Underlay Support Tray: A Drainage Check, Not a Pitch Fix
An underlay support tray can help prevent an unsupported membrane from sagging and direct drainage into a gutter. It does not replace checking the named membrane, roof detail, and current installation instructions.
Pitch measures geometry; the tray addresses a detail
Use the roof pitch calculator to record rise and horizontal run. That describes the roof plane. A support tray concerns what happens at the underlay edge and between rafters, so it needs its own product and installation check.
What the named source says
Klober's membrane support page says that unsupported membranes can sag between rafters and cause water to pond at the bottom. It says an underlay support tray can prevent this and provide drainage from the underlay into the gutter. The same page says modern underlays are UV stable for up to four months and therefore should not be exposed.
These statements are from one manufacturer's support page. Do not treat the stated UV duration or drainage detail as a universal limit for every membrane, tray, roof covering, or region.
Do I need a support tray because the roof has a low pitch?
Not confirmed from pitch alone. Pitch is one measurement; the decision also depends on the named underlay, support detail, drainage route, roof construction, and current instructions.
Sources and scope
- Klober Technical Support — Membranes — the support-tray, sagging, drainage, and stated UV-exposure information used on this page.
This page is a reading aid for named manufacturer information. It is not a roof design, code interpretation, or project approval.