The overall cost of a home depends on a great many factors. The first and most impactful factor is the home’s overall size. The complexity and layout of a home and the specific building site are also important factors. Some types of spaces cost more to build than others. Kitchens and bathrooms for example are more expensive than bedrooms or living rooms because of the plumbing, fixtures and appliances. Economies of scale also come into play. A large home with large, open rooms will have less surface area to volume and will cost less to build per square foot than a smaller home. A big home still costs more to build, but the cost relationship between the two is non-linear. With this in mind, it’s easy to see why estimating the cost of a home purely from size is a tricky proposition.
Some design decisions will impact a home's overall cost more than others and it’s true that some spaces are cheaper to build than others. During the design process we identify where your money can be most effectively spent to achieve your design goals.
Basements & Bonus rooms
Basements and bonus rooms are a typical example of what people think of as “cheap space”. It’s sometimes true that these spaces are cheaper per square foot than other types of spaces. Just how much cheaper depends on many factors and what might sound like a very cheap space might actually be just slightly cheaper or the same cost as an alternative once everything is considered. Let’s use the basement as an example. We have had many people request a house with a full basement (we’re looking at you, New England). They might not really need all the extra space, but they say it’s cheap space and is common in the area and they just cannot imagine a home without a basement! Depending on the specific circumstances, a full basement might make perfect sense, but often there are better ways to spend that money.
Basements can be cheaper space per square foot but it’s also much less pleasant space to occupy and if you do not need the extra space why add it? Building down into the ground creates a number of issues, such as moisture management and emergency egress. A good quality basement wall that is well insulated and will not suffer leaks and other issues is a much more expensive wall system than an above-ground wall. It used to be that areas with deep frost lines required the foundation to extend 4-6 feet deep, so the added cost to excavate a few more feet to turn the crawlspace into a basement was worth the money. These days, with the growth of more advanced foundation systems such as code approved, shallow, frost protected foundations, the extra cost of excavating a basement is not worth it. This requires new thinking for people who grew up in basement country, but it is often more cost effective to add a little more space on the main level than it is to add a basement. This space turns out to be more comfortable, usable and accessible too!
Rather than adding space to a home because it’s “cheap”, it’s better to carefully consider the options and add space where it will be the most cost effective and functional. We can discuss these options with you and help you make the best use of your money. It is in coaching you through these decisions that we feel our design fee pays for itself; by helping you make the most of your money.
One Story Vs Two Story
It is a common belief that two story homes are cheaper than one story homes. Again, what is actually the most cost effective strategy is a bit more complicated and depends on factors such as the size of the home and lot, the type of foundation, the program of the home and how well the structural elements line up. Just as with basements, there are some real drawbacks to building a second floor if you don’t have to. Stairs, for example, are expensive to build and take up a sizable amount of space, usually around 100 square feet. Two story homes must also address heat stratification and it might be necessary to add equipment to circulate air so the upstairs does not get hot and stuffy. It is also more difficult to design an optimized two story home and often there are competing priorities, such as keeping the structure simple while creating spaces that are exactly the right size and orientation. There is a bit of extra cost in labor to build a two story home because of the extra work hauling materials, setting up scaffolding, renting a crane to set the roof etc. It is true that a two story home has a smaller footprint and less roof area. 
These things can definitely make a two story home cost less than a one story, but if it means a more complicated structure or a bigger home in order to make the two stories line up (not to mention the extra space for stairs) it can easily end up being a wash or even more expensive. This is not to say that everybody should build one story homes, but just that the decision to build one or two story is a bit more nuanced than it initially appears. Again, this is where hiring a professional to help walk you through these options and tradeoffs based on your specific program is well worth the money.
Compact vs Spread Out Design
A compact vs a spread out design is a great example of competing priorities. On one hand, the more compact and simple the design, the cheaper and more energy efficient it will be. The more corners a home has, the more difficult the foundation, framing and roofing will be to build which will drive up the cost. The more spread out you make a home, the greater the ratio of exterior surface area to interior volume. The more exterior surface area, the more exterior wall and roof is required, along with interior and exterior finishes, wiring, insulation and windows. This increase in wall area not only effects the cost, but also leads to greater energy loss. These are all good reasons to keep a home as simple as possible. On the other hand, a more spread out design has a great many benefits. By letting a home meander a bit, you can create interesting outdoor spaces that are defined by the house. The interior spaces become more dynamic and interesting and the transitions from space to space are easier to define. The timeless design concepts in A Pattern Language often favor a more spread out design. Patterns such as: long thin house, wings of light, light from two sides of a room, intimacy gradients and positive outdoor spaces all lend themselves toward a slightly more spread out design. The decision of how spread out or compact to make a home depends on a number of considerations; the budget, the climate, the lot, the program, the level of energy efficiency and the desired aesthetics to name a few.