Can You Build on a Vacant Lot in Los Osos?

Can you build on a vacant lot in Los Osos?

Yes, but a Los Osos lot needs several County approvals before you can submit building plans. Vacant lots became eligible for building permits on October 29, 2024, according to the County of San Luis Obispo. A new home still needs a growth rate allocation, water and wastewater verification, a Title 19 water conservation certificate, and compliance with the Los Osos Habitat Conservation Plan. Requirements change, so confirm each step with the County before you make an offer.

Buyers in Los Osos are asking this right now, and it makes sense. A lot can look simple on a listing, yet the County’s process in Los Osos has several steps, and each one has its own source.

I work with buyers across San Luis Obispo County, including Los Osos and surrounding areas, and I walk every lot buyer through the County’s steps before we write an offer. Everything below comes from the County of San Luis Obispo’s own pages, so you know who issues each requirement and who to call.

The County steps before a building permit

The first gate is the growth rate allocation. The County says its Growth Management Ordinance sets an annual maximum number of new dwelling units for the unincorporated county, and that maximum is 25 in 2026. The County also says all new dwelling units within the Los Osos Urban Reserve Line must obtain a growth rate allocation.

The Growth Rate Allocation Certificate is then required when you submit for a building permit. That means the allocation comes before your plans do.

The second gate is water and wastewater verification. The County’s permitting page says you need to show a water supply, either with a will-serve, continue-to-serve, or intent-to-serve letter from your water provider or with a well report for an on-site well. For wastewater on the Los Osos sewer, you need a will-serve, continue-to-serve, or intent-to-serve letter from the County Department of Public Works.

The retrofit certificate

The third gate is the Title 19 Retrofit-to-Build requirement. The County says new development that uses water from the Los Osos Groundwater Basin must retrofit older plumbing fixtures to save twice the amount of water the new development will use. A water conservation certificate is required before a new construction permit can be issued.

Here’s how the County describes the retrofit work:

• Toilets, showerheads, and clothes washers can be replaced to generate the savings.
• The savings must happen within the service boundary of the same Los Osos water purveyor.
• The application includes photos of each old and new fixture, plus receipts for the new ones.
• The County’s Planning and Building Department reviews the submission and issues the certificate.

The County also says a fee is charged at submittal, based on the number of fixtures or appliances replaced, and that the current amount is on its fees page. If you’re comparing this with the sale-side program, which San Luis Obispo County sellers must retrofit plumbing explains how retrofit-on-sale differs.

The County says the water supply and wastewater verifications are due with the land use permit or building permit application, so gather those letters early. If you plan an addition of 120 square feet or more, including a guesthouse, the County says a permit condition requires fixture retrofits in the existing structure before the building permit final.

The order to expect

Putting the County’s own timing together, here’s the order a lot buyer should expect:

• A planning number, which the County requires before it will consider a sewer Will Serve request.
• A growth rate allocation, whose certificate is required when you submit for a building permit.
• Water and wastewater verification, due with the land use and building permit applications.
• A Title 19 water conservation certificate, required before the construction permit is issued.
• Habitat plan fees paid before permit issuance, which is how the County says you receive a Certificate of Inclusion.

For a project that needs a discretionary land use permit, the County’s letter says that once a credit reservation form is issued, you must obtain construction permit issuance within 3 years. The timeline is part of your decision before you buy.

How the Waitlist to Build works

The County says the Los Osos Waitlist to Build was originally created in 1989 for undeveloped parcels in the community sewer service area. The County says owners who don’t respond to a notice or don’t file a construction permit application don’t lose their waitlist position for future allocations.

For 2026, the County’s February 25 update to waitlist property owners said it would notify only Batch 1 properties, defined as positions 1 through 12 on the single-family waitlist and 1 through 7 on the multifamily waitlist. The same update lists a first-come, first-served phase from October 1 to December 31, 2026 for remaining allocations. The County sets a new schedule each year, so ask Planning and Building where a specific parcel stands today.

Habitat requirements come next. The County’s letter to Batch 1 owners says Los Osos Habitat Conservation Plan fees must be paid before permit issuance to receive a Certificate of Inclusion. The same letter says a Development Request Form must include a Ground Disturbance Plan and a visual survey for covered species.

