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Can You Build on a Filled-In Pool in Tucson?

Posted
Updated
ByAaron Baker

Yes, with conditions. Every filled pool settles a little, so the real question is whether the fill was placed and tested well enough for an engineer to design on it. On a removal meant for future building, Omni places engineered fill compacted to 95 percent, tested in lifts, with the fill lab tested when it arrives and an engineer’s stamped letter at the end. The engineer for whatever you build later decides everything beyond that, including footing depth, piers and slab type.

Why a filled pool settles

A pool hole is eight or nine feet of fill where the rest of the yard is native ground, and fill does not behave like native ground until it has been compacted and loaded. The PHTA Builder’s Manual puts it simply: a pool is a net unloading of the ground, so the native soil under it is rarely the problem. Settlement comes from disturbed, loose or placed soil, which has to be recompacted to its original strength or better. Four things make a filled pool sink more than it should:

  • Loose or dumped fill. Dirt pushed in all at once has air in it. Its own weight, rain and irrigation close those gaps over years, and the surface drops with them. A soils engineer quoted in Builder magazine called loose fill by far the biggest cause of damage to pools, and the same fill does the same thing to whatever sits on top of it.
  • Organic material and debris. Topsoil, roots, deck rubble and trash in the fill rot or shift, and leave voids behind.
  • Trapped water. If nobody broke drainage holes through the floor, the old shell holds water like a tub. Wet fill stays soft, and Tucson basin soils can collapse when they get wet under load.
  • The shell left in place. A partial removal leaves the floor and lower walls in the ground. Fine material above works down into the broken concrete, and a footing that crosses the edge of the old shell sits on two kinds of ground that move at different rates.

That is why Arizona cities that spell it out, Oro Valley among them, treat a removal that will stay landscape and a removal that will carry a structure as two different jobs. A slab that settles years later over a trench or an old cave-in is, in our own failure table, the signature of backfill placed without controlled compaction and testing, which is why landscape-grade fill cannot carry a footing. The settling side of this is covered in more depth in Will the yard sink after a pool is filled in? and on our page on soils, settlement and engineered fill in the Tucson basin.

What Omni does on a removal meant for future building

Most people who ask us this do not know yet what they will build, or whether they will, and almost none of them have a general contractor lined up. That is fine. On a removal you want prepared for possible construction we commit to three things:

  1. We tell you the fill will settle a bit. Compacted, tested fill settles a small, predictable amount, most of it while it is being placed. We do not tell anyone the ground will not move.
  2. We place engineered fill compacted to 95 percent of maximum dry density. The fill goes in thin lifts, moisture conditioned and density tested every lift by the geotechnical engineer’s technician, with the lift thickness set by the geotechnical engineer and the compaction equipment, and the results recorded in a stamped engineer’s letter you keep with the permit. The PHTA Builder’s Manual explains why: fill only compacts near its optimum moisture, which the Proctor test establishes in the lab, and compaction energy only reaches so deep, so fill is built up in thin lifts rather than pushed in all at once.
  3. We have the fill dirt lab tested when it arrives on site, before it goes in the hole. Whether a load is suitable is a lab question, not a visual one; see Can you reuse pool dirt as fill?

How much of the old shell comes out is set by the engineer’s requirements for the future structure. We know what the engineer will want, line up the soil testing and over-excavate to those requirements, so the amount of shell that leaves the hole depends on the job. Our backfill standard records the material, the moisture, the lift thickness, the compaction method and the test results, and maps every disturbed zone on the lot: native soil, structural fill, utility trenches, the shell overcut and any future deck support. That zone map and the test reports are what the next engineer actually uses. Two sign-offs stand between the dig and a lot we call buildable: the excavation and subgrade release, with compaction and testing records, photos and the geotechnical engineer’s acceptance where required, and the backfill release, with lift and compaction records before anything is covered.

We also pull the demolition permit, which most pool removal companies do not, so the compaction record is filed against a closed permit instead of sitting in a drawer. What the job includes beyond those three commitments, and where it falls in a building schedule, is on our page on removing a pool to build a casita, ADU, garage or addition.

What the future structure’s engineer may add

Omni prepares the ground and records what was done. Omni does not design the building, the foundation or the slab, and does not say what will be built there. That is the engineer’s job for the specific structure, and the building department will ask for that engineer’s work when the building permit is filed. Under the building codes adopted around Tucson, a footing that bears on more than twelve inches of fill has to comply with an approved geotechnical report.

