[migratory birds]

Any links for NZ-based green-built modular/prefab home construction websites?

In years past, I've thought of prefab as tacky vinyl, poor quality homes...but I believe it's a rapidly changing industry with some forward thinking architects/builders bringing higher quality offerings into the mix.

Am interested in seeing what might be available manufactured in NZ (or Australia if costs aren't prohibitive)...

Sorry if this has been discussed in past but couldn't find anything in archives.

Ta!

[Piper]

I know a lot of baches (batches) (bachs) out on the Marlborough Sounds are kit homes. Whether they're green or not, I don't know. Will ask my sister - she told me the name of the manufacturer but I forget it right now.

(I seem to remember her mentioning about $200k for a 2 bed I think but again, I will ask and don't quote me on that!)

[Nick88]

What is a green-built home? You might be thinking of transportable homes, they are built off site and delivered. Just google it and you will find a few to choose from.

[Jo Jo]

There was a thread about these a few months ago, but I can't find it now. But, yes, there are companies specialising in eco kitset houses, such as Energy Efficient Homes (http://homepages.ihug.co.nz/~eeh/model.htm).

Edit: found the old thread: here you go (http://www.emigratenz.org/forum/showthread.php?t=11000).

[Nick88]

IMHO the Energy Efficient Homes are made in much the same way as many new homes in NZ. They are very heavily insulated due to the subzero temps you will enjoy in Canada, but isn't really necessary here. The bit about the wood treatment is irrelevant, cos all new homes here must be made of H1 treated timber, anyway. The double glazing is a great feature that NZ homes could do with. The windows giving passive solar heating is a feature of any window that gets the sun in winter.

There was also a link to straw bale houses somewhere. They are really expensive to build, as the straw has to come from Canterbury. Grain crops are not grown further north on any scale due to the higher humidity and rainfall. The transport alone adds alot to the price.

Personally I would stick to some of the tried and tested newer homes that are well insulated and simply constructed. You can always specify double glazing to be added (at a cost)

http://www.initialhomes.co.nz/
http://www.sunshinehomes.co.nz/

[migratory birds]

Green builders look at using sustainable materials with the least impact on the environment and home inhabitants whenever possible in the construction (including locally acquired or renewable materials rather than those shipped from afar or use of less-renewable or non-renewable materials), materials with least potential for off-gassing (formaldehyde, VOCs in paints, adhesives for floorings, choosing less-toxic wood finishes where options exist), orienting house/choice of window size for maximum solar gain in winter, attention to overhang width for minimal solar gain in the summer, installing heat and electrical with greatest potential for maximal effect with minimal impact, etc.

What would others add to this definition of green-building?

[Piper]

I haven't had time to look at its green credentials but here's the kit home company I was thinking of.

http://www.a1homes.co.nz/

I guess this thread would help anybody viewing NZ property to figure out if it's a kit home they're looking at!

I saw a house that as built into a hillside recently, I guess that's pretty green in that it takes up very little land.

[markw55]

I haven't found any kit-set house builder who are truly green in the materials they use etc. If anyone finds any please post links! Most of the kit-set builders are all competing on cost.

We have also found that in most situations you need to do some work looking at if a kitset is cheaper than a house that is transported or just building from scratch.

From what I have found prices start at $1200 per square meter for a 'rental' style home up to $2000 per square meter for a well finished 'executive' style home, regardless of if it is a kitset or built from scratch.

If you want a green home I would suggest first finding an architect who has experience in building this type of home. They can give you ideas and should have contacts with green builders etc.

We will be building in 2008 or 2009 and are attracted by this architect's design:
http://www.poweredliving.co.nz

But haven't yet made any inquiries as we are still researching options.

[PeteS]

In years past, I've thought of prefab as tacky vinyl, poor quality homes....

You're right! Some things never change. I've done a lot of looking at "kit-set" homes, and all the ones I saw are low on specification. They will "comply" with the building rules, but that's all.

Just like the rest of the world, here in NZ you'll get what you pay for.

