Shower Membrane for Roof Deck
I have a neighbor who has neighbor who has a roof deck that is leaking. The roof deck is installed over the primary bedroom with ensuite and from what I understand is installed like a shower. I’m only able to observe the tiles on the exterior, but the following represents what I was told the installation consists of. There are ceramic tiles set in grout over a 1 inch to 1 1/2 inch mortar bed (sloped to drain to two scuppers) over a peel-and-stick waterproofing membrane meant for showers over exterior plywood sheathing. The membrane has 2 inch overlaps at the seams.
The drywall in the ceiling has been opened up for inspection and the leaks appear to be located near the field of the roof deck, not near the edges.
I’m curious if anyone has thoughts on if this is likely an installation issue or is it that this system isn’t suitable to be installed outside. I’m wondering if the temperature swings outdoors will create problems for this type of system since it’s not expected to experience the same cold temperatures. We’re in climate zone 2A.
I appreciate everyone’s time.
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Replies
The Tile Council of North America requires a roofing membrane and a drainage layer, either stone or a mat, below the mortar bed. In warm locations, solar vapor drive (and regular vapor drive) force moisture into the house, so unless the membrane is absolutely perfect without the tiniest holes, even at seams, it will eventually leak. The drainage layer is a capillary break that allows the water to drain before it causes problems.
I don't know if a shower membrane is acceptable; it's protected from UV rays so it might be fine as long as it never freezes. It's not made to withstand freezing. The TCNA recommends roofing membrane for a reason.
Thank you for the reply, this echoes how I feel. It's not only vapor drive, though. You can flood the deck and watch as water drips into the bedroom. To me it seems like they must have openings in the seams, which will be revealed eventually.
I've never heard of a shower membrane used for a rooftop deck, which is probably for a good reason. I think you're likely right about freezing, which was my original concern. I also believe most (all?) roof membranes will have more than a 2 inch overlap.
2" overlap is not typical for waterproofing membrane systems, but whether it's good or not depends on whether the specific install is according to manufacturer recommendations and requirements. Some peel-and-stick manufacturers require a double layer over the entire horizontal area, others require detailing sealant at every seam.
whether it's a manufacturer defect or installation error is impossible to know without knowing the exact product and examining the installation. too often the homeowner passes on incorrect information.
So an entire roof deck in tile?
I would not think standard shower materials would be acceptable for an outside installation
JKulka,
Flat roofs invariably leak at some point. The best approach is to decouple the walking surface from the waterproof layers below, by using tiles or pavers on pedestals or small areas of wood decking on sleepers - both of which make repairs or replacement easy. Tile in mortar, or concrete slabs are just more work and complication waiting to happen.
Completely agree. Also, this failed in less than 2 years.
I dont know what kind of membrane you are talking about but if it’s something like Kerdi they are not meant to be installed under a mortar bed. A mortar bed install generally requires a monolithic membrane like pvc. Schluter and all shower membranes of this sort will leak if permanently wet, as in under mortar bed.
Also is the neighbor of your neighbor your neighbor?
He said a cement product, and I made an assumption about mortar, and could easily be wrong. I also have no idea which product was used. It could easily be that they made a mistake that would have leaked even if this were a shower. We'll find out eventually.
(Just my neighbor, I have no idea what was going on with that first sentence)