Metal Roof: Hook Eave

Feb 10, 2023Construction, Craftmanship

Do it Right Or Do it TWICE!

When panels are placed on a roof without a hook eave it leaves an opening that allows water and debris to slowly creep in and create rot in your plywood. The photo below shows what is called the “fish mouth” effect. This gaping can be prevented by hemming the metal 180 degrees to close the gap.

A hook eave design ensures:

  1. The end of panels are locked around a piece of metal on the eaves.
  2. Wind blown water cannot divert under the end of the panels prior to entering the gutter – ruining soffits
  3. Fish Mouth effect: A half-cylindrical or half-conical opening (resembling a fishes mouth) formes as metal barometric pressure expands and contracts metal panels. This will create an opening along the eaves, otherwise known as the “fish mouth effect”.

Fish Mouth Effect

Metal is subject (and expected) to expand and contract due to barometric pressure changes. The end of a metal panel will begin to distort when lacking adequate fastening to its substrate eave metal (via hook eave or butyl tape), panels will move and eventually maintain an opened eave, therefore mimicking a fishes mouth. This metal distortion allows ease of water entry and soffits begin to rot. The natural flow of water prior to gravitational force is to move backward, hence hook eave.


The above photo shows a proper hook eave in action, closing the gap and preventing water and debris from creeping under the panels and causing damage. A sleek and quick fix to make your roof last longer and remain healthy!

The labor process behind this design ensures accurate measuring, bending and cutting for a proper fit according to manufacturer installation requirements.

A metal roof does not have the absolute requirement of having a hook eave design, if the installer or customer should decide to forego this procedure, the next best option would be to install the panels with “butyl tape” (identified in the image below as a ‘closure strip’) which is a double sided high adhesive membrane 1” wide x 1⁄2” thich similar to a roll of bubble gum, which will adhere the bottom of each roof panel to adhering to eave metal disallowing the “fish mouth effect”.