[RayBCO]

Hi There Everyone,

I have read some posts here regarding cold homes, energy costs and the things people will do to keep warm. Also concerning the types of changes proposed to keep energy costs down and the heat in...

Now I do not consider myself an expert, but in England, I am a Government Approved Energy assessor, a Building Control Surveyor and have a degree in Building Surveying amongst other qualifications and experience.

I dont consider myself an expert because I have not set foot in NZ yet...but Britain is an island too and though the climate is slightly different - depending on where you are located - the average timber frame house still works in the same manner - lets face it the house does not know where it is.

So some might agree with me and others may not. I just want to let people know the ways to keep their homes warm and their energy bills down.

The first thing I 'hear people mention' on the forum when it comes to their homes being 'freezing' is that they don't have double glazing.

Well, if you are considering double glazing for your home and think it will save you money on your heating bills, you need to consider that glazing, whether double or triple glazing, does not get included in energy calculations for houses. Only the area of glazing is considered and the less area the better.

Having looked at the current housing stock in my price range in NZ, in various locations, I almost always see over glazed homes. Great designs, I know and beautiful as they are...they will lose more heat than homes with relatively smaller windows. A consideration when buying, or refurbishing your home. I do admit though that double glazing can creat a cosy home due to reduction of outside noise and also a great reduction in draughts.

But compared to an insulated external wall the glass may as well not be there...

Another consideration is the orientation and exposure to the property. If you are surrounded by trees you will not be as exposed as on a hillside for instance... This is where insulation to the thermal envelope comes in ie. the walls, floor and roof. Insulation can be relatively easy to install in timber frame homes and reasonably priced even in NZ when compared to the saving that can be made on heating bills over a period of time.

Most timber frame homes worth buying will have 75 - 100mm timber stud walls. Just 75mm of a foam type insulation in walls will make a great difference to the heat loss. Even 75-100mm of mineral wool type insulation will improve the heat loss. Just done forget to include a vapour barrier to the interior studwork prior to boarding it. Water in the form of vapour will just sit in the timber if you forget. 500 guage polythene sheeting stapled to the wood is enough to prevent this. Not sure if you can get foil back plasterboard in NZ as this will do the job too.

Roof can be insulated with mineral wool material too at a depth to suit. Here in England the minimum is 270mm but 300mm or mor is better cross-laid between/over the ceiling joists. You must remember one thing...Ventilation. The roof must maintain its ventilation. Provision of a crossflow of air is very important. Vents a the eaves, soffit or fascia are easy to install. Make sure the insulation is pulled back about 50mm from the eaves. Provision of ridge vents also promotes good ventilation. Remember this cold crossflow of air is above the insulation so it will not affect you.

Dont forget to insulate the top of loft hatch board...!

Another area to consider insulation is the floor. Heat loss through the floor of suspended timber floors is an easy thing to prevent using the same materials or even polystyrene - known as EPS or expanded polystyrene.

Do remember to include ventilation to the floor timbers via vents along the perimeter of the house. I would provide them at 1800mm centres with a clear void of at least 150mm.

Even concrete slabs are cold until you heat them up with your heating system. Remember heat loss through a concrete floor is mainly from the edges. The larger the area, the less heat loss. In England we include an upstand of insulation below the screed around the perimeter of the floor.

Mineral wool is only stated here because it is relatively cheaper than other insulation materials except maybe polystyrene. Also it is the only material I know that you can definitely get in NZ, as I have not been there yet...

...so some could argue that I dont know what I am talking about...:)

Maybe insulation materials are expensive in NZ too...but from what I have read here... so are wooly jumpers!!!

[Kim39]

Thank you very much for a very informative thread......fancy being the C.O.T.W on my new build so i won't get cold:)

Kim

[jdbob]

Well, if you are considering double glazing for your home and think it will save you money on your heating bills, you need to consider that glazing, whether double or triple glazing, does not get included in energy calculations for houses. Only the area of glazing is considered and the less area the better.


