​Damp homes promote mould and dust mites which can cause respiratory problems. While dehumidifiers and ventilation systems help reduce the symptoms of the problem, it’s important to track down the underlying cause of dampness in your home. The problem may be relatively cheap and easy to fix.

• Signs of dampness
• Where does excess moisture come from?
• How to tackle sources of dampness inside
• How to tackle sources of dampness outside

Signs of dampnessInside

• Musty smells
• Damp or mouldy clothes or shoes in wardrobes
• Mould forming behind paintings, mirrors and furniture
• Mould, stains or watermarks on ceilings or walls

Condensation on windows, especially in bedrooms, isn't necessarily a sign of excessive dampness if it only happens occasionally during winter.
Outside

• Rotting wood in the structure of your house
• Musty smells or mould under the house

Where does excess moisture come from?InsideThe average NZ family produces up to 8 litres of moisture in the home each day from activities like cooking and showering. This is normal and can be managed by insulating, heating and ventilating.
Find out if your house is dampTo prevent mould growth, the amount of moisture in your home (relative humidity) should ideally be below 65% most of the time, and rooms should be heated to at least 18 degrees.
To assess the temperature and relative humidity in your house, try using a simple, low-cost hygrometer. Take readings over a few days or weeks in different rooms of your house, especially in winter, to find out where you might need to address dampness issues.
 Learn more about hygrometers
OutsideSources of moisture, such as leaking pipes or damp rising from underneath your house, are often hidden and can go undetected for a long time, damaging to your home.

How to tackle sources of dampness insideTop tips

• Eliminate avoidable moisture - dry washing outdoors rather than indoors.
• Extract moisture by using extraction fans (vented externally) in the kitchen, bathrooms and laundry.
• Air out the home regularly - open doors and windows to create a cross draft, or use a ventilation system.
• Keep the home warm - insulation and heating improve ventilation effectiveness and reduce the risk of mould growth on cold surfaces.

Watch: How to fix dampness in your home | 2:55 min


Bathroom, kitchen and laundry

• Avoid drying washing inside - dry it outside or under a covered verandah, garage or carport. If it’s raining, use a clothes dryer (ducted to the outside).
• Use lids on pots when cooking to reduce moisture and save energy.
• Install a shower dome to stop steam escaping into your bathroom.
• Use extractor fans - read our tips below.

Ensure extractor fans are:

• vented to the outside in your bathroom, kitchen and laundry - fans should not vent into your ceiling space
• properly sized and located for the type of room - undersized fans or ducting will be noisy but ineffective
• turned on before having a shower or bath - shut the bathroom door and leave the bathroom window open slightly to improve the fan's effectiveness
• left running for a few minutes after a shower or bath with the bathroom door shut and window open until most of the moisture has cleared
• cleaned regularly to maintain their performance.

Living areas and bedroomsAvoid unflued gas heatersUnflued gas heaters can be portable or have pipes fixed to the walls. They release large amounts of moisture and toxic gases into your house, and can also be a fire hazard.
If you’re using a gas heater or LPG portable heater without a vent or flue:

• always keep at least one window open to allow fresh air to enter the room
• never use in bedrooms.

Furniture

• Keep away from external walls (especially uninsulated walls) - leave a gap of 10cm or more to avoid mould growing behind furniture in winter.
• Keep mattresses off cold floors - put them on a bed base to let air circulate underneath.
• Leave wardrobes slightly open for ventilation.

DehumidifiersDehumidifiers are useful when it’s raining, but are unlikely to stop mould growth unless you tackle the sources of damp, and heat and ventilate your home. At low indoor temperatures, desiccant dehumidifiers tend to be more effective than refrigerant compressor dehumidifiers. Although they use electricity, it’s eventually released as heat and helps warm up the room.
Whatever type of dehumidifier you use, run it together with a heater - a warm room makes it easier for a dehumidifier to extract moisture.

