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Home Page > Additional Design Resources > Cost of 750 SF Home / ADU

COST OF 750 SF HOME / ADU

Here we break down the actual cost of a 750 square foot ADU build completed in 2025.​

 

From the Owner of 1510 Engineering, John Hockman, P.E. who owned and operated a residential construction company for 11 years.

The first question everyone has when considering a new home or ADU project is “how much will it cost?” The answer is difficult, as costs will vary widely depending on your scope of work, location, and the tradesmen you hire. Usually, people ask me for a ballpark price per square foot, which isn’t a great metric because it varies with project size and tends to increase as the square footage decreases. With smaller projects, you lose the economies of scale, and you have fixed costs like water and sewer service that are the same whether you're building a 400-square-foot house or a 2000-square-foot house.

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This write-up is intended to help people considering a smaller build, especially those with a tight budget who want to keep costs as low as possible. The ADU profiled below was about as affordable as you can get for 750 square feet.

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First off, it’s important to note that for this project, the water and sewer tap fees were already paid, so we only have the cost of tying in water and sewer service. Tap fees are expensive, typically around $20k, depending on your water utility. We do have some municipal development fees for this project, which you will find in most jurisdictions, and the amounts can vary from less than $1k to upwards of $20k. In our example, the development fees were $3,295.88.

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So first up, we have design, permitting, and development costs totaling $10,515.21. All the design work was completed by 1510 Engineering.

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  • Site Plan Drawing - $1,000

  • Complete Design & Structural Engineering - $2,880

  • HVAC Design - $450

  • Soil Engineering Report - $1,200

  • Foundation Design - $1,000

  • Building Department Plan Review Fee - $96.24

  • Municipal Development Fees - $3,295.88

  • Building Permit - $593.09

     TOTAL: $10,515.21

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Once you have your permit, you’re ready to get water and sewer service to the footprint of the new building. This typically involves tying in a buried water line at the street, or at the main house if you’re building an ADU. A buried sewer line is also tied in at the street, or a lateral is made to the existing sewer running through the yard for an ADU. If the project is in a more rural area without municipal sewer service, you’ll need a septic system, and a water well if you don’t have municipal water service. For our specific project, the cost of water and sewer excavation, plumbing, inspections, backfill, and related work totaled $10,435.84. We also have some site prep work- misc. cleanup, grading, and removing an old shed and a large tree in the way.

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  • Water & Sewer Excavation, Plumbing, Inspections, Backfill, Etc. - $10,435.84

  • Site Prep, Clean-up, Grading, Shed Removal - $2,138.26

  • Tree Subcontractor for Tree Removal - $1,893.75

     TOTAL: $14,467.85

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Now that water and sewer are stubbed out of the ground, the real fun begins- foundation excavation, concrete forming and pouring, and backfill. If your layout is super efficient, and you maximize the square footage within a minimum length of perimeter wall, you could build 750 square feet with as little as 112’ of perimeter wall, which would be $26,320. The layout we’re actually building in this example isn’t quite as efficient, with 123’ of perimeter wall for a total cost of $28,905. For this example, we’re building a crawl space foundation because we have soft, sandy soils with expansive clay lenses and also a high probability of radon in the soil. A frost-protected shallow foundation with a concrete floor is cheaper, but it may subside or heave on questionable soils. The crawl space foundation will lift the floor system off the ground, and the reinforced concrete perimeter stem wall is stiff enough to resist any subsidence or heave. We can also capture radon below the crawl space vapor barrier and expel it. As part of the foundation work on this actual build, a tree stump in the way needs to be ground and disposed of, another $643.36.

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  • Foundation Excavation, Concrete Form & Pour, Steel Reinforcement, Inspections, Backfill, Waterproofing Paint, Etc. - $28,905

  • Stump Removal - $643.36

     TOTAL: $29,548.36

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Now we’ve spent an eye-watering $54,531.42, and all we have to show for it is a concrete wall and some pipes sticking out of the ground. But the despair of these early phases and the endless piles of dirt have passed; it’s time to frame! Framing is just the best phase; it’s my favorite and always so satisfying to see a project take shape. The framing on our actual project included 2x10 floor joists and floor sheathing to make the floor frame over the crawl space. The framing was conventional 2x6 exterior walls with OSB sheathing and a truss frame roof. The total framing labor hours were 233.75, with one guy billing at $38/hr and the lead framer at $45/hr.

