Roof sagging and possible water damage - advice appreciated!

[Matt K]

Hi,

I'm quite new to DIY but having had success fixing rotten floor joists I'm keen to get onto the next job!

I've noticed that the rear roof (through which we're planning to put a flue in order to move the boiler) is sagging slightly in the middle, and the cement/mortar above that section is coming free, exposing the (what I guess should be) internal side of the lead lining. I think that water might be getting in and has compromised the rafters, hence the dip in the roof.

I have read a little about "buttering up" of roof ridges and it being a no-no, so I'm not sure if this was just a bodge job at some point in the past and if I just chip out all of the old/loose cement/mortar and replace, I'd just be repeating a shoddy bit of work all over again!

Would anyone be able to tell me what the proper fix for this would be? Maybe the steps I should take to fix it properly?

Any help would be really appreciated! What I lack in experience I make up for in enthusiasm... but I'm very aware I actually need to learn what the hell I'm doing eh!

Pics are here, sorry for the external link... DIYNot only lets me upload 500k pics which just aren't big enough!

http://www.matt-k.com/downloads/house/roof/roof1.jpg
http://www.matt-k.com/downloads/house/roof/roof2.jpg

 

[HERTS P&D]

You need a picture from the other side of the road looking at the roof.

Andy

 

[catlad]

It was probably a slate roof originally and the extra weight is straining
the roof structure.

 

[Matt K]

Thanks both,

Hertsdrainage - It's the roof at the rear (L part of terrace if you get what I mean) of the house so I can't take a pic too far away/across the road. I suppose I'm most concerned about the fact that the mortar is coming away and looks to be exposing a hole where water can get in (behind the lead flashing). Do the new pics help at all? They should show the sagging near where the mortar has fallen onto the tiles a bit more clearly:

http://www.matt-k.com/downloads/house/roof/roof3.jpg
http://www.matt-k.com/downloads/house/roof/roof4.jpg
http://www.matt-k.com/downloads/house/roof/roof5.jpg

Catlad - Yes it's a 126 year old house so I wouldn't be surprised if that is part of the problem. Would the best course of action in that case, be to replace/sister with new/stronger rafters one by one, to support the roof?

Cheers, Matt

 

[vinn]

As suggested above, it could be the extra weight of the tile causing the sagging but until you post photos of inside the roof its hard to tell if thats the case or if its water damage rotting the framing?
As also suggested above photos of the gable and the other side of the parapet would help?
A photo of the eaves/fascia line would also help.

What you seem to be calling a ridge is a parapet, and its in a bad way - its very likely, as you suggest, that water is penetrating down through the parapet.
The chimney stack might also need some attention such as pointing.


Buttering is a bricklaying term.

However, until you know whats happening and why its happening dont get involved with any remedial work.

 

[Matt K]

Thanks Vinn - I can't post photos of inside the roof at the moment, as, below is a room with angled ceiling that's been plastered. I plan to take off the plaster and redo the ceiling (it looks pretty amateurish) so perhaps I should do that then take some pics of the rafters once exposed?

Thanks for correcting the terminology, it's really useful to know the correct terms when searching/posting online so I do appreciate it!

Cheers, Matt

 

[vinn]

FWIW but I did suggest above not to do any remedial work until you have more information.
Thing is, you might end up doing the plastering, for example, more than once - just saying.

Your roof is a structural problem - best to strip away all the ceiling plaster and have exposed timbers to examine.

Your parapet must be worked on with any remedial work to the framing - both together.
Is there a neighbour on the other side of the parapet?

 

[Matt K]

Sorry I could have been clearer, I meant that as I'm taking the plaster board off the ceiling anyway (and eventually replastering once everything is fixed), it's no trouble to take it off and post some more pics to get more information. Agree, it wouldn't make sense to plaster back-up until the roof is 100% fixed.

Yes there's a neighbour on the other side of the parapet.

 

[vinn]

Any worthwhile parapet work would have to be done in conjunction with your neighbour.
At the moment the top of the parapet brickwork has a layer of sand and cement, this will break up - what it needs is parapet capping.

 

[^woody^]

The roof has dropped at the junction with the wall at the top, which is not a rafter loading issue.

That cracked render may be a cause or a symptom, but needs sorting out in any case.

You need to look inside at the wall or the rafter connection at that wall, or at the eaves for possible rafter spread.

 

[Matt K]

OK by way of an update, I've taken down the ceiling and revealed the rafters and wall plate (which runs along the dividing wall, ontop of which is the parapet in the pictures on the links above). The wall plate is badly water damaged, the centre rafters have dropped around 15cms where the wallplate has rotted away and there isn't much left holding it up.

I think that I need to replace the wall plate as a matter of urgency, there are also some rafters that are rotten/water-damaged that need to be replaced also. I'm going to take Vinn's advice and fit a cap along the parapet, then chase in some new flashing to the brickwork which will sit over the tiles. I'll also repoint and waterproof treat the brickwork as it's not in great shape right right now.

The sarking is non-breathable bitumenized which, considering the room below will be a bathroom will be a bathroom, I think I need to replace with a breathable membrane.

A few questions for you experts on here!
1. Am I right in thinking that the wood I'd need to use for the wall-plate would be C26 that's been water treated?
2. Would anyone suggest the wood dimensions/thickness I should use for the wall-plate?
3. I've read that the wall-plate should be fixed with resin bolts 100mm into the wall at a minimum, the wall-plate sits on cantilevered bricks at the moment. For a 4m length roof should I put a bolt between each set of supporting/cantilevered bricks? (there are 5 sets of bricks supporting the 4m roof).
4. The tiles on the roof at the moment are Redland49s, given the age of the house and the slates I've found whilst taking the ceiling down... I'm certain that the roof wasn't designed for the weight of these tiles, is it sensible to replace these with Marley modern roof tiles such as those on the link below? They appear to be lighter than the Redlands and thinner which should help reduce the additional space needed for insulation (point on that below).
5. I've read that to get a good U rating, I should consider putting "inbetween and over" insulation boards on the roof, as I'm taking the whole thing down this isn't a problem to do, but... is it sensible to put both inbetween and 90mm over-insulation on the roof? It'll be a bathroom so (although there are air bricks/vents in the walls) I'm concerned I'll be over insulating it which could result in condensation problems?

https://www.roofingoutlet.co.uk/pro...ACCeM2NJHQByLAD6aJWKzaqieEIVAQgLh3xoCpxjw_wcB

Again, thanks so much for all of your help!!

 

[catlad]

I would say a length of 4x2" should do for the wall plate and using treated
timber will be better but not crucial, as for fixings half a dozen wall anchors
will do. The edgemeer tiles will also save some weight.

 

[Matt K]

Thanks catlad!!

Did anyone else have any thoughts on my questions?

Cheers, Matt

 

[noseall]

You need to do away with the idea of (solely) relying upon a high level horizontal wall (pitching/pole) plate, rather you need to use some vertical timbers on each rafter end and connect with the ceiling joists forming a truss.
This 'frame' can then be supported lower down where the wall is more sturdy and less prone to damp.

 

[datarebal]

Weight is the issue here. It is likely causing some spread.
Certainly Marley moderns wont help.
Go back to slates. timber repairs will be easy during the reroofing.
If you cant run to a slate then maybe a cement fibre alternative.