Roof advice - pitched slate roof resting on flat roof

[JayD]

I've got two pitched slate roofs with a flat roof in the middle.

 

The bottom row of slates are resting directly on the flat roof. I think the flat roof was repaired or replaced in 2012.

 

With winter coming, I'm looking at preventative ways stop potential leaks (no leaks at present) and get a few more years from the roof. 

 

I was thinking of using acrypol plus to cover the flat roof and areas on the flashing that have weathered away.

 

A friend has said to cover half of the bottom row of slates in acrypol plus, and to fill in the vertical gaps on the bottom row of slates with butyl roofing sealant. The idea to create a waterproof surface so water rolls down the slate onto the acrypol flat roof.

 

I have some questions:

 

1. Is this a good robust approach?

 

1a. Should acrypol plus be used on slates?

 

1b. Will water seep behind under the bottom row of slates ? (Currently it probably does and dries out) - that's the concern for leaks to develop with rain and aging of current roof.  With this water proof idea, I've been watching how water flows down into the lead flashing when raining heavily, so I'm concerned about water creeping behind any acrypol area (via slates) and then causing more problems.

 

2. If not a good approach, what is a robust, reliable and low maintenance approach?

 

Attaching a photo, that will help.

 

 

 

Thanks

Jay

 

Edited October 7, 2020 by JayD
Added image

[Mr Punter]

The roof has been extensively repaired.  If it is not leaking I would leave it.  When it comes to repairs you may need to strip the slates, new membrane and battens and finish the flat area in GRP.

[Onoff]

If your really unlucky, like me, they'll have "repaired" just the flat roof area by sticking felt on an just lapping it under the slates (tiles in my case): 

 

 

 

Water will get under there eventually!

[Temp]

55 minutes ago, JayD said:

A friend has said to cover half of the bottom row of slates in acrypol plus, and to fill in the vertical gaps on the bottom row of slates with butyl roofing sealant. The idea to create a waterproof surface so water rolls down the slate onto the acrypol flat roof.

 

 

That would be a bodge. The flat roof almost certainly has a vertical upstand hidden by the bottom row of slates that stops water running under the slates from getting into the house. The correct thing to do would be to temporarily remove a row or two of slates and redo the flat roof and upstand properly before replacing the slates.

[Onoff]

Btw I've spent a fortune on Acrypol+, Chromapol and various other acrylic roofing compounds on my 2 dormer roofs. They still leak. 

[PeterW]

1. Get some new friends...

2. Leave it if it doesn’t leak...

 

As others have said, leave it unless it leaks..!! Do not lap anything onto the slates, whatever is done must be under them. 

[Hobbiniho]

as has been said dont add anything on top of the slates you will cause more problems, it looks like some of the slates have already been removed to allow the last bodge to be applied then they have been "pushed" back up under the second row as you can see they are not straight and the headlap is all over the place, i would suspect that these slates would be quite easy to remove

[JayD]

Thanks everyone,  appreciate your advice.

 

I spoke with my friend and explained water creep, and issues with coatings on slates. 

 

We're going to do it properly by lifting off the bottom slates and seeing what has been done.

 

From the gutter side, I can see a later of felt of the flat roof that's about 3 inches in length behind the slates.

 

We're thinking of using a fibre glass valley instead of the bottom row of slates resting on the flat roof. One we take of the bottom row of slates we see how to sort this properly so to avoid any future issues. 

[Mr Punter]

You will not easily remove the bottom rows of slates.  If you want to do the job, strip them all, starting with the ridge tiles, then re-fit after you have fitted the new GRP valley.