Journal of Light Construction - March 2000

WRAPPING THE HOUSE: Do's & Don'ts (continued)

Round windows. Half-round and full-circle windows are tricky to flash, because there's no practical way to lay the wrap on top of the flange, and metal flashings don't conform to the radius. Photo L shows an attempt to deal with the problem by taping the flange to the wrap. Unfortunately, the roof flashing at the bottom was installed on top of the bottom flange - again reverse layering. Some attempt was made to get it right by slicing the wrap at each side of the window and bringing it out on top of the metal flashing.

I would prefer to see Ice & Water Shield used around radius windows rather than tape.
 

Roof Flashings

The layering problem with the roof flashing shown in photos L and M is all too common. It's rare for a roofer to take the time to lift the housewrap or building paper and tuck the upper leg of the flashing underneath. Water runs down the housewrap, behind the flashing, and shows up as a roof leak.

These simple shed roofs are easy to get right. Either hold the paper up until flashing is installed, or slit and tuck in a strip of tarpaper after the flashing goes in.

Trickier are the step-flashed areas where roofs meet walls. Photo N shows a fancy metal roof with lousy flashing details. Not only is the roof counterflashing on top of the housewrap, but it also delivers water right onto the deck rim joist below (as does the deck membrane above). Once the wood trim board gets installed over that deck rim joist, it's only a matter of time before rot sets in.

In photo O, the counterflashing on the upper roof was carefully tucked under the lifted housewrap, while - alas - the flashing on the lower pent roof is right on top of the wrap. Photo P shows a classic case of step flashing confusion. The wrap was lifted out of the way to allow the step flashing to slip behind - so far so good. But once the wrap is laid back down, any water that runs down along that step flashing will track right down behind the wrap onto the wall sheathing below.
 

 
A situation like this should ideally be handled with a properly detailed kickout flashing, installed before the eaves trim and roof shingles. If you don't use a kickout, make sure that the housewrap is on top of the upper leg of the step flashing, but that the bottom piece of step flashing directs the water out on top of the housewrap below (and preferably, out on top of the siding). This requires careful slitting and weaving of the wrap and the metal, with Ice & Water Shield patches where necessary. In areas of severe wetting, an additional layer of tarpaper on the lower wall is a good idea.

Deck Details

If you're not careful, deck ledgers can provide a direct path for water to enter the structure. Often - around here at least - the framing crew installs the deck ledger before the house is wrapped. In many cases, the band joist never gets sheathed at this point. The housewrap gets installed, but terminates just above the ledger. Unless the top of the ledger is properly flashed - which is not always the case - any water running down the wall gets channeled into the framing, leading to long-term saturation and rot.

Our framers always bring the sheathing down over the band joist, then install aluminum coil stock to separate the deck ledger from the house. We flash the top of the ledger, making sure this flashing is behind the housewrap.

Photo Q shows a sloppy wrapping job that leaves the band joist exposed. Because the deck is already in place, there's no practical way to flash the area. In photo R, the ledger flashing extends nicely up the wall, but is laid on top of the housewrap.

Attached rails. Its always a good idea to separate railing elements from the house walls when possible, to avoid pathways for water to enter the framing. Photo S shows what looks to be a nice detail: The railing is separated from the house wall, and the wrap passes behind. The only problem is that the eventual finish on this house was EIFS, meaning the wood railing post was buried under 1-1/2 inches of foam board.

Whenever we have to attach a post to a house wall, we separate the post from the sheathing with aluminum flashing. We bring the top of flashing 6 inches above the deck rail, and make sure it tucks behind the housewrap. Our preferred method is to install the siding first, and leave a gap of a few inches (code allows up to 4 inches) between the post and the house.

Stupid details. Some details defy common sense, and are best left to your competition (photo T). Rule of thumb: If you can't figure out how to flash it, don't build it.

Patricia McDaniel runs Boardwalk Builders in Rehoboth Beach, Delaware.

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