Most facility managers who collect three commercial roofing proposals end up holding three documents that describe three different roofs. One bid assumes a full tear-off, another assumes a recover over the existing system, and the third is a single page with a total and the word "TPO" on it. Picking the lowest number in that situation is not comparing prices. It is guessing which contractor left the most out.
This guide walks through how to turn a stack of bids into a fair comparison: what the scope must spell out, which unit prices matter, which paperwork to collect before you sign, and how payment, change orders and lien waivers should be handled. It applies whether you are replacing a warehouse roof in West Columbia or a small office roof in Irmo.
Start by Writing One Scope Every Bidder Prices
The single most useful thing an owner can do is give every contractor the same written scope. Without it, each bidder fills the gaps with their own assumptions, and those assumptions are where the price differences hide. If you do not have a consultant or architect preparing specifications, a short scope letter still works. It should state the roof area or areas, the existing system as you understand it, whether you expect a tear-off or are open to a recover, the warranty type you want, and any constraints such as occupied space below or limited working hours.
Ask each bidder to price that scope as written, and to list any alternates separately. A contractor who thinks a recover makes more sense than a tear-off can say so as an alternate, with the reason, rather than quietly pricing a different job. If a bidder has found something on the roof that changes the scope, such as wet insulation, share it with the others so everyone is pricing the same building. Our guide to deciding between a tear-off and a recover explains why moisture findings change that decision.
The Line Items That Make Bids Comparable
Once every bid covers the same scope, check that each one actually states the details below. If a proposal is silent on an item, ask the contractor to put the answer in writing. Silence usually means the cheapest option, or a later change order.
Roof system and membrane thickness
"TPO roof" is not a specification. Single-ply membranes come in different thicknesses, and fully adhered, mechanically attached and ballasted installations perform and cost differently. Modified bitumen bids should state the number of plies and how they are applied. Metal bids should state panel profile and gauge. If one bid is for a thicker membrane, fully adhered, and another is for a thinner one, mechanically fastened, the price gap may simply be the difference in product. Our comparison of TPO, EPDM and PVC membranes covers how those systems differ.
Insulation, R-value and tapered design
Insulation is often a large share of a low-slope roof's cost, and it is the easiest place for bids to diverge. Each proposal should state the insulation type, the number of layers, the total thickness and the resulting R-value, along with the cover board if one is included. If the roof has drainage problems, ask whether the bid includes tapered insulation or crickets to move water to the drains, and whether that design is drawn or assumed. A roof that is re-covered with new membrane over the same flat spots will still pond.
Tear-off and disposal
Confirm how many existing layers each contractor expects to remove, and whether disposal, dumpsters and hauling are included. Two layers discovered on a roof that was priced for one is one of the most common sources of change orders.
Deck repair and wet-insulation unit prices
No one can see the full condition of a roof deck until the old roof is off. Good bids handle that uncertainty with unit prices rather than a vague allowance. Look for a stated price per square foot of metal deck replaced, per sheet of wood deck replaced, and per square foot of wet insulation removed and replaced. Compare those unit prices across bids as carefully as the base price. A bid that is low on the base number but high on unit prices can end up costing more once the roof is opened.
Flashing, edge metal and penetrations
Most commercial leaks start at flashings, not in the open field of the membrane. Bids should say whether curbs, pipes, walls and parapets are being re-flashed, whether coping and edge metal are being replaced or reused, and how rooftop units, vents and other penetrations will be handled. Ask what gauge and finish the new metal will be. If you have rooftop solar or plan to add it, raise that before bidding so penetrations are detailed once rather than retrofitted.
Warranty type
A manufacturer's material-only warranty, a system warranty and a no-dollar-limit warranty are not the same product, and the contractor's own workmanship warranty is separate from all of them. Ask each bidder to name the exact warranty being offered, its term, who issues it and what inspections it requires. Our explainer on how commercial roof warranties work covers what each type actually covers and what voids it.
