How to plan a home addition: the drawings, in order
An addition is the remodel where the order of work matters most. The lot decides how big it can be, the existing house decides where it can connect, and only then does a design make sense. Here is the sequence most homeowners follow, the drawings each step produces, and who is allowed to draw what.
Updated 2026-10-18. Zoning and permit rules are local. Use this as a map, then read your city or county planning and building pages for the exact numbers.
Step 1: find out what the lot allows
Before any sketch, look up the zoning of your lot. Three numbers decide most additions:
- Setbacks: how close a building may come to the front, side and rear property lines.
- Lot coverage or floor area ratio: how much of the lot buildings may cover, or how much floor area they may have.
- Height limit: which decides whether a second story is possible.
You also need to know where the property lines really are. A recorded survey or plat from your closing papers or the county is the place to start; when the addition comes close to a line, many offices want a new survey, which only a licensed land surveyor can make. Check for easements and, if you have one, your HOA rules.
Step 2: get a measured plan of the existing house
Every addition design starts from the house as it stands: where the outside walls are, which rooms touch the new space, where windows, doors, the electrical panel and the plumbing are, and the floor and ceiling heights you must meet. If you have no plan, our guide on how to find the floor plan of your house lists where to look, and how to measure a room for drawings shows how to measure it yourself. Measure the outside of the house too, and the height from the ground to the floor and to the eaves on the side you plan to build.
Step 3: compare layouts before you commit
With the existing plan to scale, sketch two or three ways the addition could fit: a bump out, a wing, or building up. For each, check that it stays inside the setbacks, how the rooms connect, what it does to light in the rooms beside it, and how the new roof meets the old one. A simple 3D view makes the roof and the view from the street much easier to judge than a plan alone.
Step 4: the permit drawing set
| Sheet | What it shows | Usually drawn by |
|---|---|---|
| Site plan | Lot lines, existing house, addition, setbacks and lot coverage figures | Designer, from the survey |
| Existing and proposed floor plans | Every affected floor with walls to remove and new rooms | Designer or drafter |
| Exterior elevations | Each side of the house with the addition, heights and roof lines | Designer or drafter |
| Foundation, framing and roof plans | Footings, beams, headers, rafters or trusses and how they tie into the house | Often an engineer or architect |
| Building section | A cut through old and new parts, ceiling heights and insulation | Designer, checked by the engineer |
| Energy compliance | Insulation, windows and heating for the new space, in the format your state uses | Designer or energy consultant |
Unlike most interior remodels, an addition always involves structure: a new foundation, new framing and a roof connection. Many states let a homeowner or drafter prepare drawings for a single family house, but building departments often still ask for an engineer's or architect's stamp on the structural parts. Our guide on remodel drawings without an architect covers the state rules.
Step 5: bids, then permit
Contractors can only give firm prices on a defined design, so send the same drawing set to each bidder. Online cost figures for additions vary widely because foundations, roof tie ins and finishes vary so much; bids on real drawings are the only reliable number for your house. Our guide on what a contractor needs to bid a bathroom remodel lists the inputs that make bids comparable, and the same idea applies to an addition.
What usually goes wrong
- Designing first and checking setbacks later, then shrinking the design.
- Assuming the old floor level and ceiling height without measuring, so the new floor ends a step off.
- Placing the addition over a sewer line, septic field or utility easement.
- Forgetting the room the addition covers: a bedroom that loses its only window loses its escape opening too.
Where we fit
We draw the existing conditions plan from your measurements and photos, and an overnight 3D visual helps compare layout options ($99 at the pilot price). We do not design structure or stamp drawings: the structural sheets of an addition come from a licensed engineer or architect, who can work from our plan of the existing house.
Free first 2D floor plan
New customers get one 2D floor plan of one floor of their home free, one per new customer. Use the code FIRSTPLAN on the quote form.
- What you send: the room measurements of that floor (a hand sketch with numbers is fine) and photos of each room.
- What you get: an as-built 2D floor plan of that floor as a PDF, drawn from your measurements.
- When: usually within 5 US business days after we have your measurements and photos. If we are behind, we tell you the date before we start.
- No card, nothing to pay, no obligation to order anything else.
- More plans: first plan free with FIRSTPLAN, each extra plan $10 (another floor or another property).
An existing conditions plan does not certify the structure or the lot. Structural work needs a licensed engineer or architect, property lines need a licensed land surveyor, and permit approval is not guaranteed.