Adding Up: The Challenges of Building an Addition on Top of Your Garage

Who wouldn’t want to add another 400-500 square feet to their home? That’s enough room for a luxurious master suite, a couple of rooms for the kids… there’s plenty you can fit in that kind of square footage. But finding a place to stick that extra space can be tricky—but definitely doable. We’ve found that adding a second story to an existing 2-car garage can be a relatively simple and cost-effective way to grow your home. Like all significant building projects, though, there will be challenges—and building on top of an existing structure presents unique issues to be addressed.

Here is a list of common challenges to keep in mind if you’re considering an addition atop your garage:

· Adjusting the height of the garage. You might need to shorten or heighten your existing garage walls to give your second story the right height and match the new structure’s height (if you so desire) with the rest of your home—or give enough clearance for any windows you’ll include in your second level. You’ll also need to make sure your garage keeps enough height for your garage door to remain functional.

· Matching your exterior. Depending on the age of your garage and house, it might be difficult to find a matching exterior surface. Even if you find the same shingles, brick, siding, stone, etc. that were originally used, older surfaces may be faded or stained. Keep in mind too that, whatever materials are used, you likely won’t want your new larger garage to dwarf your main house or clash with it structurally.

· Flooring and support. You’ll need a floor on your second story that doesn’t bow or flex too much—this could damage flooring and cause serious problems. Your builder will have to develop a way of making the floor sturdy enough without adding support posts that will get in the way of parking cars in the garage.

· Heating and cooling. It’s not likely that your current HVAC system has enough output to effectively cool and heat an additional four or five hundred square feet. You’ll need to come up with a strategy for keeping your addition’s temperature properly regulated. This may mean upgrading your existing HVAC unit—or possibly adding a second one. Solutions will depend on the size of your existing system, placement of ductwork, your budget, and more. Talk to your builder about how best to address this issue.

· Plumbing. This can be tricky. If your wastewater drain is in a central location, you might find yourself working through a lot of drywall to connect the new drain to the existing one. You might even have to reframe parts of some walls or move some ductwork. This is an important consideration when deciding the layout of your addition, how it will be used, and where the plumbing—if necessary—will go.

· Cost. Figuring and managing costs during any construction job can be difficult. All of the above considerations—and many other not mentioned here—will impact price. A good starting point is to estimate between $275 and $300 per square foot of your addition. This range doesn’t include issues like HVAC or extensive structural issues that might arise. This cost per square foot is based on a relatively simple, standard addition. High-end fixtures, flooring, and so forth will naturally nudge your price higher. And there’s nothing necessarily wrong with that—as long as you have it in your budget and you plan thoroughly enough to avoid being surprised by any of the challenges above.