How to tackle sources of dampness outsideUnder floors

• Look for leaks from showers or pipes under the house and fix any issues.
• Check for blocked or leaking downpipes and gutters, and ensure downpipes connect to storm water drains - this is best checked during heavy rain.
• Look for surface water flowing under your house during heavy rain - reshape the outside levels or install drainage channels or subsoil drains as needed. Ask a licensed drain layer for advice.
• Check there are vents on all sides of the house in the subfloor walls - inadequate ventilation is the most common cause of subfloor dampness. Install vents where they are missing - ask a qualified builder for help on sizing.
• Uncover vents blocked by plants, soil or pest barriers, and clear the subfloor area of obstructions.
• Install a vapour barrier (thick polythene sheeting) on the ground under your house. This keeps the moisture in the ground and stops the air under the floor from getting damp. New Zealand Standard NZS4246 has detailed instructions on how to do this.

 How to install a vapour barrier - NZ Standard for installing insulation
If you’re not sure about any of these actions, talk to a qualified builder.

Floors, walls and roofs

• Look for leaks in wall and roof cladding and flashings.
• Check plumbing pipes and services for leaks and moisture getting into walls or floors near showers and baths. Leaks like these are often hidden and can go unnoticed.

Measuring the moisture content of your home's materials is often the easiest way of finding hidden leaks. Talk to a registered or accredited building surveyor who is experienced in non-invasive moisture measurement techniques.
Registered building surveyors - New Zealand Institute of Building Surveyors website 
Accredited building surveyors - Building Officials of New Zealand website 

Concrete floors and walls

• Check for damp patches and white mineral deposits which indicate moisture is coming through. Lift flooring to check the concrete floor surface.
• Waterproofing sealants/moisture barriers can be applied to seal the concrete or masonry. Seek advice from a qualified builder about the best product for your situation, and also discuss any improvements to drainage that may be necessary.

Construction moistureIf your house is new or recently renovated, there’s probably excess moisture in some of the construction materials that needs to dry out. This may take a few months but you can speed up the process with heating and ventilation.
Find out if your home is warm, dry and healthyUse HomeFit to find out if your home is warm, dry and healthy - it's a free online check designed by the Green Building Council.
Do the online check at www.homefit.org.nz

This page links you with information about building and renovating.
Search our catalogueDesign and construction topics can be searched by subject. Start with whatever you are building, add the words design and construction and do a subject search. For example:
Some subjects have their own heading, such as shelving (furniture).
Browse our latest house and garden titles.
MagazinesRBdigital Magazines features a number of building and home renovation magazines, including Home Renovations, Dwell, Inside Out, The Family Handyman and more.
Find more magazines by searching on the subject Building – Periodicals and House Construction – Periodicals.
  
eResourcesBuilding and construction links
Building and constructions websites listed in our Internet Gateway, including useful weathertightness links.
Standards
Standards provide specifications to be used consistently as rules, guidelines, or definitions, to ensure that materials, products, and services are fit for their purpose. Find out how you can access the ones you need.
Standards New Zealand
Search New Zealand standards and access all New Zealand (NZS) and joint Australian & New Zealand (AS/NZS) Standards that are available in PDF format. Includes New Zealand Standards and Earthquake FAQs under the “services” tab.
Access this at any of our libraries.
Home Improvement Collection
Home improvement articles for the hobbyists and the professional alike. Coverage includes architectural techniques, tool and material selection, and much more.
Use at a library or enter your library card & password / PIN.Check with your council before you startBuilding and DIY projects need to follow certain guidelines – for safety and weathertightness, for example.
Before you start a building project, it pays to be informed. For most projects, such as decks, pools, or additions, building consent needs to be applied for and issued before building work commences. Resource consent may also be required.
Working with your local councilLocal councils administer the compliance process for their area, inspecting buildings and issuing consents. Consents must be applied for and issued beforebuilding work commences. MBIE's Building Performance site has a good guide to understanding the building consent process.
The consents and licences section of the Christchurch City Council web site includes information about building forms and charges, design and planning guides, as well as information on building consents. Consent application formsare available on the Christchurch City Council site.
Other district councils, such as Selwyn, Hurunui and Waimakariri will have regulations and by-laws specific to their area.
Christchurch City Council building information
Building law in New ZealandThe Ministry of Business, Innovation and Employment (MBIE) outlines building law in New Zealand on its Building Law and Compliance page.
GlossariesThis list will help you find authoritative sites that clearly define building-industry related terms, and act as an introduction to building law and the compliance process.
LIM – Land Information Memorandum
Information from the Christchurch City Council. Anyone may apply for a LIM, which gives information on any piece of land, including (among other information) any building consents or other authorisations applying to buildings on the land.
PIM – Project Information Memorandum
Information from the Christchurch City Council. The PIM provides an applicant with information relevant to the proposed building work, other than the normal requirements under the Building Act, 1991. This information enables the applicant to assess the feasibility of the project before proceeding with a Building Consent application with the Council.
Standards New Zealand Glossary of building terms (NZMP 4212:1998)
It is available at Tūhuratanga | Discovery, Level 3, Tūranga. New Zealand Standards are also accessible online in our libraries.

