Recently, I received my 20-year anniversary pin as an ASHI Inspector. This career milestone caused me to reminisce to 1998 when I first had the misconception that I was a “House Whisperer.” Boy, I had no clue how much I would learn in the daily life of inspecting homes and writing reports. In this business, it’s not how much you know, it’s what you don’t know that can bite you!
The fact that someone knows how to build, install, service and repair does not automatically make that person a good inspector. I learned early on that there is a big “know-how” difference between being a contractor and a home inspector. I continue to see this play out, as I’ve seen licensed, experienced contractors make fools of themselves in court because, although they may have had the know-how, inspecting was out of their comfort zone.
I suspect that water penetration problems are a leading cause of call-backs for home inspectors. As home inspectors, we strive to be familiar with a number of variations of roof to wall flashing details and just as many errors and defects—more than I can begin to cover. For this article, I will focus on flat roof to wall flashings, which are commonly found in single-family homes.
Wall flashing is used to waterproof the field of the flat roof anywhere it is interrupted by a vertical surface, such as a wall or curb. Home inspectors should keep in mind that flashing components are the weak links in the roof system chain. Roof to wall flashing is the stress point in the roof system, the point at which different materials make contact with each other and transition from a waterproof system on a flat roof to a wall, which is, in many cases, a water-resistant or water-shedding system.
Both my father and grandfather were roofing contractors, so I was introduced to the roofing business at an early age, more than 40 years ago. I learned that flashing required more experience and craftsmanship than installing the field parts of the roof. I still remember my stern father and grandfather giving me constructive instructions that flashing details must be able to move with the building stresses, hold up to the forces of nature and remain watertight.
Flashing details on a flat roof consist of three basic components: the base flashing, the counter flashing and the coping (or cap) flashing. The base flashing is most commonly an extension of the membrane used on the field of the roof. The idea is that the base flashing extends the waterproof membrane vertically up the wall farther than water is likely to reach during a heavy rain under poor drainage conditions. Counter flashing covers the face of the base flashing and, more importantly, diverts the excess water over the top edge of the base flashing down to the roof. Coping (or cap) flashings are horizontal coverings for the parapet wall.
Inspectors see many roofing materials in the field. I will focus on the three most common roofing membranes in single-family homes that I have inspected during the last 20 years:
- ethylene propylene diene monomer (EPDM)—usually black and feels like a tire inner tube
- thermoplastic polyolefin (TPO)—usually white and feels like a swimming pool liner
- modified bitumen—a modified asphalt that can be smooth and black or have a granule coating that is usually white
Compatibility Of Materials
It is important to remember that roof materials must be compatible with each other and with the substrate to which the materials have been applied. Membrane roofs may have some similarities, but they are not interchangeable. For example, EPDM should not be used to flash in TPO, nor should one material be used to repair the other, and modified bitumen is not compatible with either EPDM or TPO. EPDM is known to degrade when it is in direct contact with any bituminous (or asphalt) material, including plastic roof cement. When bitumen is in contact with EPDM, the EPDM undergoes an adverse reaction that causes it to become brittle and deteriorate. Supposedly, bitumen does not degrade TPO, but there can be bonding issues between the two materials.
Inspecting The Substrate
Home inspectors should first examine the wall projecting above the roof plane, whether it’s the wall of the house, a parapet wall or a roof curb. The vertical surface should be suitable for flashing—that is, smooth, no gaps or cracks, and no missing mortar or loose bricks. Rough or irregular surfaces such as hard coat stucco are problematic. Home inspectors should think of the vertical wall as part of the roof system (although technically, it is not), and remember that any deteriorated or unsuitable vertical wall surfaces where roofing materials adjoin can compromise the waterproof roof system.
Often, on homes with hard-coat stucco or brick, the membrane flashing is just turned up on the wall, anchored and sealed, but inspectors should know that minimum detail is not technically acceptable, and should report this condition as being prone to leaking or requiring close monitoring and maintenance. Rough surfaces such as stucco, stones, textured masonry or any uneven surface is not a suitable substrate to receive flashing. Such surfaces should be prepared to provide an acceptable substrate by attaching minimum 1/2-inch plywood (some manufacturers specify 5/8-inch plywood) before adhering flashing. Under no circumstance is it a good idea to turn membrane flashing over cladding-type siding. This is never acceptable and should always be reported.
