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Community and Q&A

Detailing for Water Management at Sink

roryes | Posted in Interior Design on

I am looking for a detail for the kitchen counter extending onto interior window sill.

We are starting construction drawings for our house, and the design calls for the kitchen counter (e.g. behind the sink) to extend, at the same surface height, to the window frame.

Is water management a significant risk here — either for mold to grow on the caulking, or for water intrusion to the structure?  If so, are there recommended construction details or best practices?  (My family tends towards the “splashier” side when using a sink, and the lazier side for prompt cleaning.)

Additional details:
The counter will be quartz, the windows will be flangeless triple pane windows (one tilt-and-turn and one fixed), and the exterior wall will be 2×6 with 3″ of continuous insulation outside of the sheathing.  The windows will be somewhere between “outie” and “in-betweenie” windows; i.e. about 3-5″ of window sill between the interior wall and the window frame.  We can tolerate a visible seam in the quartz countertop at the transition to the sill.


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  1. Expert Member
    Michael Maines | | #1

    I avoid that detail when possible, but I happen to be working on section drawings for a project right now that have the countertop-as-window stool. I would leave space for a good-quality, flexible sealant between the counter and window, as they will expand and contract at different rates. Ideally, use a backer rod and the sealant should be no more than half as deep as it is wide--i.e., a 3/16" gap with 3/32" deep sealant.

    Beyond that, use a window sill pan with backdam and/or a slope, so if the window were to leak it wouldn't run back under the countertop. There should be a gap between the countertop and rough sill; fill that with insulation so you don't have a cold spot.

    It's surprisingly hard to get the windows placed at exactly the right height. I like to make the rough opening a little oversized when using this kind of detail and take extra care to get the windows at exactly the right height. European-style flangeless windows are usually a bit more forgiving; North American-style windows usually have a specific place for the stool to meet so there is no room for error.

    1. DC_Contrarian_ | | #3

      That's a good point about window heights not working out exactly. The same is true of cabinet heights and counter thickness. When it comes to interior trim my motto is "it's better not to try than to try and fail."

      I would think about putting the window sill an inch higher than the counter top and having a transition so it looks deliberate. That way if you're off by a half inch either way it still works.

      1. Expert Member
        Michael Maines | | #5

        I've had carpenters follow that approach, but to my eye it's a lot nicer when the countertop extending to the window frame is clean and clear.

  2. roryes | | #2

    Thank you Michael- it is very helpful to know what to watch out for with this installation!

    1. Expert Member
      Michael Maines | | #4

      You're welcome--from my long list of lessons learned the hard way!

  3. onslow | | #6


    My spouse is half circus seal and splashes water around similarly. I deeply regret not ordering the counter top to have a recessed/lowered surface cut into the top where the faucets mount. Even a 3/16"" drop from the main counter surface would reduce the flooding to the backsplash. My counter is ever so slightly tipped to the back despite rigorous cabinet leveling. We quietly (mostly) argue about why it matters if the water flies everywhere.

    A simpler to execute alternative would be a u-shaped groove looping from the back of sink cut-out edge around behind the faucet, spray head, soap dispenser or whatever elements you have and back to the other side of the sink. Look to your cutting boards with juice gutters for guidance and imagine one cut in half. The juice/water will collect and run back to the sink. A round nose router bit would make short work of the task and be easy to sand back to finish standards. A 3/4" bit dropping in 1/4 + should at least keep the pooling from racing toward the window.

    I had also promoted the idea of grooves to the left of the sink for built in drainage under a dish rack. The fabricator didn't like the idea of any significant thinning of the soapstone. Pitching the grooves enough to drain over a 24" run would have left the thin parts about 3/4". I imagine it would create a stress point that might not survive installation. The round bit would also create a long tapering groove which would look odd if the spacing was off by even a little bit.

    I would have done the grooved half loop, but the distance from sink edge to splash board isn't enough to look like a feature and not a mistake. If you are going with the omnipresent farm sink you can nudge the sink out a bit more to gain room behind the back edge.

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