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■ BY MARTIN HOLLADAY

emodelers who open up fiberglass – insulated walls in the middle of the winter are often surprised to see a thin layer of frost on the interior side of the wall sheathing. The frost indicates that warm, humid interior air is leaking through the wall penetrations, leading to condensation on the cold surface of the sheathing.

One way to limit this phenomenon is to keep the sheathing warm by adding a layer of rigid-foam insulation on the exterior side of the sheathing. If there are no cold sur­faces in the wall cavities, condensation is unlikely. A layer of exterior foam also makes a house more energy efficient by increasing insulating performance, reducing thermal bridging, and minimizing air leakage.

All three types of rigid-foam insulation— expanded polystyren...

It never ceases to amaze me how many builders omit seam tape from housewrap installations. Although proper lapping is enough to create a watershed, all seams must be sealed to stop air infil­tration. Taping the seams also helps to preserve the housewrap’s integrity throughout construction and makes the membrane less likely to catch the wind and tear.

Seam tape also provides a means to repair cuts, but every cut or penetration should always be treated like a horizontal or vertical seam. Seam tape is never used to make up for improper lapping. In fact, assume that the tape adhesive will fail eventually, allowing water to penetrate the drain­age plane and wet the framing. In contrast, a proper lap can last forever.

Almost every housewrap manufacturer provides a seam tape for their product...