Published
Living in an RV while you build: allowed, but the septic goes in first
Yes, you can. The septic comes first.
Living in a trailer on your own lot while the cabin goes up is one of the most common plans in this country, and it is one of the least often checked against the rules. Fremont County allows it explicitly. It also attaches a condition that catches people out, because it sits at the front of the process rather than the end.
The mechanism is a temporary certificate of occupancy, and the code is unusually direct about what it permits and what it demands first.
“No such certificate shall be issued, and no such use permitted, until an approved sewage disposal system has been installed, and the temporary living quarters connected to that system.”
— Fremont County Development Code, 2011 Edition (Ordinance 2011-04), section 3.24.010(a). Retrieved 19 August 2026
So the septic is not something to sort out while you are already parked there. Installed, approved, and the trailer plumbed into it — then the certificate, then you may live there.
The four conditions, in the order they bind
| Condition | What the code requires |
|---|---|
| An approved dwelling | A single family dwelling for which a permit has been approved must be under construction. The allowance exists to bridge a build, not to authorise living on raw land |
| One vehicle | The code permits the use of one recreational vehicle as temporary living quarters |
| Septic installed and connected | An approved sewage disposal system must be installed and the temporary living quarters connected to it before the certificate issues |
| A time limit | No temporary certificate of occupancy shall be issued for more than 180 calendar days |
Read together, those four turn a vague intention into a sequence with a fixed order. The permit comes before the trailer, and the septic comes before the certificate.
The end of it is stricter than the start
Two provisions govern how the arrangement finishes, and the second is the one worth planning around.
- The temporary certificate expires with the permit. It is not an independent clock you can renew on its own terms.
- The temporary living quarters shall be removed before a certificate of compliance or occupancy can be issued for the completed dwelling.
That second one has a practical sting. You cannot finish the cabin, move into it, and leave the trailer parked beside it as a guest room or a store. The trailer has to go before the county will sign off the house you built. If the plan was always to keep it, that is a separate conversation with the county about an accessory use, not something the temporary certificate covers.
What "an approved sewage disposal system" actually means here
The code does not define it in this section, and it does not need to: on-site sewage disposal in this county runs through Eastern Idaho Public Health under state standards, which is the same route any permanent system takes. In practice that means the temporary-living plan depends on the same steps as the permanent one.
- A site evaluation to establish what the ground will carry — the process covered on the site evaluation page.
- A septic permit from the health district, on the ground's terms rather than the trailer's.
- Installation, and the inspection that goes with it — a system that has been buried before it was seen is its own problem.
- The trailer physically connected to the installed system.
- Only then, the county's temporary certificate of occupancy, applied for with the approved building permit in hand.
The consequence is that the septic timeline becomes the timeline for living on site. If the system is a season away, so is the trailer, and any build schedule that assumed otherwise needs revisiting early rather than in June.
Sizing it for two lives, not one
One thing the code does not say, and which is worth thinking about anyway: the system you install for the trailer is, in almost every case, the system that will serve the finished cabin. It is designed and permitted for the dwelling, not for the interim.
That is the right way round, and it means the interim use should not drive the design. A system sized to a cabin handles a trailer comfortably; a system sized to a trailer would not handle a cabin at all. If anyone proposes something cheap and temporary to get you parked sooner, the question to ask is what happens to it when the house is finished — and how tank size is actually worked out is the place to start.
The weather clause, and what it is really for
The temporary certificate has a broader purpose than trailers. The code introduces it for cases where weather prevents the prompt completion of required improvements, naming landscaping as the example. That is a recognisably local problem: a house finished in October with an unfinishable list of outdoor items on it.
The 180-day cap applies to that use as much as to the trailer use. It is a bridge across a winter, not an open-ended state. And because the certificate expires with the permit, the useful question when planning a late-season completion is when the building permit itself runs out, rather than assuming the temporary certificate buys independent time.
Questions worth asking before you tow anything up here
- Is the building permit for the dwelling actually approved, or merely applied for? The allowance depends on approval.
- Is the septic permit in hand, and is there an installer booked inside the season you intend to be living there?
- How will the trailer be physically connected to the system, and has whoever is installing it been told that is part of the job?
- When does the building permit expire, since the temporary certificate expires with it?
- Where will the trailer go when the house is finished, given it must be removed before final occupancy is granted?
- Is more than one vehicle contemplated? The code permits one.
- Has anyone confirmed the system is sized for the finished dwelling rather than for the trailer, since that is the design the permit is written against?
- Is there a winter in the middle of the plan? The 180-day cap does not stretch to cover one, and a build that spans two seasons needs a different conversation with the county.
Common questions
Can I live in an RV on my lot while I build?
Fremont County allows it through a temporary certificate of occupancy, for the use of one recreational vehicle as temporary living quarters while a single family dwelling for which a permit has been approved is being constructed. It is not a general permission to live on raw land.
Do I need the septic in first?
Yes, and this is the condition people miss. The code states that no such certificate shall be issued, and no such use permitted, until an approved sewage disposal system has been installed and the temporary living quarters connected to that system.
How long does a temporary certificate of occupancy last?
No temporary certificate of occupancy shall be issued for more than 180 calendar days. It also expires with the building permit, so it is not an independent clock that can be extended on its own terms.
Can I keep the trailer after the house is finished?
Not under this provision. The code requires the temporary living quarters to be removed before a certificate of compliance or occupancy can be issued for the completed single family dwelling. Keeping it would be a separate question for the county.
How many RVs can I have on site?
The code permits the use of one recreational vehicle as temporary living quarters under this provision. A second one is not covered by it.
Should I install a smaller temporary septic system?
The system is permitted and designed for the dwelling rather than for the interim use, so in practice it is the cabin's system that the trailer connects to. A system sized to a trailer would not serve the finished house, which makes the cheaper interim option a false economy.
What else is a temporary certificate of occupancy used for?
The code introduces it for cases where weather prevents the prompt completion of required improvements, giving landscaping as the example. The same 180-day cap applies, which makes it a bridge across a winter rather than an indefinite arrangement.
Does the health district or the county issue this?
They do different parts. The septic permit and the approval of the sewage disposal system run through Eastern Idaho Public Health under state standards. The temporary certificate of occupancy is a county planning and building matter, and it comes after the system is installed and connected.