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  • Framing Lumber, including Trusses and Misc. Fasteners - $11,930.17

  • Framing Labor - $10,195

     TOTAL: $22,125.17

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I want to circle back to the framing labor hours- if you’re considering building a project like this as an owner-builder, and you have some carpentry experience to where you can frame something like this in say 250 hours, that’s 13 weeks if you devote 20 hours every weekend, and you’ve saved $10,195 on your 750-square-foot house. If that sounds like a good deal to you, navigate over to my Owner-Builder Resources (Coming January 2026!) page for more information about the pros and cons of being an Owner-Builder.

750 SF ADU Framing.png

With the framing complete, it’s time to get the structure dried in by installing the roofing, windows, and doors. Keeping with our bare-bones budget build, we're using cheap asphalt shingles, builder-grade vinyl windows, and a front door from the big-box store.

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  • Roofing Subcontractor and One Roll Synthetic Underlayment - $4,375.72

  • Vinyl Window Pack - $4,695.56

  • Window Flashing Tape & Fasteners - $152.76

  • Vinyl Slider Door - $625.40

  • Fiberglass Entry Door - $555.59

  • Keypad Deadbolt & Brushed Gold Hinges - $50.33

  • Window & Door Install Labor - $845.50

     TOTAL: $11,300.86

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If your project is scheduled with trades stacked on top of each other, so it’s done as quickly as possible, and to make the tradesmen as grumpy as possible, then the plumbers are probably stubbing their vent pipes through the roof just as the roofers are starting. For this project, the plumbers supplied the water heater, and the builder supplied all the fixtures. The total plumbing cost, including fixtures and the shower enclosure installation, was $14,126.57.

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  • Plumbing Subcontractor, 2 Full Baths, Price Includes Water Heater - $9,000

  • Plumbing Fixtures including Fiberglass Tubs & Surrounds, Sinks, Faucets, Toilets, Etc. - $4,576.57

  • Tub Surround Install Labor - $550

     TOTAL: $14,126.57

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Closely following the plumbers is the mechanical contractor. This project is electric heat only via a 3-zone 27k Btu mini-split heat pump. The mechanical contractor also takes care of the dryer vent, bath fans, and crawl space ventilation fan.

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  • 3-zone 27k Btu Mini-Split Heat Pump - $2,853.32

  • Heat Pump Installation, Dryer Vent, Bath Fans & Crawl Space Fan - $5,352.22

     TOTAL: $8,205.54

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And last of the licensed trades is the electrician, who basically supplied everything except a handful of light fixtures that the owner picked out. Electric service was overhead, so no trenching was required, and no electric tap fee was required for this particular utility.

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  • Electrical Subcontractor including Service Install - $11,030

  • Lighting Fixtures Cost - $78.46

     TOTAL: $11,108.46

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While the electricians are working inside, work is happening outside to wrap the house in trim and siding, build the porches, and put on the finishing touches so the house is complete on the outside.

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  • Exterior Trim, Deck Framing & Decking Material - $3,070.93

  • Exterior Trim, Deck Framing & Decking Labor - $1,653

  • Siding Cost - $2,273.25

  • Siding Labor - $1,507.50

  • Exterior Paint Cost - $699.60

  • Exterior Paint Labor - $2,510

  • Exterior Clean-Up Labor - $500

     TOTAL: $12,214.28

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Insulation goes in next. Fiberglass batts, R-21 in the walls and R-49 in the roof. The insulation crew also provides all air-gap sealing, crawl-space insulation, and vapor barrier. A 3rd party conducts an infiltration test to assess air sealing and checks the bath fan performance per code.

