Can Internal Moisture Cause Timber to Rot?

So you’ve made sure every crack and pentration on the external cladding is sealed, so the house won’t leak… right?

Not so. Sure, the external cladding may now be all sealed up and water tight as a navy submarine, but is there a possibility that moisture can still get into the timber frame of the house? Yes… if there is no wall cavity system, most definately… especially if you don’t have a system in place to expel the trapped moisture.

How is the moisture getting into the wall if the house is ‘sealed’?

Recently I found this topic on a forum which talks about the basic theory of how moisture ‘penetrates’ walls, even when you think your home is water tight. I thought this summed it up nicely…

internal moisture extract

(Did you take note of the last sentence of paragraph 2? Nice analogy!)

In summary, if a wall can’t breathe (i.e cavity system), then it’s only a matter of time before moisture does what it does best to timber… rot.

If you fix cladding directly onto timber, and then you also cover the internal side with gib board, then what you are actually doing is creating a vaccuum. What  happens next, is that the local plumber comes along and fixes a pipe bracket through the plaster which will eventually release and create a small hole. Then what happens?

Here’s what… the outside air pressure is greater than the internal wall pressure, therefore the water gets sucked right into the tightest of holes and penetrations. Got kids? Make sure they dont slam their pushbikes up against the plaster cladding and penetrate it… same effect… in goes the water!!

As a result of many plaster homes leaking, some people will only buy old weatherboard or brick & tile homes… you know, then ones that have been standing for 50+yrs, but wouldn’t get a CCC under the new building code  🙂 . Hmmm.

Did they build with internal gutters back in the good old days (Common design issue associated with leaky buildings)? The basic issue here is that if the gutter leaks, it goes straight down into the wall… and it can’t escape because there is no cavity for it to exit. The only thing standing in the way of the water is untreated timber! Ekkk.

Here’s an interesting fact: Just about every builder I speak too says “I tried to warn the authorities that untreated timber wouldn’t work”. So why did they go ahead and build with it? Because they could, and it was cheaper etc etc. Lets not get into the ‘who’s at fault’ debate… we’ll leave that to the ‘experts’… and no doubt the experts will be the ones that created the problem in the first place (cough).

95% of plaster home owners when asked “Would you buy another plaster home?”, say “NO”. This is based on my own survey whilst inspecting homes, it’s not an official statistic. You can join the dots on the meaning of that one.

Cavity Wall Insulation

How Does it Work?

Cavity wall insulation is the process of injecting an insulating type material into the gap between your outer brickwork and the inner masonry skins of the external wall. As up to 33% of the heat produced in your home is lost through un-insulated cavity walls, it makes sense if only from a purely financial point of view to have all your walls insulated.

There is quite a variety of different insulating materials for you to choose from, however, at the end of the day, they all work in the same way. That is, they combine with the still, captive air between the bricks to form an effective barrier to heat loss in the home.

Having your cavity walls insulated couldn’t be easier. The injected material is normally applied from the outside of the wall through small holes which are drilled between the bricks. As the material is injected through the wall it eventually fills the cavity completely. Once finished the holes are filled in to make as perfect a match as possible to your home colour brickwork.

What to watch out for…

Most modern houses built post war (1945) are constructed with cavity walls, however it is only those houses built post 1990 which were designed and built with cavity wall insulation built in already. If you’re not sure what type of cavity your home has, simply contact a qualified builder… they ay even be able to tell you over the phone.

It is therefore very important when considering having cavity wall insulation fitted to ensure the walls are free of any moisture, and that there is a effective ventilation to allow air movement within your walls. This also means checking the damp proof course (d.p.c.) is intact all around the house to prevent rising damp attacking the newly installed insulation, and the bricks have all been re-pointed if necessary to remove any gaps between the mortar. Take a few minutes to walk around the outside of your home to see if there are any penetrations which water could seep in.

Also ensure all essential ventilation openings, such as those providing combustion air or underfloor ventilation, and all flues and air bricks in the cavity wall are checked. If adequate sleeving or other cavity closures are not present, installation should not proceed until these openings have been sleeved or otherwise modified to prevent blockage by the insulant. Also check for flashings above windows and decks etc.

If the walls are not able to ventilate air properly, the act of insulating the walls can lead to increased levels of moisture within the building which may, over time, result in potential problems with damp. In New Zealand, we have a wet climate, so a ‘moisture free’ home is critical to our health.

Which material?

The materials readily available for cavity wall insulation are Mineral Wool, Urea Formaldehyde (u.f.) Foam, and Expanded Polystyrene Bead. These materials all have the following properties;

– Resistant to water penetration.
– Will not transmit water across the cavity, or via capillary action from below d.p.c.
– Allow moisture to disperse into atmosphere – providing breathable construction materials have been used to ventilate the walls.
– Fire resistant.
– Resistant to rot, fungi and vermin.

These materials all have equivalent thermal insulation properties and are produced under strict quality control to ensure compliance with the building regulations and industry standards.

Mineral Wool
Urea Formaldehyde Foam
Expanded Polystyrene Bead

Other materials are also available which have a much lower embodied energy rating, that is they require much less energy to manufacture and therefore have a much greater positive impact on the environment. Currently though usuage is limited to a small number of installers who work with them.

Organic insulation materials
Natural insulation materials

Can you DIY?

Due to the nature of the products involved in cavity wall insulation, and the technical nature of the installation, it’s not a good idea to do this procedure yourself.

A specialist contractor should install your cavity wall insulation for you, as they will provide all the experience and equipment.

Contact Us today for a thermal imaging insulation inspection!