Secured Wall Flashing
Membrane roofs, including modified bitumen, EPDM and TPO, all require that the membrane flashing is adequately secured. The membrane flashing must be soundly adhered to the vertical wall and to the field roof surface without wrinkles or bridges. Minimal bridges at the intersection of the roof and walls, and parapets and curbs in EPDM and TPO, are acceptable because it’s difficult to make a 90-degree turn without some bridging. Small wrinkles are acceptable if there are no gaps or voids in the seam or lap. However, 90-degree turns are prohibited in modified bitumen, so cant strips must be installed at the intersection of the roof and all walls, parapets or curbs approaching 90 degrees that are to be flashed. Some manufacturers specify the dimensions of cant strips; 4 inches horizontal and 4 inches vertical is common (some manufacturers may specify 3 inches x 3 inches, however).
Because inspectors rarely know the manufacturer’s specifications, it is important to make sure that all corners on a modified bitumen roof have 45-degree turns and no 90-degree turns (even though 90-degree turns are acceptable on EPDM and TPO roofs). The seam at which the vertical membrane flashing meets the roof plane must lap over the field membrane a minimum of 1.5 inches on TPO, 3 inches on EPDM and 4 inches out from the cant strip on modified bitumen. The vertical seams in the membrane flashing should lap over the adjacent field membrane a minimum of 3 inches, but on granule-surfaced modified bitumen, the vertical lap must be 6 inches.
TPO and EPDM both are adhered to the substrate surfaces using a yellow bonding adhesive. This yellow color is important to remember because bonding adhesive should not be used on seams or laps. The seams or laps on an EPDM roof are adhered together with black seam adhesive or with seam tape, so if you can see yellow adhesive where the membranes adjoin, there has been an error that probably will leak.
In general, you should not be able to see the adhesive because the membrane edges on the seams or laps also should be sealed with a black edge caulk. TPO seams or laps are heat-welded together, but no additional edge caulk is required if the edges have been factory-cut. However, if it was field-cut and the polyester reinforcement is exposed, then it should be caulked. The lap-edge caulks are proprietary, compatible materials (not random caulk that could be picked up at a local building supply store) that blend in well with EPDM or TPO.
So, if you see white latex caulk on black EPDM, silicone caulk or roofing cement used with either of these roofing materials, you should report that error. Modified bitumen seams or laps are most commonly melted together with a torch, but I routinely see that self-adhering (or peel-and-stick type) materials have been used. Hot asphalt is also an option for adhering modified bitumen, but I have rarely seen it used in the last 20 years.
Critical Flashing Height
The membrane flashing on a wall should extend up the wall a minimum of 8 inches regardless of the material used. The 8 inches is measured from the top of the cant strip on modified bitumen. Curbs on a flat roof should be a minimum of 8 inches tall, the membrane should completely wrap the curb. On parapet walls, curbs on a roof-access hatch or curbs for skylights, the membrane should wrap up onto the top before the coping, roof-access hatch or skylight is installed.
The top edge of the vertical membrane flashing also must be secured. This is accomplished with capped fasteners, anchors, anchors or termination bars. The proper spacing of the fasteners range depends on the specific membrane and the height of the membrane, ranging from every 4 inches to 12 inches. Termination bars are aluminum (1 inch wide) and come in 10-foot lengths. They are designed to hold membrane tight against the wall. Termination bars should have fasteners every 6 inches.
Again, because home inspectors normally don’t know the manufacturer’s specifications, I recommend looking for fasteners along the top of the membrane and reporting if it does not appear to be adequately secured. The top of the membrane should be sealed with compatible caulk and then a counter flashing should be lapped over it. Counterflashing should extend a minimum of 4 inches below the top edge of the membrane base flashing. Inspectors should verify the 4 inches—it is commonly not what you will find—and state concerns in your report, as appropriate.
Counter Flashing And Clad-Type Siding
Counter flashings are usually metal, but they can be the wall cladding on the home. Clad-type siding (for example, vinyl, wood, aluminum, fiber cement) should always serve as counter flashing by lapping over the roof membrane flashing that is anchored and sealed to the substrate under the clad-type siding.
Home inspectors should know that clad-type sidings are not waterproof; they are more like a rainscreen that sheds the bulk water. To achieve design performance, clad-type siding must have a water-resistant barrier behind it, such as 15-pound asphalt felt or some other approved water-resistive barrier like house wrap. The water-resistant barrier and clad-type siding should come down over the top of the membrane flashing and its fasteners.
In most cases, it is nearly impossible to inspect the water-resistant barrier because it is likely to be concealed behind the clad-type siding. Home inspectors should keep in mind that there should be a drainage plane buried behind the clad-type siding that should divert any water down and out onto the roof. If not, there is potential for a leak. The clad-type siding also should have appropriate clearance above the roof surface, according to the siding manufacturer’s specifications, and although fiber cement siding manufacturers generally show a 2-inch clearance in their specifications, I personally would rather see a minimum clearance of 4 inches if the roof flashing membrane is the minimum 8 inches tall.
