100 odd year old pitched roof query

[scottS3]

Hi, my house is a stone built small cottage and as far as I know it was built around 1900. I have been removing a ceiling to renew it with plasterboard and have found that the ends of some of the ceiling joists are rotten where they are embedded into the stone work. One thing I noticed when checking the rest of the joists is that some of the roof joists come down and sit on top of the ceiling joists, some roof joists come down the side of the ceiling joists and they are hard against each other and some of the roof joists come down the side of the ceiling joists but there is a gap between the two, in some cases as much as 3". Can anyone shed any light on this weird method of construction? I'd have expected them all to be the same, but I cant see any pattern to the different ways of doing it, and I have no idea why its been done like this?

Any help is appreciated.

[scottS3]

Thanks for the replies so far, here is a photo of the worst one, this is one that the roof joist came down and sat on the ceiling joist



Here is one where the roof joist comes down the side of the ceiling joist, and the side faces of them are hard together



And here is one where the roof joist comes down the side of the ceiling joist, but there is a gap between them

[scottS3]

Ok thanks, as you can tell I'm still learning the correct terminology for house things!

[scottS3]

Hi, yes at the very top one of the rafters is checked and the other rafter sits in the check. About a meter below that there is a horizontal brace between the two rafters.

[scottS3]

No purlins, what is a king post?

[scottS3]

Ok thanks for the pic, that clears things up. So no, I dont have a king post in my roof. I'll get a photo of the bits at the top

[scottS3]

Hi roofer, I think this is old damage, there is nothing wet inside the roof structure now after the memberane and tiles were renewed a couple of years ago.

Here is what the upper parts of the roof structure look like.

[scottS3]

Is the ridge tree the same as a ridge board? If so there isnt one and it doesnt look like there has ever been one.

[scottS3]

Yes quite a few of the rafters look to be notched over the wall plate, although I cant see them all clearly I suspect they may all have been like this. So, with this in mind how do I go about repairing the rotten rafter/joist ends without causing my roof to come crashing down around me?

[scottS3]

Ok, I've repaired the ceiling joists now, and its time to rebuild the top of the wall head where I dug out some of the stone work. What kind of mortar do I need to use? The walls are built from sand stone so is it hydraulic lime I should use?