A positive meth test triggers a defined sequence of steps: a meth contamination assessment (detailed assessment), decontamination, and clearance testing. Whether you are dealing with a suspected meth house, a positive meth test on a rental property, or a meth contaminated property after a tenant has left, the process is the same. The threshold that applies depends on your situation: for rental properties, the 2026 Residential Tenancies regulations set a contamination threshold of 15 µg/100 cm² (and an uninhabitable level of 30 µg/100 cm²); for non-rental situations — property sales, insurance, and vehicles — the NZS 8510:2017 decontamination threshold of 1.5 µg/100 cm² applies. This guide explains the meth contamination investigation that follows a positive result, whatever the threshold.
Step 1: Detailed Assessment
If a composite screening test returns a positive result, the first step is a detailed assessment using discrete (individual) surface samples. This identifies exactly which rooms and surfaces are contaminated and at what concentration. The detailed assessment report becomes the roadmap for decontamination — it tells the decontamination team which surfaces need cleaning and provides the baseline against which clearance testing will be measured.
If your initial test was already a discrete assessment, you may already have this information. But if you used a DIY kit or a non-compliant screening test, you will need a proper NZS 8510:2017-compliant detailed assessment before proceeding.
Step 2: Decontamination
Decontamination is the process of cleaning all affected surfaces to reduce methamphetamine residue below the applicable threshold — 1.5 µg/100 cm² under NZS 8510:2017 for non-rental situations, or the relevant 2026 Residential Tenancies regulations threshold for rental properties. The process varies depending on the extent and type of contamination, but typically involves:
- Removing and disposing of contaminated soft furnishings, carpets, and materials that cannot be effectively cleaned.
- Washing all hard surfaces (walls, ceilings, floors, benchtops, fixtures) using specialised cleaning agents.
- Cleaning or replacing heating, ventilation, and air conditioning system components that may have been exposed to contaminated air.
- Sealing surfaces where residue has penetrated porous materials that cannot be fully decontaminated by cleaning alone.
For a detailed guide on the decontamination process, see our meth contamination cleaning guide. Decontamination should always be performed by trained professionals — attempting to clean meth contamination yourself can spread residue further and may not meet the standard required for clearance.
Step 3: Clearance Testing
After decontamination is complete, clearance testing is required to confirm that contamination has been reduced below the applicable threshold — 1.5 µg/100 cm² under NZS 8510:2017 for non-rental situations, or the 2026 Residential Tenancies regulations threshold for rental properties. Clearance testing involves re-sampling the previously contaminated surfaces using the same NIOSH 9111 protocol and submitting the samples to an IANZ-accredited laboratory for analysis.
Only when clearance testing confirms that all surfaces are below the threshold can the property be considered safe for reoccupation. The clearance report is your evidence that the property has been remediated to the NZS 8510:2017 standard — and is essential for insurance claims, tenancy disputes, and property transactions.
That clearance test must be carried out by a tester who is independent of the contractor who did the work — a business cannot credibly certify its own remediation. Our post-clean verification testing re-samples every previously affected location individually using the same NIOSH 9111 method as the original assessment, so the before-and-after comparison stands up to an insurer, a buyer or the Tenancy Tribunal.
Meth Cleaning, Meth Decontamination, and What It Costs
"Meth cleaning" and "meth decontamination" get used interchangeably, but they are not the same job. Cleaning removes what you can see — grime, staining, paraphernalia. It does not remove methamphetamine residue from surfaces: household bleach, general cleaners and fresh paint can spread it instead, and none of them produce a measurement. Decontamination is the regulated process described in Step 2 above — see our step-by-step meth cleaning and decontamination guide for what it involves.
Who is allowed to do which depends on the level. On a rental property, the 2026 Regulations treat readings below 15 µg/100 cm² as not contaminated and permit the owner to clean at that level. At or above 15 µg/100 cm² the property is classified as contaminated and the work belongs with a qualified, IANZ-accredited decontamination contractor working from your independent detailed assessment. EnviroCheck does not clean: we provide the assessment that scopes the work and the independent clearance testing that proves it, so the company finding the contamination is never the company paid to remove it.
There is no fixed price for meth decontamination, and a contractor quoting one before the detailed assessment is guessing. The cost is driven by how far above the threshold the readings are and how many locations are affected, the floor area, how much porous material (carpet, underlay, curtains, soft furnishings) must be removed and disposed of as controlled waste, containment and negative-pressure filtration, ventilation and ceiling cavities, and whether the property must be vacant during the work. Remediation is almost always many times the cost of the assessment that scopes it and the clearance re-test that closes it out — which is exactly why the independent testing belongs in the budget before anything is cleaned. See the cost guide.
Insurance and Liability
A positive meth test can have significant insurance and liability implications. For landlords, the question of who pays for decontamination depends on the evidence available. A pre-tenancy baseline test that documented the property as clean before the tenant moved in is the single most important piece of evidence in establishing tenant liability. Without a baseline test, proving that the tenant caused the contamination is significantly harder.
For property owners with meth contamination insurance coverage, an insurance toxicology report from an NZS 8510:2017-compliant test is typically required to support a meth testing insurance claim. Check your policy for specific requirements, and ensure all testing is conducted to the standard.
Preventing Future Contamination
Once a property has been decontaminated and cleared, the next priority is preventing future contamination. MethShield® is EnviroCheck's patent-pending deterrence and monitoring system that aims to help deter methamphetamine use in properties. Combined with regular property meth testing at tenancy changes, it provides ongoing protection for your investment.
If you have received a positive meth test result and need a detailed assessment, decontamination guidance, or clearance testing, contact EnviroCheck. We provide independent, NZS 8510:2017-compliant testing across New Zealand.