When I did the heating & cooling requirements for my home in Oregon the calculations do indeed take into account the insulating value of the window in addition to the area of each window, not to mention which side of the house the window is on.

"U-factor indicates the rate of heat loss of the entire window. (It's the opposite of R-value, which indicates the insulating value of the window). The lower the U-factor, the more energy efficient it is. Along with SHGC, this is the most important number to watch.

SHGC measures how much of the solar radiation that hits the window will enter the home. It is expressed as a number between 0 (0 percent) and 1 (100 percent). The lower the SHGC, the more radiation blocked by the window"

Since a double glazed window has roughly half the U-factor (or twice the insulating capability) of a single glazed window I think your statement that it doesn't matter is incorrect and the calculation methods you are using are too simplistic.

[debnjohn]

Hi There Everyone,


Roof can be insulated with mineral wool material too at a depth to suit. Here in England the minimum is 270mm but 300mm or mor is better cross-laid between/over the ceiling joists.



They call them 'Pink Batts' over here and they are considered a luxury. Standard thickness is between 7.5cm and 17cm AFAIK.
The big windows over here are to take advantage of the sun (when it is out) heating up your house. You also see a lot of flat and butterfly roofs on new builds - I think this is the Kiwi sense of style (never mind the leak probability).
(In my opinion) you cannot compare UK housing with Kiwi housing (even new builds) as the general standard of insulation & heating is light years behind Europe.

Cheers,
John

[veronica]

and its the older style villas that are the worst offenders, new builds do at least have minimum standards of insulation.

While the cost of the materials to insulate an older established house wouldn't be too bad its the actual installation and ripping out existing walls and re plastering that would make wall and window (double glazing) insulation prohibitive.

The other thing here in christchurch is that its built on a swamp so damp is a big contributing factor to the chillyness.

[Sam B]

Brrrrr, I'm freezing. NZ houses are a special kind of damp cold. I'm off to put my ski jacket on and watch lame TV.

[BaldyBeardyBloke]

38 and never owned a pair of slippers in my life.

Been here a month, it's been 'officially' winter for four days.

Went to Number 1 shoes on Friday and purchased fur lined slippers - technically free in their 'buy three pairs of shoes and get the cheapest free offer' (I needed trainers, OH needed an addition to the Imelda Marcos collection).

I look and feel like a totally nerd in them, but I don't feel like I'm going to lose my toes due to frostbite any more.

PS ours is a spanking new shiny house.

[Ana&Steve]

Thanks the the info, RayBCO. There are a lot of good tips in there to consider, even if it doesn't work for every situation. I found it very strange that NZ house walls were often very thin and really not very hollow, so nowhere for insulation. I look forward to figuring it out, to some degree, and to wearing extra socks:nice1
Ana

[RayBCO]

When I did the heating & cooling requirements for my home in Oregon the calculations do indeed take into account the insulating value of the window in addition to the area of each window, not to mention which side of the house the window is on.

"U-factor indicates the rate of heat loss of the entire window. (It's the opposite of R-value, which indicates the insulating value of the window). The lower the U-factor, the more energy efficient it is. Along with SHGC, this is the most important number to watch.

SHGC measures how much of the solar radiation that hits the window will enter the home. It is expressed as a number between 0 (0 percent) and 1 (100 percent). The lower the SHGC, the more radiation blocked by the window"

Since a double glazed window has roughly half the U-factor (or twice the insulating capability) of a single glazed window I think your statement that it doesn't matter is incorrect and the calculation methods you are using are too simplistic.

Hi Everyone... It is good to hear others opinions on this subject. Thanks.

Of course you are correct, JDBob...The calculations should take into account the U-Value of the windows, in the case of the UK they have to meet a U-Value of 1.8 W/m2K. If filled with Argon gas and with minimum of 20mm spacing between the glass panes you can achieve a better U-Value at a cost, also it helps if they are 'low E 'soft' coated' as they are in the UK.

