By the Utah ADU Builders Editorial Team · Last verified: July 2026 · Recheck planned: October 2026 (state detached-ADU law effective date).
Herriman ADU Builders: Costs, City Rules, and How to Start
Yes — you can build an ADU (accessory dwelling unit: a second, self-contained home on your property) in Herriman. As of 2026 you have two paths: an internal ADU inside your existing house, or a detached ADU in your yard, which the City Council approved on May 27, 2026. This works best for owner-occupants planning family housing or a long-term rental — not short-term-rental investors or absentee owners. Budget roughly $60,000–$400,000+ by type, expect permits, and confirm your property before you spend on plans.
Start here: your two ADU paths in Herriman
Before you call a builder, it helps to know which kind of project you're actually planning, because the rules, cost, and the right contractor all change with it.
| Internal ADU (I-ADU) | Detached ADU | |
|---|---|---|
| What it is | A separate unit inside your existing home — a basement apartment, or a unit that shares a wall with or sits above an attached garage | A standalone unit in your yard (a "backyard cottage" or "granny flat") |
| Status in Herriman | Established path, with a defined application process | Newly allowed — the City Council approved the ordinance on May 27, 2026 |
| Where it's allowed | Eligible residential and agricultural zones (certain R-1, R-2, and agricultural zones — confirm your specific zone) | Eligible lots with a legal, owner-occupied single-family home (confirm your zone) |
| Minimum lot size | 6,000 sq ft (about 0.14 acre) | Set by the 2026 ordinance — confirm the current minimum for your lot |
| Size limit | The lesser of 50% of your home's floor area or about 1,000 sq ft | Set by the 2026 ordinance (building size, height, and setbacks apply) |
| Owner occupancy | Required — you sign an agreement, recorded with Salt Lake County, that you'll live on-site and won't rent out both units | Required |
| How many per lot | One ADU per lot — internal or detached, not both | One ADU per lot — internal or detached, not both |
| Rentals | Long-term only — a minimum of 30 consecutive days | Short-term rentals are prohibited; the exact minimum stay comes from the adopted ordinance |
| Impact fees | Exempt when built inside your existing home (a statewide rule) | May apply — confirm for your project |
| Permit path | Zoning application → building permit → inspections → final approval before renting | Follows the city's building-permit process under the 2026 ordinance — confirm the current application steps |
- Owner occupancy means you (the owner) must live in the home or the ADU. It rules out a fully absentee, two-rental investment.
- Setback is the required distance between a structure and your property line.
- Impact fee is a one-time charge a city can levy to offset a new unit's effect on roads, parks, and utilities.
- Short-term rental (STR) generally means stays under 30 days (think nightly rentals). Herriman does not allow ADUs to be used this way.
One more note on the labels: "internal" and "detached" are the two legal approval categories in Herriman. The construction form can vary within them — a basement finish, an attached addition, or a garage conversion may each be handled under the internal-ADU rules when the unit sits inside or attached to the existing home, while a freestanding backyard unit follows the detached path. Which category your project falls into is what determines the lot, permit, parking, rental, and impact-fee rules that apply.
Our practical view: an ADU is not automatically a smart project just because Herriman opened a detached path in 2026. The right project depends on your lot, your utilities, your budget, and how you'll actually use the space. A feasibility check is a low-cost way to find out whether your property is likely to work — before you pay for plans or collect bids.
Can you build an ADU in Herriman in 2026?
Yes — with a real caveat. Herriman has an established internal-ADU path, and on May 27, 2026 the City Council approved a detached-ADU ordinance for eligible properties. But "allowed" is not the same as "approved on your lot." Your project still has to meet the standards for its ADU type, satisfy building and fire codes, and clear property-specific conditions like parking, setbacks, and utilities.
What changed on May 27, 2026
For years, Herriman's published ADU path covered internal units only — the kind built inside an existing home. That's why several older builder pages still describe Herriman as an "internal-ADU-only" city. That's now out of date.
On May 27, 2026, the City Council voted 5–0 to approve updates to city code allowing detached ADUs on eligible lots with a legal, owner-occupied single-family home. The city's own summary says the rules set standards for lot size, building size, height, setbacks, parking, owner occupancy, and utilities — and that short-term rentals are prohibited.
