An old asphalt roof with a surface gone gray and alligatored, a few blisters in the field, and a budget that does not stretch to a full tear-off raises a question that most single-ply membranes cannot answer without help: what can go over this asphalt without being damaged by it? A KEE membrane, one of the PVC-alloy sheets, is formulated for just that kind of situation, and it is a name that deserves more explanation than it usually gets.
In West Jordan, UT, where a roof is covered with snow for stretches of the cold season and then dries in the warm months, a membrane that tolerates contact with older roofing materials and with oils can save an owner from a full tear-off. We install and repair KEE membranes and tell owners when another sheet is the better fit.
What the alloy changes
KEE stands for ketone ethylene ester, a polymer blended into a PVC sheet in place of much of the liquid plasticizer that ordinary PVC relies on. The practical result is a sheet that holds its flexibility longer because its softening agent does not migrate out as easily. That also lets the membrane sit against asphalt, coal-tar residues and some insulations that would attack a standard PVC sheet.
The membrane is still a thermoplastic. Its seams are welded with hot air and fused into one piece, it is reinforced with a polyester or fiberglass scrim, and it arrives in rolls that are rolled out, welded and flashed in the same way as other single-plies. Manufacturers formulate their KEE products differently, so we follow the specific instructions for the sheet in the specification instead of assuming one set of rules for all of them.
Recovering over old asphalt roofs
The most common reason to pick KEE is a recover over an aged built-up or modified bitumen roof. The old roof stays in place, a cover board or separation layer is added where the manufacturer requires it, and the new sheet is laid on top. That avoids the tear-off cost, the noise and the dust, and it keeps the old roof as extra insulation and a second waterproof layer.
A recover only works if the old roof is dry. We scan the surface with an infrared moisture survey and cut core samples to find wet insulation, and anything soaked comes out before the new sheet goes down. Blisters and ridges are flattened or removed, and low areas are filled so water drains. Our recover and overlay work follows that sequence, and the old roof is judged on moisture and condition, not on how it looks from the parking lot.
Chemicals, grease and heat
KEE is chosen for roofs where oils, fats or chemical vapors would shorten the life of other membranes. Restaurant exhaust, food processing, laboratories and industrial buildings are typical places. The sheet resists many of the compounds that soften EPDM and some TPO formulations, and it tolerates the hot exhaust that blows across rooftops near vents.
Heat matters here too. The annual temperature cycle at Salt Lake City International Airport, as recorded in NOAA normals, runs from freezing in the cold season to warm summers. A KEE sheet that stays supple through that swing is less likely to shrink away from walls, though we still check flashing terminations at every inspection. A roof exposed to exhaust, in particular, gets a regular cleaning route, with a look at the drains after each cleaning because loosened grease and dirt travel to the low point and settle there.
Welds, cold air and the installation window
Welding KEE requires the same discipline as PVC: a clean, dry sheet, correct temperature and speed, and a probe test along every seam. Cold, damp or windy conditions all make a weld less reliable, and the Salt Lake Valley's winter freezing and snow limit how much membrane can be installed in the cold months. We schedule full installations for drier weather and use the winter for planning, moisture scans and repairs that can be protected.
The thickness and stiffness of KEE call for careful handling around details. Corners, penetrations and wall transitions use pre-formed pieces and PVC-coated metal, welded into the field sheet. A flashing that is formed too tightly will fight the membrane, so we relax the sheet and check each termination. Because the sheet is heavier than some single-plies, the crew also stages rolls carefully to keep them from creasing, and a roll is never dragged across a rough surface or a sharp edge, since a scuff made before the weld becomes a thin spot the weld cannot repair.
Repairing a KEE roof
KEE repairs are welded patches on clean membrane. The surface must be free of dirt and oil, and the patch needs rounded corners and enough overlap to carry stress. On a roof that has been in service for many seasons, a mild cleaner takes off the film that keeps a weld from bonding. We probe the edge of each patch and mark it for another look after the next thaw.
Damage from punctures, foot traffic and dropped tools is common near equipment, so a membrane puncture repair often comes with protective walk pads. When a roof shows repeated failures in one area, we look for the cause below the sheet, such as wet insulation, a sagging deck or a drain that sits high. A patch cannot fix any of those.
Where KEE gets specified in the valley
South Salt Lake names retail, manufacturing, warehouse and distribution businesses among its local sectors, and West Valley City's general plan retains office and industrial zones for commercial development and highlights commercial transportation as an established local activity. Whether a building in those sectors carries an older asphalt roof is a question for the roof walk, and where it does, a recover membrane is compared against a full replacement. West Jordan's own plan, which supports regional commercial, service, office and mixed-use development, sets a similar range of building types.
For owners in South Salt Lake, West Valley City or West Jordan, we compare KEE with PVC and multi-ply asphalt options for the specific roof and building use, and we say plainly when a simpler sheet is enough.
A simpler sheet is often enough, and we say so when the walk shows it.
Commercial Roofing Questions
What is the difference between KEE and standard PVC?
KEE replaces much of the liquid plasticizer with a polymer that stays in the sheet, so the membrane keeps its flexibility longer and tolerates contact with asphalt. Standard PVC needs a separation layer from asphalt.
Can KEE go directly over an old built-up roof?
Often it can, with a cover board or separation layer where the manufacturer requires one, as long as the old roof is dry and flat enough. We confirm that with a scan and core samples first.
Is KEE a good choice for a restaurant roof?
It is one of the sheets chosen for exhaust and grease. We compare it with PVC on the actual equipment and the roof layout.
How does a KEE membrane fail?
Usually at details: a flashing that pulled away, a weld that was rushed, or a puncture near equipment. Age shows as stiffness and shrinkage, though the sheet is formulated to resist both.
Does a recover change the roof's weight?
Yes, it adds a new layer on top of the old, so the deck and structure must carry the extra load. The structure's capacity is checked before a recover is chosen.
Ask about the old roof underneath
Tell us what is on the roof now, what vents onto it and where water has appeared. We will schedule a roof walk, scan for moisture and confirm whether a recover is possible before any price is set.