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.

[ATTAK Z]

Any chance of a photo ?

[TA14]

Side by side and well screwed/nailed together is the correct method; this provides lateral restraint to the roof. If the third or so of the joists that are done this way have good joints then that's probably enough depending on the pitch/joints wall plate.

I assume that you'll be doing a lot of splicing - give it a big overlap, say 750mm. I'd also put plywood stiffeners (triangular pieces or wood about 500mm long screwed in to the side of the rafter/joist) in on every alternate joist, especially the ones where the joists sit on top or there are gaps.

It's built like that because of poor workmanship; sometimes a wall that has a bow in it and the roofers try to build a flat/square roof. Just call it characterful

[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

[ATTAK Z]

Thanks for the photos, I see what you mean now ... you threw me I'm afraid by calling the rafters 'roof joists'

... I agree with TA14 and can't really add anything

[scottS3]

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

[EggsBenedict]

Is there anything above that?

So looking upwards, are there any other bracing members spanning the rafters on either side of the roof forming an 'A' shape? I'd agree that at the moment, it doesn't look like there's much stopping the roof spreading, but sometimes the roof truss is independent from joists holding up the ceiling. It can still spread if these are set too high, but if they're there, then the roof could well be OK.

[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.

[roofer]

Looks like wet rot, find the source of the water then scarf new timber in.

[Little Lofty]

It looks quite normal for the age of the property, the rafters (roof joists) are not sitting on the ceiling joist but a wall plate which is positioned to the outside of the stonework, the rafters are at different centres to the ceiling joists so don't line up with each other.It's slightly unusual for the ceiling joist to be built into the external wall they are generally notched and fixed onto a timber batten.If its a 100 years old and hasn't moved then I wouldn't worry, I assume it has purlins and a king post holding up the roof?

[scottS3]

No purlins, what is a king post?

[ATTAK Z]

scottS3 said:

No purlins, what is a king post?

This might help

[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.

[groucho]

Is that an old style bitumen felt underlay? Very weird at the top, where's the ridge tree?

Edited by groucho on Friday 19th September 20:59

[ATTAK Z]

scottS3 said:

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

The members shown are called 'collars' FYI ... as someone said, they will help to minimise lateral load on the walls; but, at that height, not by much

[groucho]

The top of the rafters seem to be mitred in a way that I have not seen before. The lateral supports will help but they are normally complimented with the ridge tree. Truss roofs excepted.

[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.

[Little Lofty]

That's certainly unconventional, but it seems to have held up ok

[Little Lofty]

Looks as though the wall plate could be fixed to the ceiling joists and the rafters are notched over the wall plate, this may explain why the roof hasn't spread, problem being if the ceiling joists are starting to rot it may compromise the strength off the wall plate, if you have to start replacing a number of the ceiling joists you will need to add some additional bracing to the roof.