Mechanically Fastened vs Fully Adhered TPO — Homeowner Checklist
How a TPO roof compares in Universal City once service life is counted, rather than on day one.
This comes down to a choice between two things that look similar on a quote and behave very differently on a roof. The difference rarely shows on the day the work is finished; it shows around year eight, which is why it is worth understanding before signing rather than after.
What actually matters
White single-ply membrane covers most of the commercial stock in this city, and for good reason: it is the most effective cool roof widely available, and on a large warehouse the cooling saving alone can justify the specification. Reflectivity does fall as the surface weathers and collects the grit that hangs in the basin air, but even a dirty white roof runs far cooler than a dark one.
The difference that shows up later
Thickness is the specification decision that matters. Sixty mil is the sensible minimum for any roof with service traffic; eighty is worth the difference where there is substantial rooftop plant. The seams are heat welded, and a weld is either sound along its whole length or it is not — which is why a proper inspection probes them rather than looking at them. Mechanically fastened systems go down faster and cost less; fully adhered systems perform better under wind uplift at the perimeter.
How Los Angeles settles it
Almost every commercial building here carries rooftop HVAC, and the majority of TPO failures attended were caused by another trade rather than by weather. A technician dragging a condenser across an eighty mil membrane will open it, and nobody reports it. Walkway pads to every unit pay for themselves the first time they prevent a puncture over an occupied space.
What we look at on an inspection
- Weld integrity at every lap, probe-tested along the full length
- Punctures and abrasion around HVAC and service routes
- Boot and flashing condition at penetrations
- Ponding persisting beyond forty-eight hours
- Drain clearance and sump condition
- Perimeter termination and edge metal
- Insulation moisture, particularly under any previous patch
Common questions
Which is better?
Neither, in the abstract. One suits roofs that drain imperfectly and one does not, and which roof you have decides it.
Can I change my mind later?
Partly. Some systems can be recoated or overlaid; others commit you to a tear-off next time. Worth asking before rather than after.
The honest summary
Laying new membrane over wet insulation guarantees failure and is the most expensive mistake available on a commercial roof. Moisture readings come first; if the insulation is saturated, that is a replacement rather than an overlay, and any contractor who says otherwise is selling the cheaper job.
Free inspection, drone photography where access is difficult, and a written estimate with deck repair priced per sheet. No obligation.