Deviation of seam alignment from downslope

G Foyle
5/2/2016
I spent about 20min searching likely terms but did not see this question asked. Apologies if it's been addressed before. We have an architectural roof design for which the eave is not aligned perpendicular to the roof's downslope for a couple facets. There are zoning and aesthetic reasons for the design that results in this, and it's not an option to just change this. One facet is ~3:12. The other is ~6:12. The roof is essentially a shed style with a max panel length of ~35ft, 14" wide panels 1.5" high seams, snap lock. If we rotated the alignment of the panels in the plane of the roof 15-20deg away from being aligned downslope, we could align the panel ends with the eaves, and some aspects of the installation would be easier. I think this is very much atypical. Stipulated, if we did this, we would orient the side of the seam with the lock "downslope." Our 50-yr rainfall rates are lower than across most parts of the country, but assume that flow rates and/or debris accumulation would be sufficient to cause water to jump over the top of the seam to the adjacent panel in rare circumstances. What do the experts think? This amateur thought that so long as the lock was on the slightly downslope edge, overflow would not really be different than rain. Obviously placing the lock on the slightly upslope edge would be inviting intrusion if and when flowing water exceeded the height of the lip of the male panel. A nice Solitex vapor-permeable synthetic underlayment would be there to take up the slack, but it's probably poor form to rely on it. We don't have overhanging pines or other debris generation, but I could also imagine this being more of a concern. Does anybody have experience with this sort of installation detail? Thanks in advance.
Todd Miller
Isaiah Industries, Inc.
5/2/2016
Where are you located? Is there any way you can post a drawing or send one to me at [email protected] I am sure we can come up with some good options.
G Foyle
5/3/2016
Hi Todd, We're in SoCal. I've attached an image that illustrates the question. We would normally align the seams parallel with the downstream direction, as I've portrayed in green. But supposing I wanted to install the panels as I've portrayed in red, parallel to the eave. I will have fewer panels (since I'm cutting across a leg and not something closer to the hypotenuse of a triangle), with a reduced max panel length, and easier end details. But, the seams in red will retain flowing water on the upstream edge to a greater extent than the green. Assume the angle between red and green is ~20deg. Thanks for any advice you may have.
Todd Miller
Isaiah Industries, Inc.
5/3/2016
Thanks much. I confess ... I am confused ... and can't figure out how the roof pitches you referenced play into the drawings or why there would be a reason to run the panels anything but perpendicular to the gutter. I'm very sorry but I must be missing something (obviously). That said, in theory, what you describe would probably work but I would avoid it if at all possible.
G Foyle
5/3/2016
Todd, We're looking normal to the plane of the roof. The black arrow depicts the downslope direction, parallel to the panels portrayed in green. This would be the conventional way of installing panels - as I have them aligned in green. The panels in red are rotated with respect to the downhill direction such that water will want to collect a bit on the upstream edge of the seam of each panel. This facet happens to be a 6:12, but the pitch is mostly immaterial, save that it factors into how deep water may want to collect along a seam. Is there a reason you would avoid this other than unfamiliarity? It seemed that if the seam was aligned appropriately - such that the lock was on the "downstream" side rather than the "upstream" side of each edge, even overflowing water would just run over the female panel lock, behaving as any rain would. Thanks.
Todd Miller
Isaiah Industries, Inc.
5/3/2016
Thanks. I guess I am understanding it better now. I see that you want to do this for zoning and aesthetic reasons -- there is nothing about the structure requiring this. I feel that it will work as described. It could possibly cause the finish on the panels to erode faster than normal ... I would suggest a very high quality coating.
G Foyle
5/3/2016
It's more like, the structure is designed for zoning and aesthetic reasons to require this - to fit in under a certain max height above grade. The coating will be a Titan Cool Roof/Kynar 500. So, you agree that there doesn't seem to be a real issue with water intrusion? I would agree it seems more likely that debris could collect and this may result in wear/blockage, though we aren't overhung by significant sources of debris. Otherwise, the less balanced flow of water seems like it's not really any different than the valley flashing that already receives the same paint detail.
Todd Miller
Isaiah Industries, Inc.
5/3/2016
Thanks. Correct. I agree. Have you checked with the manufacturer (Custom Bilt?) to ensure they do not have a problem with honoring their warranty for an application like this?
G Foyle
5/3/2016
CBM says "the paint warranty would not be affected by that installation unless it causes standing water or debris to build up."

If you would like to reply to this thread, please log in. If you do not have an Ask the Experts forum user account, create one here.

Find a Contractor

Get Started Today

Take the first step to increasing the value of your home with a great looking, durable, fire resistant and energy efficient metal roof. Browse our list of qualified MRA Member Roofing Contractors in your area for a free consultation and estimate.