Clairemont, San Diego · Equity, ADUs and rental income

A San Diego ADU running $327,756 all in is a financing question before it is a construction question.

That full breakdown, plot plans, permits, appliances, is a real number a San Diego owner posted. The part that usually gets planned last, how to pay for it, should be planned first.

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The answer

The direct answer

One documented San Diego ADU build, plot plans and permits included, ran $327,756 total. That number is a real, forum-reported build cost, not a guaranteed price for every lot. What decides whether an owner can actually build is less the total cost and more which financing structure, HELOC, cash-out refinance or construction-to-permanent, fits their existing equity.

What changes the answer

What is the breakdown of actual cost to build an ADU in San Diego?
What kind of lot do you need to build an ADU in Clairemont or Bay Park?
How do homeowners finance an ADU build?

Each one is answered further down this page, and any one can move the outcome on a specific file.

The local number: Adam King’s Corcoran Icon Properties listing at 4674 Boxwood Dr, a 1,008 square foot house on a 9,100 square foot R-1 lot, went pending in 12 days on the strength of its ADU-eligible lot.
Rule and source: Adam King, Corcoran Icon Properties, listing record
Last verified: September 1, 2026

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Answered by Nick Nagy · 23 years · NMLS 314880 · CA DRE 01444600 · Mortgage financing through Loan Factory, 237 lenders · Run this answer against my numbers →

Part of the California Mortgage Answer Desk, and of the Clairemont questions.

How it works

What that $327,756 number actually included

A San Diego owner’s posted breakdown put the total cost of building an ADU, including appliances but no furniture, at $327,756, with plot plans alone running an estimated $6,000 to $8,000 and permits in a similar range. That is a forum-reported figure from one specific build, not a countywide average, but it is a useful anchor for what a full-scope San Diego ADU project can actually run.

The reason that number matters more than a generic estimate is that it includes the parts people forget to budget for. Plans, permits and soft costs add up before a single wall goes up, and a build that only budgets for construction itself tends to run into a funding gap partway through.

The detail that matters

Why Clairemont and Bay Park R-1 lots are the ones this applies to

A build like this depends on having a lot that supports it. Adam King’s recent Corcoran Icon Properties listing at 4674 Boxwood Dr, a 1,008 square foot house on a 9,100 square foot R-1 lot, went pending in 12 days specifically because that lot size and zoning made it ADU-eligible, and buyers in this corridor are actively pricing that potential into their decision.

A lot that size is common across Clairemont, Bay Park and Bay Ho, which is part of why ADU questions show up in this market as often as they do. The zoning supports it. The financing is usually the part that has not been figured out yet.

How it works

How owners actually pay for a build this size

A HELOC lets an owner draw against existing equity as costs come in, which works well for a build where the exact draw schedule is still being finalized. A cash-out refinance replaces the whole first mortgage and pulls a lump sum, which can make sense if current rates make refinancing the primary loan attractive anyway. A construction-to-permanent loan finances the build directly and then converts to a standard mortgage on the completed ADU, which some owners prefer because it separates the build financing from their existing home loan entirely.

None of the three is automatically the right answer. It depends on how much equity is already in the home, what the current first mortgage rate looks like, and how the owner wants the finished ADU to sit on the title.

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Where this question came from

Someone asked this in public

Breakdown of actual cost to build an ADU in San Diego
Reddit r/SanDiegan, captured 2026-08-10 (LH1 demand sweep)

If nobody gave a straight answer in that thread, that is not the person missing something. The answer depends on a specific file and a specific address.

Who answers

Nick Nagy

23 years in California lending · NMLS 314880 · CA DRE 01444600 · Loan Factory, Inc.

Dual licensed, so the loan side and the real estate side of a move get looked at as one problem instead of two. Most of what goes wrong in a move is a timing problem wearing a financing costume, and it is cheaper to catch it before you write an offer than after.

Financing is placed through Loan Factory, Inc. Real estate work is under CA DRE 01444600. More about Nick.

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The desk behind the file

One file, 237 lenders competing for it, and a broker who has done this for 23 years.

Loan Factory, Inc. is the brokerage. These are its published figures.

20,907+Loan Factory Google reviews

5.0Loan Factory average rating

237Lenders available through Loan Factory

48States Loan Factory is licensed in

A retail bank has one guideline book. A broker shops the same file across the shelf and finds the lender whose box it already fits.

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Straight answers

Questions people here actually ask

The follow-on questions, answered in the order they get asked.

What is the breakdown of actual cost to build an ADU in San Diego?

One documented San Diego build, forum-reported, came to $327,756 total including appliances, with plot plans running an estimated $6,000 to $8,000 and permits in a similar range. That is one specific project’s number, not a countywide guarantee, but it shows how much of the total sits in planning and permitting before construction even starts.

What kind of lot do you need to build an ADU in Clairemont or Bay Park?

An R-1 lot with enough square footage to support a detached unit is the common profile. A recent 9,100 square foot R-1 lot in this corridor sold specifically on its ADU potential, and that lot size is common across Clairemont, Bay Park and Bay Ho.

How do homeowners finance an ADU build?

Most use a HELOC, a cash-out refinance, or a construction-to-permanent loan. A HELOC draws against equity as costs come in, a cash-out refinance pulls a lump sum by replacing the first mortgage, and a construction-to-permanent loan finances the build and converts to a standard mortgage once it is complete. The right one depends on existing equity and the current first mortgage rate.

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