Cutting across ceiling joists

[samaudio]

Hello,

I need to install a new ladder + loft hatch in my 1900's house. The opening for the old loft hatch is cut across the joists, rather than running along them, so two joists have already been cut. Because of high ceilings I will need a quite long folding ladder with a 1300mm opening, so will have to cut through a third joist. I wanted to ask for opinions on this. A hatch running along the joists is not an option because of how the space below is configured.
I've attached a drawing of the current opening. It's not great and the ceiling is already cracked where the joists aren't very supported. I'm planning to sister the outer joists and then cut through a third joist, adding doubled-up trimmers to form the new opening.

Basically I'm wary of cutting through a third joist so would value any advice on whether this is sound. I'll be using coach bolts to sister the joists and then using joist hangers and screws.

Many thanks,
Sam

 

[catlad]

Well I'm guessing if you are going to install a loft ladder you are going to board the loft.
If you can board some of the loft first that will help keep everything together, My advice is cut as few as possible.

 

[samaudio]

Yes I’ll be boarding the loft, but with loft legs, so won’t be holding it together much.
In your opinion will cutting one further joist compromise the ceiling dangerously? I can’t seem to find any info or videos about installing loft hatches that cut across joists…

 

[catlad]

Nobody can answer your question, the fact you can't find any videos should be general indicator that it isn't advisable! If you must cut through any ceiling joist I recommend laying a piece of timber across as many joist as possible and screw it down with long screws to bind the joists together prior to cutting, this way it should help stabilize things.