Image Credit: Image #1: Michael Maines
More Musings of an Energy Nerd
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:
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12 Comments
Metal pans are a problem in cold climates
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.
Response to Patrick McCombe
Patrick,
Excellent point. Thanks for your comments.
It's ironic
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.
Response to Michael Maines
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.
Response to Martin
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.
Small Points
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.
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Response to Malcolm Taylor
Malcolm,
Good points. I agree.
wrapping wrb to the interior
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.
Overhangs don't protect every door...
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.
Door sill for zero threshold door?
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.
Response to William Campbell
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.
Response to Martin
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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