01Rear bump-outTwo to six feet across the back. Often possible without a new foundation line.
02Full rear extensionA new room the width of the house. The roofline is the whole design problem.
03Side wingWhere the setback allows it. Cheapest way to add a large single room.
04Second storeyDoubles the floor area on the same footprint, and asks the most of the existing structure.
05Partial second storeyOver the garage or one wing only. Half the structural argument, most of the bedrooms.
06Great room additionOne large volume with a vaulted or trussed ceiling, opened to the existing plan.
07Glazed garden roomSteel or aluminium glazing onto the garden. Specify the glass for heat, not just for looks.
08Sunroom or conservatoryCheaper than a full extension, and only comfortable year-round if it is conditioned.
09Primary suite additionBedroom, bathroom and closet as one wing. The most common reason people stop looking to move.
10Kitchen extensionPushing the back wall out to get the island and the table into one room.
11Screened porchRoofed, screened, unconditioned. The best value per square foot of anything on this list.
12Covered outdoor livingFireplace, kitchen and a roof. Extends the season by two months at each end.
13Garage conversionInsulate, condition, floor and glaze it. Cheap area, and you lose the garage.
14Attic conversionHead height and stair position decide whether it is possible at all.
15Dormer additionBuys standing room in an attic and changes the elevation. Both matter.
16In-law suiteA wing with its own entry and bathroom. Zoning may treat it as a dwelling.
17Mudroom and drop zoneSmall, unglamorous, and the room families say changed the house most.
18Two-storey stacked additionLiving below, bedroom above, one foundation. Best value when the structure allows it.
19Breezeway to the garageConnects two buildings and creates a courtyard between them.
20Matched materialsSiding profile, brick blend and window sightlines specified against what is there, not near it.
