Ridge under flashing, alternative to lead?

[epsilonGreedy]

I am covering a roof with natural slate and I am one row below the ridge. The ridge capping will be lead flashing extending 150mm down over the top slate row each side of the ridge. The slates are 500mm long.

 

Now that I have had a chance to visualise the final overlaps of top two rows of slates and the ridge lead capping, I don't think the end result will have the same amount of head lap as the main slate portion of the roof.

 

My proposed solution is to fit a continuous linear soaker to the top batten (that is just below the ridge), before the top row of slates are nailed into position.

 

My Question: Is there a material that is cheaper than code-3 lead that can be fitted directly under slate? This material will be in direct contact with the slates nailed on top and will have minimal sunlight exposure between a few 3mm gaps between slates.

1. I was thinking of using some 200mm plastic dpc that is spare onsite but this might suffer on a hot day should the slate reach say 60 degrees (c).
2. Another idea is to use regular breather membrane but that might abrade over the years as the slates expand on hot days or shuffled during high winds.
3. There are plenty of non lead flashing substitutes on the market but these usually contain an aluminium mesh and I am concerned about galvanic action between this linear soaker and the proper external lead flashing capping the whole ridge.
4. The ideal would be a heat tolerant roll of plastic no thicker than 3mm.

 

As I type I am starting to think code-3 lead is the best option. A 180mm wide roll of lead is about £7 per linear meter.

 

 

[joe90]

Are you not putting a row of half (length) slates on at the ridge like the eaves?, this will give full coverage right up to the top batten. If the ridge does not need ventilation I like to run the felt from one side at least over the ridge.

Edited December 1, 2021 by joe90

[Conor]

Our roofers put felt over the ridge, fixed a batten down, slated right up to the two top battens, and then we fitted a dry ridge system- flexible flashing all along the ridge followed by the clay ridge tiles (this is what the ridge batten was for). From memory the top battens were pretty much tight at the top of the ridge so there was only 25mm or so at the top with no slate coverage. Ridge flashing and tiles sorts this.

[epsilonGreedy]

3 hours ago, joe90 said:

Are you not putting a row of half (length) slates on at the ridge like the eaves?, this will give full coverage right up to the top batten. If the ridge does not need ventilation I like to run the felt from one side at least over the ridge.

 

 

I think so but by accident rather than design. The Mr FixMyRoof of YouTube recommends adjusting the batten gauge to result in full sized slates right up to the ridge but with preholed slates and just 10 rows of full slates from eave to ridge it was not possible jiggle this outcome. So I ended up with 10 full slates rows plus an extra batten just 60mm further up close to the ridge. The 11th top row will need 2/3rd length slates so yes not far off an eave type row.

 

To help you guys help me I will take a photo tomorrow and also upload a diagram. Thanks so far.

 

I have run the felt from both sides right over the ridge and about 400mm down the other side so there is no concern about water ingress into the attic space. My concern about a reduction of head lap in the last top two rows that would make it too easy for water to get under the slates and then dribble down over the felt to the eave. I could widen the lead flashing ridge cap to achieve a full lap but that would look daft on a small roof.

Edited December 1, 2021 by epsilonGreedy