Reducing moisture issues and maintaining healthy air flow helps create healthier, drier, more energy efficient homes. On this page you’ll find advice and quick tips to help keep your home moisture free, while keeping your energy bills down. 

Keep the air moving to reduce dampness

The key to keeping dampness out of your home is stopping moisture at the source and keeping fresh air moving through throughout the house.  

Good ventilation prevents the build-up of humidity, which causes dampness and mould to grow in your home. You can improve this with a few quick fixes, or factor ventilation into your home design when building or renovating.

On this page

Quick wins to reduce moisture

These low-cost improvements are affordable and can be done yourself without the need for major changes or professional help.  

  • Air your home regularly — Naturally ventilate your home by opening your doors and windows for 10 to 15 minutes each morning to bring in fresh air. 
  • Use energy efficient heating — Keeping rooms at a healthy, comfortable temperature (around 18°C) is the best way to reduce the amount of humidity, and prevent dampness and mould in your home.

  • Use lids on pots when you cook — Reduce the amount of moisture that escapes while cooking — especially if your home doesn’t have a rangehood over the stove. 

  • Use extractor fans and rangehoods — Make sure kitchen and bathroom fans are big enough to do the job, regularly cleaned and are vented to the outside, not your ceiling space. 

  • Run your bathroom fan for longer — Install a run-on timer switch to keep the fan running for a few minutes after you switch it off, or a humidity sensor to turn on the fan when it detects steam. 

  • Dry washing outside — Drying clothing indoors can release up to 5l of water into your home per load.*  Use a washing line or rack outside if the weather is good, or under a covered veranda, garage or carport.

  • Move furniture away from walls in winter — This helps to prevent mould from growing in areas that don’t get much airflow — especially along colder external walls.  

  • Leave wardrobes slightly open — This improves the air flow through clothing to prevent dampness and mould growing on fabric.   

  • Install a shower dome — These are great for preventing excess steam from escaping into your bathroom while you shower.  

  • Use a bed base — Lifting your mattress off the floor will help with air circulation — for children’s floor beds, it can be helpful to lift the mattress slightly with some wooden slats. 

Common sources of moisture 

If you have a persistent problem area in your home where dampness is an issue (you may notice an earthy or musty smell), the best thing you can do is stop it at the source. There are common problem areas where water can enter the home, and most are easy to check.

  • Extractor fans, rangehood and clothes dryers — These appliances should vent air and moisture outside, not inside or into the ceiling space. The ducting for your fans and dryer should be at least 150mm diameter, in good condition, and as short and straight as possible.
  • Plumbing pipes — Pipes and connections should be leak free so that moisture is kept out of the walls and floors (common near showers or baths). You may need to check under you house to be sure.
  • Downpipes and gutters — These should be clear and leak free, and downpipes should connect to storm water drains or a soakaway that is away from the house.
  • Subfloor wall vents — These should be unblocked, and the subfloor area should be kept clear.
  • Wall and roof cladding — Check these areas for leaks, as well as your flashings.
  • Concrete walls and floors — check for damp patches or white mineral deposits which indicate moisture is coming through (you may need to lift the flooring to check).

Bigger jobs to resolve moisture issues

These improvements may need a bigger investment and require support from an expert to get the job done well.  

  • Seal damp concrete or masonry — A waterproofing sealant or moisture barrier can be used for this. Ask an expert about the best product for your home. 
  • Improve drainage — If surface water flows under your house during heavy rain, you may need to reshape the outside levels or install drainage. Ask a licensed drainlayer for advice. 
  • Install subfloor vents — Your house should have subfloor vents on all sides. Ask a qualified builder for help on sizing and/or installation. 
  • Measure moisture content — Find hidden leaks by hiring a registered or accredited building surveyor to measure the moisture content of your home's materials. Find an accredited building surveyor (external link)
  • Install a ground vapour barrier — Thick polythene sheeting installed on the ground under your house keeps moisture in the ground and stops air under the floor from getting damp.  
  • Repair damage — Any wear and tear to your roof, windows and walls can cause water to creep in. Key spots to check are fasteners and flashings on your roof, paint condition on walls and paint and putty on wooden windows.
  • Consider a mechanical ventilation system — Some homes, particularly newer builds that are more airtight, need continuous flow of fresh air using a mechanical system. 

Mechanical ventilation systems 

Mechanical ventilation help keep air fresh and moisture-free — especially in bathrooms, kitchens and well-insulated homes — where humidity can become a problem.

  • Extractor fans — Using extractor fans in bathrooms and kitchens helps control moisture build-up and humidity. These fans should be vented to the outside of the house (not into roof spaces or other cavities) using ducting that is at least 150mm in diameter, and their filters should be kept clean.   

  • Mechanical ventilation with heat recovery (MVHR) — These systems continuously filter out stale, humid air and replace it with fresh air from outside. They recover heat from the outgoing air to adjust the temperature of the fresh air and maintain your home’s temperature. If you can afford it, this is the best option. 

  • Positive pressure ventilation systems — Systems like a DVS work by pulling air into the home from outside and pushing it into the living areas. They push out damp air and, in some cases, can work well to reduce condensation – particularly in older homes.

Other ways to improve your home

To make sure your home’s thermal envelope is performing at its best, all the individual building blocks need to be working together to form a ‘seal’ around your home — without any gaps. 

  • Design for energy efficiency

    If you’re building new, or renovating your existing home, you can lock in energy savings from the start with good design choices.

  • Insulate your home

    Insulation works best when it forms a continuous thermal envelope around the home — including windows, ceilings, walls and floors.

  • Window insulation

    Windows are the biggest source of heat lost in an otherwise well-insulated home — double or secondary glazing can make a big difference.

  • Minimum requirements for rental home ventilation

    There are minimum requirements for rental homes in New Zealand. These can be used as a guide for retrofitting ventilation into an existing home — but it’s recommended to go much higher if you can.