The online check.. This will give you an idea of how well your home - or the home you're thinking of buying or renting - is performing.

Once you answer a couple of introductory questions, you’ll end up on this dashboard:

Here you’ll be asked to answer 20 or so questions spread over 3 sections: dry, warm and safe & efficient. It should take you less than half an hour to complete, including some time to check under the home and in the roof space. If you know your home well, it should take you less than 10 minutes.
If you're unsure what a question means click on the information "i" to the right of the question. This will bring up helpful information on what to look for.
The online check won't give you a HomeFit certificate - for this you'll need to get a qualified HomeFit assessor to visit the property.

Getting your home HomeFit certifiedOnce you've made the improvements suggested by the online check go to “Get HomeFit certified”. This will bring up a range of local qualified HomeFit assessors who can visit your home to do the inspection and, if your home is up to the standard, give you the HomeFit certificate. You can email the assessors directly from this website.

HomeFit PLUSHomeFit has a higher standard called HomeFit PLUS. This requires homes to have:

• more insulation (including wall insulation)
• more energy efficient lights
• more energy efficient heating
• better ventilation systems

Having a HomeFit PLUS stamp for your home will differentiate it from the rest of the market. Your HomeFit assessor will be able to tell you if it meets the standard.

Marketing a home as HomeFitIf your home is certified as HomeFit or HomeFit PLUS it will be recorded on some property websites with the HomeFit tick alongside other information such as the number of bedrooms and bathrooms. This means that anyone looking to buy or rent your home can have some peace of mind that it’ll be warmer, drier and safer. If for any reason you don’t want people to know your home meets the standard then please email [email protected].

The HomeFit online check reportWhile you’re completing the online check you can click at any time on the “Get your self-assessment checklist”. This will bring up a short report summarising where your home is doing well and where it could do with some improvements. You can print this out at any time and/or send this as a link in an email for example.

Installer DirectoryThe HomeFit self-assessment report includes a list of local installers and suppliers who can come to your home and sort out any outstanding issues. Many of these installers are also trained HomeFit assessors who will be able to complete the HomeFit assessment once they’ve finished any remedial work.

The report lets you email the installers and ask them to quote for the work. We recommend getting a number of quotes to make sure you’re getting value for money.
I want to use HomeFit to self-check multiple propertiesThat’s fine. Just register to use the HomeFit website and you can save multiple properties and retrieve these whenever you log in. They are visible under the "Account" button at the top of the screen. This could be useful if you are looking at multiple properties to buy or rent, or you hold a portfolio of properties. Remember though that you’ll need to get a formal assessment from a qualified assessor to be able to get a home certified as HomeFit.
What about the RTA Amendment regulations for rental properties?The qualified HomeFit assessor will also check whether your home meets the insulation and smoke alarm requirements of the Residential Tenancies (Smoke Alarms and Insulation) Regulations 2016 (RTA). Even if you’re not thinking about renting this home it’s useful to know if it would meet the standard. It’s also useful to know that the fire alarms are working and are in the right place.

…and the Healthy Home Guarantee Act (HHGA) Standards?The New Zealand Government is consulting on further requirements for rental properties likely to come in force after 2020. This will include standards for heating and ventilation as well as standards for insulation and smoke alarms (like the current RTA but maybe more stringent).

The latest consultation gives a number of different options, all of which are less rigorous than HomeFit so, if you get a home HomeFit certified, it is likely to meet the Healthy Homes Guarantee Act 2017 (HHGA). Once the Healthy Home Standards have been formally published we will update HomeFit to include a check on the HHGA.

I want to know all the techy details about what HomeFit requiresSure, you can find the HomeFit Technical Manual on the NZ Green Building Council website.
​
Needing to get a new building assessed?If you’ve just built, or are about to build, a brand new home that you want to be healthy, safe and warm, then go here.