Installing solar-powered roof ventilation

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Some time back we installed a R3.5 batts in the roof of the original half of the house, along with reflective foil. Despite this, the roof space still gets very hot in summer, and after a run of really hot days, we can feel the heat radiating down into the rooms over night.

For this reason, it’s highly recommended to ventilate the roof space during summer. While traditional ‘wheely birds’ are an option, what I’ve read suggests that they simply don’t draw through enough air in an hour to make a real dent on a typical roof.

We therefore focused on an active ventilation system. There are heaps of different options, but my search narrowed down to two products, both solar-powered:

In the end, we went for the Solar Star, which seemed like the better fit for our needs. For the size of our roof, a single Solar Star RM 1200 model was the recommended option, and we  bundled in a thermostatic control.

The Solar Star unit, sitting on our table before installation.

Installation was simple enough. It comes with a plastic flashing suitable for a corrugated roof, plus the necessary screws and instructions. We further simplified the process by fitting the unit directly under the ridge capping, which allowed us to skip a lot of the more fiddly waterproofing steps.

The flashing installed for the Solar Star, looking through to the reflective sarking underneath (which we cut a hole through at the end of the job).

All up, the job took about an hour, most of which involved getting the tools onto the roof and generally stuffing around.

The Solar Star installed, just under the ridge of the roof. Not pretty per-se, but far from ugly.

Ideally, at this point I’d be able to report (with graphs!) the roof temperature before and after installation, compared to the outside temperature. But life has been busy!

So I can report that the fan runs steadily and quietly, and I’ll post later with a purely qualitative assessment of the impact.

Insulating our windows

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Enough to seal five windows with plastic.

Some time back, I saw a product advertised on one of the lifestyle shows for cheaply insulating drafty windows. A recent post by Michael Mobbs reminded me that it was a 3M product by the name of “Indoor Window Insulator Kit”.

Strangely, the product isn’t actually available for purchase in Australia (I asked 3M), but it was easily ordered from

The basic idea of the kit is simple enough. Double-sided tape is placed on the window frame, and a thin layer of clear plastic is then stretched across the whole window. The goal being to seal the gaps and to create a “poor man’s double-glazing”.

Very useful in the old part of the house (the renovation is all double- or triple-glazed).

It’s cheap (just over US$20 delivered for 5 windows worth of plastic), and simple to install. It should at least eliminate drafts through our old and poorly-fitting double-hung windows. It’s cheap enough to seal the windows during winter, and to remove it during summer (purchasing a new pack the following winter).

I will say this, however: it’s disconcertingly like wrapping your windows with glad-wrap (albeit a quite thick glad-wrap). I think visitors will wonder what on earth is going through our heads. So I’m not going to rush off and do every window, just the ones that are in less-used rooms that leak the most heat.

In summary: worth considering, particularly for old houses with poorly-fitting windows. But I’d still love to have real double-glazing one day.

Contructing a reverse brick veneer wall

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Layering of the reverse brick veneer wall -- 9 layers in total!

A key part of the design for our house extension was increasing thermal mass, which helps to keep the house cool in summer, and warmer in winter. Two major elements contributed to this: the rammed earth wall and a reverse brick veneer wall.

Of these, we were expecting that the rammed earth wall was going to be the wacky-difficult-to-build element, but it proved easy. In comparison, I’d been reading about reverse brick veneer walls for ages in the green community, and was aware that they are widely used in places such as New Zealand.

And in general, they are simple: you put the single brick wall on the inside, where it provides valuable thermal mass, and you put the highly-insulated wood frame on on the outside. In otherwords, the reverse of a traditional brick veneer construction.

Surprisingly, however, when it came down to finding out exactly how to construct the wall, I came up short. I could find no clear diagrams on the web, nor was this type of construction covered in the books I had on hand. No builder I talked to had ever done one.

So we worked it out ourselves, and in the interests of sharing our experiences, this is what we did:

Layering of our reverse brick veneer wall

From the inside to the outside:

  1. Gyprock. Traditional plasterboard inside wall surface, nothing unusual there.
  2. Single brick wall. This is constructed in the usual way, and isn’t load-bearing. It’s anchored to the wood frame via brick ties (lots of them!).
  3. Air gap. This is one of the key elements of the insulation, just like a normal cavity brick wall.
  4. Wood frame (4a) and bulk insulation (4b). The wood frame is completely run-of-the-mill, and is a load-bearing structure. Inside the frame, we put Grenstuf R2.5 wall batts, which provides the bulk of the insulation.
  5. Reflective insulation. Air-cell Permishield provides a layer of reflective insulation, helping to keep radiated heat off the inside layers.
  6. 20mm batons. The reflective insulation only works when there’s an air gap, which we created via batons nailed through to the wood frame.
  7. Gyprock Fyrchek MR. Unfortunately our side wall was closer than 600mm to the property boundary, making it necessary to meet fire rating standards. Thus the layer of fire-protecting Gyprock.
  8. Wallwrap. Strictly speaking, the Gyprock Fyrchek isn’t weatherproof, despite the “MR” rating. So we added a cheap wallwrap, as per Gyprock’s installation instructions.
  9. Weathertex weatherboards. Finally, the outside cladding!


