Increasing the size of the loft hatch

[thecrater]

You can't just move it, you need to put in the joists/noggins first and double each side up to take the loading - especially as you have a joint plates in there, if you don't strength them by sistering them you are asking for problems

as for the width, you can pack it out, but each end needs to be solid timber

Noted. In terms of sistering the joists, are there any specific minimum dimensions that I need to use?

As regards the structure, I believe it's a "Standard Trusses (Fink)". I did some Googling and I believe the part I circled in red on the left hand side of the picture is a splice and the one on the right is the joint according to the diagram.

Roof terminology

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[dewaltdisney]

You said you are in a flat so before you start messing with the roof trusses you might need to seek permission especially if your alterations cause roof issues.You could be sued by others or make your flat unsaleable. You should not mess with preformed trusses as they derive thier strength from the triangle being complete. This job has moved on from when you started out wanting a cheap ladder, which I pointed you to, plus a video link of how to do it. I would revisit that and put your saw away.

DWD

[wine~o]

Have to say I agree with DWD, as it's a flat it'll be leasehold, chances are you don't even "own" the loft space. any alterations would need the approval of the leaseholder.

Get it wrong and you would be in shed loads of trouble.

[thecrater]

Sounds like it's going to be complicated. I think I'm going to stick to a telescopic ladder