff]

You don't have to use gun injected resin. Might be awkward getting the nozzle down (and bending it) through that 6cm gap. 

 

There's options. Drill a hole through the joist, into the wall. Clean out the hole with a puffer. Push in glass resin capsules or the newer, "ketchup sachet" type. Whizz a piece of studding in with a drill. That breaks the glass & mixes the resin or chews up & mixes the sachet. 

 

I didn't realise it was 3 ducts. Think I'd ask an SE ref plate thickness, bolt size and spacing etc.