Some notes

  • This is a lot of layers! There were a few different combinations possible, particularly relating to the Air-cell Permishield (inside the stud wall, air gap inside or outside). I think we made the right decision, but your circumstances may vary.
  • The requirement to have the wall fire-rated added a bit of complexity.
  • This type of wall is thicker than a traditional double-brick wall (with or without a cavity). So be warned, and factor this into your designs from the outset.
  • Make sure you seal the top of the wall (against the weather) as well as the bottom (against bugs). All the air gaps could otherwise cause problems down the track…

The good news is that this type of construction really isn’t any more effort than a traditional brick veneer, and it should pay us positive dividends for the lifetime of the house. As opposed to “normal” brick veneer, which is perhaps the most foolish possible building technique for the Australian climate…

Six types of insulation in our new house

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Our six-month renovation process finally draws to a close, and now that I’m not working so hard on the house, I can catch up on our blogging about the key environmental details.

A good starting point is a summary of the insulation that went into the house: walls, roof and floor.

Our insulation choices

  • RoofPolyair Multi, a multi-layer combination of reflective foil, foam and bubble wrap. 9mm thick, it sits directly under the corrugated iron roof.
  • CeilingR4.0 Greenstuf batts, which are conventional insulation batts but made out of recycled plastic rather than fibreglass. Manufactured in New Zealand.
  • WallsR2.5 Greenstuf wall batts, fitting into the standard studwork walls. Then R1.6 Air-cell Permishield wall wrap layered under the outside cladding, with a 20mm air-gap to allow the reflective layer to work properly.
  • FloorR1.5 Greenstuf underfloor insulation rolls, under the wooden floorboards (the house sits on piers, as is typical in Federation houses in Sydney).

So that’s six types of insulation from three different manufacturers. In each case, we looked at a range of options, and picked the one we felt would give the best outcome for a reasonable price. While there are undoubtedly a large number of possible ‘right’ choices, it shows that there isn’t a one-size-fits all product (or even manufacturer).

How does this compare to typical insulation?

This is a lot more insulation than a typical Australian house (although only a fraction of what would be installed in colder European or North American climates).

It greatly exceeds what we were required to do according to government regulations (BASIX), but more on that in a future post…

How much did it all cost?

The total spend on insulation was approximately $3,800, for a 100m2 extension. That probably seems like quite a lot, but it all comes down to the payback period.

The house had underfloor ducted gas heating when we bought it, and this will be extended to the new portion of the house. The better insulated the house is, the more warmth it will retain, and the lower our gas bills. But exactly how big a saving — hard to tell.

What we can be confident of is this: we don’t have air conditioning, and we won’t be needing it. So that’s an up-front saving of $3-5k in avoiding the purchase of an aircon unit, and then the yearly savings on electricity from that point onwards.

So the payback period: immediate. A sensible use of our money, we think.

Renovating our house

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The reason that we’ve been so quiet on this blog recently is that we’ve been preparing for the next big project: renovating our house. Tomorrow is the official start date, and we’ll be blogging progress as it unfolds.

In theory, it’s not a big renovation. Like most federation houses, we have four beautiful front rooms, which we’re leaving unchanged. Then comes the rabbit-warren of rooms at the back, lean-to extension, etc. While the new house will be just 2-4m longer, it will mean demolishing the back of the house and re-building. Fun!

Needless to say, the renovation will incorporate a number of green features, including:

  • A rammed earth wall, located in the middle of the house to increase the thermal mass of the house. (read more)
  • A reverse brick veneer wall along one side, again to increase thermal mass (the rest of the construction will be wood frame).
  • Double-glazing of all the windows (surprisingly hard to get in Australia).
  • Plenty of insulation, in the roof, walls and under the floor.
  • Carefully placed skylights to passively light the majority of the house.
  • Actively ventilated roof space, to keep us cool in summer.
  • Grey water system, with no moving parts.
  • Low VOC paints and building materials throughout.
  • Sustainable building products, where practical.

We’ll post more details on each of these aspects over the coming months. I’ll be the owner-builder and project manager, and will be directly involved in all the work for the next six months. Watch this space and wish us luck…

Green Loans Assessment Report

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For a little while the Australian Government was extremely keen on its home efficiency assessment program. This involved sending out hoards of assessors to conduct free reviews of residential houses, looking for opportunities to deliver environmental improvements. Due to fallout from some of the other programs (notably the home insulation program), this  has now been essentially moth-balled. In particular, the interest free green loans have been cancelled, one of the main reasons for having the assessment done.

