Home addition budget: design, permits, general contractor and utilities

A single-room addition mixes owner-paid lines, such as design and permit fees, with trade lines held by a general contractor, an electrician and an HVAC firm. The Contractors tab totals each firm and sets owner-paid lines in their own row.

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 design drawings and the plan review fees are owner-paid lines with no contractor, and both are paid in full. The committed construction lines are only part paid, so they still carry an unpaid commitment, and the interior finish line has no quote yet.

One general contractor holds three lines: foundation, framing and interior finish. They stay separate rows on the Budget tab, but the Contractors tab adds them into one contract with one typed % complete. Electrical and HVAC are separate contractors, so a ductwork change moves only the HVAC firm's contract.

A worked example: Home addition, 300 sq ft

Invented numbers, to show the shape. Settings on Start Here: contingency 18% (an example value you set), total project budget $67,600.

The contingency pool is $12,168 ($67,600 x 18%). That leaves $55,432 to share out as line budgets. The lines below add up to $55,400, so $32 is unallocated.

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

What the summary shows

• Committed: $46,450. Paid: $24,600. Unpaid commitment: $21,850.
• Contingency used: $1,750, what each line's committed total goes above its line budget, added up. Contingency left now: $10,418.
• Pending exposure (Proposed change orders): $600. Contingency left if every proposed change order were approved: $9,818.

Where each piece goes in the workbook

1. Start Here: Type the total project budget, which includes the contingency pool, the contingency percentage and three contractors: the general contractor, the electrician and the HVAC firm. Design and permit fees are owner-paid, so no contractor goes with them.
2. Budget: Enter the design and permit fees as lines with no contractor. Foundation, framing and interior finish each get a row naming the general contractor. Leave the accepted quote empty on interior finish until you choose a bid; it reads Not committed.
3. Change Orders: Log the roof truss and ductwork changes against their Line IDs as Approved, so they enter Committed. The stem wall change stays Proposed, which makes it pending exposure and keeps it out of Committed.
4. Cash Schedule: Add milestones for the general contractor. Percent milestones follow the original quote, so enter the approved truss change as a Fixed $ row. Put the Milestone ID on the matching Payments row or the milestone will not show as paid.

Two formulas worth a cell of their own

• Committed for one room: =SUMIFS(Budget!$K$6:$K$65,Budget!$B$6:$B$65,"Addition") returns $46,450 on this example.
• Contingency used, the sum of the Overrun now column: =SUM(Budget!$S$6:$S$65) returns $1,750.

Four tracking tips

1. The design, permit, electrical and flooring-and-paint lines are all under their line budgets. Those savings do not refill the contingency pool: only the foundation, framing and HVAC overruns count toward Contingency used.
2. The foundation line is over its line budget on the accepted quote alone, before the proposed stem wall change. Read Overrun if pending approved and Contingency left if all pending approved before you mark that change Approved.
3. The general contractor's % complete is your own typed estimate, one figure for foundation, framing and finish together. If the share of the contract you have paid runs ahead of that estimate, Paid ahead of work on the Contractors tab turns positive.
4. Percent milestones for the general contractor are worked out on the base quotes of all its lines added together. Until the interior finish has an accepted quote it adds nothing, so recheck those percent rows once you type it.

Questions

Do I enter the architect's fee as a line item?

Yes. Add a line in the Design & planning category with no contractor, a line budget, and the agreed fee as the accepted quote. Each invoice you pay goes on the Payments tab with that Line ID, so the line shows what is paid and what is still unpaid.

What do I do with the interior finish line before I have a bid?

Leave the accepted quote empty. The line reads Not committed, its Committed is 0 and its Forecast uses the line budget. When bids arrive, enter them on the Quotes tab and pick one; the choice feeds the Budget tab.

Related renovation guides

• Contractor bid comparison spreadsheet for homeowners
• Contractor payment schedule template for homeowners in Excel
• Renovation contingency tracker: how much contingency is left

More renovation budget guides

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• Owner as general contractor: budget, payments and milestones per trade
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• Whole house renovation budget: kitchen, bathroom and living spaces