[miep]

We've built our own home to be as green as possible, ie passive solar heating, solar hot water and good insulation and it certainly makes a difference!

However Markw55, we were quoted that price range as well when we started building 5 years ago! I think $2500 per sq m will be a bit more realistic. The $2000 for an "executive" finish generally doesn't include timber joinery as opposed to "weepy" aluminium, insulation in internal walls (not the norm here) solid core doors etc.

When we started designing our house there was very little info or understanding on eco measures, I did most of the research myself on the net. There seems to be a lot more info and general interest now though so it should all be easier.
I like the powered living concept, very good looking, it's nice to have a well known architect involved in green design. Ours just didn't get it, he kept saying we didn't need double glazing and for the price of timber joinery we could build a bigger house! We just didn't seem to be able to get our point across that we wanted quality rather than quantity :(

Over the years I've looked at kit set companies but haven't found one that does green in a serious way.

Migratory birds: I think your post sums up the most important points for a definition of green, perhaps recycling of old materials could be added?

[kzn2nz]

There are a few simple measures that can be taken before building the house that will go a long way to making a house more energy efficient. The design is important if you want full energy efficiency, but even regular homes can be made a lot greener than if you simply drop them into your yard.

Small things like orientation of the house and designing appropriate overhangs to shade windows in summer / allow sun in in winter will dramatically affect your heating / cooling bill. Ceiling insulation is a huge energy saver in this regard, as is your in-wall insulation.

If you are going to have a fireplace, build it on an inside wall, rather than letting half the heat radiate to the outside of the building.

At the time of construction, building a deep, rock-filled cavity below the slab will create a thermal sink. If you add a venting system to move air through the rocks, that will improve performance even more.

A grey water treatment system will also improve on energy performance, and allow you to use basin and bathwater to irrigate the garden. (Not so sure that that is really a major concern in NZ, but still...) Add a few rainwater tanks, and away you go.

A large amount of electricity goes into the geyser and stove, so getting either gas or solar geyser, and a gas cooker will again improve energy efficiency. Gas geysers are great because you get unlimited hot water, and there is virtually no energy used when you are not using hot water. They can also supplement a solar geyser. That leaves lighting, which can almost be done entirely with modern LED fittings, using a fraction of even energy saving globes.

A nice veggie patch and a garden full of indigenous plants (and a compost heap, of course) completes the project!

[ourquest]

If you are going to have a fireplace, build it on an inside wall, rather than letting half the heat radiate to the outside of the building.

At the time of construction, building a deep, rock-filled cavity below the slab will create a thermal sink. If you add a venting system to move air through the rocks, that will improve performance even more.


Informative post James. Just a couple of points to add and a question.

The use of a freestanding fireplace makes a lot of sense for quicker heating; ie one which is constructed in steel and stands in the centre of a room (or at least a meter or so from a wall). Heat radiates 360 degrees away from the fire.

Question: can you elaborate on the thermal sink concept? It's not something I have been aware of...I sort of figure how it might work though. There would be an inherent problem with ground settlement, however, so I imagine a series of backfilled pits approximating the position of each room rather than one large one?

Bear in mind that most NZ houses, being largely wood construction, are founded on individual piles and not on a slab. This is not altogether a bad thing from the point of view of the environment as concrete is environmentally toxic and a slab contains a lot (and is cast in situ). Piles are much less impactful as they are cured prior to being driven into the ground. I would think that a NZ house, having a suspended floor has some heat advantages also, particularly if one was to isolate and insulate the air pocket beneath the floor (it usually isn't), as a slab (without the thermal sink concept) transfers (conducts) the ground temperature into the house more readily, and during long winters the ground will remain fairly cold. The downside of this isolation of air is dampness, and associated rotting of the underside of the house, so it makes sense that in the absence of enough knowledge the underfloor cavity area is better left open to breath.

