Torch Down vs TPO for the Valley Flat Roof in the San Fernando Valley (Part 6)
Choosing between systems in the Valley, with a flat roof as the benchmark, and when to mix systems on one roof.
Comparisons between roofing systems usually get made on price and appearance, which are the two things that matter least in ten years. For a flat roof in the San Fernando Valley, here is what the comparison looks like once service life is included.
What actually matters
Flat roofs are not flat. They are built with fall, and the fall is what keeps them alive. Every other detail is secondary to whether water leaves the roof.
The difference that shows up later
Drainage does not fail in the storm; it fails in the eight dry months beforehand. A drain that has been dry since April collects grit, leaves and debris, and nobody looks at it until water is coming through a ceiling. Two systems that cost within a dollar of each other on the quote can differ by a decade in service, and the difference is in the detail rather than the material.
How the San Fernando Valley settles it
Most of the housing went up between 1950 and 1975, which means original decking, undersized ventilation and at least one previous layer that somebody roofed straight over rather than tearing off. Summer is the problem here. The Valley runs ten to fifteen degrees hotter than the coast and holds it for weeks, so a roof surface that reads 90 degrees in Santa Monica is well past 160 in Van Nuys by mid-afternoon. Everything on the roof expands into that heat and contracts again overnight, and it is that daily movement, not the peak temperature, that opens laps and backs fasteners out.
What we look at on an inspection
- Fall across the roof, and any area holding water beyond forty-eight hours
- Drain and scupper clearance, including underneath every strainer
- Membrane condition across the whole field, not only at the edges
- Flashing at every penetration, curb and item of rooftop plant
- Parapet termination and counterflashing along the full perimeter
- Insulation moisture, established by probe rather than by eye
- Evidence and quality of previous patching
Common questions
Is the more expensive option always longer-lived?
Usually, but not always, and installation quality closes the gap in both directions. A well-installed mid-range system beats a badly installed premium one every time.
Which option is best overall?
There is no overall. There is best for this roof pitch, this exposure and this budget, and those three narrow it down fast.
The honest summary
In the San Fernando Valley, watch attic temperature and intake ventilation, because a Valley attic that cannot breathe cooks the underside of the roof as hard as the sun cooks the top. Ponding, blocked drainage and failed penetration detail account for nearly every flat roof call we take. If a quote does not mention drainage, it is a quote to recreate the same problem in a new material.
Free inspection, drone photography where access is difficult, and a written estimate with deck repair priced per sheet. No obligation.
More on Flat Roofs
- Torch Down vs TPO for the South Bay Flat Roof in the South Bay (Part 4)Flat Roofs
- Torch Down vs TPO for a Glendale Flat Roof: The Foothills EditionFlat Roofs
- Torch Down vs TPO for the Valley Flat Roof in the San Fernando ValleyFlat Roofs
- Torch Down vs TPO for the Westside Flat Roof — Questions to AskFlat Roofs