The best choice starts with your building. Here is how to compare three roof-covering families without reducing the decision to a brand or square-foot price.
Three systems, three approaches
TPO is a synthetic single-ply membrane with hot-air-welded seams. Modified bitumen is often installed as a two-ply system. Tar and gravel is a built-up bituminous assembly protected by surface aggregate. These descriptions alone do not establish which system suits your substrate and building constraints.
Compare what will actually be installed
Ask for a proposal that also describes the substrate, insulation, slopes and connections. Two prices for a new roof may cover very different work. Check removal of existing layers and planned corrections at drains, parapets and equipment. A product cannot compensate for an incomplete work scope.
Plan maintenance and constraints
Think about future access to drains and equipment. If technicians will walk on the roof, ask how access paths will be protected. Check permitted colours and the selected system details. Read warranty conditions alongside exclusions and maintenance requirements, not just the advertised number of years.
The right question to ask
Instead of asking which material is best in general, ask why the proposed assembly addresses your problem. A useful discussion explains what stays, what changes and which uncertainties remain before the roof is opened.
Compare families without overlooking the assembly
| Family | Defining feature | What to clarify |
|---|---|---|
| TPO | Thermoplastic single ply; hot-air-welded seams. | Attachment method, weld checks, penetration details and foot traffic. |
| SBS modified bitumen | Modified bitumen with base and cap components according to the system. | Exact products and specified installation: adhesion, fastening or welding. |
| Tar and gravel | Bituminous plies with aggregate surface protection. | Condition beneath aggregate, weight and loads, removal scope and access to details. |
| For every system | Substrate, insulation and drainage belong in the project. | What is retained, replaced and checked before closure. |
What about your property?
Turn this guide into a request describing your actual situation.
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