Your wooden floor is part of your building and the performance of the floor is dependent on the temperature and relative humidity within the building.


Wood is a natural material, it absorbs and releases moisture to and from the air. While most timber used in flooring is kiln dried to reduce the moisture content, the wood’s ability to absorb moisture remains. This ability is lessened by applying a polyurethane or oil coating. To keep moisture from below to a minimum; concrete subfloors are moisture sealed prior to direct fix installations and a moisture barrier underlay is used when the floor is floated.

Throughout the year we experience a range of weather patterns; cold, damp conditions create high humidity levels causing the wood to swell, whereas heating and sunlight have the reverse effect. Therefore, a small degree of expansion and contraction is to be expected with any wooden floor and this can be visible. To allow the wood to expand and shrink, we leave expansion gaps between the floor and the wall, these gaps are covered by skirting boards or beadings and trims. Fine gaps may appear from season to season, especially in rooms which experience unusual or significant changes in humidity and temperature, from both heating and sunlight. To help minimise these effects, owners can stabilise the environment of the building through temperature and humidity control.

It is not recommended that a house is left unheated for long periods during winter, as the moisture content of the building will rise without the drying effect of the heating and venting associated with normal occupancy. After a period of being unoccupied, reheat the house gradually, to avoid drying out the surface of the flooring faster than the middle and bottom of the timber. This avoids differential shrinkage which can cause cracking of the polyurethane along the joints and cupping of the boards.


All forms of heating, including freestanding heaters, radiators, heat pumps/air conditioning units and under floor heating, affect the temperature and humidity level of the floor. Insulation in concrete slabs, dehumidifiers and heat transfer kits will similarly impact on it. The floor should remain at a temperature below 24°C or 75°F, no matter what type of heating and/or insulation is used. Heating temperatures must be adjusted gradually as any extreme temperature change can damage the floor. For this reason, we recommended that any manual control units are enclosed and positioned so that only experienced people have access to them.

Each time the heating is turned on, start at 15°C and increase the temperature by 1 to 2 degrees per day over a period of 7 days, until the required level is reached – below 24°C. It is recommended that you reduce the temperature in the same manner.


The moisture content of the floor should remain within the acceptable range of 9–13% (see Controlling your Environment below). If the timber temperature is raised higher than 24% then the relative humidity on the surface of the wood will drop, drying the timber out below 9% and leading to gaps between the boards. Should you be considering a water controlled system, it is important that the unit is controlled by the temperature of the floor, not the temperature of the water in the system.

Experience has shown that misuse of temperature controls will prove too much for any wooden floor and will eventually lead to floor failure.

Sunlight and UV

All natural products are affected by light, particularly strong sunlight and UV rays which can have a detrimental effect on wooden floors. It will dry out the timber and splits may appear. It can also cause a distinct change in colour, especially noticeable with darker woods (they can become significantly lighter). This generally happens over a period of time – colour change is most obvious when rugs are placed on the floor. It is advisable not to place rugs down initially, to enable any fading to happen evenly throughout the floor.

The chemical reaction which causes materials to fade is accelerated by high temperatures. We therefore strongly suggest that you attach UV filters and/or blinds to windows, not only to protect your wood flooring but also your furniture, fabrics and carpets. We also recommend that the temperature of the room is considered. Please be aware that we cannot be held responsible for fading.

Timber Flooring in Wet Areas

A “wet area” is an area within a building with a water supply system. It always includes bathrooms, showers, laundries and WCs but surprisingly sometimes excludes kitchens and bars/food prep areas. Wet areas are problematic for all types of flooring and nothing is 100% waterproof, including most vinyl and tiles with grouting. There are many conflicting views with regards to timber flooring in wet areas. Whether you have a slow leak or a major flood it can be a costly repair. Ultimately it is often the insurance companies that bear the costs and it is worthwhile checking with your insurer to find out exactly what type of flooring they cover in such an event. They are not all the same. That said, there have been many instances when flooded timber floors have dried out, given sufficient time, and require no remedial work at all. The most important remedy for any major spill, is to remove the liquid as soon as possible, without causing product shrinkage. See Cleaning and Maintenance.

