Build Out Build Up, or Bump Out? How to Choose the Right Home Addition

You have had the conversation more than once by now. The house mostly works. You like the street, you like your neighbors, and you have no interest in starting over somewhere else. What you do not have is one more room.

A bedroom for a parent moving closer. An office that is not the end of the dining table. A second bathroom so the mornings stop being a negotiation.

Then you start looking into it and the advice pulls three directions at once. Build out. Add a second story. Push the wall out a few feet and call it done. Every option sounds reasonable in a search result, and none of them tells you which one fits your house.

Hiring a contractor shouldn't be a gamble.

This page is about that decision. Get it right and everything after it gets easier.

Build out if the lot and the way you want to use the house allow it. It is usually simpler, usually less expensive, and often easier to make it look like it was always there.

Building up is a different category of project. Before anyone draws anything, an engineer has to confirm the existing foundation and framing can carry a second floor. Sometimes they can. Sometimes they can with reinforcement, which costs money nobody planned for. The roof typically comes off and gets rebuilt, and the rooms underneath are unusable while that happens.

There is one situation where building up is clearly right: when the lot will not let you build out. If setbacks, lot coverage limits, or an easement leave you nowhere to expand at ground level, up is the only direction available. That is a constraint, not a preference, and it moves the investment substantially.

One more thing worth saying plainly. A second story that does not match the house reads that way from the street, permanently. Proportion, window placement, and roof pitch matter more here than on any other kind of addition.

More often than people expect. A few feet in the right direction can solve the problem you actually have.

• Kitchens. An older kitchen with no room for a table becomes a kitchen with an eat-in space. An L-shaped layout becomes a U, which buys counter and cabinet run you cannot get any other way.
• Bathrooms. Enough width to separate the shower from the tub, or to turn a bathroom two kids share into one that works for both of them.
• Bedrooms. Usually not about the sleeping space. It is about a real walk-in closet, or a built-in desk that gets homework off the kitchen counter.

If a bump-out solves it, take the bump-out. There is no prize for building the larger project.

Additions in the Phoenix metro run $125,000 to $750,000 and up. Where a project lands depends far more on structure and scope than on finishes.

Building up rather than out, or folding a remodel of the existing house into the project, pushes you toward the top of that range. One clean tie-in holds you near the bottom.

For the full breakdown, the cost drivers, and what has changed since 2019, see Home Addition Cost in Phoenix.

This is the part that catches people, and it has nothing to do with finishes.

Ross and Jen came to us in Scottsdale with a growing family and a floor plan that had stopped working. We designed and built a two bedroom, one bathroom addition, and moved the kids' rooms and their bathroom to the opposite side of the house from the primary suite. A split floor plan, which is what they actually wanted and could not get by rearranging what they had.

The construction went smoothly. What surprised them was that the size of the combined addition and remodel scope required fire sprinklers throughout the entire house, not just in the new rooms.

Scottsdale has required fire sprinklers in residential construction since Ordinance #1709 passed on June 4, 1985, with the single-family requirement applying to homes built after January 1, 1986. That made Scottsdale one of the first cities in the country to do so.

The threshold for an existing house is published by the city. For a Scottsdale residential improvement that reaches 25 percent or more of the existing structure's valuation, as calculated with the city's Fire Sprinkler Valuation Worksheet, fire sprinklers are required throughout the residence. The city makes that determination during plan review.

This is not a small line item, and it is not a reason to avoid an addition. It is a reason to find out early. A requirement identified during design is a decision you get to make. The same requirement discovered later is a problem.

Here is one worth telling, because it did not go smoothly and the answer to that question is the whole point.

We were building a new primary suite in the Arcadia area of Phoenix. Bedroom, walk-in closet, spa-like bathroom. The homeowners planned to redo their backyard landscaping once we finished, which is common enough that we sequenced it with them and told them when to bring their landscaper in.

The landscaping company they hired brought in several tons of dirt to raise the yard up to the height of the slab at the back of the house, and changed the drainage path of the yard while they were at it. Both of those are serious mistakes.

We got a monsoon rain roughly 24 hours before we were scheduled to install new hardwood throughout the whole house and the new addition. The homeowner called in a panic. Water was coming in under the new back door.

We started drying the slab immediately. Then we tore out a section of the new landscaping and dug the dirt back down to create an isolation point between the yard and the house, so another rain would not do the same thing. The landscaper told us he could not get anyone out for a week. We did not wait, because the house needed protecting that day and the work was going to have to be redone regardless.

The homeowners brought us into every conversation with that company afterward, and the building inspector and I walked them through what they had gotten wrong. Getting them to redo the work to something close to correct was still a fight.

This is what hiring on price alone tends to look like from the inside. The savings show up first and the cost shows up later, usually to someone else.

More on that: The Risks of Hiring the Low Bidder.