The Bedroom Cap: Why Septic Rules Dictate Home Size on Fox Island (And nearby)
I recently worked with a client, Danielle, who found what looked like a dream property in Port Orchard.
It was a waterfront parcel with an existing home and plenty of acreage. Her vision was simple: Keep the main house and build a charming ADU down by the water for guests. On paper, the lot was huge. In her mind, it was a slam dunk.
Then we opened the maps.
We discovered a private road easement cutting right through the middle of the property. To the county, that invisible line meant she couldn't build the ADU "across the street" from the main house, even though she owned both sides.
That was the start of many red flags we uncovered, one after the other. The vision of a waterfront guest cottage evaporated in a single Feasibility Review.
But here’s the rub: Even if the road hadn't been there, the dirt likely would have stopped her anyway.
In a city, if you have the money, you can build the bedrooms. You just pay a connection fee to the sewer department.
On Fox Island and the Key Peninsula, your bank account doesn’t determine how many bedrooms you can have. Your dirt does.
The "Bedroom Cap"
When you buy rural land, you aren't just buying a view; you are buying a septic capacity.
The soil on your lot has a specific absorption rate. It can only handle so much "load" per day. In the eyes of the Health Department, "load" isn't measured in people; it’s measured in bedrooms.
I have seen clients buy "perfect" 5-acre lots intending to build a sprawling 5-bedroom estate for their large family. Then the perk test comes back. The soil is too clay-heavy or the water table is too high. The ideal septic locations X’ed due to environmental regulations. The result?
"Approved for 3 Bedrooms."
It doesn't matter that you have 5 acres. It doesn't matter that you have a $3M budget. Unless you can engineer an expensive alternative system, your 5-bedroom dream just became a 3-bedroom reality.
The ADU Trap (The "Dirt Tax")
Everyone is talking about the new 2025 ADU laws. Yes, the zoning code has finally relaxed to allow larger guest houses and more flexibility. That is the good news.
Here is the bad news: The Health Department didn't get the memo.
Adding an ADU isn't just about pouring a foundation. It’s about adding "load."
If you attach the ADU to your home, you might be able to share the septic tank, if you have the capacity. I have YET to find a house with room in its septic capacity for any addition or ADU.
If you build a Detached ADU (like Danielle wanted), the rules often trigger a requirement for a completely separate septic system with its own tank and drain field.
Suddenly, you aren't just paying for a guest house. You are paying for a second infrastructure project.
And that is assuming you have the space for it. A standard drain field needs room, depending on the design sometimes a lot of it. We often find that once you draw the 100-foot well setbacks and the reserve drain field areas, there is literally nowhere left to put the guest cottage.
The "Office" Gray Area
"Okay Andrew," you say. "I'll just label the two extra bedrooms as a 'Home Office' and a 'Library'. Problem solved."
Building departments are wise to this. If a room has a closet, a door for privacy, and an egress window, they will often count it as a bedroom regardless of what the blueprints say.
It is a gray area, and trying to "trick" the septic permit is a great way to get your Certificate of Occupancy held hostage at the finish line.
Don't Guess. Test.
I am not telling you this to scare you out of building. I am telling you this so you don't end up like the countless landowners who own "unbuildable" lots.
The "Dirt Tax" is real. It is the hidden cost of building in the Pacific Northwest.
Before you fall in love with a floor plan—and certainly before you close on the land—we need to verify what lies beneath the grass. We need to know if your soil supports your vision.
Don't buy a 3-bedroom lot for a 5-bedroom dream.