For projects that need a discretionary land use permit, the County says approvals can be appealed to the Board of Supervisors and the California Coastal Commission. I explain how coastal permits work in coastal development permit rules in San Luis Obispo County.

The sewer connection and its fee

A new sewer connection needs a Will Serve letter from County Public Works. The County says it only considers requests tied to a valid planning number, so you can’t apply during pre-planning.

For a single-family residence in Los Osos, the County’s Will Serve fee table lists a capacity fee of $23,852. The County’s finance page says the capacity charge must be paid in full before the will-serve letter is issued.

The County also says the installation must be done by District staff or a licensed contractor on contract with the County. Fees change, so confirm the current amount with Public Works at (805) 781-5252.

What to check before you buy a Los Osos lot

Here’s what I ask for before a client makes an offer on a lot:

• Whether the parcel is on the Waitlist to Build, and its position if it is.
• Whether the seller has a growth rate allocation, a Certificate of Inclusion, or any habitat credit paperwork.
• Any water or sewer will-serve letters and any capacity fee already paid.
• Any prior planning number, plans, or County correspondence tied to the parcel.

Use your investigation contingency period to ask the County, not only the seller. A seller’s paperwork shows what was done in the past, and the County is the source for what the parcel needs now.

Then build the costs into your budget before you commit. The capacity fee, the Title 19 fee, the habitat fees, and the retrofit work each have their own source, and several amounts aren’t posted as one number. Ask for the current figure in writing.

For the sewer charges that arrive on your tax bill once a Los Osos home is built, my Los Osos real estate guide is the place to start. And if you’re weighing another community, the same question for building on a vacant lot in Cambria has a different set of rules.

Rates, fees, and requirements change. Verify current details with the County of San Luis Obispo Planning and Building Department through the County phone directory at 805-781-5000, and with the Public Works Department for sewer service.

Frequently Asked Questions

Do vacant lots in Los Osos qualify for building permits?

Yes, since October 29, 2024, according to the County. A new home also needs a growth rate allocation, water and wastewater verification, a Title 19 water conservation certificate, and compliance with the Los Osos Habitat Conservation Plan.

What is the Los Osos Waitlist to Build?

It’s the County’s list for undeveloped parcels in the Los Osos community sewer service area, created in 1989. The County says owners who don’t respond to a notice or don’t file a construction permit application don’t lose their waitlist position for future allocations.

Do you need a plumbing retrofit to build in Los Osos?

Yes. The County’s Title 19 requirement says new development that uses water from the Los Osos Groundwater Basin must retrofit older plumbing fixtures to save twice the water the new development will use, and the certificate is required before a new construction permit is issued.

How much does it cost to connect a Los Osos lot to the sewer?

The County’s Will Serve fee table lists a Los Osos capacity fee of $23,852 for a single-family residence, and the County says the capacity charge must be paid in full before the will-serve letter is issued. Fees change, so confirm the current amount with County Public Works.

Who do you call first about a Los Osos lot?

Call County Planning and Building through the County phone directory at 805-781-5000 for the growth rate allocation, retrofit certificate, and permit steps. Call County Public Works at (805) 781-5252 for the sewer Will Serve letter.

Building in Los Osos comes down to getting the County’s steps in the right order, and a lot buyer should know that order before making an offer. I’ll help you map the allocation, water and sewer letters, retrofit certificate, and habitat fees for the parcel you’re considering, so the timeline and the costs are clear first. That’s what Luxury Care For Every Move means to me: you see the whole path before you commit. You don’t need to be ready to buy to ask, and Start a Conversation is the place to tell me which Los Osos lot you’re weighing.

About Wina Gill

Wina Gill is a Realtor and Certified Negotiation Expert with Century 21 Masters, based in Arroyo Grande and serving San Luis Obispo County and North Santa Barbara County. With more than 10 years in real estate, she has completed more than 100 sales totaling over $90 million in sales volume. Wina works as a solo agent, so clients work directly with her from the first conversation through closing. She writes about Central Coast communities, neighborhood differences, local market conditions, and the property-specific factors that can affect buying, owning, and selling a home, helping people understand their options before making a move. Reach her at 805-550-0161 or winagillhomes.com. DRE #02006343

Buying or selling in San Luis Obispo County or North Santa Barbara County? Call or text Wina Gill for clear answers about your property, from your first question through closing. 805-550-0161 | Century 21 Masters Luxury | DRE #02006343