Roof Drip Edge Flashing Installation

For New or Re-roof Jobs
Do we really need drip edge?
Does it need to be spaced off the fascia?

Instal Drip Edge on a New Roof or Re-Roofing Job

Without functioning drip edge flashing, water leaving the roof edge wants to run down building fascias, soffits, and walls, sometimes even entering and damaging the structure.

Our illustration just above shows illustrates the end profile of roof drip edge flashing on a new roof and shows its placement on the roof.

On a new roof, the drip edge will be nailed right to the roof deck, integrated with ice and water shield or roofing underlayment, before the first shingle course goes on.

On a re-roof job, if the old shingles are torn off down to the bare roof deck, most likely you'll be getting new drip edge as well.

On a re-roof job, if new shingles are being installed as another layer, the roofer might or might not need to install drip edge, depending on the condition of and amount of projection of the existing drip edge and shingle layer.

But in general, adding a new drip edge atop the lowest edge of existing shingles is still a good practice, giving extra spacing of the drip edge vertical lip out from the fascia board, helping to assure, even further, that roof runoff falls into the roof gutters or eave troughs, not behind them.

Once the shingles are installed, you won't see much of drip edge as it's under the roof shingles, under the underlayment, and behind the roof gutter.

But you can still see the vertical edge of the drip edge and you can confirm that it is properly spaced off of the fascia board.

Watch out for these two most-common roof drip edge mistakes:

1. Omitting the drip edge entirely:
   
   water runs down the roof fascia board, not into gutters, damaging the building
2. Drip ege installed without sufficient spacing
   
   away from the fascia board - the "OVERHANG DISTANCE" shown in our sketch should be about 1/4".

Details for Drip Edge on a New Roof or Re-Roofing Job

Our photo illustrates several details of roof drip edge, eaves flashing, and gable end flashing at an asphalt-shingle re-roof job we documented in Dutchess County, New York.

From left to right our colored arrows point out the following details:

• Roof Eaves Drip Edge - Green arrow:
  
  Points to the white aluminum drip edge installed at the lower roof edge. Drip edge is also sold in brown, black and some other colours.
  
  Drip edge flashing directs roof runoff away from the roof fascia and edge and into gutters or at least not down the fascia board (if no gutters are installed) and it is recommended by roofing standards, manufacturers, and experts.
  
  Space the drip edge away from the roof fascia:
  
  I like to install the drip edge so that the inner surface of the vertical lip of the drip edge is about 1/4" proud (away from) the surface of the fascia board.
  
  Even though the outwards bend of the lower edge of the vertical lip of the drip edge is intended to send water away from the building, this added 1/4" space improves that performance, avoiding the travel of water back up under the drip edge by capillary action where it then wants to drivel down the fascia.
  
  This space also reduces the chances that an idiot installs the roof gutters on top of rather than up under the drip edge - another detail that can cause trouble.
  
  See BACKFLOWING GUTTERS for more about gutters installed on top of rather than up under the drip edge lip.
  Also
  
  see GUTTER INSTALL ERRORS for more examples of what happens if the gutter is installed over rather than behind the drip edge.
  
  Nail the drip edge 
  
  to the roof sheathing at roughly 18-24" spacing intervals using roofing nails.

• Ice & Water Shield - Orange arrow:
  
  Points to the installation of ice and water shield along the lower roof eaves - protecting against ice dam leaks that are common on unvented roofs in cold weather or snow climates.
  
  Install the ice and water shield membrane so that it laps securely over and bonds to the surface of the drip edge.
  
  The membrane does not have to extend fully to the outer edge of the drip edge flashing, but it should be on top of the upper surface of the drip edge in a best-practices roofing installation.
  
  Otherwise as we repeat just below, some water is going to run under the drip edge rather than be directed off of the roof surface.
  
  Watch out: if the roof is not using peel-and-stick eaves flashing membrane (ice and water shield), you will use roofing felt in this location. In that installation the lower edge of the felt must be on top of, not underneath the drip edge.
  
  That is, the drip edge flashing is the first item installed onto the roof sheathing (or atop old shingles in a multi-layer shingle re-roof job). If you install the drip edge on top of the felt, any condensation or water running down the roof surface between shingles and felt will run underneath the drip edge, down the fascia, and perhaps into the building soffit or walls - not a nice thing.
  
  See PEEL & STICK FLASHING MEMBRANES
  and also
  
  See ICE DAM PREVENTION on ROOFS
• Felt Underlayment - Blue arrow:
  
  Points to the first course of 15# roofing felt on this roof.
  
  The lower edge of the felt is overlapped 3-4" on top of and over the upper edge of the lower course of ice and water shield.
• Shingle Course - Brown arrow:
  
  Points to the first shingle course, doubtless installed as a reference point for this roof job.
  
  Install the starter course (normally a 3-tab shingle installed upside down or a solid asphalt strip) so that its low edge is parallel to the drip edge and extends no more than 1/4" past the drip edge itself.
  
  Watch out: Longer overlaps of asphalt shingles past the drip edge will hang over into the gutter, will send roof runoff off of the roof rather than into the gutter, and will eventually crack, break, and look gross.
  
  See OVERSHOOTING GUTTERS
  
  Just below we illustrate shingles installed with too much overhang into the gutter.

• Gable-End Drip Edge - Pink arrow:
  
  At the right of the roof along the gable end we see more drip edge being used to flash the roof gable end fascia / trim and roof edge.
  
  I prefer to install the gable drip edge under the felt though that detail is less critical than at the lower roof edge or eaves.
  
  When understanding all metal flashings on buildings it makes sense to consider the direction in which water wants to flow: normally "down" (though small up-flows occur by capillary action).
  
  It is a fundamental axiom of roof flashing and materials that all materials should be installed in a position such that any water that enters the roof or flashing system is directed back out onto the roof surface - to daylight, not into the roof layers or structure.
  
  I suspect this roofer argues that the over-felt installation reduces the chances of felt blow-off before the shingles are in place.

Shown below: roofing white drip edge on a re-roof job.