Q: I’ve noticed that wood fascia trim at the juncture between dormer eaves and the main roof is often subject to premature decay. Is there a good way to protect this joint from water damage and rot?

A: Doug Horgan responds: This is a complex area, and implementing a workable detail is tricky when the roofers and carpenters are different crews. One way to make this area better is to use solid blocking at the rafter tails (assuming there’s an overhang) and apply ice-and-water membrane over the blocking. That at least protects the framing.

To protect this vulnerable juncture from water intrusion and rot, install solid blocking at the eaves to provide a substrate for peel-and-stick flashing, then install the flashing shingle-fashion to protect against water, ice, and snow. When installing trim, provide sufficient clearance as shown, or use a moisture-tolerant material such as PVC or Boral.
Tim Healey To protect this vulnerable juncture from water intrusion and rot, install solid blocking at the eaves to provide a substrate for peel-and-stick flashing, then install the flashing shingle-fashion to protect against water, ice, and snow. When installing trim, provide sufficient clearance as shown, or use a moisture-tolerant material such as PVC or Boral.

Protecting the fascia board itself is another story, however. One way to install the fascia is to have the board touching the roofing material, or nearly so. This looks neat and clean, but it makes it impossible to paint the end of the board, where the end-grain cut will soak up water very effectively. So our company has started generally holding wood products off the roof by a fairly substantial margin. The Western Red Cedar Lumber Association (WRCLA) follows the fiber-cement and stucco industries in recommending a 2-inch clearance from roofs for siding and trim. This is our normal standard, and it allows the end to be painted down the road.

Not all clients and architects are OK with this look, though. So we often borrow a detail from the excellent Hardie best practices manual and fill in the 2-inch space with bent flashing—or, more frequently, with a piece of synthetic trim such as PVC or Boral, as they have no clearance requirements.

Having said all that, we’ve had so many issues with wood trim of all types that we most often use synthetic trim materials these days. In that case, clearance and rot are not issues anymore. Even so, if I’m applying synthetic trim, I still prefer installing solid blocking at the eaves first. This provides a nice framed box for all the roofing and flashing to terminate to and allows a full ice-dam wrap of a vulnerable area.