Comparing the guarantee on each commercial roofing quote
Two commercial roofing quotes for the same roof can carry guarantees that are worth very different amounts, even when both say "20 years". The guarantee line is where quotes are hardest to compare and easiest to misread. This page gives you five questions to put to every roofer, what the common guarantee types are, and how to set them side by side before you compare prices.
Five questions for every guarantee
- Who issues it? The contractor, the system manufacturer, or an insurer. This decides who you claim against.
- What does it cover? Materials only, workmanship only, or both under one document.
- For how many years? A term in years. A guarantee always has an end date, so treat "lifetime" as a word to question.
- What happens if the contractor stops trading? Only an insurance-backed guarantee, or a manufacturer guarantee that covers workmanship, normally survives that.
- What voids it? Missed inspections, unapproved alterations, foot traffic, new plant or solar panels fixed without approval.
The guarantee types you will see
| Type | Who stands behind it | What to check on the quote |
|---|---|---|
| Workmanship guarantee | The contractor alone | The term, and what happens if the firm closes. On its own it is only as good as the firm. |
| Manufacturer materials guarantee | The membrane or sheet manufacturer, for the product | Whether it covers the product only, leaving fitting faults with the contractor. |
| Single-point manufacturer guarantee | The manufacturer, for materials and workmanship together | That the firm is approved for that exact system and the manufacturer inspects before issuing it. |
| Insurance-backed guarantee | An insurer, usually for a set term | The policy document, the insurer's name, the term and any excess. |
Setting guarantees side by side
When you line up three quotes, write the guarantee as one row per quote: issuer, cover, term, backing if the firm closes, conditions. A long workmanship guarantee from a small firm and a shorter single-point manufacturer guarantee are not ranked by the number of years alone. Ask yourself who you would claim against in year twelve, and whether they will still be there.
Then check that the guarantee matches the scope. A manufacturer will usually guarantee a system only when it is installed to its specification, which may include a full strip, a set insulation build-up and particular details at upstands and outlets. A quote that offers a manufacturer guarantee on an overlay of a wet roof is worth questioning, because the specification and the guarantee may not agree.
What usually voids a roof guarantee
- Missing the inspections or maintenance the guarantee requires, such as clearing outlets and gutters.
- Other trades cutting into the roof for plant, cables or rooflights without the guarantor's approval.
- Fixing solar panels, plant or walkways without an approved detail. If solar is planned, ask before you sign how the array will be fixed without voiding the cover.
- Damage from foot traffic where walkways were not installed.
- Repairs by a firm that is not approved for the system.
Guarantees on refurbishment and coatings
Overlays, over-sheeting and coatings extend the life of a sound roof rather than replacing it, so their guarantees are usually shorter and more conditional than those on a new roof. That does not make them a poor choice: on the right roof they are the honest option. It does mean the guarantee line on a coating quote and a full re-roof quote cannot be compared year for year. Our repair, refurbish or replace guide sets out when each route makes sense.
What to keep when the work is finished
- The guarantee document, with the issuer, the term and the conditions.
- The system specification and the as-built drawings, including falls and outlets.
- The wind-uplift design and fixing schedule.
- The Building Regulations compliance certificate or building control completion certificate.
- The maintenance schedule the guarantee depends on.
These documents matter at a sale, a lease event or an insurance review, and they are what a future buyer or tenant's surveyor will ask for. Ask every roofer to confirm in the quote which of them you will receive. Use the quote sense-check to tick the guarantee line against each quote.
Commercial Roofing Quotes is an independent publisher run by SEO Dons Ltd. We do not issue, sell or arrange roof guarantees. Last checked 25 October 2026.