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State House to Passive House 2 - I wasn’t going to do this again

I had told myself that I would never again refurbish an old house. What went wrong? Apart from living in a construction site with babies?

Almost 20 years ago, I came back from 5 years in the UK, full of ideas from its emerging focus on sustainable building and brought the ultimate doer-upper. I used all the knowledge I had at that time to transform what was little better than a shack. Much of what we did is still better than our current Healthy Homes Standards, but I was unsatisfied with the result.

After a lot of work, it might have looked good, and it might have performed a bit better, but it was still an old home. A windy cold night in Wellington was still a windy cold night inside the house.

I think this shows the extent of retrofit or deep retrofit that we need for our existing buildings. Anything less will just be a halfway house, that will maybe cost less, but it will be poor value, fail to perform, and provide substantial benefits.

Looking back, I had a shopping list of ideas, but no way to bring this together as a holistic system with a performance goal with accurately modeled predictive performance.

The biggest issue was the lack of airtightness, still missing from our building code today. In 2000, one of my projects in Edinburgh had to have blower door tests to be signed off by the council. Where are we New Zealand, nearly a quarter century later?!

Insulation will help with what we call transmission heat loss, but buildings also lose heat ventilation heat loss. Airtightness reduces this. If your insulation isn’t protected from air movement, its effectiveness is reduced through thermal bypass.

I did my best to improve the airtightness of a 19th-century building with the bottom plate under the floor joists, but we didn’t have the specialist products and techniques we now have. I installed building paper from the inside between the studs, something I wouldn’t do today unless using a 3D separation mesh to keep the insulation dry. Just relining by itself didn’t improve airtightness.

My worse mistake was the windows. I wanted to keep the look of the sash windows but couldn’t find anyone that could provide better performance. There are a few options now, but I wouldn’t again prioritise the look of the window over performance, especially when these rattled at night when my eyes were closed. Windows is the weakest link and needs to be the priority.

I had read about ventilation systems that maintain good indoor air quality with heat recovery, so you were not just losing all your heat, but they were not common even in the UK, let alone New Zealand. Without airtightness, MVHR would not have been effective.

What would still be challenging today is the floor. It was an old timber strip floor with lots of gaps and no access underneath. I think it would need to be raised to insulate effectively and install an external refurbishment airtightness product like Proclima DASATOP.

The next article will be on what features make a house more suitable for refurbishment.


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