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Serialrenovator 01-30-2010 01:11 PM

condensation leak with metal roof on cathedral ceiling in Canada
I had a metal roof (ideal roofing H-16) installed last year on a steep pitched roof that is joined on top and on bottom by two flat roofs. It was professionally installed by our roofer. We are getting moisture inside our home where the base of the metal roof meets the flat roof. We are trying to determine whether the moisture is caused by leaks or condensation.

I am also curious to know whether metal roofing with a cathedral ceiling application should be vented. We have vented roofing on both flat roof systems and an air space behind our metal roof but there are no breathers on our metal roof. I am wondering if that might be the cause of a possible condensation issue. Are there such things as breathing vents meant for metal roof products?

We have experienced leaks on days where there are large melts outside (+5 degrees C). To me this means that it is either ice and snow that have worked there way in and stayed somewhat frozen until the melts and then come in OR it is condensation. If it is condensation, there must be something wrong with the application that we can fix so we don't get this every winter! Please help!

Thanks for your advice (in advance).

Tom Struble 01-30-2010 01:29 PM

depends on what your ceiling insulation is as to whether venting is required

you seem to have the problem at the transition,maybe the flat roofing material does not go up high enough,or is not lapped to the roof underlayment properly

Serialrenovator 01-30-2010 01:48 PM

The roof layering is as follows. Standing seam metal roof panels, ice and water shield, plywood, air space (around 1"), fiberglass insulation(about 12"), vapour barrier, drywall.

I have been told that the underlayment where the metal roof meets the valley only goes up 4" where 18" might have been preferable. I opened the flat roof area near where the flat roof meets the lower end of the sloped roof and it is bone dry there - but a few inches away - where the exact intersection of the two roofs are above is where we have had water come through.

Tom Struble 01-30-2010 04:30 PM

sounds like you should have a ridge vent with continuous soffit venting

the flat roof material should go up past the transition intersection more than 4'' and the flat roof material should be sealed to the roof deck around the edges with i&w or some other compatible self stick flashing,then the roofing felt shingled over that you cant go up to high imo

the i&w your roofer did is on the entire roof?or just at the eaves

if just the eaves did he use roofing felt on the rest of the roof?

Serialrenovator 01-30-2010 09:11 PM

1 Attachment(s)
Thanks for your response.

There is no ridge vent at the peak. Unless you can make one out of flashing (that is what is up there). Previously we had a shingled roof in its place with three roof vents that we were told 'we no longer need'.

I am attaching a picture of the front of house before the metal roof went on. Maybe it can answer some questions I cannot.

There is no soffit in the front section. The flat roof has a scupper on either end for drainage, and three mushroom vents placed two / thirds of the way back towards the sloped roof.

In order to improve the situation, do I need to remove the metal roof to increase the transition intersection beyond 4". Is this wrong by building code? I ask because if I have to pay to redo the damn thing I want to go after my roof to get some money back.

I do not recall any roof felt being used on the slope. What exactly does roofing felt do for this application? The i&w is across the entire sloped roof under the metal (as can be seen in the pic). It might be important to note that the i&w was exposed to the elements for about 4 months before the metal went on. Might that have compromised its strength?

Thanks again. I appreciate the light you are shedding on this.

jlhaslip 01-30-2010 11:36 PM

Where are you in Canada?

yes, you need an air space above the insulation.
it also helps on the cathedral roof to have cross-bay ventilation so that if one bay is blocked there is a secondary path for the ventilation.
One way to do this is to cut notches along each rafter if the rafters are large enough. Another way is to strap the roof horizontally.
Ridge venting is absolutely required. period. no exceptions. I don't care what your roofer says.

I am willing to bet that lacking the top ridge venting, the water you are seeing is condensation from the missing ventilation.

Tom Struble 01-31-2010 08:24 AM

the manufacturer of the metal roof [shingles?] probably have a vented ridge and eave trim

the ''tar paper'' underlayment would help keep condensation off the back of the metal,and if installed by shingling it from top to bottom help drain any water down to the bottom

metal is a great roof,but it has to be the right one and installed correctly

go to the manufacturers web site download the install instructions and see how it supposed to be done and then check the install on your roof
they should match

Serialrenovator 02-01-2010 11:43 AM

Thanks for the responses. I am following up with the manufacturers directly today. I am betting ridge vent myself too. Should the roofer had known this would cause issue?

Also, I am in Toronto.

Tom Struble 02-01-2010 09:27 PM

hot roof systems don't require venting...but thats not what you have
so it should be vented,i think you may also have issues at that flat transition

Serialrenovator 02-01-2010 10:11 PM

I spoke to the manufacturer this morning and he suggested putting square ventalators (like you would use with shingled roofs) on it. I somehow doubt this would work though as 1. how would you mount it 2. how would you protect against rain and snow coming in. Your thoughts?

jlhaslip 02-02-2010 12:18 AM

Which Manufacturer did you speak with?

If it was the metal Roof dude, he should have a print showing how to do the vents.

I have always used part sheets of metal for vents. Overlap by at least 6 inches, install the lower sheet with the vent installed and have the upper sheet running long past the vent. Can't recall having a problem using this method.
Another method is to 'slit' the tin, but it is more likely to leak, mind you, we get more snow than Toronto.

See my comments about cross-bay venting, too. Do you have any cross-bay venting? If not, you would need venting up each rafter bay.

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