Sill Pans for Exterior Doors

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Sill Pans for Exterior Doors

Flashing the rough openings of exterior doors isn’t just a good idea; it’s a code requirement

Posted on Dec 8 2017 by Martin Holladay
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Most residential builders understand that window rough openings need sill pan flashing — either a site-built sill pan made with peel-and-stick tape, or a commercial sill pan made from metal or plastic. Window manufacturers’ installation instructions began requiring sill pans about 20 years ago, and by now these details are standard at most residential construction sites.

For some reason, though, many builders are neglecting to install sill pans under exterior doors. It's time for a gentle reminder: If you skip the sill pan under an exterior door, you are risking a very expensive callback.

If your exterior doors are protected by porch roofs, you may think that sill pan flashing can be omitted. You may be right. But in the future, it’s possible that homeowners may remove the porch, exposing the door to wind-blown rain. If that happens, the subfloor under the door could rot.

In all cases, sill pan flashing is cheap insurance. Not only that: sill pan flashing under exterior doors is code-required. For more information on code requirements for sill pans, see 2012 IRC Codifies Window and Door Pan Flashings.

What happens if you skip the sill pan?

If an exterior door is exposed to wind-blown rain or splashback, the door jambs can get wet. When water dribbles down the jambs, it will find a crack between the jamb and the threshold, soaking the subfloor under the door. Eventually, you end up with a rotting subfloor and a rotting rim joist.

If you’re a remodeler, you’ve probably been called in to repair this type of rot. A surprising percentage of exterior doors are unprotected by roofs, and a surprising percentage of these unprotected doors also lack sill pan flashing.

Different types of sill pans

Many builders buy sill pans from a manufacturer. Available products include:

Other options include:

  • You can bend your own sill pan from sheet metal, using a brake.
  • You can order copper sill pans with soldered corners from a sheet-metal shop (see Image #3, below).
  • You can make site-built sill pans with peel-and-stick flashing.

Note that the use of metal sill pans is best restricted to warm climates; for more on this issue, see Comment #1 (below) from Patrick McCombe.

Features of a good sill pan

Sill pans under doors are similar to sill pans under windows. Ideally, a sill pan:

  • Is watertight, without leaks in the corners.
  • Either has a back dam on the interior side, or is sloped to the exterior. (A piece of clapboard siding under the sill pan can be used to create the slope.)
  • Has ears that run up the jambs, so that the jamb flashing can overlap the sill pan at the jambs.
  • Overlaps the water-resistive barrierSometimes also called the weather-resistive barrier, this layer of any wall assembly is the material interior to the wall cladding that forms a secondary drainage plane for liquid water that makes it past the cladding. This layer can be building paper, housewrap, or even a fluid-applied material. (WRB) below the window rough opening.

What about slab-on-grade homes?

If you are building on a slab, you may think that you don't need a sill pan (since water won't harm the concrete). Remember, though, that water can damage the finish flooring — so you still need some type of sill pan.

One approach is to ask your concrete contractor to create a recess in the slab under each exterior door (see Image #4, below). This recess acts as a sill pan. In most cases, you'll want to line the recess with a peel-and-stick membrane.

Attention to detail

Further information on installing sill pans can be found in the resources listed in the “Related Articles” sidebar above. If you decide to install a manufactured sill pan, it's important to follow the installation instructions provided by the product manufacturer.

In all cases, careful installation practices matter more than the brand of the sill pan you choose to install.

Martin Holladay’s previous blog: “Lumber from a Bandsaw Mill.”

Click here to follow Martin Holladay on Twitter.


Tags: , , ,

Image Credits:

  1. Image #1: Michael Maines
  2. Image #2 - Bauer & Son Construction - https://bscconstruction.wordpress.com
  3. Image #3: Riverside Sheet Metal - www.riversidesheetmetal.net
  4. Image #4: Building Science Corporation
  5. Image #5: NAHB Tech Notes

1.
Dec 8, 2017 10:01 AM ET

Edited Dec 8, 2017 11:29 AM ET.

Metal pans are a problem in cold climates
by Patrick McCombe

I'd avoid metal sill pans in cold climates. Builders with firsthand experience have told me that the direct line from inside to outside with a highly conductive material (metal) makes the inside of a sill pan a condensing surface. The condensate can damage finished flooring and the subfloor. The same thing happens with metal pans under windows. I think a plastic pan, which is less conductive is a better idea in cold climates.


2.
Dec 8, 2017 10:11 AM ET

Response to Patrick McCombe
by Martin Holladay

Patrick,
Excellent point. Thanks for your comments.