- The specific numbers live in the adopted ordinance, not the public summary. The city confirmed the categories it regulates, but the exact minimum lot size, maximum size, height, and setback figures — and the current detached application steps — come from the codified ordinance text. Confirm the current figures and process for your lot through a feasibility check or directly against the adopted code.
- Don't build a plan around old draft proposals. Earlier planning-commission discussions floated various numbers that were still being debated. Those are not the adopted rules.
How Utah state law fits in
You may have heard that "Utah made ADUs legal." More precisely: Utah Code makes one internal ADU a permitted use in areas zoned primarily for residential use — so a qualifying internal ADU generally can't be banned outright — while still allowing cities to impose specific requirements and listed exceptions. (Utah Code §10-21-303.) Internal ADUs built inside your existing home are also exempt from impact fees under state law. (Utah Code §11-36a-202.)
For detached ADUs, a statewide rule takes effect October 1, 2026 that requires a "specified municipality" to allow a detached ADU on a qualifying lot of 11,000 square feet or larger, while letting cities also permit them on smaller lots. (Utah Code §10-21-304.) One nuance worth checking: that state rule does not override detached-ADU restrictions written into a city development agreement signed on or before May 6, 2026 — so a master-planned community's agreement can still limit what you build.
Here's the key point for Herriman homeowners: Herriman acted early. Your current ability to pursue a detached ADU comes from Herriman's own 2026 ordinance — not from a state law that isn't in effect yet. So the standards that govern your project are Herriman's local standards.
What "allowed" does not mean
- Not automatic permit approval.
- Not permission to skip plans, permits, or inspections.
- Not a resolution of any HOA, development agreement, or recorded private restriction on your property.
- Not a guarantee you can rent it, connect utilities easily, or that the numbers will pencil out.
For the full statewide picture, see our Utah ADU permits guide and Salt Lake County ADU guide.
Will your property qualify? A Herriman ADU feasibility check
Qualification is property-specific, and a few common issues stop or reshape projects before they start. Run through this before you pay for full plans or collect contractor bids. It gives you a likely yes / maybe / no — a feasibility review then screens it for your specific address.
| Check | Good sign | Caution sign | What confirms it |
|---|---|---|---|
| Jurisdiction | Confirmed inside Herriman city limits | You only know the mailing address | Parcel/jurisdiction record |
| Zoning & legal home | Qualifying zone, lawful single-family home | Unclear use or permit status | Current zoning/property record |
| Lot size | Meets the minimum for your ADU type | Near the threshold, or detached figures still to confirm | Parcel area + applicable rule |
| Existing ADU | None on the lot | An existing second kitchen or unit | Permit history |
| Owner occupancy | You plan to live on-site | It's an absentee-investment plan | Your ownership/use plan |
| Parking | Existing setup already works | You'd need to redesign to fit spaces | A measured site plan |
| Entrance & egress | Separate entrance is feasible, and any bedroom can meet emergency-escape (egress) rules | Window-well, stair, or grade problems | Concept plan / site photos |
| Buildable area (detached) | Clear space after setbacks | Tight setbacks or narrow access | Survey / site plan |
| Easements, drainage, slope | No visible conflict | A utility/drainage easement or steep slope | Survey / title / site review |
| Utilities | Water, sewer, electrical, and stormwater look reachable | Long runs, or an unknown-capacity electrical panel | Utility review |
| Development agreement / HOA | None applies, or you've reviewed the terms | A master development agreement or HOA rule that may restrict ADUs | Your subdivision's recorded documents |
| Permit history | Existing work appears documented | A finished basement or garage change with no records | Permit history |
How much does a Herriman ADU cost?
There's no honest single "average Herriman ADU cost," because the type, existing conditions, site work, utilities, and finishes swing the number dramatically. What we can give you is a realistic set of Utah planning ranges by type, then the factors that move your project up or down. Treat these as estimates for planning, not quotes.
| ADU type | Estimated all-in cost (Utah planning ranges) |
|---|---|
| Internal / basement conversion | $60,000–$150,000+ |
| Garage conversion | $60,000–$175,000+ |
| Attached addition | $150,000–$275,000+ |
| Detached new build | $200,000–$400,000+ |
These are statewide planning ranges from our Utah ADU cost guide and cost methodology — not Herriman-specific measurements or bids. Per-square-foot costs vary widely by type (roughly $100–$450), and small ADUs tend to have higher and less predictable per-square-foot costs because fixed costs — permits, mobilization, a kitchen, a bathroom — spread over fewer square feet.
