Replacing sill plate

[Sausage]

Hi,

Due to long term leakage from a sink, we have some areas of rotted joist and sill plate in our bungalow kitchen. The sill plate is in an external brick wall, and is badly affected for about 4 feet either side of the corner, as are those ends of the joists that rest on the affected parts of the sill plate.

Until I discovered the ghastly truth about the sill plate, I was thinking this was going to be relatively straightforward to fix just the joists. But how do you replace a sill plate? As I understand it, the wall actually sits on the plate, which is itself bolted down on the foundation wall. I've heard varying suggestions from: 'don't even think about it...get a builder', to: 'it's ok to chop out a metre or so of sill plate and poke in a new bit as long as you support the joists'. Are the rotted ends of the joists supporting the wall, at all? Otherwise, if there's nothing on top why do they need to be supported at the ends during the repair? It's actually my elderly mother's bungalow and she really wants to avoid having builders in, if at all possible. Can I do this? Can anyone give any advice, please?

[Rich]

How wide is the sill plate versus the foundation wall? What is directly outside the sill plate -- covering wise siding/sheathing?

[Sausage]

I'm afraid I don't really understand how it's constructed. Hanging upside down peering into the crawl space through a hole in the bottom of the sink unit :-) I can't tell much about the width of the plate from edge on. Even where I've lifted floorboards on the other side of the corner (the side parallel with the joists) I can't really tell anything about the width of the plate. The inside face of the wall above the floorboards appears in line with the face of the foundation wall. The wall above is actually two brick walls with a cavity in between. So I don't understand how it works in relation to the sill plate. On the outside, the brickwork is covered in pebble-dash on top of something else - render (?), Sorry, that's not much help is it?

[Sausage]

Ok, I've had a better look (and have the scrapes all over my chest and elbows to prove it).

The outer brick wall's brick foundation seems to be in two layers. As far as I can tell, the sill plate rests on the inside layer only. The joists rest on the sill plate only. There's brickwork built directly on top of the sill plate, with gaps for the joists. Although I can only see as far as two rows of bricks above the sill plate, in certain places there's some larger, rough, black looking 'bricks' (I think they are) above the first row of red bricks on the sill plate. There's a gap next to a joist and I can see through to the brick wall behind the front layer. I can only see one row of bricks, but there's no evidence of a sill plate in that layer of brickwork.

The two joists that I was intending to repair actually have a small gap between their tops and the red brick/'mystery black bricks' above them. So those joists obviously aren't supporting the wall at the moment. In view of this, would it be reasonable to cut out a section of sill plate directly under each of those two joists and replace those joists and the pieces of plate? I could squeeze them in so as to be supporting the 'brickwork' above them. The sill plate in this area is bad, so I'm wondering about cutting small pieces out at a time and squeezing new bits of timber in to replace it. But I thought sill plates are supposed to be bolted down for some reason. If I did this, would pressure treated, 'joist timber' be suitable for a sill plate?

[Rich]

That's kind of where I was heading with the questions.. if there are gaps you could slowly replace the sill plate as you remove other sections.. little by little.

[Sausage]

Ok, so have you any idea what kind of lengths I could risk at a time?.. a foot?...a yard? And what's the best way to secure the plate down under these circumstances; they're currently on a strip of damp proof material btw (which I'll replace).

I take it there is no reason to leave a gap between the top of a joist and the masonry above - the wood isn't going to swell up and cause some other issue I hope. [Even I'm thinking that sounds like a daft question. lol]

Sorry for all the idiot questions Rich - your helps much appreciated - it's just I don't want a calamity in my mother's house; unfortunately she doesn't want a builder either.