This is a checklist for comparing commercial roofing bids. It assumes you have two or three in front of you and the numbers do not line up, which is the normal situation rather than an unusual one.
The aim is not to find the lowest price. It is to find out what the differences actually are.
What each bid must state
| Item | Why it matters |
|---|---|
| System, named by manufacturer and product | Type alone does not define what is being installed |
| Recover or tear off | The single largest cost difference between two bids |
| Insulation type and thickness | Invisible once installed, and easy to reduce quietly |
| Attachment method | Governs wind performance and deck suitability |
| Surface preparation | Governs whether anything sticks to anything else |
| Detail treatment | Upstands, curbs, penetrations, edge metal |
| Drainage work | Outlets, strainers, clamping rings, overflows |
| Deck repair rate | A number per unit area, not a sentence of reassurance |
| Disposal | Where the old roof goes and who pays |
| Exclusions | Written down, rather than discovered later |
Where the differences hide
| Look at | What to ask |
|---|---|
| A much lower price | What is excluded that the others have included |
| A much higher price | What is included that the others have not |
| Insulation thickness | Whether it meets current code for this building |
| Preparation allowance | How it is specified and how it is verified |
| Detail work | Whether each detail type is named or covered by one line |
| Drainage | Whether it appears at all |
| Equipment handling | Who lifts, disconnects and reinstates rooftop plant |
| Phasing | Whether the price assumes an empty or an occupied building |
The commercial terms
| Compare | What to watch for |
|---|---|
| Payment schedule | A deposit proportionate to materials, not to the project |
| Change order process | How a variation is priced and who authorizes it |
| Retention | An amount held until completion and sign off |
| Programme | Duration, and the weather assumptions behind it |
| Liability during the works | Who carries the risk of water entering an open roof |
| Lien waivers | Provided as payments are made |
The warranty, as its own column
| Compare | Why |
|---|---|
| Issuer | Manufacturer, contractor, or both |
| Scope | Material only, or material and labor |
| Duration | And the date it runs from |
| Conditions | What voids it, and what maintenance it requires |
| Transferability | Whether it survives a sale, and at what cost |
| Who performs the required maintenance | And at whose expense |
The five questions for every bidder
| Ask | What a good answer sounds like |
|---|---|
| What preparation have you allowed? | A method and a way of verifying it |
| How will the details be formed? | Named details, not a general assurance |
| What is your deck repair rate? | A figure per unit area |
| How is the roof secured each night? | A described, practiced routine |
| Who will be on site? | Named crew, directly employed or named subcontractor |
What to do with it
- Write one scope and issue it to everybody. This is the step that makes the rest possible.
- Put the answers next to the prices. The differences show up in the answers.
- Ask the lowest bidder what is excluded. Neutrally, and expect a straight answer.
- Treat the warranty as a separate column. Not as part of the number.
- Accept a cheap bid when the reason is explainable. Cheap is not the same as thin.
Want the reasoning behind these checks? Read how to choose a contractor and what drives commercial roofing cost.
Walked by Date Roof
Common questions
Why are three bids so often not comparable?
Because each contractor wrote their own scope, and each one solved the problem slightly differently. One quoted a recover, one a tear off, one a coating, and the three numbers describe three different projects rather than three prices for the same piece of work on the same roof.
- Different scopes produce different numbers for the same roof
- Insulation thickness varies and is invisible once installed
- Detail treatment is where the quiet savings are made
- Drainage work is often omitted entirely by one bidder
- Deck repair may be included, excluded or simply unmentioned
The fix is to write the scope yourself and send the same one to everybody. It takes an afternoon with a condition report, and it converts a confusing spread of numbers into a straightforward comparison. Where a bidder proposes something different, ask them to price your scope as well as theirs, so you get the comparison and their better idea at the same time.
What does the lowest bid usually leave out?
Preparation, detail work and drainage, in roughly that order. These are the items a client cannot see on completion and cannot easily check afterwards, which is precisely why they are the ones that disappear when somebody is pricing to win rather than pricing to build.
- Surface preparation, which governs whether anything adheres
- Detail treatment at upstands, curbs and penetrations
- Drainage work, including strainers, clamping rings and overflows
- Thinner insulation than the specification asks for
- Deck repair, excluded entirely rather than priced
None of this means the lowest bid is wrong. It means the difference has to be explained before it can be accepted. Ask the lowest bidder directly what they have allowed for the items above, and ask the highest what they have included that the others have not. Both answers are usually given freely and both are informative. Put the two answers side by side and the real spread between the bids is usually much narrower than the headline numbers suggested it would be.
How should the warranty figure in the comparison?
As a separate column, not as part of the price. A longer warranty from a manufacturer whose system costs more is a different proposition from a longer warranty offered by the contractor on their own workmanship, and the two are frequently presented as though they were equivalent.
- Manufacturer warranty and workmanship warranty are different documents
- Material only cover is narrower than it sounds
- Length means little without the conditions attached to it
- Nearly all require documented maintenance somebody must perform
- Transferability matters if the building might be sold
Ask each bidder for a specimen warranty document rather than a description of one. Comparing the actual conditions side by side usually collapses what looked like a meaningful difference, and occasionally reveals a real one. Either way it is a ten minute exercise that happens before the contract rather than during a claim. A warranty is also only as good as the company standing behind it, which is a reason to check trading history alongside the document itself.
What questions separate a good bid from a cheap one?
Questions about the things that are not visible on completion. What the preparation is, how the details are formed, what happens when the deck is found to be damaged, and what the plan is if weather arrives while the roof is open on an occupied building.
- What preparation is allowed for, and how it is verified
- How upstands, curbs and penetrations will be detailed
- The stated rate for deck repair per unit area
- How the roof is made watertight at the end of each day
- Who will actually be on site, and whether they are directly employed
Ask the same five questions of every bidder and write the answers down next to the prices. The differences between contractors show up far more clearly in those answers than in the numbers, and the bidder who answers them specifically and without hesitation is usually the one who has done the work rather than estimated it.
Does the cheapest bid ever win on merit?
Regularly, and it is worth saying so. A smaller contractor with lower overheads, a crew already working nearby, or a genuinely better method can be both cheaper and better. The point of the comparison is to find out which kind of cheap you are looking at.
- Lower overheads are a real and legitimate advantage
- A crew already in the area saves mobilization cost
- A better method can reduce both price and risk
- A quiet period in the schedule produces keen pricing
- An established relationship with the manufacturer can help on price
The test is whether the contractor can explain the difference. A bidder who says clearly that they are cheaper because their crew finishes a job two streets away that week has given you a reason you can check. A bidder who cannot account for the gap at all is a bidder whose number is likely to move once the work has started.