Moisture Readings

Contact Moisture Detection Company for information, help and pricing for the Mdu Moisture Probe System. 

Tel: (09) 271 0522 or email

Wood is absorbent and contains moisture depending on its surrounding environment. The most accurate way of measuring the moisture content is to remove a 100mm long piece of framing, weigh it, then dry it, and weigh it again –  then express the lost weight over the final dry weight as a percentage.

WetWoodTesting a home at all the places it might leak would need at least 30-50 moisture content tests which would destroy the framing in the process.

A less destructive way to measure moisture contents of walls is using conductance meters. These have 2 needles that are inserted into the wood and pass a small current through the wood which is converted into moisture contents. More moisture in the wood means less resistance, more current and higher reading. The needles need to be inserted at least half way into the framing otherwise temporary condensation or surface wetting would distort the reading. The needles they must be insulated otherwise the sides may be in contact with something other than wood which may influence the current and give a false reading. This is called invasive readings.


The Mdu Probe from Moisture Detection Company has insulated sides and the length of the needles is designed to reach into the timber framing where moisture of concern may be found. The Mdu Probes are permanent so repeat readings can be undertaken with accuracy at the same location without damaging the gib or cladding.

ProbeInWall     ProbeAdapter

How often should the probes be read?

An accurate survey of your home will include taking moisture content readings at least in a summer to see how dry walls become and in winter to see how and where framing gets damp. If the timber is well treated and the readings are fine ongoing readings could be done every 2 years as little if any damage can be caused even if a new leak develops because the treatment protects the framing. The less well treated framing will require more regular readings as exposure to dampness can cause significant damage in as little as 6 months. Another good time to read the probes is after repairs to ensure they were effective and met your expectations.

Many owners of plaster clad homes are concerned that they will have trouble selling them, or that they will have to sell for rock bottom price.  A moisture probe system, read regularly, provides proof to potential buyers that your home is sound, dry and a good investment for them.

What other useful information do the probes provide?

During the probe installation process, our technicians also collect timber samples from each location.  The samples are inspected for decay and selected samples are also tested for timber treatment.

So at the end of the process you will know:

  • if your house is leaking, where the leaks are and how bad they are
  • if your house has decay, where the decay is located and how bad it is
  • if your house was built with treated timber, what treatment was used and how strong the treatment is

A full debrief is provided to make sure that you understand the evidence, what it means for your house and what repairs and future maintenance are recommended.

You will be able to see all of the data overlaid onto plans of your house, on the MDC BNet data portal.

Who installs the probes?

The probes are installed by Moisture Detection Company, who own the patent for these devices.  You can phone them on (09) 271 0522 or email at

How many probes should be installed?

This depends on the size and complexity of your house.  A small, basic house may only require 25 – 30 probes however a large complex building may need 80 or more to test and monitor the higher risk detailing like beside doors, under windows, below gutter intersections with walls, below rain heads and under decks. Basically anywhere where doubt exists, a probe should be installed.

What is a ‘normal’ moisture reading?

This is a bit like genetics. Different cladding systems perform differently. Ground floors are always cooler than upper levels so moisture is higher around the ground. South walls get less sun so they have higher readings. Cavity construction allows ventilation so this alters the humidity which affects the readings. Acceptable moisture contents range between 9% very dry to 14%. This does not mean 15% is high. What we find is most of the readings will be in this range so if any deviate from this normal range something will explain the reason. The wetter homes are Tripple S, Stucco and Harditex as they are absorbent claddings and the insulation is inside the walls. Bricks are a little drier. The driest homes are generally EIFS or poly claddings.

How much do moisture readings vary between summer and winter?

Normal variations are 1%-3% depending on the cladding type and how the cavity works. Where moisture variations exceed this it is likely the wall is becoming wet through a leak, wicking, and capillary or vapour transfer. These are the spikes indicating work is required.

What moisture level does decay start?