But compared to a thermally insulated external wall the windows cannot compare...so less glazed area is better according to current thinking here.

In the UK the government don't want to include the windows U-value in the calculation. Of course, there are solar gains to take into account that will warm up our home significantly and as others have mentioned this can reduce your heating bills...

However, in the UK rightly, or wrongly, the government are more concerned that their calculations are designed with something else in mind...CO2. They dont seem to care about your household bills...

The calculations are designed to measure the amount of CO2 that your home releases into the atmosphere. And the calculations are designed to make your home comply if the CO2 emissions are below a certain value.

They take into account the solar gains and try to reduce them also, to prevent people using Air Conditioning which of course = greater CO2 emissions.

I do understand that I cannot compare NZ with the UK. As I said I am no expert, and have not set foot in New Zealand. But I was trying to get people thinking and discussing the ways to save on their heating bills and keep warm...

I understand that materials in NZ may be more expensive...but I understand that the energy costs are as high, if not higher than the UK also...

I hope I have stirred a debate/discussion on ways to make homes more energy efficient for those moving to NZ...I am sure many will appreciate the thoughts and information from those with knowledge of this area.

One other thing to mention, something I was reading about 'Global Warming'... Apparently scientists have discovered that the ice caps on Mars are melting also...so maybe it should be called 'Solar Warming'..a purely natural phenomena that should not be taxed !!!

[debnjohn]

Slippers, yes, wouldn't be without them. When it's cold outside (and colder inside) the kiwi answer is to 'rug-up', i.e. layer on the clothing.

Having said that, yesterday morning was a really frosty start (even frost on the beach), so I was amazed to see one lad happily whizzing by on his micro-scooter in T-shirt, shorts and bare feet!
Cheers,
John

[jess]

Slippers, yes, wouldn't be without them. When it's cold outside (and colder inside) the kiwi answer is to 'rug-up', i.e. layer on the clothing.

Having said that, yesterday morning was a really frosty start (even frost on the beach), so I was amazed to see one lad happily whizzing by on his micro-scooter in T-shirt, shorts and bare feet!
Cheers,
John Yep, I started up the woodstove yesterday, and it kept the house toasty warm all day. I mentioned it to some Kiwi's down the road, and they said, "Used the woodstove?! But it hasn't gotten cold yet!" And I still see kids in shorts too.

[hball]

Check out the following site for in depth info re Energy Saving ideas and Heating Solutions www.buildyourdream.co.nz - but beware, there are some very vocal Europeans with strong feelings about NZ residential construction!!

However, NZ is not so backward on this subject as many assume. One of the important factors here is that many people commission their own homes to be built, and so they decide exactly where to spend the money, be it on beefing up the insulation or adding another bedroom. There are quite strict minimum standards which new homes have to adhere to, and these standards are to be upgraded later on this year in order to cut current residential energy consumption.

DebnJohn, Pink Batts are probably the most commonly used brand of fibreglass insulation. They are economic, so not a luxury, and are often the product of choice by most builders as without wall/ceiling insulation no new home would get a Building Consent. (Been in force many years) A nicer product is Greenstuff which is made of polyester as found in duvet inners. We used it for our house as I am not a fibregalss fan but if you really want to spend, the luxury insulation is wool! Strange really as we have all of these sheep wandering around - yet wool insulation is arm and a leg stuff!!!

[debnjohn]

DebnJohn, Pink Batts are probably the most commonly used brand of fibreglass insulation. They are economic, so not a luxury, and are often the product of choice by most builders as without wall/ceiling insulation no new home would get a Building Consent. (Been in force many years)

But as you say the minimum standard (thickness) required is woeful. Its's only my opinion that NZ lags (no pun intended) European standards... but then if New Zealand wasn't 'backward' (your choice of word) then why would the standards be upgraded later this year?

