I guess the more you learn about building the more concerned you become about everything that is involved. The more problems you see on site the more cynical you become and it can happen that you just don't see how things can get better.

This happened to me. I was walking around building sites and one of the things I remember is a moment when I stepped in a dark room that is to become a toilet. The cladding was on, windows are finished, Gib placement is to happen tomorrow. The windows where covered on the outside and it was just dark enough that I could clearly see a light coming through a very small gap outside windows reveal. If light is able to come through and no-one noticed... what else is missing in this building envelope.

I am following a group of building scientists on LinkedIn. Its great to hear some technical backing to what I always struggled to accept myself. Timber walls are very difficult to make right. I guess it all started when this post came out:

This is a photo of a wall in a hospital Counties Manukau DHB, posted publicly. Lets talk about the real issue here... The system doesn't perform. What is clear from this picture is that internal moisture slowly progresses through the wall as warm internal air. When it reaches the outside of the insulation layer, we can all understand that this warm air cools down. And cool air is less capable of holding moisture, so it releases this humidity in form of condensation. It does so on the cooler outer side of timber studs.

There are more examples like this. Picture below clearly show condensation happening on colder side of the building envelope, even when the steel studs (in this case) had a so-called thermal break sheet. The problem is they were still cooler than most of the wall.. steel conducts heat very well. Its a great thermal bridge... don't use it! It either needs to be outside or inside... but not right in the middle and certainly not penetrating the building envelope. Also the problem is that the air was able to get inside the wall in the first place, holding moisture...

This moisture can potentially be absorbed by the insulation, increasing the weight of insulation, so it slowly slumps inside the wall, creating even bigger gaps around the insulation. And as soon as you have small gaps in insulation, its almost the same as not having insulation at all.. I think this is why soo called "insulated houses" sometimes just don't perform, although in theory have a hight R-value. Or at least two walls both claiming say R2.8, but one build in Sticks and one in SIPs, just will not feel the same...

Roof situation is the same or sometimes worse. The warm air rises so it is the roof that is even more critical. And if have continuous moisture building up in the cavity, we know what follows.

To get even worse... if warm air managed to get inside the building envelope... what makes it not get back inside the house in summer? This time with all the mould and other nasty things... inside the air we breathe.

This is why airtightness does matter. And is something that SIPs do really well. The SIP it self is completely air-tight. The joints between panels are best to be constructed using expanding foam and glue, so that all joints remain air-tight as well, for the whole building envelope to remain performing well.

So instead of having a "panic attack".. how are we going to build houses... thankfully I came across SIPs. Share this with friends that are planning to build and save them from making a mistake...

...next time on Vapour control... yes we are not done yet, but rest assured, there is a light at the end of the tunnel.