Is it cheaper to build up or out when you add on to your home?

Why is building out usually cheaper than building up?

Building out is new work on open ground, while building up is new work stacked on top of old work. A ground floor addition needs its own footings, walls, and roof section beside the house, and the old house is touched only where the two meet. A second story puts new weight on walls and footings that were sized for a single story, so the old structure has to be checked, reinforced, and partly opened before the new floor goes on.

Going up also pays for work that adds no usable room: taking off and rebuilding the roof, protecting the house while it is open, the staircase, and running plumbing, wiring, and ducts up through finished rooms below. Building out has costs of its own, mainly the new foundation and the roofline tie-in where the new roof meets the old, but they sit at one edge of the house instead of running through all of it.

The tie-in is where we slow down on an addition. Valleys and flashing where two roofs meet are where leaks start, so we lay out the new roof to carry water away from that joint wherever the design allows. The exceptions come from the lot and the house: a yard the zoning will not let you build on, or an old structure that turns out to need little help to carry a second floor.

What does adding a second story actually involve?

Adding a second story is a structural project first and a room second. Before the design goes far, an engineer works out how the weight of a new floor, and the extra sideways force a taller house takes in an earthquake, will travel down through the old structure to the ground. That answer decides how much of the house gets opened and reinforced.

In an older house the weak links are usually the ceiling joists, which were sized to hold up a plaster ceiling rather than people and furniture, and walls that were never braced for the forces a second floor adds. Strengthening them can mean opening plaster in rooms you were not planning to touch. The usual order of work:

• An engineer checks the existing foundation, walls, and framing against the new loads.
• New footings and posts go in under the points where the added weight will land.
• The roof comes off, and the new floor is framed over or beside the old ceiling joists.
• Walls and a new roof go up, and the shell is closed against weather as fast as possible.
• Shear walls go in below, the stair opening is cut, and new plumbing, wiring, and ducts are run through the old house.
• Inspections at each stage sign off the work before walls and ceilings are closed.

Can your foundation carry a second story?

Sometimes, but only an engineer looking at your actual foundation can tell you. Many pre-war Pasadena houses sit on a raised perimeter foundation over a crawl space, poured decades before anyone imagined a second floor on top, and those footings can be shallower and narrower than a new one would be. Whether the foundation for a second story is already there, needs strengthening in places, or needs replacing is the first question to answer.

We start that conversation in the crawl space. Cracks in the footing, sections that have settled, old repairs, and whether anchor bolts tie the house to its foundation all tell the engineer where to look, and they tell you early whether the second story plan has a foundation job hidden inside it. That job can mean new footings under posts, a strengthened perimeter, or at worst a new foundation under the whole house, which changes the comparison with building out.

Where does the staircase go, and what room does it take?

The staircase has to land somewhere on the ground floor, and wherever it lands, it takes space from a room you use today. A stair needs its full run of floor, headroom above it, and landings at top and bottom, so in a compact bungalow it often costs a bedroom corner, part of the living room, or a hall closet and some of what sits beside it.

Placement also decides the upstairs plan. A stair that arrives near the middle of the new floor wastes less space on hallways than one pushed to an exterior wall, but the middle of an old house is often where the bearing walls and plumbing run. Settle the stair location before anything else is drawn, because moving it later means redesigning both floors.

Where the plan is tight, a small ground floor bump-out can hold the stair, so the new floor goes up without taking a room away downstairs. It combines both approaches, so it needs room inside the setbacks as well.

Will you have to move out while the roof is off?

For a full second story, usually yes. Once the roof is open, the rooms below sit under tarps and new framing for a stretch, and ceilings get opened where the posts and the stair go through. Some families stay through it, but it is hard living, and we would plan the job assuming you are out while the house is open.

An older house adds a health reason. Opening ceilings in a home built before 1978 means treating the paint as lead until it is tested, and some older plaster, joint compound, and popcorn ceilings contain asbestos, so testing comes before anything is torn out. Timing matters too: an open roof is most exposed to the winter storms that arrive from late fall into early spring, so the weeks with the roof off belong in the dry months.

A ground floor addition is a different experience. The new rooms are framed, roofed, and closed in while the old exterior wall still stands, and that wall is opened only near the end, so staying home is usually workable. For either type, the open stage stays shorter when the crew is not split across jobs; ours works one job at a time, so the house is not left under tarps while we are somewhere else.

How do your lot and setbacks make the choice for you?

They can rule out one option before cost comes into it. A ground floor addition has to fit inside the setbacks from each property line, and many cities also cap how much of the lot buildings can cover or how much floor area it can carry, so a house already near those limits may have no legal room to build out.

South Pasadena shows it clearly: its older lots are often narrow, and the required distance from each property line can use up the room to build out before design even starts. Going up has limits of its own, though. Height caps apply, and in some cities the upper floor must sit farther from the side lot lines than the floor below, which can shrink a second story to less than the footprint under it. Ask the city for both sets of rules before you compare costs.

Building out also spends yard. Before you commit, count what the footprint would displace: a patio you use, the driveway turn to a detached garage at the back, or the only level ground on the lot. Going up keeps all of that, which is part of what the extra structural work buys.

What does design review mean for a second story in Pasadena?

In a Pasadena landmark district such as Bungalow Heaven, a second story visible from the street goes through design review before the building permit, and that review becomes part of the price of going up. Review can ask for changes to height, roof form, or where the new floor sits, so get the engineer's read on the existing house early, but hold the detailed structural design until review has settled the shape, rather than paying to engineer a plan twice.

A second story counts as a major change, so its review can go to the Historic Preservation Commission rather than stay with planning staff, and that adds time and drawings before plan check begins. A rear ground floor addition that cannot be seen from the street often faces a lighter review, which in a landmark district can tip the whole decision toward building out. Before a second floor is drawn, confirm at the city's planning counter what historic protection, if any, covers your house.

The same logic applies beyond Pasadena. San Marino runs some of the most demanding residential design review in the San Gabriel Valley, and a second story there can draw close attention to how it fits the street.

When is a separate unit a better answer than an addition?

When the person who needs the space would rather have a door of their own. A parent moving in, a grown child, a home office, or a guest suite may be better served by a converted garage or a small backyard building than by rooms added to the house, and building separately leaves the main house's roof and structure alone.

The trade is connection. A separate unit means walking across the yard, building a second kitchen and bathroom if it is to be a full dwelling, and following a different set of rules. If what you need is a bigger kitchen, a family room, or a third bedroom down the hall from the kids, it has to be part of the house, and the choice is still up or out.

Which checks settle the choice for your house?

Five checks, done in order, settle most build out versus build up decisions, and the early ones can end the comparison before price is even discussed. Once they are answered, a builder can price the path that is left for your house rather than a generic one.

• Check for level ground inside the setbacks and lot limits before pricing a ground floor addition.
• Have an engineer judge the foundation and framing before pricing a second story.
• Confirm with the city whether a street-visible second story would need design review.
• Decide what the yard is worth to you before trading it for floor space.
• Plan where your household would live during the open-roof stage, and in which season.