Masonry Wall Counter Flashing
On masonry walls, counter flashing must be designed to prevent moisture infiltration. All metal flashing should be a corrosion-resistant stiff gauge—technically, not less than 0.0019 inch or 26 gauge (some manufacturers specify a heavier 24 gauge). If you can easily bend it with your fingers, it’s probably too thin. Ideally, through-wall flashing should be used on parapet walls, but I rarely see this in my inspections.
The next most desirable detail is that the masonry wall should have a horizontal slot cut into the masonry (called a reglet) into which the metal counter flashing is inserted. This slot is usually approximately ¾ inch deep. If it is any shallower, the metal flashing usually pops out on the first hot day, due to expansion. Keep in mind that if the reglet slot is cut too deep, it opens a potential pathway for water penetration. The least desirable situation (but something I see all the time) is the metal counter flashing fastened directly to the face of the masonry. This rarely works in the long term, because the sun heats the metal, causing it to expand, and the caulking splits, opening a water infiltration point. Inspectors must closely evaluate the caulking seals and report them as appropriate. It would be prudent to recommend an annual inspection and maintenance.
Problematic Parpet Walls
Parapet walls are short walls that have three sides exposed to the weather. Home inspectors should know that flashing along a parapet wall is a problematic area that demands close evaluation. Failures in the flashing, resulting in leaks, are common due to differential movement between the roof deck and the wall.
Parapet walls must be properly coped. Coping is basically a cap on top of the wall. The coping (or cap) must be made of non-combustible, weatherproof materials. Common coping materials are sheet metal, concrete or terra cotta tiles on older buildings. The best practice is for membrane flashing to be installed under the coping because the joints in coping always end up leaking, but I rarely see that. Ideally, the coping should slant in toward the roof so stains don’t occur on the outer walls. Also, metal coping ideally should have a hemmed drip edge. Coping material must be secure, joints must overlap a minimum of 3 inches and they must be sealed watertight.
Inspectors should think of the coping as a roof for the wall, closely inspecting joints for weather-tightness or for any spots that could allow water penetration, and making sure it will withstand the force of wind. Metal coping is subject to a lot of thermal movement and it is very common to see that the joints are no longer watertight. I rarely find this on historic, attached row-type homes; instead, I commonly see old, porous bricks, and I often find that these bricks are in poor condition, which can easily compromise the waterproof roofing system.
All parapet walls should have a waterproof coping detail that prevents moisture from penetrating the wall and into the roof system. Whether you should recommend this for an old, historic home that never had the coping is a business decision, but I would recommend the improvement.
More Issues To Consider
Home inspectors should remember the many factors that could affect the performance of the flashing system such as poor design, cracking, splitting, open gaps or deterioration. You rarely will see TPO or EPDM material itself deteriorated as it usually fails at seams, laps or flashing details, but modified bitumen material will deteriorate and usually show symptoms of advanced age (such as cracking) after 12 to 15 years.
Inspectors should report cracked or open mortar joints in a masonry wall or anything that could allow water to penetrate behind flashing. Plastic roof cement is never a substitute for good flashing and if you see it smeared around, you can almost be sure that there has been a leak, so I would recommend reporting it. Never assume great-looking flashing is flawless, regardless of how good or bad the flashing appears. Always closely inspect for stains on the ceiling below and report them, even if they measure to be dry with your moisture meter.
Home inspectors also routinely encounter doors or windows that lead out to a flat roof that lack clearance for acceptable flashing. These situations demand a close evaluation for indications of leaking. It is wise to document that, due to the lack of clearance to provide the proper 8-inch flashing height above a potential high-water level, the door or window may be more prone to leaking and that monitoring is recommended. Keep a sharp eye and report wisely!
John Cranor is the founder and owner of Cranor Inspection Services, LLC, in Midlothian, VA. He is licensed through the Commonwealth of VA as a Home Inspector with a New Residential Construction endorsement. He joined ASHI in 1998 and has been a full-time home inspector for 20 years. He has served as chair of ASHI’s Technical Committee and Standards Committee. Under his leadership, the Technical Committee developed the high-profile Virtual Home Inspection on the ASHI website. As a third-generation roofing contractor, his experience in roofing spans more than 40 years. He offers litigation support and has testified in court in cases related to roofing, home inspection and construction. Cranor currently serves on the licensing board of the Commonwealth of VA Asbestos, Lead and Home Inspectors. He is the current president of the Central Virginia Chapter of ASHI and is pastpresident of the Virginia Association of Real Estate Inspectors. He assisted the Examination Board of Professional Home Inspectors to develop the National Home Inspector Examination. Cranor is an associate instructor for KC Hart & Company, providing training for those actively involved or pursuing a career in the home inspection industry. Visit his website at www.house-whisperer.com or call 804-873-8534.