Solar power for providing lighting uses batteries to store power. Solar panels charge the batteries, and low voltage LED's run off the batteries and provide very efficient lighting. As always, the environmental cost of the set-up (manufacturing impact and ultimate discard of batteries etc) needs to be weighed up against the use of normal grid electricity.

The ultimate goal in a green-build house is to minimise impact. Consider that the purchase of an existing home creates no new impact and is thus a greener option than building a new home, even if the original home was not eco-friendly. Buying an existing house is sort of like recycling. Don't let this stop you, and definitely if you are going to build then build with the environment in mind, but remember to remain objective about your real impact, and once you apply your green attitude in one area of your life you will find it infiltrating every other.

[benandclare]

Bear in mind that most NZ houses, being largely wood construction, are founded on individual piles and not on a slab.

In the short time we've been here all the new houses going up seem to be placed on top of a concrete pad.

Ours was built 5 years ago and is the same .

[PeteS]

Question: can you elaborate on the thermal sink concept? It's not something I have been aware of...I sort of figure how it might work though. There would be an inherent problem with ground settlement, however, so I imagine a series of backfilled pits approximating the position of each room rather than one large one?

Thermal sink; A large mass that absorbs heat during the day usually from solar. It could be a wall or a floor. This heat is then released as the house temperature falls. One of the laws of thermodynamics, heat flows from a hot body to a cool body. The floor slab version would be quite thick, say 150 to 200mm thick, and the underside of it, where it sits on the ground, is insulated with building grade polystyrene. And of course it is cast in situ concrete.

Bear in mind that most NZ houses, being largely wood construction, are founded on individual piles and not on a slab. This is not altogether a bad thing from the point of view of the environment as concrete is environmentally toxic and a slab contains a lot (and is cast in situ). Piles are much less impactful as they are cured prior to being driven into the ground. I would think that a NZ house, having a suspended floor has some heat advantages also, particularly if one was to isolate and insulate the air pocket beneath the floor (it usually isn't), as a slab (without the thermal sink concept) transfers (conducts) the ground temperature into the house more readily, and during long winters the ground will remain fairly cold. The downside of this isolation of air is dampness, and associated rotting of the underside of the house, so it makes sense that in the absence of enough knowledge the underfloor cavity area is better left open to breath..

Modern building methods are normally to cast an insulated floor slab and build the house on that, either of timber or concrete block. Airated concrete block offers sound deadening and thermal advantages.

Kitsets are usually built on piles are put into holes in the ground and cast into position with concrete. The piles could be H5 timber or concrete, but usually timber. The timber is treated with several "unpleasant" and quite toxic chemicals. There are definate heat DISADVANTAGES to floors built on piles. freezing in the winter.

So, if you want a warm house, cast a thick insulated concrete slab into the ground, insulate the walls and ceilings at least double the code requirements, fit low E argon double glazing with uPVC or timber frames. Then sit back with small heating bills and the sound of Kiwi's telling you "I bet this place is exspensive to heat, and with all that insulation it's ok in the winter but it'll be too hot in the summer......" :D

[dilanium]

A grey water treatment system will also improve on energy performance, and allow you to use basin and bathwater to irrigate the garden.


couldn't this potentially lead to problems?

you can find fecal parasites in bathwater- (especially from the bath, but also water from the shower), and depending on the type, they'd be able to either survive tanking, and then you're spreading it onto your garden. This would be fine for a flower garden, but a vegetable garden? Even with washing your vegetables it seems like putting yourself at risk.

[ourquest]

Thanks for filling me in, PeteS. I guess that the cavity that James referred to is the insulation then, not the heat-sink itself. I wonder how this is created, ie, what supports the slab during pouring and curing of the concrete? That aside, the goal would then be to maintain the slab at a warm temperature in winter and cool in summer, which will only occur if the slab is separated from the environment by an insulating layer (the house on top of it effectively being one of these layers). Heat from the sun would not contribute to its warming directly because of the presence of the house, unless there is an extended apron around the house (which is usually there to prevent differential expansion of soils in certain areas taking place directly under the structure, by extending the size of the consistent moisture level area under the house).