Bathrooms and laundries have higher moisture levels. In these areas the timber should be well looked after and the following steps should be taken:

  • Use venting kits to vent clothes dryers to the outside.
  • Prevent water leaking from washing machines, shower doors and other plumbing fixtures.
  • Do not leave puddles of water, damp towels, bathmats or clothes on the floors.
  • Use extraction fans and heaters, as well as heated towel rails.

We apply/install a waterproofing membrane to all concrete subfloors, this helps stop moisture coming up through the concrete and into contact with the timber. Similarly, with a wood substrate in a wet area, we can apply a waterproof barrier. Both these protect the timber from below.

Timber flooring, whether prefinished or finished on site, does not have a continuous membrane above. Timber flooring moves seasonally, as it reacts to the humidity level within its environment and the coating will crack between the boards during this process. A gap sealant is applied to the expansion gap left around the edge of the flooring when skirtings/toespaces are not being installed, it can also be placed under a skirting in bathrooms, toilets, laundries, etc. However, as with tile grouting, water can still work its way in and through capillary action, travel some distance.

The polyurethane we use is waterborne. This is a two-pot coating with a hardening agent in it. It is much more waterproof and hard-wearing than water-based polyurethane. We would not recommend either oiled floors or floating floors in wet areas.

In summary, we feel that a suitably coated and installed wooden floor in a wet area is as suitable as any other flooring type. Please discuss any concerns you have with regards to ‘wet areas’ at the time of quoting.

Wear and Tear

A certain amount of wear and tear, along with some minor scratches, are to be expected over time. These can add to the character of the wooden floor. Prefinished engineered floors can be sanded and recoated with polyurethane 3-4 times, while solid timber floors can be sanded and recoated 4-5 times. Sanding and recoating floors extends their lifetime and helps eliminate the possibility of moisture seeping into the timber. In high use areas, for example adjacent to kitchen sinks or in doorways, the polyurethane or oil coating can wear faster. We can sand/buff and re-apply your coating for you.

Controlling Your Environment

As mentioned in Movement above, timber absorbs and releases moisture in its environment depending on the temperature and relative humidity of the air. The moisture content of timber in a building moves towards the Equilibrium Moisture Content (EMC) of that building. EMC is a function of the average temperature and relative humidity of the building. The average EMC for NZ dwellings is around 11%, however this average will differ between buildings and also seasonally. Within the same building the EMC will vary from one part to another depending on factors which affect temperature and relative humidity. This variation can be from 8% to 14%. Unless otherwise specified your floor has been prepared and installed for an expected average EMC of 11%-13%.

Where the building design creates a sudden change in EMC over a small area, small gaps may appear in the low EMC area. Examples of this are under sky lights or in front of large glass walls (where direct light focuses on the floor), in front of heaters or fireplaces, below some types of self defrosting fridges or anywhere else where spot heating causes a drop in relative humidity, bringing the moisture content below 9%.

Your installed floor is designed to perform to its optimum at the average EMC of 11%. It should perform well within the range of 9% to 13%. However, at 9% small gaps may appear and at 13% minor peaking (cupping) may appear at the edges between boards, as the pressure causes the boards to press upward against one another. At 8% the gaps will be more significant and at 14% the floor will be more obviously under strain. In general, floating floors will react more to a high EMC than direct fix floors and moisture problems can result in cupping and/or swelling. When the EMC falls back within the 11-13% range, cupping and shrinkage should correct itself.

Please be aware that there are potential problem areas within a house where the floor may be more likely to take on moisture. This may result in expansion, possibly damaging the coating. Please ensure that your architect is aware that you are considering a timber floor, so that the correct type of door frames are used to all outside areas.

Most houses are maintained at a comfortable temperature and relative humidity, so the EMC does not go above 13%. High moisture content above this usually indicates a problem such as inadequate ventilation, moisture egress from the subfloor or plumbing or drainage problems.

We design our flooring installation systems to be as strong as possible. We will discuss your individual circumstances when quoting for your project.