Garage conversion budget: multiple trades and owner-bought materials

In this example the money moves on two lines: floor prep, where the slab needs more than was quoted, and the electrical service. Each has its own line, its own flag and its own change order, while flooring, paint and the permit sit outside any contractor.

General information only, not financial, construction or legal advice. Contingency, holdback and payment-split percentages are your own inputs, and payment and deposit rules vary by contract and by state or province; check yours. Names and numbers in the example are invented.

What changes for this kind of project

In this example the bay door comes out first, the slab is leveled, then insulation, electrical and HVAC go in ahead of drywall. The Budget tab gets one row per scope item, so demolition and floor prep are separate lines even though Valor Demolition does both.

The slab needed more work than quoted. The floor prep quote already sits above its line budget and the approved change order adds more, so that line draws on the contingency pool. The service upgrade is only Proposed: pending exposure, outside Committed until you approve it. Flooring, paint and the permit have no contractor on the Budget tab, so they are owner purchases and fees here.

A worked example: Garage conversion, 450 sq ft

Invented numbers, to show the shape. Settings on Start Here: contingency 16% (an example value you set), total project budget $39,000.

The contingency pool is $6,240 ($39,000 x 16%). That leaves $32,760 to share out as line budgets. The lines below add up to $32,700, so $60 is unallocated.

Change orders on the Change Orders tab. Only Approved rows move into Committed:

What the summary shows

• Committed: $29,700. Paid: $13,450. Unpaid commitment: $16,250.
• Contingency used: $1,400, what each line's committed total goes above its line budget, added up. Contingency left now: $4,840.
• Pending exposure (Proposed change orders): $2,200. Contingency left if every proposed change order were approved: $2,640.

Where each piece goes in the workbook

1. Start Here: Type the total project budget, the contingency percentage and the four contractors with their trades: demolition, electrical, HVAC and insulation. The percentage is an example value you overtype; the pool is worked out from it.
2. Budget: Demolition and floor prep are separate rows even though one company does both, so floor prep gets its own flag. Flooring and paint have no contractor: type the accepted quote. Drywall has no quote yet and reads Not committed.
3. Quotes: Enter each bidder's price per item side by side (up to five bidders), with the Line ID on the row. The tab shows the lowest, the highest and the spread. Picking a bidder feeds that price into the Budget base quote when the typed quote is empty. Drywall is still waiting for a pick.
4. Payments: Log each payment with its Line ID: a payment to Valor Demolition goes on L01 or L02, depending on what it covers. A blank or misspelled Line ID makes the tie-out check show a difference, so you can find it.

Two formulas worth a cell of their own

• Committed for one room: =SUMIFS(Budget!$K$6:$K$65,Budget!$B$6:$B$65,"New room") returns $29,700 on this example.
• Contingency used, the sum of the Overrun now column: =SUM(Budget!$S$6:$S$65) returns $1,400.

Four tracking tips

1. Keep floor prep on its own line, apart from the bay door demolition. That is the line that grew here: its quote already sits above its line budget, the approved slab change order adds more, and the demolition line stays OK.
2. Before you approve the service upgrade, compare Contingency left now with Contingency left if all pending approved. The electrical line already sits above its line budget on its quote, so the upgrade stacks on an overrun that already draws on the pool.
3. Owner-bought flooring counts as committed as soon as you type its accepted quote, but nothing is paid until a Payments row carries its Line ID. Until then it shows in Unpaid commitment, so a purchase you have agreed to stays visible.
4. The drywall row names HomeBase Insulation but has no accepted quote. It reads Not committed, adds nothing to that company's original contract on the Contractors tab, and its line budget stands in the Forecast column until you type a quote.

Questions

Where do I record a change order for the slab or floor leveling?

On Change Orders, add a row with the Line ID of the floor prep line, a short description, the extra amount and the reason Unforeseen. Keep the status Proposed until you agree to it; only Approved rows raise Committed on that line.

Can one company's two jobs share a single quote line?

Keep them as two lines with their own accepted quotes. Valor Demolition does the bay door and the floor prep here: the Contractors tab adds the two lines into one original contract, while the Budget tab keeps a separate flag for each job.

Related renovation guides

• Contractor bid comparison spreadsheet for homeowners
• Renovation contingency tracker: how much contingency is left
• Renovation change order tracker: a spreadsheet for homeowners

More renovation budget guides

• Renovation budget spreadsheets by room and project type
• Budget for adding a new bathroom: rough-in, fixtures and permits
• Attic conversion budget: handling structural surprises
• Basement finishing budget spreadsheet: quotes, change orders and contingency
• Deck budget spreadsheet: material upgrades and impact on contingency
• Exterior renovation budget: comparing roofing, siding and window bids
• Fixer upper budget: everything at once, commit as quotes arrive
• Home addition budget: design, permits, general contractor and utilities
• Laundry and mudroom remodel budget: owner-bought appliances and small change orders
• Owner as general contractor: budget, payments and milestones per trade
• Primary suite renovation: bedroom, bathroom and closet with separate trades
• Whole house renovation budget: kitchen, bathroom and living spaces