Nov 9, 2018: A Tale of Two Houses

A lovely little house near Mittagong.

House No 1.

This afternoon I was driving past the house of a friend of mine (shown in the photo above). In the interests of full disclosure I should say from the start that I had a hand in the design and siting of this particular little gem. But what struck me most today was the contrast between this house and the one four doors down on the same side of the same street which was built at the same time a couple of years ago.

Same street, same side, four doors down.

House No 2.

Can you spot the difference?

From the point of view of building sustainably, they make for an interesting comparison.

Small is Beautiful

Even though what you can see in the first photo is actually only half of House No 1 (H1), the total floor area of the two halves combined is only 124sqm which is about half the size of the average new home in NSW. As for House No 2 (H2), I’m guessing but it looks to me like the combined area of the first and second floor is at least 300sqm.

Obviously, a smaller house will use much less of everything, both to build and to operate for its entire life. Fewer materials and energy to build, less energy to heat and cool, less effort and expense to maintain, etc. This adds up to a huge saving in cost, resources and environmental footprint over the life of the home.

I wrote more about the size issue in this Newsletter article back in 2015 entitled K.I.S.S. My House.

Simplicity Means Savings

In the article mentioned above, K.I.S.S. stands for Keep It Small and Simple and, as far as I’m concerned this is Rule Number One for building sustainably.

H1 is a very simple structure with a rectangular floor plan and a straight gable roof. H2 is pretty complex (although nowhere near as bad as many new houses I see these days) especially the roof shape. Not only does it add a lot of cost to build a complex roof like this, it also makes it much more difficult to mount solar panels on the roof.

Is Your Solar Active or Passive?

Speaking of solar panels, you’ll notice that H1 has them and H2 doesn’t. Solar panels and solar water heaters are sometimes referred to as Active Solar Systems. Don’t ask me why because neither seems to get much exercise. However it’s the Passive Solar Design that makes H1 so much more sustainable than H2. Just to get you oriented, both houses are viewed from the west side so their north walls are both facing to the left in these photos.

Window Placement

Both houses are oriented so that their north wall gets lots of sun. However H1 has lots of windows in the north wall to let that sun into the home to warm it in winter. H2 on the other hand has very few windows in the north wall and lots of bricks to soak up the heat in summer.

Roof Overhang

H1 has the right amount of roof overhang on the north wall to allow the low winter sun to come in but to shade the home from the high summer sun. Because H2 is two storeys high it would require a huge overhang (or an awning half way up the north wall) to adequately shade all that brickwork in summer.

Meanwhile the west side (facing the street) of H1 is very well shaded from the hot afternoon summer sun by both the existing trees that were left on the site and by the front verandah. H2 has some shading on the west side but also lots of dark, exposed bricks to soak up and hold that afternoon heat and no trees to provide shade (although it does look like they might have planted one).

Room Layout

In a good Passive Solar Design, you want the living areas and rooms that you use mostly during the day on the north side of the house to take advantage of the warmth and natural light that comes in through those big north-facing windows. I know this is true for H1 because I helped design it. Looking at the photo of H2 and the arrangement of windows, my guess is that the rooms on the north side of both the first and second floor are either bedrooms or bathrooms. This means that the living areas can’t be getting much sun and light through the day, especially in winter.

Is Your Thermal Mass in the Right Place?

Thermal Mass means heavy masonry materials like brick, stone and concrete that can be used to store heat from the sun during the day in winter and keep the house warm through the night. In summer the thermal mass can be cooled at night by opening the windows and doors and this will help keep the house cool through the day BUT…

…this ONLY works if the thermal mass is in the right place which means it has to be on the INSIDE of the insulation and air-barrier. In the case of H1 one I know that it has an exposed concrete floor which gets directly heated by the sun coming in through those big, north-facing windows and works to keep the house comfortable through the cold winter nights. In H2 I would bet $100 that the ground floor has a concrete slab but that it is covered with floor coverings everywhere. Tiles are okay for covering Thermal Mass but carpet, vinyl, timber, cork, etc, all act as an insulation layer which reduces the ability of the Thermal Mass to absorb and release heat.

H2 also has LOADS of Thermal Mass in the wrong place. All that dark-coloured brick on the outside of the building does nothing to help keep it warm in winter (because there’s a layer of insulation between it and the inside of the house). On the other hand, in summer it soaks up a LOT of heat and holds it there around the outside of the building. Yes, the insulation will also help to stop some of that heat from getting in, but it’s pretty hard to cool a house at night if the whole outside of the building is radiating the heat it soaked up during the day.

This is why brick veneer is such a stupid way to build in Australia’s hot, sunny climate. But hey, at least H2 doesn’t have a dark tile roof on it as well.

Light Materials, Light Colours

While we’re on the subject of colours, you don’t have to be Einstein to notice that H1 is light and H2 is dark. The light colours of H1 help it reflect away the summer heat. It doesn’t make it colder in winter though because Passive Solar Design does not rely on the heat soaking in through the skin of the building. The winter sun comes into the building via the big north-facing windows which are properly shaded in summer.

You might also notice that all the exterior material on H1 are light-weight as well. This means they will cool down quickly once the sun goes down in summer and not hold heat around the building like the bricks on H2. Have a look too at the landscaping. You’ll notice that the gravel drive and paving around H1 are also light coloured. This, and the lawn out the front, helps to keep the area around the house cool during the summer.

Compare that to H2… They’ve got the lawn but check out that black concrete driveway! Image what that’s like to walk on at 2pm on Christmas Day! I reckon it would melt the hooves right off Santa’s reindeer.

In Conclusion

It’s a pity that H2 is what I see going up in new subdivisions all over Australia because I know which house I’d rather live in and which one has a much smaller ecological, financial and social footprint.

That would be H1 every time!


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