I have a felt 'flat' roof on an extension. It does not leak but is nearly
20 years old and I'd like to ensure that it remains waterproof. I like the
sound of adding an EPDM (rubber) membrane on top of the roof to keep it
waterproof but am finding it difficult to choose between the three methods
of fixing the membrane to the roof surface. The first - and easiest
method - involves covering the membrane with 20mm round ballast at the rate
of 50kg per square metre. With a 20sqm roof that will add 1000kg to the
roof! I'm not sure that's a good idea. The second method involves glueing
the membrane to the existing roof surface (felt covered with solar
reflective paint) but I'm not entirely convinced how well this would work on
what is not an entirely even surface. The third method involves screwing
plates into the roof joists (a bit hit and miss I bet) to hold down an under
membrane and then glueing the top membrane to the one beneath it. Has
anyone any experience of these three methods and what would you recommend?
Thanks.

Steve York wrote:
I have a felt 'flat' roof on an extension. It does not leak but is nearly
20 years old and I'd like to ensure that it remains waterproof. I like the
sound of adding an EPDM (rubber) membrane on top of the roof to keep it
waterproof but am finding it difficult to choose between the three methods
of fixing the membrane to the roof surface. The first - and easiest
method - involves covering the membrane with 20mm round ballast at the rate
of 50kg per square metre. With a 20sqm roof that will add 1000kg to the
roof! I'm not sure that's a good idea. The second method involves glueing
the membrane to the existing roof surface (felt covered with solar
reflective paint) but I'm not entirely convinced how well this would work on
what is not an entirely even surface. The third method involves screwing
plates into the roof joists (a bit hit and miss I bet) to hold down an under
membrane and then glueing the top membrane to the one beneath it. Has
anyone any experience of these three methods and what would you recommend?
Thanks.

Have you considered a Moisture Trigger Polyurathene Coating over the
felt. I used to sell this very sucessfully some years ago. In fact the
felt roofs of the NEC are coated with this material. Simple to apply,
with roller or brush. Solar reflective with excellent adhesion to
firmly adhered felt. It breathes so no moisture trap which you can get
with EDPM Rubber Membranes, (they dont breathe).

I do not represent any company that sells it now. Decothane by Liquid
Plastics Ltd is one excellent one and another is made by Tor Coatings
Ltd of County Durham.