I want to talk a little about chimney flashings. I find many poor chimney flashing details while performing home inspections in New Jersey. Proper chimney flashing details are very important because where the chimney comes through the roof is a very vulnerable area to water infiltration. Even if the chimney is located on the side of the home, proper flashing details are necessary in order to keep the water out. What I see on home inspections is metal flashings that are sealed with roofing cement only. Roofing cement or silicons will get brittle after a couple of freeze and thaw cycles and will allow water into the attic space. There are several very important flashing details, some or all are usually missing. There should be a step flashing which is installed between each layer of shingles and then is covered with a counter flashing. The step flashings should extend roughly three inches under the shingles and the counter flashing should be let (cut) into the mortar joints roughly one inch. I never see this this type of detail. During most home inspections I see caulk, or tar or silicone at this vital connection. To finish out the chimney flashing details there should be a head flashing at the high side of the chimney and an apron flashing at the low side of the chimney. The head flashing should be at least six inches high because this is were the water is going to end up first and be hopefully diverted around the left and right sides of the chimney. I usually recommend the installation of a cricket at the back of the chimney in order to help divert water around it, and tohelp keep ice and snow from building up at the back of the chimney. Chimneys and chimney flashing are often neglected but we will be looking hard for chimney and flashing defects on your home inspection.
John Martino is an independent New Jersey home inspector and member of the Americal Society of home inspectors.