The Gruen Eco Design blog about how to convert your dream from an energy efficient home into a reality.


Over the last couple of months, we kept fine-tuning the design for our own house. Typically, all my ‘actual’ projects are a priority, so I only ever work on the design at night when the kids are in bed, meaning things are a bit slower than the usual. Slow but steady…

We are finally at a point that we like what we have come up with. Therefore, now was the time to have a chat with the builder, the one that will be building our home. I wanted to run the design past him. To make sure that we didn’t overlook anything. And to explore if there were any potential areas to optimise the design further; to make it easier or cheaper to build. I am a strong believer that having a conversation with a builder at this point of time is an imperative step, especially when you are building on a budget.

To my relieve he didn’t see any problems. We have designed the house in such a way that upper floor walls sit on top of lower floor walls. Also due to the layout of our block we have a relatively skinny home, only 7 meters internally at its widest point. With maximum spans of under 5 metres throughout the house (due to internal wall locations) This simple design element means that we don’t need expensive steel beams throughout and will be able to use timber beams instead. Yay!

We also have located wet areas on top of each other, making sure the plumbing will be all in one place. Plumbing fixtures and fittings are located at internal walls, so that we won’t need to penetrate our airtight layer on the external walls.

These meetings are extremely valuable, because your builder might raise a topic, you would have never thought about yourself. Like in our instance, the timing implications when you do want a polished concrete floor. For once, if you do want a polished concrete floor it can add a big chunk of money to your build. Even more so if you do want a white-ish flooring, like we do, and if you do want some nice special aggregate in the flooring. For us this little feature could easily add 50,000 – 70,000 to our build cost. Quite a lot of money, isn’t it?

So, this got my partner and myself thinking. Is the polished concrete floor really that important for us? I would say if you do build a house that follows passive solar design principles, then thermal mass is an imperative factor. I would say without a doubt that you should go for a polished concrete floor, or maybe a burnished concrete floor (similar thing, looks more industrial but does cost a lot less), or you could put tiles on top. For us personally neither a burnished floor nor tiles would be an option.

On the other hand, when you are building a house according to the passive house standards, things start to look a bit differently. The thermal mass is not that crucial anymore. Given that we do want to build our home as a passive house we are contemplating to put a timber floor onto the concrete slab now. Not sold yet, but it has become a viable option.

One other thing that had never crossed my mind is the time of construction. Assuming you do want a nice polished concrete floor without cracks all over, you must make sure that the temperature is relatively mild when the concrete is poured and drying. This means you CAN NOT pour the concrete during summer. Apparently for us in Melbourne here some time between May and September would be ideal. Given that we were planning to start construction in January or February, pouring a concrete floor then would not be possible, which would drag out our build time, with a potential build start in April.

Another point that makes putting a timber floor on top of the concrete slab even more appealing…

Once we have made up our mind about the flooring it is time to start with some more detailed drawings and to think about the structure, how it will all come together and what we have to do in order to comply with the strict passive house principles.

 Exciting times ahead.