What Type of Timber is My House Built With?

Do you know what type of timber is behind your walls?

What type of timber is used in leaky buildings?

Coming up in this article, you will see an outline of what H1, H2, H3, H3.1 and the different stamping on timber means… and which timbers are associated with leaky buildings, or potential leaky homes…

1 in 5 phone calls we receive will ask, “How do I know what type of timber my house (or the house i’m looking to buy) is built with?“. You can actually find out quite easily, but you do need to be able to see the woodmark stamp on the timber frame in one of your external walls:

What is treated timber and what is untreated timber?

Which timber will rot if I get leaks?

Hazard classes vary in treatment levels from 1 – 6, so depending on what you use the timber for will depend on treatment type:

H1 : The treatment level for low hazard situations where timber is not exposed to the weather. Its major use is for framing timber and interior linings. This type of timber has been used in external walls of ‘leaky buildings’, and the reason its failed is due to moisture ingress through the cladding and directly onto the timber! H1 timber also has sub-categories:

  • H 1.1 : Timber used in situations protected from the weather, dry in service and where resistance to borer only is required. Do not use this timber in external walls unless additional chemical treatment has been added.
  • H 1.2 : Timber used in situations protected from the weather but where there is a risk of moisture exposure conducive to decay (Pink or Blue in colour). Minimum standard to use in external walls. Check with council to confirm this minimum requirement has not been upgraded before building.

H2: This level is very similar to H1 but includes an insecticidal treatment to protect against termite attack… normally for use in Australia.

H3: For moderate decay situations where timber is exposed to the weather but is not in contact with the ground. H3 is also split into sub-categories.

  • H3.1 : Timber used outdoors above ground, exposed to the weather – generally in non-structural applications; i.e. fascia boards, weatherboards.
  • H3.2 : Timber used outdoors above ground, exposed to weather or protected from the weather but with a risk of water entrapment; i.e. decking, fencing and pergolas. Used in areas of high risk to water penetration, such as balconies.

H4: Used in high decay areas such as ground contact or fresh water. Generally used for fence posts and landscaping timbers.

H5: Used for severe decay hazard risks such as ground contact where conditions of severe or continuous wetting may occur. End uses for this hazard class are house piles and poles, retaining walls, crib walling and horticultural supports.

H6: This hazard class is for marine use. Wharf piles and fenders, marine and jetty components regularly immersed in seawater or estuarine ground.

Sometimes you may need to remove a small section of interior lining on an external wall to see the timber stamp on the frame. Otherwise it could be written on the original building plans.

Moisture Meter – Measuring Moisture Content of Wood

We have a serious moisture problem in this country when untreated timber comes into the picture!

The moisture content within timber has a very important bearing on the uses for that type of wood. Having a good understanding of how moisture and leaks effect timber types is therefore critical to determine utilization. Moisture meters are the fast way to read moisture levels in wood.

Here’s a quick lesson about wood moisture, how it works in timber… and why we have leaky homes and leaky buildings in NZ:

The makeup on wood is best described as 1000’s of tiny cells… and within those cells are cell walls and cavities. Heartwood and Sapwood in their raw form (freshly cut) are saturated with moisture, and you may have noticed this yourself when you cut down a tree. In between the saturated cells are very small spaces of air. Once the wood has been cut, and the drying out process of the timber begins, the first part of the cell to loose it’s moisture content is the cell cavity, and then the cell wall.

Important to understand: Once the moisture from the timber cell walls has completely evaporated and the timber itself has somewhat shrunk in the process, the woods moisture content will then be in equilibrium with its surroundings (EMC – Equilibrium Moisture Content).

Once the timber framework of your home has been put in place by the builder, from then on its integrity and life span will be subject to the variations in surrounding relative humidity (and to a lesser extent, temperature). In general, most countries around the world including New Zealand, will have wide variances in humidity between winter and summer months, therefore the Equilibrium Moisture Content of the timber will affected (swelling and shrinking) if it wasn’t originally dried to the average moisture content is will attain in use. That’s why moisture meters quickly help us to determine if the timber is either dried out, or wet.

Are you starting to get the picture about why the high moisture content in untreated timber is causing major issues here is NZ with leaky buildings?

How does temperature affect moisture readings?

Most companies will initially calibrate their moisture meters around 19 -21 degress. The problem with people who aren’t experienced and don’t know how to use a moisture meter correctly, is they aren’t aware of how to add or subject readings based on temperature corrections. The basic rule of thumb, is that you subtract 1 from the meter reading either way per 5 degrees in temperature variance (this only applies up to 70 degrees in temp). The best moisture meters for sale in NZ will have this correction feature as a function.

You should have knowledge about the different timber species used in NZ buildings prior to arriving at a benchmark moisture percentage to work with. Treated and untreated timber will require adjustments. Untreated timber will actually give the most true reading because there aren’t any chemical preservatives to throw the moisture reading out.

We use a moisture meter to test NZ houses daily, and it works out cheaper for us to do the moisture inspection for you then buying one for yourself. 

(Source: Some of the above info was provided by NZ Forest Research Institute)