False dormer gable

[TonyW2]

Help please.
I have searched under everything I can think of, but cannot find a framing diagram and valley layout for a false dormer.
I am just trying to understand what is going on with my existing one that is causing rot on the adjacent roof fascia.
Could someone please point me in the right direction?

 

[TonyW2]

Dormer Gable

• TonyW2
• 23 Jan 2017

Photo added in case my terminology is incorrect.
Rot has occurred in the fascia behind gutter end and on the "box end" and barge board of the gable part. The verge has been repointed.

 

[garyo]

I'd say it's going to have more to do with your valley detail than the roof framing - i.e. secret gutter, or if wet valley then has all the pointing fallen out. Does the lead extend in to the gutter okay. I presume you've got up there and checked that it's not just backed up with leafs and back-flowing in to the fascia/boxing?

Is that the actual roof or a photo of a similar one?

 

[TonyW2]

Thanks.
It is the actual roof. The valley and gutter are clear of debris. The valley discharge area looks to be shaped OK, but I do not know what type of valley is installed

 

[garyo]

Can you get access to take a couple of photos of the valley detail - get right in where the cement pointing between the lead valley and the underside of the tiles would be (assuming that's the detailing you have)

 

[TonyW2]

No chance. (Scared of heights in this weather!)
I did not realise that mortar was needed on the valley surface.

 

[vinn]

You have an intersecting pitched roof, framed exactly as any intersecting roof on a say, intersecting one story extension.
A valley rafter with valley jacks on either side, and a valley board or boards supported by the valley and jacks.

Go into the loft and examine the framing but, as above, its usually a case of the barge tail and the fascia starting to rot due to lack of maintenance or discharge from the valley.
Unless the valley material itself (eg lead) is leaking?

edit: I've just noticed the ref to lead and mortar - is it a mortared-in lead valley?

OP, you must put up a more clear and detailed pic or pics.

 

[TonyW2]

Thanks.
I am sorry but further external examination or photos will have to wait for better conditions.
It looks like a plain sheet of lead. There is very little to see in the loft. This has a trussed roof covered with felt and all that is visible are two thin ply lengths that run where the valley is, nailed flat on top of the main roof trusses and under the felt.
There is a cross noggin between two trusses that supports the end of the dormer ridge.

 

[garyo]

No chance. (Scared of heights in this weather!)
I did not realise that mortar was needed on the valley surface.

You may or may not have mortar. It really needs a photo. Smartphone camera on the end of a stick has worked for me before.

 

[TonyW2]

I think it may be referred to as a Scotch Valley, with pitching plate and creeper rafters.
I am guessing that the valley is then formed by thin ply boards and overlaid with felt, and lead sheet.
I presume the lead sheet is tucked under the edge of the felt.
Then battens are fixed with slates on top.
Where would mortar be involved, as I can't think of what it could stick to, without lead thermal movement causing it to crack.
What maintenance is possible, apart from normal cleaning of the fascia gutters below the discharge point?
The soffit can be seen from inside the roof space and appears dry.

 

[garyo]

Your lead will hopefully be turned up on to a batten running down either side:

http://c8.alamy.com/comp/AFF71H/the...onstruction-showing-the-breathable-AFF71H.jpg

And/Or there may be some mortar, see this cross section:

http://rcimag.co.uk/sandtoft-blog/how-to-ensure-the-correct-detailing-of-pitched-roof-valleys

 

[TonyW2]

Many thanks, that is a good explanation.
Roll on a sunny day.

 

[noseall]

I'll bet the roofers were a bit stingy with the lead drip at the bottom of that valley and have not left it long enough to turn into the gutter or not wide enough to collect all the run off and turn that into the gutter.

Either way probably poor lead detailing at the bottom.

 

[noseall]

That's not a false dormer but a real faux gable.

 

[^woody^]

It's actually a real dormer, not a false one.