Sharp Pencil › Guides

Alternates and unit prices on a commercial roofing bid: how to take off each alternate as its own scope and set unit prices for deck repair and wet insulation

By The Sharp Pencil team

Take off the base bid first. Then take off each alternate on its own, with its own quantities, material list, and price. Do the same for unit price items. Name the unit. Say what it includes and what it does not. Price deck repair and wet insulation from the work the crew will actually do in the field. Do not bury a guessed allowance in the base bid. Blend the alternates into the base and you cannot defend the add, the deduct, or the change when the owner accepts only part of the bid.

What is the difference between an alternate and a unit price?

An alternate is a defined change to the base scope that the owner may accept or reject. In a typical project manual, the Division 01 alternates section describes an alternate as an amount stated on the bid form for work that may be added to or deducted from the base bid if the owner accepts that change. A unit price is different. It is a price per unit of work, such as per square foot of deck replacement, that is used to adjust the price when the actual quantity differs from the quantity assumed at bid time. Section numbers and wording vary by project. The bid form and the specifications for that bid control.

That distinction matters on the takeoff. An alternate needs complete quantities for a defined scope. A unit price needs a clear unit and a small, complete cost build-up for one unit. Treat a unit price like a mini alternate, or an alternate like a loose allowance, and you get the disputes that show up after award.

For the documents that frame the bid, start with the bid form itself, then read the instructions to bidders and Division 01. Our guide to the roofing RFI register covers how to log the questions those documents leave open.

How should you take off each alternate?

Give each alternate its own quantity set, even when most of the roof does not change.

1. Lock the base bid quantities first. Do not keep editing the base while you build alternates on top of it.
2. Copy only the affected area or system into a separate alternate quantity set. A tear-off alternate, a thicker membrane alternate, or an added cover board alternate each changes a different list of lines.

In a Sharp Pencil takeoff workbook, bid alternate quantities are broken into separate priceable lines.

3. List what is added, what is removed, and what stays. For a deduct alternate, state the removed work plainly so the credit is not argued later.
4. Carry the related work with the alternate. Fasteners, flashing, edge metal, disposal, and night tie-in work move with the membrane or insulation change that causes them. An alternate price that covers only the headline material will be short.
5. Price each alternate on its own. Do not spread base bid margin across alternates to make one option look cheaper. If the owner accepts an alternate by itself, that price has to stand by itself.
6. Reconcile the totals. Base plus accepted alternate should equal a complete roof. Base minus a deduct alternate should still equal a complete, buildable roof.

A worked example (hypothetical, not a real job)

Say the base bid is a mechanically attached single-ply roof over new insulation on a 40,000 square foot warehouse. Alternate 1 adds a cover board. Alternate 2 changes the membrane thickness.

For Alternate 1, the quantity set is not just cover board area. It also includes any change in fastener length or count, adhesive quantity if the attachment method changes, added handling, and any change in lead time or crew days you choose to price. For Alternate 2, the membrane quantity stays tied to the same roof area and roll layout logic, but seam, flashing membrane, and accessory quantities need a check because a thicker sheet can change the material list even when the area does not change.

Each alternate gets a complete, short list you can price and later build from. One blended spreadsheet total cannot do that.

How should you set unit prices for deck repair and wet insulation?

A good unit price answers four questions before bid day: what is the unit, what work is inside that unit, what work is outside it, and how will the quantity be agreed in the field?

Deck repair and deck replacement

Separate repair from replacement if the bid form allows it, or state clearly which one your unit covers. Then define, in writing on your bid notes or proposal:

• Unit: per square foot is common for deck work. Confirm the unit on the bid form and do not change it silently.
• Included: removal of damaged deck in that unit area, the new deck material for that area, fastening to the supporting structure as specified, and disposal if you intend to include it.
• Excluded or separate: structural repair to joists, bar joists, or purlins; added framing; and work to correct a deck that was never built to the drawings. If the bid form does not let you qualify the price, raise it as a question before bid day and log it in your RFI list.
• Field agreement: who marks the area, who approves it before it is covered, and how partial areas are rounded. Write that process into your internal bid notes so production and billing use the same rule.

Do not set the deck unit price from material cost alone. The crew has to open the roof, inspect, cut out, replace, refasten, and keep the building dry that day. Price the unit for the smallest repair you are likely to be handed, because small patches carry the same setup cost as larger ones spread over fewer square feet.

Wet insulation replacement

Wet insulation is similar, but the unit has to address the layers above and below the insulation.

• Unit: per square foot, per board, or per square. Match the bid form exactly.
• Included: removing wet boards in that unit area, disposing of them, supplying and installing dry boards of the specified type and thickness, and refastening or adhering them as the system requires.
• Membrane and cover board above: state whether patching or replacing the layers above the wet insulation is inside the unit or priced separately. This is the most common source of argument, so do not leave it implied.
• How wet is decided: state the evidence you will rely on, such as a core cut or a moisture survey provided by others. If no survey exists at bid time, say so and price the unit as a rate, not as a promise about how much wet material is present.

If the documents do not define these items, ask. See how to price a TPO roof for related line items estimators often miss, and keep unanswered items visible rather than guessed.

What should you check on the bid form before you submit?

• Each alternate is numbered and worded the same way on the bid form, the drawings, and the specifications. If the names differ, ask which governs.
• Add and deduct are stated correctly. A deduct alternate that removes work should show as a credit, not as a smaller add.
• Unit prices use the exact unit on the form. If the form says per square foot, do not submit per square.
• No alternate depends on another alternate unless the form says they must be taken together.
• Your exclusions and clarifications do not contradict the bid form. On public or hard bid work, a qualification can make a bid non-responsive. Confirm the rules for that bid before you attach conditions.

FAQ

Should alternate quantities be kept separate from the base bid?

Yes. Keep a separate quantity set for each alternate so the base bid, each add, and each deduct can be priced, accepted, and later tracked without rebuilding the takeoff.

What should a deck replacement unit price include?

At minimum, removal and disposal as you define it, the new deck for that unit area, and fastening as specified. State whether structural framing repair is excluded, and agree how the area will be marked and approved before it is covered.

How do you price wet insulation if you do not know how much is wet?

Price the rate, not the total. Define the unit and what it includes. Say what evidence will decide which boards are wet. Let the final quantity be agreed in the field. Do not hide a guessed quantity in the base bid.

What happens if the bid form and the specifications describe an alternate differently?

Ask before bid day and log the question. Bid the form the owner will actually sign, and note the assumption you used if no answer arrives.