An important step in the roof inspection process during a home inspection or four point inspection is to check all roof penetrations and inspect the condition and installation of its flashing materials. The most common flashing material for this application is often referred to as a plumbing boot since every home will have at least one plumbing vent on the roof. Unfortunately this Tallahassee based Home Inspector sees more defects on plumbing boots than one should.
The purpose of plumbing boots
In a perfect world, a roof would have no penetrations and have an uninterrupted 100% watertight covering. That’s just not realistic and there are systems that need to penetrate the roof to perform their intended purpose. The most common system is the plumbing, where the stack pipes allow for proper venting of your drain waste vent system, keeping the toxic sewer gas out of your home. We also see the use of plumbing boots around the exhaust stacks for radon mitigation exhaust vents, and the electrical mast if there is an overhead drop. Each stack pipe literally represents a hole in your roof. The plumbing boot is what helps seal this hole and still allows for the pipe to come up through the roof to function as intended. Oftentimes the plumbing boot was either installed incorrectly or has been damaged by either the elements or animals. For a long time the most common material these boots were made out of was lead and they worked well and held up well to the environment. The downfall for lead plumbing boots is that squirrels loved chewing on them and can quickly eat away all the exposed boot. While some damage to the plumbing boot may appear small, like a tear in the rubber gasket, causing one’s first thought to be, “how much water could really get in there?”, a continual leak for years can add up to quite a bit and cause areas of the roof deck to rot away. Since wood is a naturally absorbent material, it will wick water away from the source causing the damage to spread over a larger area as time and repeated wetting occurs. A lot of the time these leaks aren’t seen inside the home on the ceiling because the small amount of water is caught in the insulation, but during extreme weather events staining or wet areas occur. Unwanted moisture intrusion into the attic is never a good thing
Best practices for plumbing boot installation
The new style of plumbing boots (non-lead) should be installed properly so that they can perform their intended function. All too often roofers install them in a manner that causes the rubber collar to be stretched which can cause the base of the boot to lift. This can also speed up dry rot in the rubber causing premature failure or tears. Another commonly seen defect is where the roofer pushes the rubber collar too far down and now has created a concaved surface that will hold water. The base should be sealed to the shingles below with roofing mastic or cement. If a mechanical fastener is used it should be sealed as well. Only the lower half of the base flashing should be exposed.
Every time the roof is replaced, the plumbing boots should be replaced too. A common short cut by a low quality roofer is to re-use the old plumbing boot vents and this almost all leads to a leak well before the end of the expected life for the roof covering. A common handyman or homeowner fix is to just apply roofing mastic or “tar” around the damaged areas. While this may visually cover the damage and stop the leak this should be viewed as a temporary repair, because the with time and exposure the sealant will cracked or lose its seal between the materials. A much better solution would be to use a product like Perma-boot to properly repair it.