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Community and Q&A

Advice on Air Sealing Mud Sill

scottwoodward | Posted in Energy Efficiency and Durability on

It’s finally happening – framing starts this coming Tuesday. Thanks to those who have offered valuable input in past threads. Now the rubber meets the road. For reference, I’m in climate zone 6 (New Hampshire), building a 24′ x 32′ two-car garage with apartment above. My goal is Code+. I currently have 2 inch Blue Board perimeter insulation around the foundation and will also be installing Roxul Comfortboard as exterior insulation in conjunction with batt insulation in the walls. I also intend to install my windows in “innie” configuration when the time comes.

I want to make sure I do a good job air sealing the mud sill when we start the first level framing. My questions are:

1.) Is it best practice to overlap the corners on the sill seal?
2.) Should I apply a sealant under the sill seal, such as DAP Dynaflex 230?
3.) Once the sill plate is in place (flush with the outside foundation wall?), should I place a bead of sealant like Dynaflex 230 on the interior side of the sill plate to air seal that joint?
4.) I’m using 7/16th’s ZIP sheathing and planning to overlap the sheathing 1/2 inch below the bottom of the sill plate/top of the foundation wall (have read varying opinions about whether to overlap or not). Is the overlap the best practice these days?
5.) Does the flashing on the exterior side go under the ZIP sheathing or on top? What are the recommendations between tape or liquid flashing?

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