Two bids land on the same low-slope roof, one PVC and one TPO, and the totals look close enough that the choice feels arbitrary. It is not. Kitchen grease, chemical exhaust, weld quality, Title 24 listing, and whether the deck actually drains decide it. We will not print a winner-for-everyone or a per-square-foot table.
Top Pro Roofing SD is a referral service. We do not install, we do not hold a C-39, and we do not register manufacturer warranties. Call (760) 750-5557. Ask the matched commercial or low-slope roofer to walk this deck before they pick a sheet.
Other systems on the same buildings: TPO vs modified bitumen, EPDM. Service pages: flat and low-slope, commercial roofing.
What actually separates the sheets
Both are white single-ply thermoplastics over insulation on a flat or near-flat deck. Both are joined with hot-air welds, not seam tape. That is why they look identical from the lot.
PVC is polyvinyl chloride with plasticizers that keep the sheet flexible and help it resist oils. Those plasticizers can leave the sheet over a long service life. TPO is a polypropylene-based polyolefin with no plasticizer package. That chemistry split drives grease resistance, chemical tables, and how fussy the weld window is.
Neither always wins. A roofer who says one product is always better is selling a pallet.
Grease, chemicals, and what vents onto the roof
This question settles most San Diego choices, and it is the one property managers skip.
| Exposure | Usual direction | Local examples | What to put in writing |
|---|---|---|---|
| Commercial kitchen exhaust | PVC is the common spec | Gaslamp, Convoy, Chula Vista and Escondido strip centers, inherited fryer curbs | Manufacturer chemical table for grease; who owns hood-grease cleaning |
| Solvents, plating, lab, hydraulic leaks | Ask the chemical table, do not guess | Kearny Mesa, Miramar, Otay Mesa | Named substances vs the PDF, not a verbal “it’ll be fine” |
| Sun, HVAC foot traffic, rain only | TPO is often enough | Offices, warehouses, churches, medical, apartments | Thickness, attachment, and drainage, not a grease story you do not have |
A prior tenant’s rooftop fryer still counts. Roof-mounted equipment that weeps hydraulic fluid is a local PVC or protection-pad conversation even on an office building.
If the exposure is unusual, the manufacturer’s technical department settles it. A salesperson’s memory does not.
Seams, weld window, and slope
The seams are the roof. A good weld is stronger than the sheet. A bad weld is the first leak.
PVC and TPO weld at different temperatures and speeds. TPO formulas have changed over the years, so last decade’s machine settings do not transfer. Ask how long this crew has run this membrane, and how they test seams (hook probe after cool-down; air lance or consultant sampling on larger decks).
Details fail before field rolls: pipes, curbs, drain flanges, scuppers, inside and outside corners. Photograph every penetration at close-out.
Minimum slope is a spec question, not a blog number. Many single-ply warranties exclude ponding. Ask the AHJ and the manufacturer what positive drainage they expect on this deck. Existing San Diego bungalow and 1970s commercial decks may not drain as a new deck would. Tapered insulation or crickets are how you buy slope. A PVC vs TPO argument on a ponding deck is the wrong argument. Read ponding water first, then pick a membrane.
Ask the bid to name: design slope, whether they will correct it, and whether the warranty PDF allows standing water.
Coastal UV, heat, and Title 24
San Diego low-slope roofs take high UV with mild winters. That is easy on freeze-thaw and hard on polymers. We will not publish a lifespan for either sheet. Thickness (often quoted as 45, 60, or 80 mil) is the lever you can actually specify: more polymer above the scrim.
The California Energy Commission publishes the current Title 24 energy standards. Look up the CEC climate zone for this address. Confirm with the AHJ whether a listed cool-roof product applies to this low-slope replacement. Do not treat Title 24 as a countywide default. Compliance, when it applies, uses aged reflectance and emittance, or SRI, not the shiny-new brochure. The Cool Roof Rating Council tests new and weathered values. White PVC and white TPO products are commonly listed. The SKU on the bid has to be the listed one. Primer: cool roof Title 24.
Coastal salt (Mission Beach, Imperial Beach, Ocean Beach, La Jolla) is harder on edge metal and fasteners than on the white field. Name the metals. The membrane brand does not save painted steel.
What drives the price gap (without fake dollars)
PVC sheet usually costs more than TPO at the same mil thickness. We will not put a San Diego per-foot number on either. Compare bids only when they describe the same job:
- Mil thickness
- Mechanically fastened vs fully adhered vs ballasted
- Tear-off vs recover (layer count and wet insulation)
- Insulation type, R-value, tapered packages
- Penetration count and parapet length
- Access, crane, and after-hours work
- Material-only vs manufacturer system warranty (read exclusions, especially ponding)
Tear-off PVC against overlay TPO is not a membrane comparison. Warranty PDFs beat slogans.
Occupied buildings
Both systems weld with hot air, not roofing torches, which is why single-ply shows up over restaurants and medical. Fully adhered assemblies can push adhesive odor into rooftop intakes. Mechanically fastened assemblies mostly avoid that. Raise it before you pick attachment, not after the dining room complains.
Get sequence in writing: tear-off sections, rain plan, hoist location, parking, HVAC lifts, and noisy fastening hours. San Diego’s long dry season is an advantage. It is not a reason to open a large roof in a February storm track.
When to call
Choosing PVC vs TPO needs a licensed low-slope roofer on the roof counting exhaust, drains, and wet insulation. Verify CSLB. For flat roof work or commercial roofing, call (760) 750-5557. We connect you with a local C-39. You still check the license.