My personal take on the Pink Batts series of adverts 'warm, dry, quiet......' 'so comfortable you won't want to go home' is that it is pitched as an aspirational luxury product. Theys are certainly not being sold on the basis of being economic. The fact that prime time advertising is being plugged for fibreglass insulation tells me so. (I had a similar reaction when I saw the winter full shop-window display for Briscoes - fan heaters and oil-filled radiators. Not to mention those super-humidifying 'Super-Ser' style calor gas heaters.) But then that's just my opinion.

Cheers,
John

[Ana&Steve]

if you really want to spend, the luxury insulation is wool! Strange really as we have all of these sheep wandering around - yet wool insulation is arm and a leg stuff!!!
I'm curious, what is the shelf life of wool as insulation? Seems like it would be susceptible to moths, bugs and damp, but maybe that's just sweaters (jumpers).
Ana

[John Z]

Fibreglass insulation isn't a product of choice (anymore): the small particles that get airborn (could) get stuck in your lungs and give (permanent) damage. These particles are alien to the human body and it doesn't have the capacity to dissolve it them...

What is prefered now is "Rockwool".

Cheers, John Z.

[hball]

The ads for Pink Batts are (I think) to make the public aware of the wider range of product they offer in the hope that anyone having their own home built will ask the builder to upspec to say Pink Batts Silencer for a "quieter home" and so on. (At a higher cost of course!!!) If the client has no interest in this area of the building contract they will stay with the required thermal insulation according to the zone in which they live.

What is suprising, considering the interest here on this thread, is that in the twelve years I have been involved with the residential construction industry and with over 200 houses built, I have NEVER been asked to upgrade any insulation from the level demanded in the Building Code.

Maybe that's why Pink Batts feel the need to advertise!

[debnjohn]

What is suprising, considering the interest here on this thread, is that in the twelve years I have been involved with the residential construction industry and with over 200 houses built, I have NEVER been asked to upgrade any insulation from the level demanded in the Building Code.

Maybe that's why Pink Batts feel the need to advertise!

Exactly that. Public awareness (or lack of) is the reason for so many cold and damp houses in NZ. Doesn't matter if it doesn't meet WHO standards for health, the Kiwi response would be to toughen up, after all, we are neighbours to therefore enjoy the same climate conditions as Australia :laugh

I have ZERO experience of the building trade, so as said before it's only my opinion that NZ building standards are sub-European, but I do know from first-hand experience that the loft insulation in my (built 2003) 'G.J.Gardner Homes' in Christchurch NZ house is FAR thinner than the loft insulation in my previous (built 2000) 'Westbury Homes' in Swindon UK house. I was never informed how harsh the zoning would be, or asked to upgrade insulation - I would trust such things to the 'experts'(but then I never saw prime-time advertisements for insulation in the UK - so perhaps my aspirations of luxuriant living are askew). Perhaps Swindon requires a much higher thermal insulation?

Cheers,
John

[hball]

I have no knowledge about the type of insulation you would have had in Swindon unfortunately so can't compare. In Christchurch you would have minimum ceiling insulation to R2.6 and walls to R2.2, and that is the building authority recommendation. Auckland is R1.8 for both. Have you thought about buying additional insulation and laying it in the loft to get over the problem?

Thought... Did you have central heating in the UK? And do you have it here? If not are you using a form of heating which is manually controlled, and which you have to turn on when you enter a (cold) room? Maybe that is part of the problem?

You say you were never informed how harch the zoning would be - I take it you had your own house built and so went through the contract process - maybe your builders don't think of the area as a harsh one and if asked they would probably say that towns in the lower part of the south island would be, but not theirs!

Have to add we went down to Christchurch a couple of weeks ago for short weekend visit and it was bl**dy cold by Auckland standards!!! Needed a coat for the first time this year so do appreciate the issue.

[debnjohn]

I have no knowledge about the type of insulation you would have had in Swindon unfortunately so can't compare. In Christchurch you would have minimum ceiling insulation to R2.6 and walls to R2.2, and that is the building authority recommendation. Auckland is R1.8 for both. Have you thought about buying additional insulation and laying it in the loft to get over the problem?

