Enlarging loft hatch

[Sprinkles]

Hi,

Looking to make a loft hatch bigger. It's in a Victorian terrace with a traditional cut roof.

I've added a photo below that marks out what I am hoping to do here...

The blue lines are where internal walls are supporting the joist on the left and also where the joists overlap.

The red box is where I will add a batten to support the joist when cutting.

The purple bit is the section of joist I aim to remove.

And the green is where the new hatch frame will go.

Does this look/sound reasonable?

I've added another couple of photos that show where I thought it might be worth adding extra support before cutting the joist and also the view up to the hatch from below.

My main concern is whether or not the new frame will be sufficient to support the cut joist if I remove the batten. Wondering if there is a permanent solution to shore this up - steel plate instead of timber batten?

Any advice/feedback greatly appreciated.

Thanks.

 

[bathjobby]

This is not intended as instructions, so don't try to sue me if your roof caves in, but a few observations on what you suggest.
Firstly the 2 forces that act on items:
Compression is a force that acts to compress or shorten the thing it is acting on.
Tension is a force that acts to expand or lengthen the thing it is acting on.

Your rafters are under tension by the weight of the roof pressing down (trying to collapse) and the rafters are opposing this i.e. they are trying to be stretched. So if you remove one rafter you are putting extra Tension on the 2 either side. So in addition to framing the new hole - your green lines) doubling up the rafters either side would take that extra load.
The option I have seen employed most (in newer houses so you would need to take a view as to if this is suitable for your construction) is to take a large (much larger than the hole you want) thick sheet of strong wood, something like 25mm marine ply. Lay it across the rafters so that it covers the proposed hole and is large enough to be in full contact with the rafters either side and goes at least a metre either side of the hole down the length of the rafters (the longer the better). Firmly screw it down to all 3 rafters, the 2 either side and the one your going to remove. Then cut out your hole through this sheet including the section of rafter, and the sheet surrounding the hole will take some of the Tension from the cut rafter i.e. it is being transferred through the overlapping sheet around the hole and it will also transfer some of it to the adjacent rafters - sharing the tension.

 

[geraldthehamster]

Hi,


And the green is where the new hatch frame will go.

Does this look/sound reasonable?


Thanks.

The green ought to be in the form of trimmers - ie timbers the same size as the joists, screwed or nailed to the joists. You build the frame for your hatch inside them.

Otherwise, looks fine to me. You're only cutting one joist, so as long as it's supported while you do it, and trimmed solidly as above, you shouldn't have any difficulty.

Cheers
Richard

 

[Sprinkles]

Many thanks for your reply's. I think I'll make a start on this over the weekend.