Rotten roof wall plate in Edwardian terrace - what to do?

[lubemonkey]

EDITED to put pics in context, add plans and tidy up terminology.

Hi All,

I am refurbishing an Edwardian terrace and have uncovered a roof issue that I would like some advice on please.
The roof in question is not the main roof but the smaller pitched roof over the rear original two storey “extension” and has a span of 3.8m and a length of 4.5m. The extension is adjoined by the matching neighbouring extension. The party wall continues upwards externally forming a low parapet which has a lead lined valley gutter formed between it and the roof eaves.




And this is what the layout actually looks like from inside:


View from old bedroom out to landing


View from landing into old bedroom

Under the valley gutter the joists are supported by a wall plate attached to the inside face of the party wall. This wall plate is lapped into the brickwork at both ends (extension gable end and into rear wall of the terrace) and has the original steel/iron supports every metre or so which are set into the party wall.


Plate laps into terrace wall (next to old conduit)


Exposed plate and underside of valley gutter above landing


View of plate/joists and old steel supports in old bedroom




View straight up from old bedroom. Flat board is the underside of the valley gutter. Rafters are tied onto a plate that runs across the joists (just under the insulation in the pic)


The only thing in this loft is a water tank as it's low and hard to access. The room immediately below has been split into a bathroom and bedroom with a partition wall (old lath and plaster) and that will be coming out to create one large bathroom including new ceiling throughout.

The problem is that having uncovered the valley gutter from below, it is obvious that at some point there has been serious water ingress that has caused rot in the wall plate along pretty much the entire length. It is bone dry now and looks like it has been so for some considerable time. The roof slates were replaced 20 years ago and any lead flashing (including the valley gutter) looks to have been new at the same time, possibly later. The weakened wall plate has sunk around the metal supports to varying degrees so the joist ends are no longer level. It was the wavy ceiling and plaster patching that made me investigate in the first place!

The wall plate has a batten fixed to its front allowing double notching of the joist ends. The joist timber seems sound enough but the slumping has pulled the joist ends a little away from the remains of the wall plate in places.

I've been over thinking what to do as usual, so thought I'd ask for some advice on a way forward.

Options I've thought of are:
1) If it's stayed up this long it'll be fine. Construct suspended ceiling to level.
2) Prop it, try to get a new plate in and hangers, joist extenders possibly. May still need suspended ceiling as joists may not level.
3) Take part of roof off to access and replace as necessary

Window frame is tight to current ceiling which could make suspended ceiling more tricky.

As you can see, I'm stuck. My main concern is safety especially as I'm looking to rent/sell later in the year. Any pointers on how I go about repairing this will be very much appreciated.


Cheers,
Lube

 

[dann09]

FWIW: check some of my, or others, posts requesting further information. Pics in context of where inside or outside the property will orient us to help you.

A scanned, hand drawn, plan view is invaluable for instantly seeing whats what and where.

 

[lubemonkey]

Cheers dann09 - I'll edit and repost.

Out of curiosity, could you see the pics plus descriptions in the album that was linked too? Just checking in case I'm the only one who can see them!

 

[dann09]

I did see some "roof" pics - not very informative without a context, plus they were a bit dark.
There were no descriptions.

 

[lubemonkey]

Erm ok. In the interests of me finding out what my "Roof" album looks like to someone else on here, this is what I see when I follow that link:

Seven clickable thumbnails in an Album called "Roof". Click the thumbnail to get large version of image. This has a title at the top (as per thumbs) and a description below the title (ranging from one word to three sentences). Flick between images with prev and next links. Happy days.

None of the images look dark to me on this lappy. How odd.

I'll edit the images into the post and add a plan when I can get the scanner fired up!

 

[lubemonkey]

OK I've pulled pics in to original post and have added plans too.

Fingers crossed!!

 

[Nige F]

Exellent pics. now but what a poxy detail I`ve never seen a party wall penetrating a tapered flat roof - making in effect 2 box gutters . Well you look to have about 8 foot to 8`6" ceilings , and you mention a suspended ceiling . I would consider getting some metal gallows brackets made - one for each ceiling joist - to take the weight from each joist before it is cut into the ( rotted ) plate , and bolted to the wall - that`s my basic idea FWIW - details like loads etc need a better brain than mine brackets made then galvanised , with resin anchors into the wall- and a suspended ceiling to hide it would be my way .

 

[dann09]

Thank you for the revisions. Nige too, for helping me sort my mind for possibilities.

1. Talk to the neighbours and view their interior if it's possible.

2. Get some light and a pair of eyes up inside the opened up area to view the rafter tails and their supporting plate for possible damage. At inaccessible areas hold an arms length camera in.

3. Typically, fungal damage does not go away, although it might become dormant. Replacement of the entire plate is the way to go.

4. A possibility is to drop a base plate on the floor to acrow off for each individual ceiling joist.
After the acrows take the weight, the plate and all fungal damage could be cut out.
The whole area, including masonry, could then be pasted with remedial "mayonnaise".

5. A new plate/RSJ/beam could then be slipped into position and bolted to the wall.
Cutting off the joist tails and splicing back in, or bolting on might then work, but a site view is necessary for an opinion.

6. The above might involve a SE's view. If so, get it in writing with some kind of sketch.

7. Without being on site it's too difficult, too many variables, to give you clear advice. It's all professional work, not DIY.

8. The gutter should be cleaned off, and inspected for irregularities or weeping leaks. No length of lead more than 1500mm, and falling to discharge into ...what?

9. You might remove some more ragged bits of fibrous plaster and push back the insulation for a few more clear pics.

 

[lubemonkey]

Big thanks to Nige F and dan009 for the all the info. Just what I was looking for. I'll open it up some more as suggested in case I haven't seen the entire extent of the damage.
I need to get someone in to quote for the install of a steel for a downstairs knock through job so, given the suggestion that the roof is a professional job and not diy, I'll try to get someone who is able to quote/do both jobs.
I'll let you know how it goes!
Cheers,
Lube

 

[catlad]

If you think the rot is dead could you build a stud wall along the party wall which would add extra support for the rafter feet and ceiling.