And then there were walls

One of the first questions we asked ourselves when we started to design our house was “what materials will we use?”. In South Africa, the predominant building material is bricks, but here in Chile there is a far greater variety from wood to bricks to concrete. Coming from a country where wooden houses are not that common, I loved the idea of using wood. But over my time here in Chile I have also heard many prejudices about the use of this material. For instance “wooden house are for poorer people” or “wooden houses are riskier in terms of withstanding earthquakes”. Both of these are simply not true. Wooden houses are far more flexible when it comes to an earthquake and though they may suffer damage, the chances of them collapsing is low. And in socioeconomic terms, in a country with a thriving forestry sector, it makes sense to build with wood, no matter what your economic level is.

So we decided fairly quickly that our house would be made of wood, and this lead us to the decision to use SIP (Structurally Insulated Panels). Honestly, until I started to write this post, I didn’t even know what SIP meant. I just knew that it is basically like “an oreo biscuit for walls” – two wooden panels with insulation sandwiched between them.

This week, I got to see first hand just how amazing this construction method is. It is like putting together one giant puzzle, and the best part is, the “puzzle” comes with built in insulation that we need for the house to be “well wrapped up”. After a month of working on the foundations and the slab, it is finally starting to feel like we are getting somewhere.

But I digress from the technical…why did we choose SIP?

When we compared all the building options with similar characteristics to SIP, we realised that these panels gave us a high level of continuity in terms of insulation and less thermal bridges where heat loss is a problem. In terms of the Passivhaus Standard and also the Chilean CEV Standard, less thermal bridges is definitely a good thing.

The panels come in different widths according to the amount of insulation included. The narrowest panel is 11,4cm, then 16cm and 21cm. You probably think that since we are so obsessed with insulation that we would have chosen the thickest panels with the most insulation. But we chose the thinnest panels with 11,4cm of insulation. The reason for this is to give ourselves more flexibility to improve the u-value* of the walls with further insulation on the outside of the house. The reason we need this flexibility is because we are unsure whether we will be able to comply with one of the most stringent Passivhaus criteria (0,6 renovations of air in an hour, which no house in Chile has achieved to date). This criteria on air tightness will be dealt with in a future post. Right now our plan is to put 10cm more insulation on the outside of the house, but if by some miracle we manage to achieve the magic “0,6”, or even if we achieve 1,5 (our humble goal is to at least achieve 2,5 in the airtightness value), we can reduce the amount of insulation to 5cm on the outside and still achieve our goal of less than 15Kwh/m2/year. This may all sound very confusing, and I promise you, even writing it I get confused myself, but I promise you that over the next few months a lot more of these technical details will become clear.         

Apart from thermal bridges and more flexibility, one of the best advantages of using SIP is definitely the speed of building:

 I never thought that in just 5 working days we would have the perimeter of the house complete.

One final comment on SIP though, make sure you have the right tools to cut the polystyrene insulation. We unfortunately did not, and to try and keep making progress, we ended up with millions of tiny polystyrene balls floating around the property. This meant spending a Sunday morning picking up the biggest pieces and using the vacuum cleaner to suck up the tiny pieces. I am very quickly realizing how waste management is a huge challenge in a building project.

*u-value: measures how effective a material is as an insulator. The better-insulated a structure is, the lower the U-value will be. Workmanship and installation standards can strongly affect the thermal transmittance. If insulation is fitted poorly, with gaps and cold bridges, then the thermal transmittance can be considerably higher than desired. Thermal transmittance takes heat loss due to conduction, convection and radiation into account.