I had an interesting meeting with potential clients, who want to build a new home. They are currently looking at a potential vacant site to buy and we have been discussion the pros and cons. But also, the difference between a home that is designed according to passive solar design principles and one that has been designed according to the passive house principles.
Simply explained, the difference between a passive house and a house that follows passive solar design principles is, that a house that follows passive solar design principles uses the free energy of the sun, in combination with thermal mass, appropriate shading and so on to regulate the indoor temperature of the house. Whereas a Passive House is designed and detailed in a way that the shell and building fabric of the house is so energy efficient in itself, that the performance is not compromised, if solar access is poor.
The couple were looking at a nice large size block. With good solar orientation. No obstructions, that might hinder good solar access. And of course, a flat site, since they want to include thermal mass in form of a concrete slab into their house.
The problem is that when you look at larger blocks, say above 700 square metres, you often compete with developers, that want to do a subdivision. Hence the prices go up and the land is expensive. Even more so, when the land has great orientation and a north facing backyard.
Obviously, when you do want to build a passive solar house, you need a great orientation and unobstructed solar access, right?
But what if I tell you that building a passive house can actually end up costing you less money than building a highly energy efficient home following passive solar design principles?
Reason being, when you build a passive house, good solar access and thermal mass is not that important anymore. This means, you can build a highly energy efficient passive house, on any block. Even when the orientation is poor.
You also don’t rely on a concrete slab for thermal mass, which means you don’t need a flat site. A passive house can easily be built on a timber sub floor. Either as a split-level home, or as a double storey home. Without affecting the performance.
Suddenly this means that you can look at different blocks. Smaller ones, maybe even odd shaped ones. The sites that others aren’t interested in. Which means, less competition and a lower cost.
After our meeting yesterday, the couple has decided to change their search criteria and they will start looking for smaller sized blocks that don’t’ have an ideal location, which hopefully should save them quite a lot of money.
My partner and I were able to buy such an odd shape block. Not only is the orientation not that ideal, it has a slope of about 1 metre from the front of the house to the back (which means we will have split level home), but there is also a 2.5m wide easement along side the block, which means we only have a very narrow strip to build our home. But because of this, we got the land about $100,000 cheaper than comparable sites in the area. For once, because the site was not suitable to do a subdivision. But also because of all the restrictions, the site wasn’t that interesting for other buyers. Which meant we got it for a good price.
This means, we have an extra $100,000 available for the construction of our house. And although it is a bit hard to quantify exactly how much more it will cost you to build a passive house, rather than a regular energy efficient home following passive solar design principles, it will most likely only cost you $20,000 – $30,000 more. Which means in our case we are still $70,000 in plus.
Not bad for a saving, right?