building sciences Installing Windows in Housewrap Openings A B C D E F A) Install beveled wood siding in frame wall opening at sill to create slope; B) Modified “I” cut in housewrap; C) Fold housewrap in at jambs and sill; housewrap at head temporarily folded up; D) Install formable flashing at sill; E) Install sealant bead at head and jambs; install window plumb, level and square; F) Install flashing tape at jambs. Photo 5: Fully Adhered Membrane. In commercial and institutional buildings fully adhered membranes are the “gold standard.” But it took 20 years. These are now true “peel and stick” systems when primers are used. Photo 6: Liquid Applied Membrane. Becoming common now. Note the joint treatment tape reinforced mastic is installed at the joints first – then over coated with a liquid applied membrane creating a seamless, jointless system. about water that enters through fasteners wandering around between the two layers. But we had to learn a great deal about how to get the membranes to “stick.” We found we had to “prime” concrete and masonry block surfaces to get things to stick. And when we had “reverse laps,” we had figure out a way to “terminate” the lap; otherwise it would “fishmouth” and begin to peel away. In the early years it was so bad we used to call “peel and stick” membranes “stick and peels.” When these products were first introduced in commercial buildings, they had horrible reputations. Now they 58 ASHRAE Journal are the gold standard. But it took almost 20 years and major advances in adhesive technology. This “terminate” the “reverse lap” thing is a big deal. There are a couple of ways we have learned to do this. In commercial buildings we often use “pressure bars” or a continuous bead of sealant to glue the top edge of the reverse lap to the underlying membrane or sheathing (Photo 7). A pressure bar is just what it sounds like: a strip of metal with a gasket attached to it that is mechanically fastened though the layers to the structure, compressing a gasket to seal the reverse ashrae.org Photo 7: Termination. This “terminate” the reverse lap thing is a big deal. A continuous bead of sealant is used to glue the top edge of the reverse lap to the underlying membrane or sheathing. February 2013