Thought... Did you have central heating in the UK? And do you have it here? If not are you using a form of heating which is manually controlled, and which you have to turn on when you enter a (cold) room? Maybe that is part of the problem?

You say you were never informed how harch the zoning would be - I take it you had your own house built and so went through the contract process - maybe your builders don't think of the area as a harsh one and if asked they would probably say that towns in the lower part of the south island would be, but not theirs!

Have to add we went down to Christchurch a couple of weeks ago for short weekend visit and it was bl**dy cold by Auckland standards!!! Needed a coat for the first time this year so do appreciate the issue.
Thanks for the advice. :cheers Yes central heating does make a difference; in the UK we had it set to a minimum of 15degC so all rooms felt warm.
As for my problem, well I don't really have one. In comparison to Swindon the winters are a lot shorter and dryer here in Christchurch, so although we have considered central heating its' not really economically viable ($13k to instal). I'm quite happy to rug up and put on the electric blanket. I only contributed to this thread to add my opinion (and mine only) that NZ housing insulation standards are poor when compared to Europe. But this is only my personal experience (comparing windows and loft insulation on two new houses).
My reference to Pink Batts was just to highlight my own amusement and incredulity at prime time tv advertising for insulation products - it just struck me as odd. But then so does electric heater displays in shop windows (again I would categorise that as aspirational marketing), the proliferation of 'stylish' flat and butterfly roofing, 'indoor outdoor flow' and 'weeping windows'. During my first winter here I was re-introduced to domestic de-humidifiers (something I hadn't used in the UK since the seventies). But that's just me. I'm odd and I find amusement with odd notions. It wouldn't do for us all to be the same.

Cheers,
John

[hball]

Agreed!!

We deliberately choose to live in Auckland to get the warmer temperatures and still have our central heating set at 19C (only turned it on at the beginning of this month though)! Think I have become acclimatised to the warmer summers and so feel the cold even more!!!!!

[beano_bill]

my own amusement and incredulity at prime time tv advertising for insulation products

Thoroughly off topic but I was surprised to see adverts on Sky for John Deere tractors during prime time.....:laugh

We started to stoke up the wood burner last week - on Sunday we could see our breath it was that flippin' cold :eek:

Beano

[Super_BQ]

Having looked at the current housing stock in my price range in NZ, in various locations, I almost always see over glazed homes. Great designs, I know and beautiful as they are...they will lose more heat than homes with relatively smaller windows. A consideration when buying, or refurbishing your home. I do admit though that double glazing can creat a cosy home due to reduction of outside noise and also a great reduction in draughts.


I'll have to agree. Too many windows and you might as well call your home a greenhouse.

In order to build warmer homes in NZ, the whole building code and practices need to be change.

For starters, get rid of the dwangs and cross supports between studs. Though they may serve to make the wall stronger, it is a for sure good way to extract heat inside the house directly outside. You can put as much fiberglass insulation in the walls and it won't help stop the heat that transfers through by conduction.

In Canada, the strength of the wall is not done by putting dwags between each stud. Instead, the wall is strengthen at the circumferance around the wall.

The extra wood used in dwags could be better used by building in 2 x 6 framed constructions. Not only you get less conduction through the timber framing to the exterior but also you can pack far more insulation between the walls. This is the minimum build standard in Canada and for places like Vancouver (which it's climate is not much different than Christchurch), I don't see why such building techniques can be used in NZ.

In many new NZ home construction, I see insulation between floors. IMO it's a waste as heat will always rise to the highest level. The insulation should be concentrated in the roof. R20 - R40 is normally seen. Ever see the attic space in older NZ state houses? The cold air blows in from 1 side of the eaves to the other side. Where's the air tightness in the roof? I can see why so many people complain how cold it is in the winter when it's only -5°C.