What moves your number
- Type of construction. Reusing an existing shell (basement, garage) is usually cheaper than building from the ground up.
- Existing conditions. Egress windows, a separate entrance, ceiling height, and older electrical or plumbing can add real cost.
- Site work and utilities. Excavation, grading, drainage, utility trenching, and electrical service are common surprises — an electrical-panel upgrade, or a separate service for a detached unit, can add meaningfully to a budget.
- Finish level. Cabinets, countertops, flooring, and appliances can move the total significantly.
- Design, engineering, and permits. Plans, any required engineering, and permit fees.
How long does a Herriman ADU take?
Herriman estimates its I-ADU plan review at roughly 7–14 business days — but that's just the review step, not your whole project. Total time depends on the project type, how complete your documents are, whether corrections are needed, contractor availability, utilities, and site conditions.
A realistic way to think about the timeline is in phases:
- Feasibility
Confirm your lot, existing conditions, and project type.
- Design & engineering
Concept, site/floor plans, and any required engineering.
- Application & corrections
Submit, get reviewed, fix anything flagged, receive permits.
- Contractor scheduling
Deposits, selections, subcontractors.
- Construction
The build itself.
- Inspections & final approval
Plus the rental/business-license step if you'll lease it.
Which type of ADU makes the most sense for you?
Start with your goal, then match it to the most practical path. This is where a lot of homeowners save money — by choosing the right project instead of the flashiest one.
| Your goal | Path to look at first | Why | Main tradeoff |
|---|---|---|---|
| Lowest-cost, least disruption | Basement or garage conversion | Reuses your existing structure | May still need egress, entrance, or utility corrections |
| Maximum separation & privacy | Detached ADU | A fully independent structure | Higher cost and more site, utility, and setback questions |
| Housing for a parent or adult child | Depends on mobility & privacy — internal, attached, or detached | Several layouts can work | Accessibility (stairs, entrance, bathroom) and parking |
| A separate, self-contained unit for a long-term tenant | Detached, if your lot supports it | Full independence and its own entrance | Cost, and confirming your lot has the buildable area |
| A short-term / nightly rental business | None — reconsider the plan | Herriman doesn't allow ADUs as short-term rentals | Your intended business model likely isn't permitted |
If a nightly-rental income model is the reason you're building, pause. Herriman's rules point to long-term tenants (a 30-consecutive-day minimum for internal ADUs, and a short-term-rental prohibition for detached), so a plan that only works as an Airbnb-style unit probably won't clear the rules.
You can go deeper on any single path in our guides to detached ADUs, basement/internal ADUs, and garage conversions.
How should you compare Herriman ADU builders?
Not every "ADU builder" is the right fit for your project. A basement conversion, a garage conversion, and a detached build involve different design, structural, site, and utility work, so compare companies with real experience in your project type — and confirm the basics yourself before you sign anything.
Match the builder to the project
- Internal / basement conversions: look for a remodeler or design-build firm experienced with legal conversions — egress, separate entrances, ceiling and life-safety work, mechanical/electrical/plumbing changes, permit drawings, and dealing with concealed or previously unpermitted work.
- Detached builds: look for a residential new-construction or detached-ADU design-build team comfortable with site planning, foundations, utility trenching, drainage, and full building permits.
- Garage conversions: first confirm whether the garage is attached or detached and whether you'll need to replace parking; the structure and slab drive the real cost.
- Prefab / modular: factory construction can shift where the work happens, but it does not remove local zoning, a foundation, utility hookups, site access, or permit requirements. Evaluate a prefab builder the same way, and get clear on exactly which parts of design, engineering, foundation, transportation, utilities, and site work they contract for versus what you have to arrange.
Verify the basics yourself
- License. Confirm the company holds an active Utah contractor license in the right classification through the Utah Division of Occupational and Professional Licensing (DOPL). A license check is one signal, not a guarantee of quality.
- Insurance and references. Ask for current insurance and recent, relevant local projects you can actually check.
- Owner-builder note: ADU construction almost always involves licensed trades, so plan to hire a licensed contractor for the build — or, if you use Herriman's owner/builder path (you sign an Owner/Builder Certification), understand that you take on the responsibilities a licensed contractor normally carries, including code compliance and liability.