I was contemplating how earthquake dynamics affect the use of slabs, and decided it was not significant as the slab will move as a unit during seismics, and the wooden structure above would still flex as required during oscillation (unless you were unlucky enough to be directly over a surface expression of a fault, but then not much will survive anyway).

I am not convinced that a house standing on piles would necessarily be thermaly inefficient, as non-circulating air is a very good insulator as used in double-glazing. The trick would be to encapsulate the air under the floor and above the ground; I admit that might not be logistically easy, particularly in a wet and windy climate, and without doing that the floor itself is the only insulator and thus critical (and probably won't work!).

As with any of these factors it requires synergy...each factor contributes slightly and the net product is an improvement in energy efficiency. ;)

[miep]

Hi Ourquest, I think what KN2NZ means is an actual rock pile. There's a house in Welly somewhere (I can't find the website, but there is one) that literally has a room full of rocks under the house which is being constantly ventilated with air from inside the house. The theory being that in summer it will heat the rocks and cool the house and come winter it will release the heat that has built up in the rocks and do the reverse.
It will have been in operation for around 2 years now but I haven't heard how well it works.

In our case the heat sink is the insulated concrete slab itself, with the design of the eaves helping to allow as much sun in in winter and very little in summer.
Incidentally, insulating the underside of the slab is also not the norm here, something to keep in mind when pricing your new build.

[kzn2nz]

Miep has it right. It is like a 'basement full of rock chunks'. An insulated slab merely stops the cold / retains the heat in the house, whereas the thermal mass of rock actually serves as a 'battery', storing heat or cool in the rock for later distribution through the house by means of the fan. It can radiate heat upwards into the home in winter as well.

The system can be built using water tanks instead of rock, but that has a whole new dimension in complexity.

@ Liz - the greywater system should only be used for flowerbeds - if it is intended for irrigation of veggie patches, then a UV steriliser would definityely be recommended to take care of any nasties, especially E. coli and the likes.

@ Ourquest - The LED Lighting usually works off a transformer but draws very little current compared to even CF globes. It is still rather limited to decorative lighting, though.

What I initially meant to say (didn't come across so well) is that the kit houses can, with a few very simple and almost cost free modifications at building, be a lot more environmentally friendly in terms of their energy consumption as opposed to the exact same design just placed parallel to the street.

[migratory birds]

I read about this American architect several months before traveling to NZ

http://www.marinij.com/lifestyles/ci_6963634

She speaks to exactly what I saw in real estate in the communities I visited in NZ - tear-downs or major renovation projects with exhuberant asking prices.

While I'm not sure I care for the exterior look of her designs, the idea of green-built modulars is growing on me.

http://www.mkd-arc.com

Thanks for the links to architects familiar with green building. I'd much rather work with a builder who already "speaks the language" and knows how to resource and integrate necesary materials

[miep]

I really like those designs, I think they'll work well in NZ too. Although they look a bit pricy at US$200 per square foot starting price. Aren't there 9 or 10 of those in a sq metre?

[migratory birds]

...they look a bit pricy at US$200 per square foot starting price. Aren't there 9 or 10 of those in a sq metre?

1 sq ft = 0.0929 sq metres

1000 sq ft = 92.9 sq m

At $200 USD/sf, this architect's rates are approx what you and markw55 quoted at $2000-2500/sq m

[miep]

OK, thanks for the translation. It seems fairly reasonable to me but after converting to NZ$ it still comes out high, (for here) but probably more realistic than NZ$1200 that people still use.

[dragon56]

I suspect there may be a little confusion in this thread between the operation and benefits of insulation as opposed to the practical use of geo thermal energy which relies on a heat pump and can not only warm the house via a wet central heating system but also provide domestic hot water.
I have just read that through & it sounds a bit pompous, sorry it wasn't meant to be. http://www.emigratenz.org/forum/images/smilies/smile.gif
:)

Anyway if interested have a look at this site http://www.kensaengineering.com there are others but this one has loads of good info

best wishes Duncan