david ohearns
6/17/2014
I need some clarification about capillary action before I tackle this job. I have a corrugated iron roof fitting under the main roof. The pitch looks to be between 10 and 15 degrees. And of course it is leaking. All efforts up to now have been at the top where it goes under the main pitched roof. I am now firmly convinced that the water is not getting in there. Where the sheets overlap the top sheet is pretty tight against the bottom sheet and comes a good way down into the valley. I suspect that the water is being sucked in via capillary action but I cannot be sure. Depending on your reply I intend to apply a bitumen coated membrane along the joins. But first........... Is it feasible that capillary action can cause this to happen and is it common? I am inclined to think that it can then run uphill ( only 10 to 15 degrees remember ) is this in fact the case? If yes, at that angle, how far down the join from the top would I have to go, in other words how far could it travel up? Last question. Having been sucked into the join, could it then spread into other valleys or would it stay only in the first one, hope this makes sense. Apologies for a long and rambling letter but this thing is driving me mad and I am determined to beat it. With your help :-) Eagerly awaiting your response. Dave
Info @windowsonwashington.net
An informed customer is our best customer.
6/17/2014
In a non-porous substrate, it is somewhat unlike that the water would crawl uphill. That being said, I am not sure how they sealed those joints, if at all and that material could be the capillary draw if it was a tape closure. Covering the roof with a non-absortive coating should get you your answer if the leak origination is not more clearly defined or identified.
Dick Bus
6/17/2014
Yes, it is possible. I have seen capillary move sideways, not up hill. Negative pressure in a structure will also pull moisture through any small opening; including overlaps and joints in the roof assembly. Negative pressure is caused by an imbalance of exhausting air and inadequate intake. If the structure is sealed tight and a large exhaust fan is turned on, and a door is difficult to open then you would know you have negative pressure. Back to the capillary action question. It is recommended that all overlaps (that do not have a capillary grove designed into the part) receive at least one row of butyl tap or caulking. in the case of valleys I recommend two. Before you start recoating the roof verify that there indeed is nothing in the overlap. Use something thin that will not scratch the paint like a specula that is used for icing a cake. feel free to posted any other questions.
Info @windowsonwashington.net
An informed customer is our best customer.
6/18/2014
+1 Mr. Bus. Didn't consider the negative pressure aspect of things.

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