Compare bids on the same scope
The most useful comparison isn't the bottom-line price — it's who's responsible for what. Ask each builder to spell out:
- Which ADU type and scope the estimate assumes.
- Who handles design, engineering, the permit application, and any correction requests.
- Which site, utility, drainage, and access assumptions are included — and what's excluded.
- Which "allowances" (cabinets, flooring, appliances, fixtures) could change, and how.
- Deposit and payment schedule, and what triggers a change order.
Red flags
- "No permit needed" without a documented reason.
- Guaranteed city approval, guaranteed rent, or guaranteed value increase.
- A price with no drawings, inclusions, or site assumptions.
- Large, vague allowances or missing utility/site-work scope.
- Pressure to sign before your property's feasibility is confirmed.
- A company name on the proposal that doesn't match the license or contracting entity.
- Project photos with no clear ownership or context.
When a Herriman ADU is not the right move
We'd rather you find this out now than after paying for plans. An ADU may not be the right project when:
- Your lot can't fit a detached unit after setbacks, or the buildable area is too tight.
- You already have a second unit and the one-ADU-per-lot limit applies.
- You can't (or don't want to) occupy the property — owner occupancy is required.
- Parking can't be met without an awkward redesign.
- A basement can't reasonably meet egress and life-safety requirements.
- An easement, slope, drainage, or utility-capacity problem drives the cost past what makes sense.
- Prior work was done without permits and may need to be opened up and inspected — Herriman notes that finishes can have to be removed so concealed work can be checked.
- A development agreement or HOA restriction on your community limits ADUs.
- Your goal depends on a short-term rental, which isn't allowed.
- The honest budget simply doesn't work for the value you'd get.
A feasibility review is allowed to tell you "not this lot" or "not yet." That's a useful answer when it saves you from spending on plans and bids for the wrong project — and it often points to a smaller or different path that does work.
What we verified
We built this page from primary and current sources, not by repeating what other builder pages say:
- Herriman's current internal-ADU page and application materials — eligible zones, the 6,000-sq-ft minimum, owner-occupancy and the recorded agreement, the one-ADU-per-lot limit, the 30-day rental minimum, the $559 application review fee, and the plan-review estimate. (herriman.gov/iadu)
- The Herriman City Council's May 27, 2026 action approving the detached-ADU ordinance (5–0) — the categories it regulates and the short-term-rental prohibition. (herriman.gov)
- Utah state law — Utah Code §10-21-303 (internal-ADU permitted use), §10-21-304 (detached ADUs, effective October 1, 2026), and §11-36a-202 (the internal-ADU impact-fee exemption). (le.utah.gov)
- Utah DOPL for contractor-license verification. (commerce.utah.gov/dopl)
- Our Utah ADU cost guide and cost methodology for the planning ranges, which are statewide estimates — not Herriman measurements. (utahadubuilders.com)
Sources
- Herriman City Council meeting recap, May 27, 2026 (detached-ADU ordinance approval) — herriman.gov
- Herriman City — Internal Accessory Dwelling Units (I-ADU) page and application materials — herriman.gov/iadu
- Utah Code §10-21-303 (internal ADU as a permitted use) — le.utah.gov
- Utah Code §10-21-304 (detached ADUs; effective October 1, 2026) — le.utah.gov
- Utah Code §11-36a-202 (impact fees; internal-ADU exemption and definition) — le.utah.gov
- Utah Division of Occupational and Professional Licensing (DOPL) — commerce.utah.gov/dopl
- Utah ADU Builders — Utah ADU cost guide and cost methodology — utahadubuilders.com
This page is general information for Utah homeowners, not legal, tax, financial, engineering, or contractor-licensing advice, and it does not guarantee permit approval, financing, builder availability, rental income, or property-value increase. Rules, fees, providers, and property conditions change; confirm current details for your lot before you design, budget, or build.
Related resources
- Can I build an ADU in Utah? Statewide guide · Utah ADU permits guide
- Utah ADU cost guide · Cost methodology
- Detached ADU guide · Basement ADU guide · Garage conversion guide
- Prefab ADU Utah · ADU financing in Utah · ADU rental income in Utah
- Salt Lake County ADU guide · Is an ADU worth it in Utah?
- Nearby city rules: Riverton · Bluffdale · South Jordan · West Jordan · Draper