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I cut the jamb pieces about 3 inches longer than the height of the door frame, and cut the head piece about 10 inches longer than its width. Since the aggressive adhesive backing is tricky to work with, I begin by scoring the release paper into thirds, lengthwise. As with the sill pan, I'm careful to cut only the paper, not the membrane. After scoring, I fold the membrane material back on itself and crease all the score lines to make sure the release paper is cut all the way through.

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I lay the door frame facedown on sawhorses, and because I'm working from the back of the door, I install the head flange before the jamb flanges to avoid creating a reverse lap when the door is upright. I fold one-third of the flange back on itself, remove the release paper from the middle third of the flange, position the piece at the door head, and press it onto the back of the head casing. Then I remove the release paper from the folded-back portion of the flange, fold this outer third up against the door-frame head, and stick it in place.

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With the J-roller, I press the head-flange adhesive tight against the frame and casing, then slice the flange material at the jambs and fold it down on the jamb casing. With the head flange in place, I install the jamb flanges in the same manner, and at the door head, slice the material and apply it to the back of the head flange.

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Counter Flanges Are the Final Step

I now install the door frame. First, I run a bead of elastomeric latex caulk along the interior edge of the threshold. (Caulk along the exterior edge of the threshold could trap moisture instead of allowing it to drain out.) I peel off the remaining release paper from the jamb flanges, peel back enough release paper on the head flange to expose the jamb portion, and then apply a StraightFlash counter flange over the jamb flanges.

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I've got to stay on my toes when applying the counter flanges — I'm joining two adhesive faces of the membrane, and once they touch, they're stuck together for good. To make sure the counter flanges are positioned correctly, I remove a portion of the release paper from the top of the jamb counter flange and adhere that much to the head flange. Then I pull the jamb counter flange taut and slightly away from the wall, and work my way down the counter flange, pulling the release paper off in stages as I stick the upper portion to the flange.

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After the jamb counter flanges are in place, I peel off the remaining release paper from the head flange and install a drip cap — which I make from painted aluminum coil stock or bendable vinyl — directly on the adhesive of the head flange. Then I remove the release paper from the counter head flange and install it over the vertical leg of the drip cap, with the upper portion adhering directly to the wood sheathing. I roll all the counter flanges tight to the wall to ensure a good bond to the housewrap and sheathing.

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I fold the housewrap head-flap down over the door-head counter flange, skip-tape the flap in place (35), and tape the diagonal housewrap cut. The small gaps created by skip-taping allow any moisture that works its way behind the housewrap to drain off the drip cap. I also tape all horizontal seams in the housewrap.

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Interior Threshold Trim Detail

On the interior of the threshold, I fold and tape the exposed portion of the sill pan against the interior edge of the threshold (38). This lip serves as a dam, preventing outside moisture from working its way under the sill and into the house. I run the finish flooring tight to the threshold and use a utility knife to cut back any portion of the sill pan still exposed. The result is a very clean flooring detail that requires no trim.

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After the siding is installed, I sometimes apply a 1 1/2-inch strip of membrane material to the underside of the sill and to the face of the siding. This added flange prevents wind-driven moisture from blowing beneath the sill, while still allowing the sill pan to drain out over the housewrap.

Carl Hagstromis a builder in Montrose, Pa., a JLC contributing editor, and a speaker at JLC Live.