Home Addition Cost Per Square Foot Guide

Inside the actual 64-page edition

This original handbook follows a complete planning sequence: preface, space alternatives, property feasibility, existing-home records, design roles, area definitions, addition scope, complete scenarios and closeout. Chapters 2–20 each contain an explanation, an accurately worked hypothetical example and a dedicated planning sheet. The PDF has 95 fillable text fields across 19 worksheets, plus printable space for handwritten notes. Fields do not calculate automatically.

Try the method before buying

A fictional 20 × 15 ft footprint is 300 sq ft. A $90,000 building package gives $300 per footprint sq ft, while a broader $105,000 scenario gives $350 using the same area. The difference is included scope, not a new footprint. Neither figure is a local price benchmark.

Use the free HomeCostEngine calculators for individual arithmetic and the quote comparison calculator with complete proposals. Retain the actual area and cost definitions.

Complete chapter list

1. Preface: how to use this book
2. Define the home addition brief
3. Compare the space alternatives first
4. Check local feasibility and property constraints
5. Record the existing home and site
6. Assign the design and coordination team
7. Define the area behind a cost-per-foot number
8. Budget foundation and structural scope
9. Connect roof, walls and weather protection
10. Price openings and existing-room changes
11. Coordinate plumbing, electrical and comfort systems
12. Build the room fit-out and selection schedule
13. Include site work, access and restoration
14. Connect approvals, selections and the occupied schedule
15. Compare complete addition scenarios
16. Build the all-in home addition budget
17. Normalize contractor proposals
18. Review the live cost forecast
19. Approve changes and reconcile the reserve
20. Close out and retain project records
21. Afterword and source notes

What the examples cover

Work through matched space alternatives, professional fees, cost-per-foot denominators, complete structure and envelope scopes, existing-room connections, service packages, allowance replacement, site logistics and all-in ratios. Six general owner-budget chapters use the HomeCostEngine renovation method with addition adaptation; thirteen chapters add addition decisions. No construction design or local permit rule is supplied.

What you receive after payment

One 64-page English PDF, formatted at 6 × 9 inches, with a clickable chapter outline and 19 printable, fillable planning sheets. After payment, the order page provides your download and our thank-you email contains a link to that order page. Use a compatible PDF reader, save a local copy before entering information and confirm your saved entries persist. No separate account or subscription is required.

The book purchase is £16.99 GBP. Project examples use hypothetical USD amounts because the planning guidance is for U.S. homeowners. They are teaching examples, not local price benchmarks.

Editorial scope and sources

Written by the HomeCostEngine Editorial Team and reviewed October 25, 2026. Source notes link to FTC: Home Repair Scams, Seattle: House Additions and Remodels (local example), EPA: Lead Renovation, Repair and Painting. These organizations do not endorse the book.

This handbook organizes planning decisions; it does not replace a site inspection, engineering design, professional installation, local permit review or a written contractor agreement. Personal use includes printing worksheets and sharing your completed project records with your contractors and advisers.