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  • Insulation Subcontractor - $4,064

  • Infiltration Testing - $500

     TOTAL: $4,564

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Things are getting close now! We’re ready for drywall, painting the walls, setting the kitchen cabinets and bath vanities, and installing the flooring. Drywall is finished with a level 4 smooth finish, which is essentially a more budget-friendly option than level 5. Not as perfect as a level 5, but you won’t see the imperfections as long as you pick a lighter wall color. Paint is applied to all walls and ceilings once drywall is complete, and trim painting is done after the trim is up. After painting, all the cabinets go in, and vanity tops and kitchen countertops are set. Being a budget job, all the cabinets are off-the-shelf from a big-box store, and the kitchen countertops are butcherblock, also from the big-box store. Flooring is click-lock laminate throughout, except in the bathrooms, which have sheet vinyl.

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  • Drywall Subcontractor, Level 4 Smooth - $6,400

  • Interior Paint Cost - $1,252.23

  • Interior Paint Labor - $2,000

  • Kitchen Cabinets, Vanities, Tops & Misc. Cabinet Supplies - $5,685.28

  • Cabinet Labor - $1,312

  • Laminate Flooring Cost - $1,545.05

  • Laminate Flooring Install Labor - $1,400

  • Sheet Vinyl Flooring for Bathrooms - $172.70

  • Sheet Vinyl Flooring Install Labor - $400

     TOTAL: $20,167.26

750 SF ADU Front Windows.png

Now we’re close enough that the owner has started moving stuff in, even though we have a ton of work to do. But we’re not worried, we love moving their stuff around so we can work. We need to set all the doors and install all the trim, which includes closet shelves. And then a bunch of misc. button up task, and we’re finished! We’ve also had trash disposal throughout the job and a portable restroom on-site for what was probably a 6- or 8-month project. And we might as well go ahead and install all the appliances- range, refrigerator, dishwasher, microwave, and laundry center.​

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  • Interior Doors Cost - $1,191.67

  • Millwork & Interior Trim Cost - $1,479.85

  • Millwork & Interior Trim Labor (Includes Setting Doors) - $2,200

  • Miscellaneous Button Up Task - $330.22

  • Trash Disposal - $2,758.41

  • Portable Restroom - $1,520

  • Appliances - $3,651.85

     TOTAL: $13,132

 

Wow! That’s a lot of work and a lot of numbers! If you’ve made it this far, then you’re probably really serious about pursuing this sort of project. I encourage you to reach out to me to discuss the next steps. I’ve designed 7 ADUs and built 5, so I’ve got quite a bit of experience with them. And an ADU is just a small house- all these numbers work for your small home or mountain cabin project as well, and I’ve designed and built many homes and cabins, too. Anyways, back to the numbers, the one you’ve read this far for, the GRAND TOTAL of $171,475.56. Remember, these are real costs from an actual 750 SF ADU project and can serve as a guide for your project decisions and as a reference as you select bidders. HOWEVER, we have one more critical number to include. *The Builder’s Fee*

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  • Builder’s Fixed Fee - $40,634

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Adding the builder’s fee brings the grand total to $212,109.56. And for a 750-square-foot build, that works out to $283/square foot for a very basic, budget build. You might look at that fixed fee number and intuitively think that by acting as your own general contractor, you’ll save $40,634. The reality is that subcontractors probably won’t give you the same price they give an established contractor. All the trades working on this job were people I had developed a working relationship with over many years, and many even became my friends. Subcontractors like working for good general contractors; it makes their work easier, and they know they’ll make money on the job and get repeat business from the same general contractor. An owner-builder rarely knows exactly what they’re doing, which can lead to frustrating, money-losing problems for the subcontractor, and they aren’t expecting repeat business from an owner-builder. It’s difficult to say by how much more subcontractors might charge an owner-builder, and it will vary by trade, but let’s assume an average of 10% across all trades, which would increase the project's price by $8,040. So acting as your own general contractor will save you $32,594 versus the $40,634 builder's fee... still a substantial savings. If you’d like to read more about being an owner-builder and all the nuances of taking on such a task, check out my write-up on that here (Coming January 2026!).

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So now we’ve looked at the numbers of an actual build done in Colorado’s Pikes Peak region in 2025. These are the real costs; I have all the receipts, and getting them down much below what you see would be difficult. This was a budget build without much room to cut further. From here, the cost really only goes up. If these numbers look doable and you have a project in mind, the first step is to get a conceptual design put together so we can ballpark the cost. Contact me so we can get started!

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