Depending on the structure and the soil, that engineer may call for any of the following. None of them is a default, and Omni does none of them on its own:

  • A geotechnical report or a letter that reviews the compaction record and adds borings if needed
  • A higher compaction target in the zone under the footings, or the modified rather than the standard Proctor test
  • Deepened footings or piers carried through the fill to native soil
  • A stiffened or post-tensioned slab that spans the fill and the native edge as one unit
  • Flowable fill, a low-strength cement slurry, instead of compacted soil when construction will follow within months

If a designer or engineer is already on board before the pool comes out, their fill requirements come to us first and take precedence over the standard scope. Who orders and pays for the soil work on a new project is covered in Who pays for the soil report?

What to tell a buyer or lender

A filled pool follows the house. The Arizona Residential Seller’s Property Disclosure Statement asks whether a pool on the property was removed, capped or filled, and separately whether permits were obtained for work done on the property. A buyer’s inspector who sees a low rectangle in the yard, an old equipment pad or capped pool plumbing will write it up. Lender rules on unpermitted work differ by loan program, so nobody can promise what an underwriter will accept, but every one of them can work with paper: a closed demolition permit, the compaction test record and the engineer’s stamped letter.

If you are the one buying a house with a filled pool and you want to build on it, get the fill evaluated by a geotechnical firm before design starts, and do not assume the old fill is buildable because the yard looks flat. What the disclosure asks and what inspectors look for is on our page on selling or buying a house with a filled-in pool in Pima County. We are pool contractors, not attorneys, so your agent or attorney should guide the wording.

What it costs

There is no single number for a pool removal, and anyone who gives you one on the phone is guessing. Our removals have run from about $6,000 for a small spool with full dump truck access, no deck, about 60 tons of fill and the permit included, up past $200,000 for a large pool converted into a pond. A spool or spa sits at the low end of that band, and a large pool with limited truck access sits at the high end. Build-over removals sit inside that band and are priced per site. What moves the number:

  • Partial removal, full shotcrete removal, or fill only
  • Whether the deck stays, comes out, or is broken up and used as fill
  • Any wall that has to be opened and rebuilt for access
  • Fill volume, which follows pool size and depth
  • Truck access, which is the biggest multiplier of all
  • What the space will become: turf, pavers, a slab, a building or a pond
  • Which jurisdiction issues the permit

To see what the pool costs you each year until it comes out, use TerraSpec, the pool removal cost calculator. Methods and what each one leaves you with are compared on the pool removal page.

Common questions

Will a filled-in pool settle even if it was compacted?

Yes, a little. Compacted, tested fill settles a small and predictable amount, most of it while the fill is being placed. Loose, untested fill settles a large and unpredictable amount, sometimes for years. The lift-by-lift test record is what tells an engineer which one is under your yard.

Can I build a casita, ADU or garage over a filled-in pool?

Yes, if the ground was prepared for it: engineered fill, compaction tested in lifts, and an engineer’s letter that records it. Your building permit will ask for that record. The engineer who designs the structure decides whether the footings bear on the fill or are carried through it to native soil, and how much of the old shell has to come out before the fill goes in.

The pool was filled years ago and there is no permit. Can I still build on it?

Not without finding out what is in the hole. A geotechnical firm can assess the old fill and tell you whether it can carry the structure or has to come back out. Start there, before any design work, and read our page on filled-in pools with no permit in Pima County.

Does Omni design the foundation or the slab?

No. Omni removes the pool, places and tests the fill, pulls the permit and hands you the engineer’s letter. The foundation, slab and anything added to the fill, such as piers or flowable fill, are decided by the engineer for the structure, and Omni acts on those only when that engineer directs it.

Do I need a general contractor before the pool is removed?

No. Most owners we talk to do not have one yet and do not know what they will build. The removal is done the same way either way, and the record waits for whoever designs the building. If you already have an architect, engineer or general contractor, we want their fill requirements before we dig.

Does the pool removal permit cover the building I put there later?

No. The demolition permit covers taking the pool out and closes when the fill and inspections are done. The casita, ADU, garage or addition needs its own building permit, filed by your contractor, and that application is where the compaction record and engineer’s letter get used. Pima County’s pool permit rules are summarized in Pool permit requirements in Pima County.

Get a written quote

Call (520) 222-8503 and tell us what you might build. The site visit is free, and you do not need a plan or a contractor to have it.

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