bricks

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!

Phew.

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…

Recycling building materials after a demolition

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Trees are cut down, bricks are fired, metal is smelted; all to produce the building materials that go into a house. When a house is demolished, what happens to all this? By default, it all goes into landfill, never to be used again. It’s a terrible waste.

In keeping with our green principles, we tried to recycle or reuse our building materials where possible. But let me tell you, it isn’t easy! This is how we fared in Sydney:

  • Metal: Sims Metal will pickup old metal (corrugated roof sheets, pipes, etc) for free, and the matal is recycled. For some reason they didn’t take everything, but this was still the easiest stuff to get rid of.
  • Interior fittings: before the demolition started, we stripped out all the interior fittings worth keeping. Some of these were put on eBay (such as the dishwasher), but most went to a new home via Freecycle. (More on this in a separate post.)
  • Floorboards: our beautiful hardwood floorboards were bought by a local lumber yard for $800, and these will end up in a new home. Plan for half a day of backbreaking work to get the floorboards out. (They also gave us $200 for a pile of old hardwood, plus some doors and windows.)
  • Wood: we kept some of the better beams for use during building, but most ended up in the skip. In theory, wood can be chipped and used sold as garden mulch, but we couldn’t find a way of doing this on our scale. (Taking stuff in a trailer just doesn’t work when demolishing a house.)
  • Treated pine: considered industrial waste, the only option is landfill.
  • Kitchen: a tragedy, straight into the skip. Kitchens are very cheaply constructed, with mixed materials that don’t last well. Too poor condition to sell or give away.
  • Intact bricks: kept, to be recycled back into the building. Be warned though: probably only worth doing if lime mortar was used, rather than concrete. There’s also a lot of manual labour to clean 3,000 bricks by hand.
  • Broken bricks: plan on 10-30% of the bricks getting broken during demolition (old bricks are very weak). Luckily these can be recycled via Botany Building Recyclers (ask them for a recommendation on a skip company to pick up the bricks). Cheaper than a disposing of normal waste, and the bricks are ground down to form road base.

In all, three skips of waste left the building site. Better than it could’ve been, but not up to Michael Mobb’s standards.

The reality is that new materials are cheap, and labour is expensive. For most people, it’s simpleynot worth the time and money to recycle materials, easier just to start afresh with new stuff. No doubt this will change in time when resources get more scarce, but at least some practical steps can be taken now despite the challenges…

Any tips on recycling options we missed?