3.
Dec 8, 2017 1:33 PM ET

It's ironic
by Michael Maines

It's ironic that the lead photo, and the blog post "Don't let this happen to you," is my work, as I continue to struggle at my own house getting a Vycor-panned fiberglass entry door I installed last year to stop leaking. I agree with Patrick about metal pans, though they were my go-to before flexible membrane pans became available; the bulky size of the solid plastic ones can be a bit hard to deal with, depending on the installation detail.


4.
Dec 8, 2017 2:20 PM ET

Response to Michael Maines
by Martin Holladay

Michael,
Sorry to hear about your continued problems. I'm indebted to you for your 2009 GBA article on this topic (the first article listed in the "Related Articles" sidebar), but your continued problems remind us all that a belt-and-suspenders approach is probably best.

In your original article, you noted that "Overhangs should protect every door," and I couldn't agree more. The better the roof protection, the longer a rough sill will last.


5.
Dec 8, 2017 3:07 PM ET

Response to Martin
by Michael Maines

Martin, you are 100% right about the overhang. A former boss of mine said that all doors leak eventually, and he was right. I may recall you saying or writing that as well. My entry door will eventually have an overhang but it's a ways down the long to-do list. In any case, I think a brand new door should be able to withstand a light rain without weeping through the sill, but I'm certainly glad I put down a sill pan.


6.
Dec 9, 2017 6:35 PM ET

Small Points
by Malcolm Taylor

Illustration 5 has what looks like a membrane sill-pan installed after the house-wrap. The disadvantages are:

- By not lapping the wrb over the pan, the membrane relies in its adhesive to stop any water making it's way down the jambs and ending up underneath it.

- The adhesive on the membrane is stuck to the house-wrap, rather than the framing, so it ends up relying on the staples below to secure it in place.

-


7.
Dec 10, 2017 4:31 AM ET

Response to Malcolm Taylor
by Martin Holladay

Malcolm,
Good points. I agree.


8.
Dec 11, 2017 5:33 AM ET

wrapping wrb to the interior
by David Goodyear

I have seen many installations like the one pointed out in illustration 5. A couple of points: relying on mechanical fastening through adhesives works in the short term but without long term real world data I prefer not to rely 100% on adhesives. Gravity has been around for a long time! It works, so people should flash accordingly and use gravity to their advantage. planning with the motive to move water "down and out" is the key. The adhesive is really just there to make fastening simple and convenient.

I am not a huge fan of wraping the WRB to the openings for windows or doors. Depending on the position of the primary air barrier or vapor retarder or both, the fenestrations should become part of that barrier. When the flashings are applied, they too must become part of the air seal for the building to which the windows and doors are sealed. Although the WRB can protect the fenestration, it makes air sealing the windows and doors impossible.


9.
Dec 12, 2017 12:48 AM ET

Overhangs don't protect every door...
by David McNeely

A really great contractor would tell me, when I was an apprentice long ago, that the worst-case scenario for flashing and weatherproofing is a homeowner with a firehose nozzle on their hose, pointing it up against the shingles or under the door sill, trying to wash away cobwebs. He told me to build such that the house would be protected even from that.


10.
Dec 13, 2017 7:13 PM ET

Door sill for zero threshold door?
by William Campbell

I am planning an "aging in place" home and would like to have a zero threshold entry door. Are there any additional concerns for the door sill pan in this case? The detail drawings that I have seen show a small step up from the exterior to the interior. I am building in rainy Beaverton, Oregon and the entry will be covered (8' of extended roof overhead). I am planning a small slope away from the threshold.


11.
Dec 14, 2017 6:54 AM ET

Edited Dec 14, 2017 6:55 AM ET.

Response to William Campbell
by Martin Holladay

William,
Your designer or architect should be able to draw the details for you. The exact detail depends on whether this is a slab-on-grade home or a home with wood floor joists over a basement or crawl space.

Assuming that the sill pan drains to the exterior (exactly like any other sill pan), it's always possible to build a wooden ramp or an entry deck that provides a smooth entry method for wheelchairs. If there is an 8-foot-wide roof protecting the entry door (always a good idea for accessible doors), then you shouldn't need to worry much about water entry.


12.
Dec 14, 2017 9:36 AM ET

Response to Martin
by William Campbell

Martin,

The home is wood floor joist over an ICF crawlspace. I am my own designer, architect, and builder. The last house that I designed and built was thirty years ago (we are still occupying), but much has changed since then. I am determined to have every detail right, before I submit plans to the city and break ground.

Thanks for your help, GBA has been a mother lode of information since I joined!

Bill Campbell


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