| Tar and gravel (BUR) | Spray foam (SPF) | TPO | |
|---|---|---|---|
| What it is | Layers of felt and hot asphalt, topped with gravel | Sprayed foam with a protective coating | White heat-welded membrane |
| Seams | Built in layers | Seamless | Heat-welded seams |
| Insulation | Little on its own | Adds insulation | Insulation board under it |
| Drainage fixes | Hard to change | Easy to build slope | Tapered insulation |
| Maintenance | Gravel, edges, drains | Recoat every several years | Seams and details, no scheduled recoat |
| Typical new cost | Rarely installed on homes now | About $4 – $8 / sq ft | About $8 – $14 / sq ft |
When to keep tar and gravel
If it's dry, drains well and leaks only in a spot or two, repairs can buy years. See tar and gravel repair.
When foam makes sense
Foam is often the best value when the old roof is dry and can stay, and when drainage needs improving. Plan on recoating on schedule.
When TPO makes sense
When the old roof is coming off anyway, or you want a very reflective surface without a recoat schedule.
Common questions
Which lasts longest?
Well-maintained foam and well-installed TPO can both last 20 years or more. Maintenance and drainage matter more than the label.
Which is cheapest?
Foam over a dry existing roof is often the least expensive new roof. Tear-off adds cost to any system.