Dormer Cheeks - Cant Rail And Soakers

[EViS]

I need a bit of advice about the detail required between an existing pitched roof and dormer cheeks,

WBP ply has been fixed to the dormer cheeks and I'm ready to install the membrane prior to battening and tiling. This is where I need a bit of advice,

1. Should a cant rail be installed at the junction of the dormer cheeks meeting the existing roof? The membrane would then overlap the cant rail and finish at the existing roof, correct?

2. If the above is correct, how would soakers be installed as the cant rail would mean that the soakers cannot be 'L' shaped? Would this not also mean that the soakers would be visible as the cant rail would prevent the dormer cheek tiles and the pitched roof tiles from being installed close together?

If anyone has a diagram on how to detail this, that would probably answer all of my questions .

 

[palaceray]

Normally you fix the main roof underlay and battens first, turning the underlay 100mm up the cheeks.
You then fix the underlay to the dormer cheeks overlapping main roof undrlay.

Generally you should fix counter battens to the cheeks as they are boarded.

 

[datarebal]

no cant rail or arris required simply turn your membrane up the side of dormer cheek put your battens on, slate or tile into the cheek fitting soakers as you go. these will have been bent through 90 degrees.. even if your not using a double lap tile or slate the timber detailing is the same.

http://www.dreadnought-tiles.co.uk/plain-clay-tiling-guide1.pdf

page 39 has an abutment detail same will apply to your dormer. depending upon your dormer cheek detailing you shouldn't need the step flashing mentioned

there will be a bit of careful fiddling where the dormer fascia comes close to the tiling. not to brain taxing..

 

[EViS]

Thank you for the prompt replies and the attached diagram. A couple of further questions spring to mind:

1. The existing roof doesn't have any underlay (you can see the tiles from the underside of the roof). Would it be worth installing an underlay on the existing roof approx 500mm from each dormer cheek, and turn this up the cheeks?

2. Counter-battening sounds like a good idea. How common is this on a dormer as I haven't seen this mentioned anywhere?

3. Finally, should I buy lead or aluminium soakers? And what size?

 

[palaceray]

If the existing main roof has no underlay there is no point fitting a strip by the side of the cheeks,
Lead soakers are best, the size will depend on the covering you are using on your dormer cheeks, For plain tiles use 195x180 code 3 soakers with a 75mm upstand

 

[EViS]

Out of interest, what makes a lead soaker better than an aluminium one?

 

[palaceray]

Lead soakers will last far longer than cheap preformed soakers and can be dressed as required also the preformed soakers usually only have about 50mm upstand which is not really enough with plain tiles.

 

[EViS]

What's the best way to fix the soakers? One nail in the top corner of the soaker on the dormer cheek?

 

[EViS]

Any chance that someone could please offer some insight on the above question?

 

[datarebal]

which tile are you using?

 

[EViS]

Standard 265x165 plain tiles.

 

[datarebal]

ok you have a choice, soaker sits slightly higher than top of tile bend one corner down over the top of the tile to form a hook. soaker will hang there also trapped under the tile above.
or it's perfectly ok to tack the top corner to the cheek with a copper nail.

 

[EViS]

Great, thanks for the response. Are there such things as 'corner soakers' to install at the corner where the cheek meets the front wall of the dormer and the main roof tiles continue down?

 

[Alastairreid]

Great, thanks for the response. Are there such things as 'corner soakers' to install at the corner where the cheek meets the front wall of the dormer and the main roof tiles continue down?

The lead apron at the front of the dormer is dressed round to accept the 1st soaker.

 

[EViS]

In my mind that would leave a square gap without flashing. I don't suppose anyone has an example of this (photo or diagram)?