Roof leak
user-7555954
| Posted in Green Building Techniques on
We have a building approx. 10 years old. There is a slow leak in a green roof assembly. The roof construction is as follows: open web steel joist 4′ o/c, 4″ concrete slab, 5″ 2lb spray foam (under side of slab), PVC water proofing layer (top of slab), high end green roof system (felt, 3″ drainage layer, 4″ soil). There is significant moisture between the PVC and concrete. Could this be condensation? Is this a poor technique. All of the layers are properly installed and in good condition. Building is located in north of Toronto, Ontario. Interested to hear your thoughts.
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Replies
Does the leak slow or increase during summer/winter to rule out condensation
It appears to leak in all seasons. The leak is slow and behind finishes. So very difficult to connect to any specific event.
It sounds like you have a roof leak. But I'm just going on what limited info you've given.
This is close to home as I have a green roof in Toronto.
I know green roofs add a bit of insulation especially with as thick if a system you have, but that's only good in the summer months, winter months you can consider it having no insulation value.
By pvc roof membrane, do you mean the root barrier? How do you know there is high moisture between the slab and roof membrane?
Also, Do you have a record of if/how the roof membrane was leak tested before the green roof went down?
Either way, this is my thought process: there are two approaches. If it is in fact condensation, I think you'd need to remove the green roof and add insulation on top of the slab to move the condensing point above the membrane (just like with a wall assembly). Then add a new roof membrane on top of insulation and replace green roof.
If it is a membrane leak, then you'd call in a specialist to come do an electronic roof leak test (Electric Field Vector Mapping) to determine if/where it's leaking and address it.
I would guess the best bet it to call the roof leak guy first before you start ripping everything down.
I second the idea of identifying the cause of the leak before ripping things apart.
If you do end up redoing the roof, I think many would use the Protected Membrane Roof (PMR, also called an Inverted Roof Membrane Assembly) approach that Jamie B suggests. The people at Building Science Corp have a number of related articles, e.g. BSI-052, where Lstiburek lays out some risks of "green" roofs and shows how they can be designed to reduce risks if a "green roof" is a requirement.
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