Paperwork to Collect Before You Sign
The price comparison only matters once you know each contractor is legally able to do the work and properly insured to do it on your property. Request these items from every finalist:
- Certificate of insurance (COI): issued by the contractor's agent, naming your company as certificate holder, showing general liability and auto coverage that is current for the project dates. Many owners also ask to be named as additional insured.
- Workers' compensation: proof of active coverage. If a worker is hurt on your roof and the contractor is not covered, the question of who pays can land on the property owner.
- License: the contractor's license number and classification, which you then verify yourself (see below).
- References: two or three commercial projects of similar size and system, with a contact name you can call.
- Submittals: product data sheets for the membrane, insulation, adhesives and fasteners, plus any manufacturer approval needed to issue the warranty you were quoted.
- Safety plan: how the crew will handle fall protection, material hoisting and access, especially if your building stays occupied.
Verifying a South Carolina contractor license
In South Carolina, commercial roofing contractors are licensed through the Department of Labor, Licensing and Regulation (LLR) Contractor's Licensing Board. You can look up a license by name or number on the LLR website and confirm it is active and in the right classification. Pay attention to the license's financial limit: South Carolina contractor license classifications carry a per-job dollar limit, so a contractor can hold a valid license and still not be licensed for a project of your size. Check the limit shown on the license against your contract value rather than taking anyone's word for it.
Calling references the useful way
Generic questions get generic praise. Ask references specific ones: Did the final cost match the contract, and if not, why? How were change orders presented? Was the roof dried in at the end of each day? How did the crew treat tenants and staff? Has the roof needed any service since, and how quickly was the contractor reachable? If the project is old enough, ask whether the roof has been through a major storm.
Payment Schedule, Change Orders and Lien Waivers
The contract terms matter as much as the scope. Three areas deserve a close read.
Payment schedule
Payments should follow progress. A reasonable structure ties payments to milestones such as material delivery, completion of defined roof areas and final completion, with a final payment held until punch-list items are done and warranty paperwork is in hand. Be cautious about any proposal that asks for most of the contract value before work starts.
Change orders
The contract should say that no extra work is billed without a written change order you have signed, and that hidden-condition work such as deck replacement is billed at the unit prices in the bid. Ask how the contractor documents hidden conditions. Photos of the damaged deck, with location and quantity, should come with every change order before the area is covered back up.
Lien waivers
Suppliers and subcontractors who are not paid may have lien rights against your property even if you paid the roofing contractor in full. Ask for lien waivers with each payment: a conditional waiver when you pay, and an unconditional waiver once the payment has cleared. At closeout, ask for final waivers from the contractor and the major material suppliers. Your attorney can tell you what form your contract should require.
Reading Price Differences Correctly
With scopes aligned and paperwork in hand, the remaining price differences are easier to interpret. Across the Midlands, commercial roofing typically runs $4–$12 per square foot installed, depending on system, roof size, deck condition and access. Where a bid falls in that range tells you less than why it falls there. Our guide to what drives commercial roof replacement cost covers the factors in detail.
When one bid is far below the others, go back through the line items. Common explanations include:
- A thinner membrane or a different attachment method than the scope called for.
- Less insulation, or no tapered insulation where the scope asked for it.
- Reused edge metal and flashings where others priced new.
- Disposal, permits or crane time left out of the base price.
- Low base price paired with high deck and insulation unit prices.
- A material-only warranty where others priced a system warranty.
Sometimes the low bidder is simply efficient, and that is fine. The point of the comparison is to know which case you are in before you sign, not after the roof is open.
A Simple Bid Comparison Sheet
Put every bid into one spreadsheet with a row per item and a column per contractor: base price, system and thickness, attachment method, insulation and R-value, tapered design, layers removed, deck unit prices, wet-insulation unit price, flashing and edge metal scope, warranty type and term, workmanship warranty, insurance verified, license verified and its limit, references called, payment terms and exclusions. Any blank cell is a question to send back to that contractor. When the sheet has no blanks, the decision is usually much clearer than it looked with three loose proposals.
If you want a proposal you can put on that sheet line by line, our commercial roofing services team can walk your roof and price it to a written scope. You can request a free commercial roof assessment to get started.