Decay begins by germination which requires liquid wetting normally for at least 10 days. This can be by rainwater through a leak, or by condensation. NB: Treated timber becomes toxic to decay spores when wet which prevents successful germination. Once germinated decay fungi need moisture levels of around fibre saturation of about 30%-36%MC to become what is termed incipient (early) decay. NB: Treated timber prevents the development of incipient decay unless the germination occurred in nearby untreated material eg flooring. This level of decay is not threatening to the structure. After a couple of months continual wetting decay moves to advanced decay which is where it becomes visual and by then affected at least 30% of the integrity of the framing. Once the decay is mature it can continue growing in as little as 16%MC as recorded house 217 and as low as 12%MC house 985. It is believed once decay establishes in untreated timber they evolve into reproductive phase and digest cellulose mixed with air to produce their own moisture. Historically treated timber homes (pre 1987) had levels of treatment to manage the severity of decay.

Does treatment chemical affect readings?

Yes. Copper, Tin and Boron are all conductors so reduce resistance which increases the moisture readings. In a well treated house, MC readings from probes of 22% can be lowered approximately 2%. Surface applied treatments like Framesaver and injected RotStop will allow even more current and require greater adjustment.

Does temperature affect readings?

Yes but only marginal so no adjustments are considered necessary.

Does surface condensation affect MC accuracy?

Yes substantially. Condensation is liquid water so readings can be generated up to 100% yet after a few moments evaporation will read lower and maybe less than 14%MC. You can try this by testing MC with needles and then wiping a damp cloth over the surface and it will instantly read 30%MC or more.

Invasive tests can be used to benchmark other forms of non-invasive readings but not the other way around. Relying on non-invasive moisture readings can be expensive. Think twice.

How do we test moisture in the timber?

Get the Mdu Probes installed and our technician will read the moisture levels by connecting a moisture meter to each of the probes.    We recommend probes to be read twice every year to check seasonal variations, at least until you understand how your house is performing.  Getting accurate results means that leaks can be picked up before they cause expensive damage.

Do we do non-invasive readings?

Yes. There is a time and place for these generally after we have confirmation of leaks – we use these devices to narrow down the likely sources instead of removing cladding. We use the standard qualifications re limited reliability and we will not be held responsible for any inaccuracies.

What is proof of condition?

This relates to presence of timber treatment, decay and moisture. In other words if the framing is well treated and not already decayed and moisture content readings are all in the acceptable range that is evidence of good condition – but only if adequate probing is done, the results are recent and include a winter reading. Relying on moisture contents only is misleading and can lead to surprises.

If the Mdu probe system and installation testing find elevated moisture levels, decay or inadequate timber treatment, then this is evidence of problems that should be addressed before they become expensive repairs or even re-clads.

The probes are installed and read by Moisture Detection Company.  You can phone them on (09) 271 0522 or email at

What do the thousands of probes you have installed tell us?

Figure below shows the first 27156 Probe results comparing incidents of decay (visual colour rating C and D) and moisture content readings. Of concern is 6044 probes show VCR C yet dry and 719 probes were decayed and dry. Scanners at best would pick up 1407 VCR C and 843 VCR D or less than 12% of problems. To date we have around 250,000 probes installed.VCRvsMCGraphDoes decayed framing hold moisture?

No. Well not reliably as moisture is absorbed by the fibres of the framing. When the fibres are damaged they don’t hold water hence what is called false positives have evolved. Immediately after rain a probe may read 100% as the water is shorting it, but after a few hours may read zero again. This is why it is important to consider treatment, wood condition and moisture contents. No one result in isolation tells the complete story.

1 Response to Moisture Readings

  1. Christina Gera says:

    Hello I live in New Zealand and it is the middle of winter. I have a holiday home that had stucco put overtop of a weather board house. It had been locked up for 6 months plus prior to the testing it had rained off and on for weeks. I had someone come to check the house. In most of the house the readings were 12 to 15 % but in two bedrooms on one side of the house the readings ranged around the windows from 11 to 20 and on a wall near some nails there was a reading of 26. In the other bedroom on the outside wall the readings ranged from 13 to 22 around the window. There are no visible signs of damp in the house. The colour steel aluminium garage was also tested and around doors and windows there were readings of 24, again with no visible signs of moisture. The garage is unlined. The wooden window sills look perfectly dry. It is now believed I have a leaky home. Can you advise please. The testing equipment looked quite old. The person was unsure of the model, but the name we found on it was Carrell and Farrell. He said the testing equipment was set to pine wood and everything should read 15. I am unsure if the house was made of pine, some neighbours believe the weather boards were made of matai.

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