Elaborating on a couple of things: timber windows don't perform in the sense durability requires ongoing maintenance. They can be composited with a veneer of aluminium on the outside to remove the maintenance factor. The aluminium strip can be powdercoated to have a wood colour. It shouldn't be confused with aluminium joinery with a cosmetic veneer of wood on the inside.
By typical winter situation I mean where most New Zealand houses are located (disproportionately in the warmer areas). If you're in a colder area or have an above code insulated house there's going to be more benefit to thermally broken, timber or PVC over solid aluminium.
Do you have a reference for that claim? This page shows uPVC as being more efficient than aluminium whether or not it's thermally broken, although there's not a heck of a lot in it - they're all fairly poor insulators.
The standardised numbers on that page have little relationship with the real world. Likely they date from the mid 2000s from older products including terrible cheap hardcoat low e glass with a heavy dose of worst-case pessimism on top. Both frame types and mainstream low e perform better than that.
PVC is popular in certain countries because it is cheaper to manufacture there. When aluminium has under 10% market share in a large country versus 80% for PVC the price gap is further exaggerated by economics of scale and greater automation. Often the same companies manufacture both with architectural/commercial clients who buy aluminium being less price sensitive and uninterested in PVC. There is less incentive to cheapen or market aluminium and the public is often unaware it's an option. Not many people are aware of how much longer the lifespan of aluminium joinery is and may not think that far ahead. Passivehaus certified triple-glazed aluminium windows are available in Europe so it's not like it can't thermally make the grade with enough engineering.
In New Zealand houses are more likely to be run into the ground and demolished than maintained. In Europe they're kept going and centrally heated. So windows companies deal direct with the public and take on a role similar to passive ventilation companies do here with marketing and dedicated salespeople. People call them "double glazing companies" which tells a story. PVC is pushed because they could quote to price-sensitive clients for £10,000 instead of £14,000 for aluminium which also has longer lead times from lower automation and volume. There has been a culture of marketing and push-the-envelope claims surrounding PVC.
We are planning to retro-fit double glazing in our place in the near future, I am dreading the quotes as most of our windows are floor to what would be the ceiling if we had a ceiling.
Be careful about the air gap width in retrofit glazing units (retrofitting double glazing is not the same as full joinery replacement). A good low e glass like XCel makes retrofitting double glazing more worthwhile and it doesn't perform well with a 6mm air gap compared with 10mm+. Most old sliding and hinge doors don't cope well with the weight of double glazing. You can reglaze to low e R0.27 single glazing (versus R0.31 for 6mm air gap plain double glazing) if you really don't want to replace a door. Low e single glazing should be cleaned carefully as it's more easily scratched than uncoated glass.
PVC frames typically costs more than standard aluminium, but less than thermally broken aluminium. The raw material cost is only one factor in making a finished product.
Thermal breaking can add as little as 3.5% to manufacturing costs to an aluminium window. In New Zealand the price gap is often larger because except for APL they are only thermally breaking medium width profiles. So the price gap is mostly not because of the thermal break costs but because we're comparing a medium width premium profile with a thermal break against a mass market narrow width solid aluminium profile.
PVC frames vary in quality grade too. Most sold in New Zealand are German branded budget profiles manufactured in China while others import direct from the western hemisphere. Some companies place huge margins, others thin margins. Overseas joinery manufacturers can have many different quality grades so check the OEM's website if you're interested in imported joinery.
uPVC windows usually use more sophisticated hardware, which doesn't seem to be offered on aluminium frames.I am thinking of the 'tilt and turn' system, which is really very good.
Placing blinds behind tilt and turn joinery can be problematic. It is possible to integrate blinds into glazing or on its surface.
Multipoint window locking is supported by Nulook and Fairview/Elite thermally broken profiles. New Zealand aluminium profiles normally support multipoint door locks. European aluminium and timber windows supports the same hardware as European PVC including tilt and turning. There are 2 or 3 importers of European aluminium and wood-alu joinery in New Zealand. I do think they should support tilt and turn/side joinery with New Zealand aluminium. One minor Australian manufacturer does so there is no good reason why they couldn't. They are losing more and more business because they talk to builders instead of the public.
Concrete doesn't have a good reputation as an insulator though the plaster may be helping. An architect selected Pacific Architectual? That's amusing but unsurprising.
That would be an issue here. Summer sun is harsh and there is no easy way to shade the windows due to placement of the building on the site without significant architectural enhancement.
Metroglass "Xtreme" is similar to Xcel but lets in 1/3rd less heat. Not ideal in winter but if the bigger problem is summer it may be useful on affected windows. Viridian's Performatech 206 is more effective at solar heat rejection but as it negates so much winter heat gain it may be too effective.
@bfginger do you agree with @Disrespective that thermally broken joinery is essentially pointless if the windows is installed outside if the thermal line of the wall?
It is more effective if it's installed recessed but it does still help over solid aluminium when installed the standard way. Unless it's a fixed window a percentage of the aluminium frame isn't near the frame perimeter. The inner frame around the perimeter does have more exposure to the cold than if it was recessed but it will be warmer than if the entire outside frame area was connected. This youtube video shows the deficiency of installing this way but you can see the benefit too versus the break being absent.
We are in the process of planning our build, and I assume our windows will be installed in the "standard NZ way" which sounds like is generally outside the thermal line of the wall.
It shouldn't be a great expense to install recessed, the issue is builders won't have heard of it. Altus does supply instructions for Pacific Thermal and AllSeasons to be installed this way and other brands can be too if someone knows what they're doing.
EDIT: Would thermally broken also be pointless if you went with something like Low E Plus that doesn't use a thermal spacer?
Probably. Glass is a poor insulator and an aluminum spacer means a thermal bridge is being created between the inner and outter frame which is what the thermal break is there to prevent. Their XCel is a better product with a 50% higher R value and 1/7th more visible light admitted than Plus. You can get plain glass with a thermal spacer too.
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