The first question about building an ADU will likely be, how much will it cost?
Let’s go over what’s involved and how cost is established.
Project Cost Components
Total project cost is comprised of two components: Hard Costs and Soft Costs. Hard Costs are the tangible “bricks and mortar.” Soft Costs are everything else: surveys, engineering, permits, documentation, fees, contingencies, etc. Budgeting for the work must include both components known or estimated.
The bottom line cost question is complicated because there are so many variables. First some macros.
The construction industry tends to lead the cyclical national economy. That means that when the national economy is down you are more likely to get lower numbers than when the economy (and building) is hot. It’s economics 101 aka Supply and Demand. You probably won’t want to wait through a cycle but it’s useful to understand. A second macro is the cost difference between urban and rural areas. Construction cost in rural areas is typically lower.
The third macro is the most dependable. The final cost will be higher than you anticipated. This is what contingencies are designed for. So, the larger your contingency the smaller your frustration over final cost. We recommend 8% to 10%. Sounds high? You’ll remember this warning when closing out your project.
Construction cost numbers date quickly so we’re not using them.
Our simplified Cost Range Comparison below gives you the big picture. View in Landscape Mode (Horizontal) on a mobile device.
CARPENTER with a pickup truck ◼︎◼︎◼︎◼︎◼︎
RESIDENTIAL BUILDER ◼︎◼︎◼︎◼︎◼︎
GENERAL CONTRACTOR ◼︎◼︎◼︎◼︎◼︎
Generalizations are deceptive. For example pick any design and incorporate high end structural systems, materials, details, appliances, plumbing fixtures and mechanical systems. Cost it with a carpenter with a pickup truck. Then, take the same design using the simplest, least expensive structural system, materials, details, appliances, plumbing fixtures and mechanical systems. Cost it with a General Contractor and the cost will likely be close to the same.
Building less costs less, but don’t expect a small house to have a much lower square foot cost than a conventional size house, it’s usually higher. Kitchen and bath costs are not lowered by total area reduction. With less area over which to average fixed costs the square foot price of a small house is usually higher. However, savings appear over time as the lower long-term costs of operation and maintenance accrue.
For materials, components and equipment we recommend quality. Choices based on quality and durability yield long term value. The jargon is Life Cycle Cost.