So my advice, before anyone should considering putting more insulation, double pane argon gassed windows with pvc framing, central heating, etc.. One must realising the benefits of these are not that great on your wallet because we're dealing with houses that aren't built to with energy efficiency in mind.

BQ

[bozandhelen]

This weeks been absolutely freezing, the wood-burner has been on for 4 days solid now but the heat just vanishes through the hollow walls, uninsulated floors or the laughable roof insulation. I would really like to get the insulation up a bit but we are building a new house so the greenbacks are going on that!

Our new house which unfortunately won't be ready until spring will have the thickest pink-batts in the walls and ceiling, the windows will be double-glazed (though using crappy aluminum frames as you just get a funny look in Marlborough if you mention PVC!) All the big windows and conservatory face to the North (coz thats where the sun is down here!) and we're putting in solar water heating, a heatpump and (sorry Greenpeace) a wood-burner. A heat transfer system is going to be fitted to give the illusion of central heating (which I really wanted but again got a funny look off the builders!)

They really do have a lot of catching up to do here!

[RayBCO]

Hi SuperBQ, Hope you dont mind me jumping in here and explaining a few things from a UK perspective...



In order to build warmer homes in NZ, the whole building code and practices need to be change.

The Building Regulations in NZ are going to be changed soon, especially in relation to Conservation of Energy. Remember that all of the Regulations ask for insulation at the bare minimum to achieve a target of reduced carbon release from buildings. Putting more insulation into the construction is very cost effective in the long term.

For starters, get rid of the dwangs and cross supports between studs. Though they may serve to make the wall stronger, it is a for sure good way to extract heat inside the house directly outside. You can put as much fiberglass insulation in the walls and it won't help stop the heat that transfers through by conduction.

In the UK we have 'dwangs' or Noggins as we call them to prevent the upright timbers or studs from twisting under load, as they would in timber frame construction. They also have external plywood sheathing that provides some structural integrity to the external walls.

The noggins are not removed, nor do we use 'inferior' fibreglass or mineral wool insulation. 'Rockwool' is a trade name for one company's mineral wool.

We use PUR foam based products that are around 90mm thick to match 300mm or 12" of fibreglass. We do however, overlay across the insulated studwork with another 40mm of the PUR foam to prevent the cold bridging that you have already mentioned. This allows 100mm or 4" thick studwork, to save on costs, but most of these timber frame homes in the UK have external brickwork cladding. As in the case of Canadian homes, using Stucco or cement rendering, then 150mm or 6" timbers would provide better structural integrity. It is also possible that timber is cheaper in Canada than it is in the UK?

Homes in the UK are even air tested to reduce the air leakage from the construction... air leakage = heat loss. This also catches all of the poor workmanship of course, a very good thing.


In Canada, the strength of the wall is not done by putting dwags between each stud. Instead, the wall is strengthen at the circumferance around the wall.

The extra wood used in dwags could be better used by building in 2 x 6 framed constructions. Not only you get less conduction through the timber framing to the exterior but also you can pack far more insulation between the walls. This is the minimum build standard in Canada and for places like Vancouver (which it's climate is not much different than Christchurch), I don't see why such building techniques can be used in NZ.

In many new NZ home construction, I see insulation between floors. IMO it's a waste as heat will always rise to the highest level. The insulation should be concentrated in the roof. R20 - R40 is normally seen. Ever see the attic space in older NZ state houses? The cold air blows in from 1 side of the eaves to the other side. Where's the air tightness in the roof? I can see why so many people complain how cold it is in the winter when it's only -5°C.

Insulation under floors is a good idea because, your heat will not only rise as everyone understands it...but your heating system will also try to heat up the elements around it i.e the walls and floor including, the ventilated space below the floor in the case of timber joists. It is the same with a concrete slab. You will heat up the concrete. So insulation will help if it is within the floor construction or between the joists.
In actual fact with concrete slabs the outside perimeter is actually the cold spot. An upstand of insulation here is used for cold bridging from the side of the slab.

