House retrofit, knee wall/roof structure

[HugoR]

Hi all,

I’m retrofitting a 1930's end of terrace and renovating/insulating 2 rooms in roof at the moment.

I've stripped out old wallpaper and opened up sections of a knee wall (lath and plaster) to gain access to the eaves and install much needed insulation. While doing so I exposed a few timber studs which are directly nailed to the roof rafters (150x50mm @ 400 centres) at a height of 1.6m. I thought it would make sense to move these studs back a bit to gain some extra space and square off the room. 

It seems logical and fairly straightforward but I'm not sure if these studs (70x50mm) were simply holding the lath and plaster dwarf wall or if they have any structural function. I'm convinced they're not structural but may help to prevent sagging, although there's no indication of sagging on any of the rafters (they barely touch the top of the studs).

I took some photos of the roof structure/studs and I was wondering if you could give your opinion on this?

Much appreciated.

 

[HugoR]

If anyone has any thoughts on this it would be really helpful to hear. I understand I may need professional advice from a structural engineer but it would be useful to test how likely and feasible this change is before spending significant money on professional fees.

Thanks.

[syne]

I'd say it's kinda impossible to know without a, the original designer telling you or, b. removing them and taking a wait an see approach..

 

If it were my own house...

I would add an extra timber of the same dimension on the left and right, form a 'goal post' arrangement with a cross member of decent size to take any potential rafter sag.

Cross member needs to be on top of uprights not screwed to sides

 

At the back of the 'cupboard' I'd add a further triangulation uprights. That would form the rear wall.

All this is not really about rafter sag but about roof spread.

 

Looking at those rafters tho, they appear to be quite substantial so perhaps all the above would be excessive...  but that method is what I'd feel confident with and its still going to give you extra storage.

 

Edit to add,

with the uprights being built before the floorboards I would definitely err on the side of caution and not square the room.

They are likely part of the roof structure. A SE would be able to calculate properly if they are superfluous

 

I'd still build the cupboard though, as when a roof meets a floor in a room the space is practically useless anyway.

 

Edited June 23 by syne
Extra waffle

[HugoR]

Thanks Syne, 

 

That all makes sense.

 

I don't intend to move the uprights all the way back but just 400mm or so, enough to gain an extra bit of space and form a cupboard or recessed shelving (and insulate btw/under rafters).

 

Here's a sketch of my idea below, seems feasible...

 

[joe90]

In my opinion you would be fine, the timbers look substantial, as said above you need to create a goal post to support the middle two short uprights above the new opening.

[ProDave]

While you are at it, create an access hatch to each eaves space, e.g. a removeable back to your built in bookcase.

[George]

Are they wobbly?

[HugoR]

Thanks everyone.

 

Yes I'll incorporate back access to the eaves space for maintenance.

 

Studs not wobbly and rafters look robust, they're nailed but there's a 1-2mm gap between them.

 

I'll do the same in the other small bedroom for consistency, the eaves space used to have a water cylinder but that's now been removed so I'll gain some extra room here too and insulate properly.

 

[HugoR]

Also wondering why the timbers and brickwall have this white staining? No signs of rot so perhaps previous timber treatment?

 

This is where the hot water cylinder was located so presume there's an history of leaks and lack of eaves/roof ventilation...