You're thinking about adding an addition or a dormer to the top floor of your home. Where do you even start with that? The first thing you'd really want to start with is ensuring that the local zoning ordinance is going to allow you to do work like that without applying for any variances. After confirmation that you can do those things as-of-right, you're off to the races…but really, we want to make sure that budget is in line with reality from the start.
One of the main ways to start thinking about how much an addition is going to cost is just by using a rule of thumb that starts with a baseline. That means you're probably not going to get an addition for less than $450 per square foot and up, depending on what is in the addition. That depends on the scale, the site, and the complexity of the site. Is it on a hill? Are there different soil types? You probably won't know if there are different soil types without a geotechnical engineer, or unless you can see actual rock coming up above your grass — because this is going to complicate your foundations. But starting with a baseline of $450 per square foot is a good way to think about how much an addition would cost. In a place that is a wealthier neighborhood, you're starting at $500 per square foot or more.
When you're adding an addition, you don't want a Frankenstein appendage that doesn't look like the rest of the house. You're trying to meld it into your home and make it look like it's always been there and make not only the outside but the inside flow, because now you have a real opportunity to change the way that you move around in your house. You don't want to just have added space. You want to improve the entire way that you move through your house and how all the rooms are interconnected. So that may involve adding a hallway, changing a bathroom, or changing your existing kitchen into a bathroom and moving the kitchen into an addition. These are the drivers (especially when it comes to things like plumbing points and gas lines) that are going to bring more cost to the project, because moving each plumbing point and all of those things will always be increasing the cost.
Some general pricing that I've spoken to a local contractor colleague of mine includes:
Full bath gut renovation: starting at $30,000*
Full kitchen gut renovation: starting between $55,000 and $85,000*
Powder room gut renovation: starting at $20,000*
Laundry renovation: starting at $10,000 to $20,000*
Mini-split (wall-mounted or ceiling cassette): about $5,000 to $6,000 per unit*
These are not hard costs (every project is different) but it is something to begin getting a sense of how much things cost.
Finishes are going to move the needle, but not overall that much. Obviously, if you're going for really premium things, that can move the overall cost significantly. But with a good architect or interior designer that includes selection services, you can keep your budget in line and get a unique, bespoke appearance and finishes with a personalized aesthetic in the end that is personal to you.
It's also important to include a 10 to 20 percent contingency buffer, especially when it's a renovation. Renovations — and especially older home renovations — tend to have more funky and unknown conditions that can't be anticipated until walls are opened up or foundations are exposed.
One more thing to keep in mind: most contractors and architects will tend to give a very wide range from only a verbal description, because without drawings, it's impossible to know exactly what the scope of work is — and therein, what it will cost. So if you're getting ballpark numbers early on, expect them to be broad until the project is more clearly defined.
It's an exciting prospect, and you don't want to skimp on the design process in order to make sure that even the floor plan and the overall functionality of the project is right.
*Written in February 2026. Costs and conditions may vary by location and market.