Yes, a qualified flooring installer absolutely should advise you on moisture testing before laying your floor — and in many cases, it's a critical step that can make or break the longevity of your new flooring. Skipping moisture assessment is one of the most common causes of flooring failures in New Zealand homes, particularly in older houses, new concrete slabs, and areas with high humidity.
Why Moisture Testing Matters
Excess moisture in a subfloor can cause timber floors to cup, warp, or buckle, adhesives to fail, and vinyl or laminate to lift and bubble. New Zealand's varied climate — from the damp winters of the South Island to the humid summers in Northland — means moisture is a genuine concern across the country. Even a slab that looks and feels dry can hold enough moisture vapour to damage a floor over time.
A reputable installer will factor moisture assessment into their pre-installation process, not treat it as an optional extra.
What Methods Do Installers Use?
There are several recognised moisture testing methods, and a good installer will choose the right one for your subfloor type:
Concrete Subfloors
- Relative Humidity (RH) in-slab testing – Considered the most accurate method for concrete. Probes are inserted into drilled holes and left to equilibrate before a reading is taken. Most flooring manufacturers specify an acceptable RH level (commonly 75–85% RH depending on the product and adhesive).
- Calcium chloride test (surface emission test) – A sealed dish of calcium chloride is left on the slab surface for 60–72 hours to measure moisture vapour emission. Less common in NZ than RH testing but still used.
- Moisture meter (pin or pinless) – A quick, non-destructive scan useful for initial screening, though not always sufficient on its own for concrete.
Timber Subfloors
- Pin-type moisture meter – Pins are pressed into the timber to give a moisture content (MC) reading. Most timber flooring manufacturers require the subfloor MC to be within a few percentage points of the flooring product itself.
- Pinless (radio frequency) meter – Scans a wider area without leaving marks, useful for checking sheet flooring or engineered boards.
A good installer will document their readings and discuss the results with you before proceeding.
What Are the Acceptable Moisture Levels?
Acceptable levels vary by product, so always check the manufacturer's technical data sheet. As a general guide:
| Subfloor Type | Typical Acceptable Level |
|---|---|
| Concrete slab (RH in-slab) | ≤ 75–85% RH (product-dependent) |
| Timber subfloor (MC) | ≤ 16% MC (check manufacturer specs) |
| Engineered timber subfloor | Often ≤ 14% MC |
Your installer should always defer to the flooring manufacturer's specifications. BRANZ publishes useful guidance on moisture in building materials that both installers and homeowners can reference.
NZ Building Code and Moisture
The NZ Building Code includes provisions relevant to moisture management in floors. Clause E3 (Internal Moisture — which covers wet areas such as bathrooms and laundries, not flooring generally) and Clause B2 (Durability) are particularly relevant — floors must be installed in a way that protects the building from moisture damage over time. While flooring installation itself is generally not restricted work requiring a licence, the installer's obligation to follow manufacturer guidelines and good trade practice is well established.
If your home is a rental, the Healthy Homes Standards also require adequate subfloor moisture barriers in many cases, which can affect what your installer needs to address before laying the floor.
What If Moisture Levels Are Too High?
If testing reveals elevated moisture, a professional installer should advise you on remediation options before proceeding. These may include:
- Allowing additional drying time – New concrete slabs typically need at least 30–60 days to cure, though this varies.
- Installing a vapour barrier or DPM (damp-proof membrane) – Products from suppliers like Sika or Ardex include moisture mitigation systems designed for use under flooring.
- Applying a moisture-tolerant adhesive – Some adhesives are formulated to handle higher RH levels.
- Improving subfloor ventilation – Particularly relevant for suspended timber floors.
An installer who simply proceeds without addressing high moisture readings is putting your floor — and your investment — at risk.
When to Call a Professional
Always use a qualified, experienced flooring installer for moisture assessment and floor laying, particularly for:
- New concrete slabs – These require careful RH testing and often a waiting period.
- Solid or engineered timber floors – Moisture-sensitive products that can be expensive to replace if installed incorrectly.
- Homes with known dampness issues – If you've had leaks, flooding, or rising damp, a building inspector or waterproofing specialist may need to be involved before flooring work begins.
- Rental properties – Healthy Homes compliance may require specific subfloor treatments.
If there are concerns about structural moisture or subfloor integrity, your installer may recommend involving a Licensed Building Practitioner (LBP) before proceeding.
You can find qualified local flooring installers on tradedirectory.co.nz who can assess your specific situation and advise you properly before a single board goes down.
