How to pass a building inspection

1. How building inspections fit into the permit process

When a building permit is issued, it comes with an inspection schedule — a list of stages at which the work must be checked before it can be covered. The permit is the contract between you and the building department: you agree to build to the approved plans and the applicable code, and they agree to inspect it along the way.

The terminology differs slightly between countries. In the US and Canada the person who visits is a building inspector employed by or contracted to the local authority having jurisdiction (AHJ). In the UK, inspections are carried out by a building control officer from the local authority or an approved inspector from a private registered firm. In Australia, the role is typically filled by a building surveyor or certifier (government or private, depending on the state or territory). In New Zealand, the building consent authority — usually the territorial authority — sends an inspector. The process and purpose are the same everywhere: an independent check that the work meets the code before it is hidden.

2. The main inspection stages and their timing

Most residential projects trigger several inspections, each at a different stage of construction. The specific list on your permit tells you which ones apply to your project. The common stages are:

Never cover rough-in work — pipes, wiring, or framing — before the corresponding inspection has been signed off. Covering work before inspection is one of the most common and most expensive mistakes on a permitted project: the inspector can require you to open the wall at your own cost.

3. What the plumbing rough-in inspection checks

The plumbing rough-in is one of the most detailed inspections on a residential build. The inspector is typically looking for:

• Correct pipe material. The material must be permitted for the application — some materials are not rated for hot supply lines, for example, and ABS and PVC are not interchangeable in all jurisdictions without an approved transition fitting.
• Consistent drain slope. Drain lines must slope toward the sewer or stack. The exact required slope is set by your local code; use a drain-slope calculator to verify your lines before the inspector arrives.
• Proper trapping and venting. Every fixture must have a trap, and every trap arm must connect to a vent within the distance your code allows. Missing or improperly located vents are a common reason for a failed rough-in inspection.
• Pressure test. Supply lines are typically tested under air or water pressure for a set period. A pressure drop indicates a leak somewhere in the system.
• Pipe support at required intervals. Unsupported runs sag, stress joints, and eventually leak. Your code specifies the maximum unsupported span for each pipe type and size.
• Protected penetrations. Pipes passing through framing members may require nail plates or sleeve protectors to prevent accidental puncture by drywall fasteners later.

4. What the electrical and framing inspections check

Electrical rough-in: The inspector verifies that wire gauge is appropriate for the circuit (see the wire-size calculator), boxes are correctly sized for the number of conductors and devices they contain, all wiring is secured and protected, there are no exposed splices outside junction boxes, and ground fault circuit interrupter (GFCI) or arc fault circuit interrupter (AFCI) protection is installed where required. The panel layout and labelling are also reviewed.

Framing: The rough-framing check confirms that load paths run continuously from the roof to the foundation, the correct nail schedule was used for sheathing and structural connectors such as joist hangers and hurricane ties, headers above openings are properly sized and supported, and fire blocking is in place at the required locations — typically at floor and ceiling lines in wall cavities and at horizontal concealed spaces longer than the code-specified maximum. In seismic or high-wind zones, the inspector pays close attention to shear-wall nailing patterns and hold-down hardware.

5. How to prepare so you pass the first time

The single most important step is to have the permit card and the approved construction documents on site before the inspector arrives — not a photocopy, but the stamped originals the building department returned to you. Without them, many inspectors will not start the inspection.

Beyond the paperwork, the practical preparation checklist is:

• Make sure the work is genuinely complete. Do not call for inspection hoping the inspector will overlook something you know is not done. If they find incomplete work they will fail the inspection and you will pay for a reinspection visit.
• Clear access. Move stored materials, scaffolding, and debris away from what needs to be inspected. Provide adequate lighting in crawl spaces, attics, and utility areas. An inspector who cannot safely reach the work cannot sign it off.
• Do a self-check walk first. Walk through the work yourself against the approved plans. Flag anything that changed from the plans and be ready to explain why — a minor approved change is fine, but the inspector needs to know about it.
• Do not apply insulation or drywall before rough-in sign-off. Even a single sheet of drywall over unseen rough-in work is enough for the inspector to stop the job.
• Be on site or have someone there who knows the work. An inspector with a question needs an answer, not a voicemail box.

