I wish there was an easy way to judge construction costs. There are so many factors involved, even a 40 year licensed architect should avoid PFA, (Pulled From Air) hypothetical numbers. Some people try to apply a simple cost per square foot. Applying capricious blue-sky numbers don’t take into account all the design factors that can change the outcome. Determining what parts of the design can affect the cost is hard but not impossible to judge. It should be obvious that the simpler the design, the cheaper to build. Everything from the land configuration and location to design details affect the costs. Starting with a budget can always be difficult because of all the unknowns. Rather than trying to get into too many details, let’s discuss initial design issues that can affect costs regardless of it being an ADU or a mansion. I am not including the land cost, location, lot preparation or hook-up fees which one must check independently. I see 6 factors that affect the costs and I’m sure I will be reminded of many more:
The Shape of the Structure: Count the corners; the more there are, the higher the construction costs. Four would be ideal…..if you want a box!
Complexity of foundations: Concrete flat labs are generally cheaper than a raised wood floor. On sloping ground or a hillside, foundation cost will go up. A soil report is becoming standard practice in the North Bay as we discover more faults and poor soil condition. Today if someone brings me a vacant lot, I remind them, there was a reason it hasn’t been built on!
Complication of structure: Wood is the most standard means of residential construction. Using alternatives like steel studs or ZIP Panels will drive the costs up, no matter what the salesperson tells you. A structure can be designed prescriptively, that is, per building code without detailed structural calculations or complex design. Using smaller wood members is always less expensive. Using pre-manufactured components such as trusses and wall panels saves time and money. In California, we have to consider earthquakes and tremors so big door and window openings will add to the costs. Again, the simpler, the lower construction costs.
Complexity of exterior finishes: Windows, doors, siding, roofing all can add a lot to the cost. Todays, high energy requirements and structural requirements force us to use higher priced products. The simpler, the cheaper, but don't compromise on quality. Simple, clean exterior designs can be an architectural statement in itself. When possible, choose “off the shelf” products.
Utility installation: Plumbing and electrical has become major construction costs. Naturally, back-to-back or stacked plumbing lines save time and money. Simple electrical design and controls can be very effective and energy efficient.
Complexity of Interior finishes: This is the most unpredictable, depending on the showroom versus internet interplay. Today, building supply shops are simply showrooms for the internet. But this is still a crapshoot. I try to direct my clients to simpler interior finishes but inevitably the latest issue of “Home & Garden” changes the specs and budget. Pre-manufactured cabinets and other components save time, headache and money.
Getting accurate construction proposals is always a challenge. The more complex the project, the more complex the bid. When we bid a project to multiple qualified general contractors, we try to answer their questions as quickly as possible, and we circulate the responses to ensure everyone is on the same page. When we get back multiple proposals and they’re all close, I feel confident the plans were easy to follow. When they come back miles apart, I’m concerned there were unanswered questions or too many unknowns.
So, I ask you again: do you want a Yugo, or a Mercedes....or perhaps a DeLorean that will be a precious piece of art 50 years from now? Whatever your decision, keep sustainability and long-term maintenance in your decision making.
Chris d Craiker AIA/NCARB would never be satisfied building his own custom home!