From my experience in Canada -20 to -30, USA -20, Russia -40 to -50 and the UK -2 :roll ...I found that the UK has bitter cold due to the humidity. The cold here is not the same as the dry cold in the aforementioned countries. I have not set foot in New Zealand yet...but I imagine as an island it is similar, ie not a dry cold...it seems to get into your very bones!

The air flow across the roof is a necessity in a humid climate as you have to ventilate the roof space or all of the timbers will eventually rot. This is why we insulate at ceiling level. With the new breathable membranes as a roof covering under the tiles, we now have no need to ventilate the roofspace as before. There are other new products that allow just 35mm of insulation and are equivelent to 200mm or 8" of 'fibreglass'. Great for insulating the Skillings of a roofspace in the case of loft conversions.
(Skilling = sloping ceiling).

So my advice, before anyone should considering putting more insulation, double pane argon gassed windows with pvc framing, central heating, etc.. One must realising the benefits of these are not that great on your wallet because we're dealing with houses that aren't built to with energy efficiency in mind.

It is true that the payback of all of these products on your home is at least 15 - 30 years in energy savings...but that depends on how you heat your home??

BQ

Don't want to stand on your toes here...just provide information to those that are happy to receive it.

RayBCO

[Angelonthemove]

Just got to update. We have bought a house in windy Wilton up on a hill and you all asked had it got central heating and double glazing. No it had neither. 1 week in and we have 2 new heat pumps for the whole house. Boy are they efficient and no more streaming window. We set them on timer its a 24 hour mode so we just push a button and reset for next 24hrs. Its has air filtration for my asthma.

Cost $5700 incl instaltion. We have to keep turning them down as its so warm. shoudl cut our bill cost as we had gas central hot air heating last rented and it was costing far too much to heat.

[Super_BQ]

Glad to hear your perspective RayBCO, as i'm not familiar with UK building construction techniques.

The Building Regulations in NZ are going to be changed soon, especially in relation to Conservation of Energy

My uncle is in the middle of it and he's built houses for over 40 years in NZ. Despite the newer changes, they are still miles away from what i'm use to in a comfortable home. R2.4 - R6 just isn't enough in the walls. As I mentioned before heaps of insulation won't stop the energy conduction in the timber frame.

The air flow across the roof is a necessity in a humid climate as you have to ventilate the roof space or all of the timbers will eventually rot.

That's part of the problem. Home construction techniques in N. America are so different to NZ (or perhaps the UK) because the focus is different. You have homes in NZ where people tend to heat only 1 room leaving the rest of the whole house not much warmer than the outside. While in N. America you build homes with the intent to heat all the rooms centrally. When you build to heat the whole house, all forms of air gaps in the walls and roof are evil. The more insulation you have, the less likely condensation will occur. Furthermore the use of materials is very important. Many houses in NZ have roof tiles made from steel and have aluminium window frames. From my last knowledge, metal is a conductor and NOT an insulator which means, well more condensation.

I'm a fan of gas centrally heated homes. The furnance continuously circulates air in the already air tight house, preventing stagnant stale air. The air is also passed through a filter which you replace like an air filter in the car. The furnance is also responsible mixing the inside air with the outside air through the heat exchanger - so it's not like you're breathing in the same stale recycled air. As an option, many of the furnace ducts can have dehumidifiers installed to rid any of the dampness - and increase energy efficiency.

The focus of double glazed windows is overrated. One must consider the framing. If it's aluminium framed, then there should be some thermal air gap built in that completely separates the inside aluminum with the outside aluminum framing. Or better yet, use PVC or wood framed windows as they are insulators. Anything else and you're just conduction inside heat to the outside.

What I find interesting is in Canada, so much has been done about energy conservations in residential homes when electricity is only around 6 cents / kW. But in NZ people pay about 20 cents /kW and the homes still leak the heat out as fast as portable heater can put out.

BQ