Still, many months after having an assessment out of curiosity, the report turned up in the the mail this week. I’ve scanned the two pages of the report (click on the images to get a PDF version):

In general, our house is above average on all counts: running costs, greenhouse gases and water usage. The recommendations made were as follows, alongside my comments:

Recommendation My thoughts
When renovating, consider installing an on-demand hot water recirculation system to reuse the cold water in the pipes between the tap and the hot water service. This is probably the best tip. I have vaguely heard of this technology, so now it will go on the list for our upcoming renovation.
Replace your hot water system with a gas-boosted solar model. I had already replaced our ancient hot water system with a 6.9 star gas on-demand system, so this recommendation misses the mark I think. (We also don’t have the available roof space for solar hot water as well as solar power.)
Replace your toilet with a water efficient model (min 4 star) or a composting toilet. Yes, definitely on the list. A pretty obvious recommendation.
Install insulation with a minimum of R2 in external walls if you have, or expect to have, access to the well cavity. One slight problem: our house is double-brick without a cavity. So nowhere to put any extra insulation.
Install under-floor insulation (if access is available) This is an interesting one. I did a lot of research early on to understand the potential benefits of under-floor insulation, and the results were ambiguous. I couldn’t find clear indications of benefits, and I’m concerned that it will cut down on the cooling effect during summer. More research required.
Install photovoltaic panels to generate electricity (min 1KW system capacity) Done! These were installed after the assessment was done.

In summary, the results were somewhat interesting, but hardly earth-shattering. We already know a lot, but even taking that into account, I’m not sure the assessment would really help the average family to make changes. In the absence of a proper cost-benefit analysis, some of the recommendations seem very costly in terms of the benefits they might bring.

I’m hoping that the results of all these assessments are being passed to some Australia-wide research project, as this would probably deliver more benefit than the changes made by individual houses.

Understanding the house

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While endeavouring to improve the sustainability of our house, it’s proven useful to build an understanding of every aspect of how the house is put together.

As we’ve had things fixed by our do-all tradesman Wilhelm, I’ve been working alongside him. Now I need to highlight that I have absolutely no handyman skills at all, and have struggled to hammer in a nail in the past. Nonetheless, I’ve been able to provide a second pair (of unskilled) hands, helping to speed up jobs, reduce the cost, as well as allowing me to see what’s done.

This has meant working under the floor to remove old building rubble (to remove hiding places for rodents, etc). It’s meant helping to nail insulation up in the roof.

This has led to a number of observations:

  • It’s very cool under the floor. When we extend the house, can we put in place a wine cellar or “root cellar”? Can we make use of the cool air to ventilate our pantry, or maybe even the whole house?
  • It’s very hot up in the roof. We’re putting in place reflective foil to reduce the amount of heat getting into the roof space, but once it’s in there it’s trapped. Can we do something to get the heat out?

Too often, houses can be a mystery, with hidden corners and spaces. Before making any major changes, it’s worthwhile exploring these spaces to understand how the house ticks.

Insulating the roof

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One of the obvious ways of improving the energy efficiency of a house is to improve the insulation. In our case, there were tatters of 40-year-old insulation left in the rooft, but they weren’t going to do much for us.

We were lucky to get in quickly enough to receive the $1600 grant from the Australian Government for insulation. This applied even though we had some (useless) insulation in place:

The program targets homes that are currently uninsulated, or have very little ceiling insulation and were built before the mandatory thermal performance requirements under the Building Code of Australia were introduced commencing in 2003.

For us, the required insulation cost $1650, leaving us only $50 out of pocket. The standard insulation used by our chosen insulation installer was also excellent: Autex GreenStuf. It is:

  • made of recycled plastic
  • fire resistant
  • free of any loose particles
  • unappetising for bugs or rodents

It will basically last forever, and is even made in New Zealand, much closer than the European products on offer.

(The Government program has now dropped to $1200, but that should still be enough to do a moderate-sized terrace.)

That was just the beginning of the process. Doing some research, the insulation provides useful “bulk insulation”, slowing down the transfer of heat across the ceiling. But the roof space still gets extremely hot, as the corrugated iron roof heats up, and then re-radiates the heat into the house. After a while, this heat works its way down through the insulation, and into the living area.

Working with Wilhelm to install reflective foil insulation

The solution (or at least part of one) is to install reflective foil, also called sarking. We are using Aircell Retroshield, which is like giant bubblewrap covered in reflective foil on both sides. The shiny surface reflects the heat, and the air bubbles provide additional insulation (upwards of R3.2 in summer, R1.5 in winter).

For a new house, this is simply laid down at the same time the roof is put on. It’s a much slower job retrofitting it.

Thankfully I’ve got Wilhelm, our handy fix-everything-guy, to help me. So we’ve spent a number of afternoons up in the roof, nailing up the foil to the underside of the joists.

I think all of this is making a difference. Even with the back of the house completely uninsulated (old extension; flat roof), the house stays upwards of 10 degrees cooler than outside. Which is a good thing with the 35+ degree weather we’ve been having recently!