An addition is the part of your house that has to negotiate with everything already there — the foundation, the roofline, the drainage, the property line and the local code. Most of the cost and nearly all of the risk are decided before a single wall goes up, in decisions that depend on one another in a fixed order.
Why planning comes first
The reason to plan hard before requesting bids is simple: contractors can only price what you describe. If your idea is still loose, each firm will quietly fill the gaps with its own assumptions, and their numbers will not be comparable. Tightening the plan first is what turns three quotes into a real comparison rather than three different projects wearing the same name.
Treat the pieces below as dependencies, not a menu. Each one constrains the next, so working them out of order usually means redoing them.
Start with the site
Before anything else, understand what the site allows. Which direction can the house grow — out into the yard, or up over existing structure? Where do setbacks, easements and the septic or drainage field fall? What is under and around the addition matters as much as the addition itself: a footprint that works on paper can be ruled out by a property line or a buried utility. Site realities set the outer bounds of everything that follows.
Design and approvals
Once the envelope of the possible is clear, design within it — and design with approvals in mind. Zoning rules, any homeowners' association covenants, and the permits your building department requires are not paperwork you attach at the end; they can reshape the design itself. Confirming what is permitted, and what review it will need, before the drawings are final saves the expensive loop of designing something you cannot build. Permits and zoning vary widely by locality, so verify the specifics with your local building department.
Write the scope
With a workable design, write down exactly what the project includes and, just as importantly, what it does not. A clear scope names the finishes, the fixtures, the structural work, the utilities to be extended, and how the new work meets the old. This is the document that makes bids comparable and change orders rare; ambiguity here is what later arrives as an unexpected line on an invoice.
Set the budget
Only now, with site, design and scope settled, can a budget mean anything. Set a figure you can defend, and hold back a contingency for the surprises that additions specialise in — what the existing structure hides until it is opened up. A budget attached to a firm scope is a tool for comparing bids; a budget attached to a vague idea is a wish. If the numbers that come back do not fit, the honest fix is usually to adjust the scope, not to hope a low bid holds.
Pre-bid checklist
Before you request bids
Aim to check every box; each unchecked item is a place where two bids can silently diverge.
- Direction of expansion decided (out vs. up), consistent with the site.
- Setbacks, easements and drainage/septic locations confirmed.
- Zoning and any HOA covenants checked against the design.
- Permit requirements and review steps confirmed with the building department.
- Design resolved enough to price — not still in flux.
- Written scope listing inclusions, exclusions and finishes.
- How new work ties into existing structure and utilities specified.
- Defensible budget set, with a contingency for hidden conditions.
- Identical scope package prepared to give every bidder.
Sources
Hiring and contract guidance informed by the National Association of Home Builders consumer checklist for finding and hiring a builder or remodeler. Zoning, permit and setback requirements are local and must be verified with your building department. This is an editorial project; no professional credential or client relationship is claimed.