The Rot Doctor


Subject: advice (windowsill rot)
Date: Wed, 17 Apr 2002

I received your confirmation of my order. Thank you. I have attached a photo showing my rot damage.

Window Rot

This area of my home is a dormer that was built only seven years ago. The window sills crumbled in my hands, I started removing clapboards and discovered that the contractor had installed a rubber membrane on the exterior plywood sheathing. This is the stuff normally used on roofs. I think this probably held in vapor escaping from the house and caused the decay. Do you have an opinion on this?

Gary B.


Oh boy! A fun project, huh? You ordered all the right stuff, and come on back to us any time you have a question as you work your way through the project. You can "sister" some of that damaged wood, perhaps, and if you do, be sure and treat the new wood with CPES, including any screw/bolt pilot holes.

I'll hold your picture in our files so I can reference it if you have a question.

I think you are probably right. These membranes will work, but only of there is some other means of ventilating away moisture and trapped air. It's a kind of systems-approach. In the absence of the ventilation, the membrane should not be there. Unfortunately, many contractors do not understand the conditions that promote wood rot and what they need to do to keep that from happening.

As I said, come on back if you have questions.