Commercial Skylight Repair

Phoenix UV and thermal cycling degrade skylight curb flashings, glazing seals, and acrylic domes faster than in any other North American market. We repair the full skylight-to-roof assembly - the leak is rarely only in the dome.

Commercial skylights on Phoenix flat roofs operate at the intersection of two of the harshest conditions in the built environment: direct UV exposure at Phoenix's average UV index of 11 in summer months - among the highest in the continental U.S. - and thermal cycling from 25°F winter nights to 175°F surface temperatures in August. Acrylic and polycarbonate dome glazing on commercial skylights in Phoenix yellows, chalks, and develops micro-fractures within ten to fifteen years under this load. Glazing seals at the curb-to-dome connection harden and crack within five to eight years. The curb flashing that integrates the skylight into the roof membrane system follows the same thermal-cycling failure pattern as every other parapet and penetration flashing in the Phoenix market.

Skylight leaks on Phoenix commercial buildings are almost never a single-point failure. When water enters at a skylight, the failure sequence typically involves a hardened glazing seal that no longer compresses against the dome gasket, a curb flashing that has delaminated from the membrane below, and in older installations, a skylight curb that has settled differentially relative to the surrounding membrane due to insulation compression. Addressing the dome seal without addressing the curb flashing produces a repeat callback within one monsoon season.

We repair the full skylight assembly - glazing seal, dome hardware, curb flashing, and membrane transition - as a single scope. We specify repair materials for Phoenix UV and thermal conditions, not standard commercial glazing sealants that are rated for moderate climates. If the acrylic dome is beyond repair - extensively yellowed, structurally compromised, or cracked through - we provide dome replacement options including high-UV-transmission polycarbonate that meets the daylight performance of the original installation.

Skylight Failure Modes in Phoenix

Acrylic dome degradation: Phoenix UV exposure accelerates acrylic oxidation - the chalk-and-yellow progression that reduces dome transmittance from 90% to 60% or lower within fifteen years. Chalked acrylic also loses impact resistance, making the dome more susceptible to puncture from haboob-entrained debris during monsoon events. A dome that was structurally sound before the 2021 haboob may have sustained micro-fractures from debris impact that are not visible until water penetrates during the next rainfall. We include dome impact assessment in every post-haboob skylight inspection.

Glazing seal and gasket failure: The sealant bead between the dome frame and the curb - and the gasket that provides compression seal at the dome-to-frame contact - is the primary water barrier at the skylight opening. Phoenix heat softens polyurethane and butyl sealants in summer and hardens them in winter, progressively converting a flexible sealant into a brittle film that cracks and separates from the dome frame under the same thermal cycling that affects all Phoenix flashing assemblies. We remove failed sealant to the substrate - not re-apply over existing sealant - and install a skylight-rated silicone sealant with ASTM C920 classification appropriate for the movement range at the dome joint.

Curb flashing delamination: The skylight curb sits inside the roof membrane system on a raised curb, with the membrane running up the curb face and terminating under the dome frame. Phoenix thermal cycling and UV exposure degrades the membrane adhesion at the curb face - the same failure mechanism that affects HVAC curb flashings throughout the Phoenix commercial inventory. Delaminated curb membrane provides a water pathway behind the dome frame that bypasses the glazing seal entirely - water enters not at the dome but at the wall of the curb below the dome frame.

Condensation and ice-damming at the curb: Phoenix winters produce occasional below-freezing conditions - the January 2023 Phoenix freeze produced ice formation on exposed metal skylights across the metro, damaging condensation seals and expanding crack patterns in aged acrylic domes. Condensate inside the dome assembly on December and January mornings is not a roof leak - it is a thermal bridging condition at the metal frame. We distinguish the two in our assessment and address each appropriately.

Skylight Repair Scope and Materials

Glazing seal replacement: Full removal of failed sealant, substrate cleaning and priming, installation of ASTM C920 silicone sealant at all dome-to-frame and frame-to-curb joints. We use silicone - not polyurethane or butyl - because silicone maintains flexibility across the full Phoenix thermal range without the brittleness failure mode that ends polyurethane's service life in the Phoenix climate. Curb-to-dome compression gaskets are replaced when they have lost their original shore-hardness rating.

Curb flashing replacement: We remove delaminated curb membrane to the substrate, clean and prime the curb face, and install new membrane flashing - compatible with the field membrane system - up the full curb height with a minimum 6-inch cap at the top before the dome frame. On single-ply systems, we heat-weld compatible membrane to the field membrane at the base of the curb. On BUR and modified bitumen systems, we flash-in compatible base and cap sheet.

Dome replacement: Where the acrylic dome is structurally compromised, extensively cracked, or transmittance-degraded beyond useful function, we coordinate dome replacement through the original manufacturer or compatible replacement product. We install replacement domes as a complete unit - dome, frame, and hardware - not field-cobbled partial replacements. Polycarbonate domes with UV-stabilized coating are the current specification for Phoenix commercial skylight replacement: better impact resistance, slower yellowing rate, and maintained transmittance at twenty-plus years in the Phoenix UV environment.

Frequently asked questions

How do we know if the skylight is the actual leak source versus the curb flashing?

We use a controlled hose test at the skylight - flood the dome first while monitoring for interior response, then test the curb flashing separately. This distinguishes dome-seal failure from curb-flashing failure because the water pathway is different for each. Dome-seal failure produces immediate interior response when the dome is flooded. Curb-flashing failure produces a response only when water is applied at the curb face below the dome frame.

My skylight dome is yellowed but not leaking. Should I replace it?

Yellowed acrylic domes transmit less visible light and more UV than the original specification - the yellowing is partly the UV-absorbing layer that protects the polycarbonate substrate, and when it goes, UV transmission increases while visible light transmission decreases. Chalked domes also have reduced impact strength. If the dome is not leaking and the building is not occupied below the skylight, a replacement timeline of three to five years is reasonable. If the dome serves an occupied space and the glazing is structurally compromised by haboob impact micro-fractures, replacement is a safety scope, not just a maintenance scope.

Can you repair a skylight leak during the monsoon window?

Yes. Skylight leak repair - glazing seal, curb flashing, or dome hardware - can be performed during the monsoon window because the scope is limited and the work duration is short enough to dry-in before afternoon storm development. We schedule skylight work for morning production during July-September and use silicone sealant products rated for installation in ambient temperatures up to 120°F.

Do you handle smoke hatches and roof access hatches in addition to skylights?

Yes. Smoke hatches, roof access hatches, and equipment access hatches have similar curb-and-frame flashing assemblies to skylights and fail by the same Phoenix thermal-cycling mechanisms. We inspect and repair hatch curb flashings, hatch frame seals, and the membrane transition at the hatch curb base as part of our general penetration repair scope.