Cost Per Square Foot is Deceiving

Cost Per Square Foot is Deceiving Granny flats cost more per square foot than typical single-family homes for several reasons. There are fixed costs associated with permitting and design fees. Margins are smaller for general contractors, subs, and architects. ADUs require new foundations, new walls, plumbing, electric, heating and cooling, and a separate roof, just like a regular house.

There are no economies of scale. You know how you get a significant discount if you buy groceries from Costco because you’re buying in bulk? Building a tiny house is the opposite. Granny flats still require a bathroom and kitchen, which are ‘expensive’ square footage. Since the units are smaller the cost per square foot isn’t offset by extra bedrooms, large living rooms, and hallways you find in larger homes. This space is considered ‘cheaper’ square footage and brings the average cost per square foot down. What all of this means is, yes, the cost per square foot of a granny flat is most likely going to be higher, but you are packing a lot more value into a smaller space. It makes sense that you may pay a little bit more from the get-go.

Here are some general rules of thumb to consider: The larger the unit, the cheaper your cost per square foot. Detached units can be up to 900 square feet depending on your lot size. A 900 square foot unit is likely to be cheaper per square foot than a 450 square foot unit. Regardless of the size, ADUs have fixed costs such as those for utility trenching, instant water heater, kitchen and bathroom finishes, and those costs are divided by the total square footage to calculate the cost per square foot of the ADU. Thus, smaller ADUs end up having a higher cost per square foot. Building up is expensive!

Most people instinctively want to build an accessory dwelling unit above their garage. It can add ~$50 per square foot to your project. If your budget is tight, stick to a single - story. A garage conversion is the cheapest way to convert space into a granny flat.If your budget is very limited, keep the existing envelope of the garage, meaning don’t expand on the current footprint. That would only add to the cost.