new loft floor advice

[plasticpigeon]

Hello, I will soon be embarking on making the loft of my house a useable space, mainly for storage. I'm not too bothered by regs as it will not be a bedroom or living space, but having it clean, with a floor and with lights would be nice. At the moment the ceiling joists are 3 x 2 and the ceilings bow considerably. I have been up there but it is necessary to put boards down as I shuffle about to stop the floor bowing even more and cracking the plaster even more than it is already.

I have decided that the best course of action is to build another floor above with bigger joists, say 8 x 2s or something like that. I am hoping I can then tie the original ceiling to the new joists to stop movement and then repair the lath and plaster. I think the 2 best ways to put in the new floor are either to screw a wall plate into the party walls and span the house (around 15 ft) hanging the joists off joist hangers hanging off the wall plate, or alternatively, chisel out a section of mortar every so often and glue joist hangers into the party wall that way. The second method sounds better to me as it is less destructive as no holes are drilled in the wall. Also the weight of the floor will be taken on the bricks and hangers rather than on the screws holding the wall plate onto the wall. I'd be grateful for thoughts, advice or other suggestions. Many thanks.

 

[Me!]

I had a similar problem once and I simply glued and screwed another length of 2x2 on top of each of the existing 3x2 joists. Once it was boarded over with long boards to spread the load even more, it was fine and didn't seem to bow or crack the ceiling below at all.

 

[plasticpigeon]

I have thought about this, but the ceiling is really bowed, and I think if i just fix new joists to the old either on top of, or perpendicular to i will definitely crack the ceiling beyond repair. I am also happier about hanging joists off the party walls as the ceiling joists are not tied into the rafters, and i don't want to straighten the ceiling joists and risk pushing the walls out front to back. In fact i would ideally like to tie the bottoms of the rafters together. The only problem is that front and back are not the same height.

 

[davidbrac]

It sounds as if you are on the right lines as what you do not want to do is add the weight of the new floor and the stored items to the existing celling. If the weight is taken on the wall and all the joists are tied together and tied to the celling it will pull the structure together.

One suggestion is to leave traps so you can get to wiring etc. if needed.

What will it be like to get the 8*2 up into the loft?

 

[88v8]

8x2 ?? :shock:
Jeez, what are you planning to store, elephants?
And that's a lot of headroom gone by the time you add a floor.

4x2 or even 3x2 would be plenty I'd have thought. The loft joists in our previous house were 4x2 and we ended up storing a lot of stuff up there... as one does...
They can be screwed above the existing bowed joists by counterboring the 4x2s so as to use reasonably short screws, and spaced off by making graduated spacers of ply &/or hardboard &/or those multi-thickness plastic spacers, that way there'll be no tendency for the new joists to straighten the old ones, and the load is shared between the new and existing joists.

What are the existing rafters sitting on? A wall plate you said but I don't understand about it being screwed onto the wall?? Is this a party wall that goes up to the roof apex and them the wall plate is screwed onto the side of it? OK, so could you put in some more fixings that you can drill through the existing plate, like this
http://www.fischer.co.uk/Home/tabid-1429/tabid-1434.aspx/cpage-details/pcategory-1001001015/usetemplate-productdetails/
and then screw them tight.
There are also hammer fixings that one doesn't post-tighten, but they have an inferior load capacity.

Ivor

 

[plasticpigeon]

Ok I realise I haven't fully explained the situation. The present ceiling joists run from front to back of the house and are nailed into wall plates I think (I haven't been up there in a while) the rafters also run front to back. I am proposing running new joists perpendicular to the existing, and hang the new ones off the party wall somehow.

I suppose running the new joists on top of the old with packers between new and old to maintain the shape could work. I will have to investigate exactly what the present joists are fixed to on the front and back walls of the house.