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Question DetailsAsked on 1/5/2015

My exterior door is leaking under the door sill, what could be the issue? It is a new door.

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1 Answer

Voted Best Answer

It is amazing how common this is, and how few doors are designed to properly handle water hitting their outside faces - manufacturers seem to assume that all doors are fully protected by entry enclosures or porch roofs !

Six common causes, assuming door unit was not put in facing the wrong way in the first place. Most common is probably the last one:

1) deck or porch tilts toward house, and water is saturating that wood or pooling on house side of porch concrete/brick and passing through the framing into the house - either directly (especially if deck boards/joists extend into entry as is common with cantilevered landings), or water is running along the porch and deck to the house, then in at rim joist or sill. Free water would almost always be showing up at the entry subfloor level or lower if this is the case, though could wick up higher. Tough to fix if there is no physical gap between porch/deck and house, especially if framing runs under door.

2) Water is running under the wood sill (the bottom piece of wood under door - may be a 2x4 across under bottom of door frame (common in snowy or rainy country where doorsill is elevated) or may be the base piece of the threshold unit like shown here -

Long-life siliconized paintable latex caulk might solve this, though the sill should actually be set in caulk when first installed to minimize this type of infiltration, and if there is a gap between porch and doorframe, ice and water shield installed to keep water from getting to the bottom of the door.

3) Rain hitting porch/deck might be pooling or splashing up under protruding threshold and penetrating the threshold unit at the interface between different materials in the threshold - like between the wood and the aluminum walk-on plate. Caulk again, but commonly takes removal of threashold to get at it. Obviously, if water pools there, solve that by adjusting deck/porch tilt, providing drainage holes in the deck near the foundation, building up a slight sill or slope on concrete porch, etc as applicable.

4) Rain hitting door and running into the seam between the door and doorstop strip, and running down edge of door or frame to the threashold, then inside - solve with adhesive-backed foam weatherstripping on the stop strip so the door closes tightly against it. In areas with extreme blowing rain, there are overlapping lip seals for that - or put a porch roof on to protect door from frequent blowing rain events.

5) Rain getting into door window unit due to poor or non-existent seals, and draining out bottom of door onto threashold, then off interior threshold ramp into house.

6) Rain hitting threshold and running down door face is splashing/seeping under door, on top of the threshold. Solution is a tight bottom-sweep doorseal, and a rain splashguard or dripcap on the bottom outer face of door like the following link, the type I use unless a fancy appearing one is desired - easy to DIY on most doors. If this is an occasional thing, only with sporadic blowing rain, just this type drip cap without a door-bottom sweep commonly works, but while it handles the water it is not as air-tight. Be sure to caulk the interface before applying it so water cannot run down the door face behind the cap.

Answered 3 years ago by LCD


The sill pan was not flashed prior to installing the door. thats my guess. Try caulking under the sill.

Answered 3 years ago by the new window man

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