Clear scope. Clean execution.
Parapet walls are the most exposed element of any commercial flat roof. They project above the roof membrane level, face full wind and UV exposure on three sides, and contain more flashing transitions - vertical to horizontal, inside corner, outside corner, through-wall penetrations - than any other roof component. When parapet flashing fails, the consequence is not a slow seep but often a catastrophic interior intrusion, because the water enters at the top of the wall and has the full wall height to travel before reaching the ceiling.
San Antonio commercial parapets face conditions that parapets in most other Texas cities do not: the Edwards Aquifer karst limestone substrate beneath most of the city produces differential foundation movement patterns that show up as parapet cracking, flashing stress, and cap displacement on buildings of all ages and construction types. The downtown core - along the Riverwalk corridor, near Alamo Plaza, and in the Frost Tower district along Houston Street - has masonry-clad commercial buildings from the 1960s through the 2000s where karst-related movement has been accumulating in the masonry and flashing details for decades. Repair scopes on these buildings require awareness of the structural-movement origin of many cracks - a sealant-only repair on a moving crack is a temporary measure at best.
We execute parapet flashing replacement, masonry sealant restoration, cap installation, and through-wall flashing repair on San Antonio commercial buildings. When a parapet condition has a structural-movement origin, we say so in the report and recommend the appropriate coordination with the building's structural engineer before we execute a roofing repair.
Flashing Replacement - What It Involves
Counter-flashing and cap flashing: On masonry parapets, counter-flashing is regletted into the masonry and laps over the base flashing. When reglet sealant fails or masonry cracks at the reglet, the counter-flashing separates from the wall and water enters behind it. Repair requires removing the failed counter-flashing, repairing or re-cutting the reglet, and installing new counter-flashing with compatible metal and fresh sealant. On San Antonio downtown buildings where the masonry has experienced karst-related movement, reglet repairs are often temporary unless the movement source is stabilized.
Base flashing: The base flashing is the membrane material that runs up the parapet wall from the field membrane - typically 8 to 12 inches up the wall face with a termination bar at the top. Base flashing failure at the termination bar is common on older buildings and on buildings where the parapet wall has moved relative to the deck. Repair involves stripping the base flashing back to sound membrane, cleaning the wall substrate, and installing new base flashing per the manufacturer's published detail.
Inside and outside corners: Inside corners - where two parapet walls meet - are the highest-failure locations on any commercial flat roof. Field-fabricated corners require multiple laps in the correct sequence and full adhesion of all laps to the substrate. Outside corners are less critical but still require a formed piece or strainer to prevent membrane bridging. We rebuild corners with pre-formed corner pieces when the geometry allows, or field-fabricate when the corner geometry requires custom work.
Masonry Sealant Restoration and Cap Repair
Masonry coping cap joints: The coping cap - the stone, concrete, or metal cap that covers the top of the parapet wall - has joints between cap sections. Those joints are filled with sealant that must flex with thermal movement and building movement. In San Antonio's climate, sealant in exposed coping cap joints deteriorates in 5 to 7 years under full UV and thermal cycling. Failed coping joints are a direct water entry path to the top of the parapet wall. Sealant restoration requires removing all failed sealant, cleaning and priming the joint, installing a backer rod to the correct depth, and applying a UV-stable polyurethane sealant compatible with the coping material.
Masonry crack repair: Cracks in masonry parapets fall into two categories - cosmetic shrinkage cracks in the mortar that do not compromise structural integrity or waterproofing, and structural cracks that reflect building movement or karst-induced settlement. Cosmetic cracks are cleaned and repointed with compatible mortar and sealed. Structural cracks require engineering assessment before roofing repair - the roofing scope cannot close a crack that is still moving. We identify crack type in our report and route structural-origin cracks to the appropriate engineering review.
Karst-movement context for San Antonio parapets: The Edwards Plateau limestone karst that underlies most of San Antonio produces localized subsidence patterns as dissolution voids in the limestone shift over time. These patterns appear in commercial buildings as diagonal stair-step cracks in masonry above windows and door openings, vertical cracks at re-entrant corners, and horizontal cracks at floor lines - and they also appear in parapets as diagonal cracking at wall intersections and flashing stress at locations of differential movement. We flag these patterns when we see them because a roofing repair over an actively moving crack is money spent twice.
Through-Wall Penetrations and Scuppers
Scuppers: Open scuppers through parapet walls provide overflow drainage when roof drains are blocked. Scupper flashing - the metal sleeve that lines the through-wall opening - deteriorates at the junction with the base flashing and at the exterior face of the wall. Scupper repair requires removing the failed metal sleeve, cleaning the opening, and installing a new primed and sealed metal sleeve with compatible laps to the base flashing.
Through-wall conduits and penetrations: Electrical conduits, gas lines, and other through-wall penetrations in parapet walls are sealed with expanding foam or caulk during original construction - a seal that typically fails within 5 to 10 years. Each failed through-wall penetration is a water path into the wall cavity. Repair requires removing failed sealant, installing appropriate backing material, and resealing with a compatible two-part sealant.
Frequently asked questions
Is the cracking in my parapet a roofing problem or a structural problem?
The honest answer is: it depends on the crack pattern, and you need both a roofing contractor and a structural engineer to make that determination on a building in San Antonio where karst-related movement is a possibility. We assess crack pattern as part of our parapet inspection and flag any cracks that exhibit movement signatures - width variation along the crack, diagonal stair-step pattern through masonry units rather than mortar joints only, or displacement of one face relative to the other. We will tell you directly when a crack pattern requires engineering review before roofing repair makes sense.
How long does parapet flashing typically last in San Antonio?
On a well-installed system with a compatible membrane and proper sealant, parapet base flashing should last the life of the roof membrane - 20 years or longer. Counter-flashing sealant and coping cap joint sealant requires maintenance every 5 to 7 years under San Antonio UV and thermal exposure. Buildings that receive no parapet maintenance typically show flashing failures within 8 to 12 years of installation, regardless of membrane quality.
Can parapet repairs be done while the building is occupied?
Yes. Parapet flashing work does not typically require building shutdown. We coordinate with the building's facility manager to avoid noise-sensitive operations during critical business hours. Masonry sealant work involves minor surface preparation noise. Flashing replacement requires membrane torch or hot-air welding - we coordinate with building management to confirm that existing smoke detection or sprinkler systems are not triggered by rooftop work. We have executed parapet repair on occupied medical office buildings near the South Texas Medical Center on Fredericksburg Road with full infection-control coordination.
Parapet cracks, failed flashing, or cap joint failures on your San Antonio building?
We inspect, document the condition and its likely origin, and execute a repair scope that addresses the water entry path - not just the visible symptom.
Request a Roof Scope