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I am adding aluminum gutters to my new detached garage. I hadn't originally included them in the design, but want to add them to protect the doors and siding from splashing water, and to prevent soil runoff/erosion.

I've been observing gutters, watching YouTube, etc, but haven't found a satisfying answer to a few questions...

  1. Should the gutter slide up under the drip edge?
  2. If gutter is under drip edge, will it be low enough to prevent possible ice damage?
  3. Should the gutter hangers penetrate the drip edge?
  4. Do the penetrations for gutter hangers need to be sealed in any way?
  5. If the gutter is not installed under the drip edge, do I need some other sort of flashing?
  6. Should a spacer be installed behind the drip edge to allow air movement between gutter and fascia? (I know this is recommended for wood fascia, but is it necessary with aluminum?)

Here is the structure I have:

  • Roof pitch is 6/12
  • Aluminum drip edge overlaps fascia about 1.5"
  • Adhesive ice/water barrier installed over drip edge
  • Asphalt shingles overlap drip edge by 1/2", giving total of 1" overlap from fascia
  • 2x6 subfascia board with aluminum fascia cover
  • Total gutter run will be 22'
  • Structure is in Wisconsin, USA (cold, snowy winters), and will be insulated and (moderately) heated.

Roof edge showing overhang

Roof edge showing pitch and extension

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You want the gutters about right where the ruler is, maybe a smidge higher.

When you install your gutters you can caulk the back. However I have never done this as it is an exercise in futility. If you can caulk the back the water will go to the failure point and honestly who wants to check and caulk their gutters continuously - this may be a yearly exercise. Doable? Yes. Works? Yes. Time spent well? No.

What you want to do is after you install your gutters is pull the drip edges out. They should not be flat against the fascia like your picture. Yes you have a good install right now but when gutters are put up you need to pull them out a bit. This is especially true in colder climates that have drips and ice. With your drip edge flat you will surely get ice dams behind the gutter - yes I know very slim ones but still.

Yes I know most fascia boards are made out of wood anymore. If yours is, these dams will speed up the rotting especially after a few seasons of the paint breaking down. Even with a pvc board these ice dams do damage too because the pull the screws out of the gutter. Just pulled out a bit your gutter weight (when snow or rain hits) will cause it to droop over time.

Generally I like to see the drip edge about a 1/2" out at the bottom. You do not need spacers for these as they would have to be fastened and I don't like that idea.

For the screws, you can caulk them but this generally is a low risk area of the gutter. If your screws are tight (and given they are towards the top of gutter), there is very little risk that water pools behind them compared to the water dripping down behind the gutter from the fascia.

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If your drip edge (and the shingle protrusion) are working properly, water will fall from that outermost point. Obviously this means that the gutter shouldn't need to slip behind the drip edge flange. In fact, in cases where the run is long and the slope requires enough drop, this isn't possible anyway without additional flashing. That's not usually necessary, especially with newer construction and a 6:12 pitch.

Start at the high end of each run with the gutter just below the drip edge flange. Slope down from there. Nothing should penetrate or result in modification of the drip edge.

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  • They're definitely aluminum -- I installed them myself :). Any need to seal the gutter hanger penetrations?
    – LShaver
    Sep 1 '20 at 17:12
  • They're usually not. That's at your prerogative, really. You could use o-rings or caulk.
    – isherwood
    Sep 1 '20 at 18:01
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You should not install gutters at all unless you absolutely must. The only place they are truly needed is over a doorway where the roof would sheet water onto people entering or leaving. The erosion from the drip edges should be dealt with by thick turfgrass or gravel.

The gutters going to downspouts concentrate the roof runoff water and cause erosion where they are ejected. Many people in my locale connect the downspouts into underground drains which go directly into the street, either from emitters near the street or alley in back or even by penetrating the curb. This runoff then goes rapidly into the storm sewers and so into creeks which rise astoundingly in heavy rain. The creek near us rises 6 ft but the current is 12 mph. It feeds a larger creek which rises 20 ft to 30 ft. This causes severe erosion in the alluvial banks of these creeks.

The city discourages curb penetrations but they are common.

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  • 2
    This doesn't answer the question, and it's not really applicable to large swaths of civilization in general. Around here it's almost a necessity to keep rain out of basements where the landscape is flat and wet. We have no such street drainage from downspouts (though sump pumps are another matter).
    – isherwood
    Sep 1 '20 at 21:12
  • IMHO it is relevant in that the OP expressed concern about caulking the edge and screw supports to limit water ingress. With no gutters there is no caulking and sealing needed. But I do admit to having no experience with keeping basements dry in a wet climate.
    – Jim Stewart
    Sep 1 '20 at 23:03

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