What is a building envelope or NAOS easement on an Arizona custom lot?

On a North Scottsdale custom lot, two layers of rules split your land into what you can touch and what you cannot: the City of Scottsdale's Environmentally Sensitive Lands (ESL) ordinance, which requires a share of every property to be preserved, and the community's own design guidelines, which draw the exact line on your specific lot. The "you can touch this" side is the building envelope, the specific area where the home, driveway, pool, and other improvements are allowed to sit. The rest is the NAOS easement, short for Natural Area Open Space easement, recorded against the property so it stays undisturbed natural desert and can never be built on. The result surprises many buyers: on a steep, large lot, well over half the land can be off-limits to construction, and the buildable footprint is much smaller than the lot size suggests.

This page explains what each term means, how they get recorded, how much of a lot they can lock up, and how to check before you buy. For the wider review these rules sit inside, see how HOA design review affects building a custom home.

What a building envelope and a NAOS easement are

A building envelope is the "yes" zone and a NAOS easement is the "no" zone, and together they decide where your home can go. The building envelope is a defined boundary on your lot. Inside it, you can place the house, garage, driveway, patios, pool, and walls, subject to the normal setbacks. Outside it, the land is meant to stay in its natural state.

The NAOS easement is how that "stay natural" promise becomes permanent. An easement is a recorded right over land that limits how the land can be used. With a Natural Area easement, that right runs in favor of the city or the community. It bars grading, clearing, building, and often even landscaping in that area. Because it is recorded against the lot, it binds you and every future owner. Troon North's standards say it plainly. Scottsdale's ordinances "require that the Building Envelope be made a part of the public records by recording a 'Natural Area Easement' over the portion of the Lot" outside the envelope, and that envelope "may be changed only through an amendment process with the City of Scottsdale."

So the two terms are mirror images. The building envelope is the area you control for construction. The NAOS easement is everything else, recorded to protect the desert. Both show up on your plat or a recorded exhibit, not just in a brochure. For the underlying legal concept, see our easement glossary entry.

Where these rules come from in Scottsdale

The building envelope and NAOS easement come from the City of Scottsdale's ESL ordinance first, then the community layers its own design rules on top. The Environmentally Sensitive Lands overlay governs development across about 134 square miles of Scottsdale's desert and mountain land north and east of the Central Arizona Project canal. Its core requirement is open space. The ordinance "requires that a percentage of each property be permanently preserved as natural area open space (NAOS) and that specific environmental features, including vegetation, washes, mountain ridges and peaks, be protected from inappropriate development."

How much you must preserve depends on the land itself. The NAOS share is set by two factors, landform and slope, and it climbs steeply on rougher ground:

• Lower desert, gentle slopes: a minimum near 15% of the lot preserved as NAOS.
• Upper desert: preservation rises into the 25% to 45% range.
• Hillside, steep slopes over 25%: preservation can reach 80% of the lot.

The Scottsdale Foothills Overlay adds design controls on the same kind of terrain, including keeping washes "in natural conditions where practical," a 15-foot minimum setback for walls, and muted exterior colors capped at an LRV of 35. Inside a gated community such as Troon North, the community design committee then draws the actual envelope on your lot and requires the Natural Area easement to be recorded before you build. City rules set how much; the community sets exactly where. For how the two layers fit together, see how HOA and community design review works in Scottsdale.

How much of your lot you can actually build on

The buildable area on a North Scottsdale custom lot is often far smaller than the lot, because the NAOS easement carves out the rest. This is the single biggest planning surprise for buyers who price a lot by its total acreage. A two-acre hillside parcel that must preserve 80% as NAOS leaves only about a third of an acre to hold the home, driveway, and pool, before setbacks even apply.

Two forces shrink the footprint:

• The NAOS percentage removes a fixed share of the lot from any construction, driven by slope and landform under the ESL ordinance.
• The building envelope and setbacks then limit where, inside the remaining land, the home can sit. Troon North notes that an owner is not even meant to fill the entire envelope.

This is why a flat lot and a steep lot of the same size can yield very different homes. The flat lower-desert lot may preserve only 15% and leave a generous pad. The steep hillside lot may preserve most of its area. That forces a compact, stepped design that follows the natural grade. The slope you are paying a premium for is often the same slope that limits what you can build.

Here is a simple way to picture it. Take a one-acre lot, which is about 43,560 square feet. On gentle ground with a 15% NAOS rule, you keep roughly 37,000 square feet to work inside, then subtract setbacks. On a steep hillside lot with an 80% NAOS rule, you keep only about 8,700 square feet before setbacks. Same acre, very different homes. Always run this math on the actual parcel before you price a build. See what is the biggest house I can build on my lot in Arizona for how this stacks with height and lot coverage.

What to check before you buy a custom lot

Before you buy, confirm the recorded building envelope, the NAOS percentage, and any community design easement, because those three numbers decide what you can build, not the lot's total acreage. A lot can look large and still hold only a small home.

A practical checklist:

• Pull the recorded plat and any easement exhibits. Look for a mapped building envelope and a Natural Area Open Space easement. If the envelope is small, the buildable pad is small.
• Ask the city for the ESL NAOS requirement on that parcel. It is driven by the lot's slope and landform, so get the actual percentage, not a neighborhood average.
• Get the community design guidelines. A gated community can require the envelope and easement to be recorded, set where the home sits, and add its own grading and disturbance limits.
• Walk the slope with a designer. On steep ground, the NAOS and grading rules can force a stepped, single-story, or split-level home rather than the plan you pictured.

A builder who works in ESL and gated communities, like Jematell Homes, reads the recorded envelope, the NAOS easement, and the community guidelines at the start of design, so the home is drawn to fit the buildable area from day one instead of being redrawn after a failed review. The land tells you what it will allow. Confirm the envelope and the NAOS easement before you commit, and the lot's real capacity stops being a surprise. For the design committee that enforces these on your build, see our design review committee glossary entry and setback glossary entry.

How Jematell Homes helps

Vetting whether a parcel is truly buildable is where we start every project. We would rather answer your questions before you build than after, so get in touch any time.

Sources

• City of Scottsdale: Environmentally Sensitive Lands Overlay (ESL); NAOS requirement
• Troon North Association Architectural Standards (Building Envelope; recorded Natural Area Easement)
• City of Scottsdale: Foothills Overlay District (natural desert preservation)