6. Common reasons inspections fail — and how to avoid them

• Work started before the permit was issued. This is also a code violation separate from the inspection failure. The inspector may require the work to be undone and redone after the permit is in hand.
• Work covered before inspection. As noted above, this is one of the most expensive mistakes. Always call for inspection before closing up any rough-in work, even if it causes a delay.
• Deviating from the approved plans without a plan change. If something changed during construction — a different pipe route, a relocated panel — that change needs to be approved before the inspection. Some changes are minor and a verbal note to the inspector suffices; structural or material changes typically require a revised plan set.
• Wrong materials or fittings for the application. Using a drain fitting on a pressure line, or a material not listed for the service temperature, is a fail even if the installation is otherwise clean.
• Missing fire-blocking, draft-stopping, or required clearances. These are easy to miss and often overlooked during the build — inspectors know it and look for them.

7. What happens if you fail an inspection

A failed inspection is not the end of the world — it is a list of corrections. Ask for the correction notice in writing (most inspectors issue one automatically). Read every item carefully before you start fixing anything: inspectors sometimes use shorthand or reference code clauses, and misreading a correction leads to fixing the wrong thing. If anything is unclear, call the building department and ask for clarification — that is what they are there for.

Fix all the listed items, then schedule a reinspection. Many jurisdictions allow one reinspection at no extra charge; a second reinspection for the same items often attracts a fee. Do not cover or proceed past the stage that failed until the reinspection is signed off.

If you disagree with an inspector's finding, you have the right to appeal to the building official or an appeals board. Bring documentation: the code clause you believe the work satisfies, the product data sheet for any materials in question, or an engineering letter if the point is a structural one. Polite, factual disagreements based on code language are resolved this way regularly.

Common questions

What does a plumbing inspection look for?

At a rough-in inspection the inspector checks that the right pipe material is used for each application, that drain lines slope consistently toward the sewer (local code sets the exact requirement), that every fixture has a trap and each trap has a properly vented trap arm within the allowed length, and that supply lines pass a pressure test without dropping. They will also check that pipes are supported at the intervals your code requires and that penetrations through framing are protected. Nothing should be covered with drywall or concrete before this inspection is signed off.

What is the 135 rule in plumbing?

There is no standard building code rule called the 135 rule. The term appears in some trade training materials as informal guidance about limiting consecutive sharp-direction changes in drain lines — the idea being that too many tight bends in sequence can trap waste and cause blockages. However, it does not appear as a named rule in the IPC, UPC, NBCC, or other major model codes. If an inspector references it, ask them to point to the specific clause in your local code. The real requirements for drain-line direction changes are found in the pipe-fittings and horizontal-to-vertical sections of your jurisdiction's adopted plumbing code.

What is the first thing an inspector wants to see?

The permit and the approved construction documents. The permit card (or printout) must be posted at the site and the approved plans must be on hand — not a photocopy you made before the office stamped them, but the actual set the building department returned to you. The inspector works from those plans, so if they are missing the inspection may be refused on the spot. After the paperwork, they want unobstructed access to the work itself — cleared floor space, no insulation laid over rough-in pipes or wiring, and adequate lighting.

What things are big red flags in a home inspection?

A home inspection (the kind a buyer commissions before purchase) differs from a permit inspection, but the biggest concerns are: active or historic moisture and water intrusion anywhere in the structure (roof, basement, crawl space), evidence of structural movement such as sagging floors, stair-stepped cracks in masonry, or an out-of-plumb foundation; electrical systems that are outdated or undersized for the load; signs of unpermitted additions (finishes that do not match, missing permits in the records); and mechanical systems at the end of their service life. Any of these warrant a specialist report before proceeding with a purchase.