Scandinavian timber windows - durability of recent product?

[beenthere]

Hi all, new here and just posted an introduction. Pardon the length for a first - but it may be of interest to some.

We're shaping up to buy new replacement aluclad Scandinavian pattern timber windows for our 1980s brick cavity wall self build, and finding it much less straightforward than expected. The position may be somewhat different in the UK (we're in Ireland) but we're running into two issues:

1. Highly aggressive terms and conditions, and despite the usual noises in the sales material miles of blatantly one-sided fine print. (especially from the well known large Danish guys). HIgh end pricing and premium billing doesn't seem to deliver much that's customer friendly in this regard.

Payment in full is demanded before installation with no mention of standards for this work (the window companies tend to do it themselves here), the warranty is very highly constrained (12m on finishes, 3yrs on hardware, 6 yrs on the structure; 'natural' processes like knots weeping and presumably warping and/or splitting in the wood are excluded, lots of fine print about maintenance requirements), it doesn't matter what you agree with the sales guy or what’s in the brochure -  it's what's in the quote that determines their specs, deliverables etc.

None of this would matter terribly given a reliable product, and rock solid installation work, but….

2. Uncertainty about likely window longevity. 

We may be overly cautious, and the Danish brochures in question claim very long lives (80 years in one case) with correct maintenance - but the documentation is decidedly weak on technical specification or standards information, and the fine print seems to really only commit to use of Scandinavian ‘softwood', flow coating with preservatives and water based finishes. Suggested specifiers wordings are notably toothless.

The previously more or less traditional/gold standard selling points of laminated slow growth Baltic pine heartwood of specified max growth ring spacing/density, and double vacuum impregation seem to have gone by the board in their cases. (these days it's all about environmental sustainability etc. which is excellent, but what about basic functionality and longevity?)

Much is made of compliance with DVC (Danish Window Control - an industry body/regulator run out of one of the technical colleges there) technical and other standards, but it’s proving hard to dig up what this means in practical and specific technical terms - and how it relates to BS 8417 window durability/life ratings.

My superficial understanding is that the British Standard (anybody around with a better understanding?) at minimum requires joinery for external use (hazard/use class 3, actually 3.1 if painted - which reportedly delivers at best a 30 year life) to be from at minimum timber of durability class 3 (moderately durable). Class 2 timber (durable - and I can’t find any species of redwood/pine with this rating, even for heartwood) is reportedly required to achieve a 60 yr life. The problem is that the various pine species seem to be at best class 3 (moderately durable = heartwood of the better species), but often class 4 (slightly durable) - while the sapwood (which it seems may be be used also - if only laminated behind the heartwood) is regarded as class 5. (not durable)

This suggests that highly effective and deeply penetrating (the traditional double vacuum?) preservative treatment is essential to achieve 60 year durability with even top quality pine heartwood. Trouble is it’s not by any means clear whether or not the recently adopted flow coating does that sort of job. Especially not if lesser grades of wood are mixed in. Minimisation of moisture take up to minimise movement with changes in moisture content is also a serious consideration - impregnation can it seems greatly improve stability in this regard. Then there's the question of water based coatings.

 

There’s an industry funded body called the Wood Window Alliance that has published research into wood window longevity in the UK that suggests 30 yrs plus before maintenance for aluclad windows, but research into experience with long installed windows isn’t of much use where very recently adopted practices are concerned. Plus it's generic, and not maker specific.

 

It’s clear that there’s been all sorts of moves recently in play to reduce the cost of the wood (mixing heart and other woods?), and to reduce manufacturing costs. (like avoidance of vacuum impregnation) The question is whether or not those using these techniques (which may well be fine, but might also seem reminiscent of how the supermarkets still tick the boxes on selling points while stripping the good out of food products) are delivering their claimed durability. The terms and conditions (see above) suggest that some of the makers may be taking no chances - may not be putting their money where their mouths are.

 

This might seem picky, but the prospect (if this was to turn out to be a possibility) of trying to deal with rotting windows at age 80 doesn’t appeal. Never mind that claiming on warranty (at any point)  sounds very much like tilting at windmills...

 

 

3. Different makers, different specs?

 

One stand out maker may be NorDan. They seem popular in the wet and windy highlands and Isles of Scotland (could be down to effective local marketing rather than real advantages though), and there are signs that they may still use the more traditional laminated pine heartwood and vacuum impregantion construction method. 

 

Anybody with experience of and fimiliarity with Nordan? Strengths and weaknesses?

 

Thoughts on the other topics above, especially on how the Danish DSV standard cross references to BS window durabilities?

 

 

All help and input appreciated. Thanks

Edited July 22, 2016 by beenthere
typo

[ProDave]

Do you have to get "supply and fit" what about buying the windows and getting a local joiner to fit them?

Have you tried Rationel? Certainly up here they are doing some good pricing. They were the cheapest of my window quotes, and almost the best (only slightly beaten my intermorm who were twice the price)  Very good windows with an "expected" life of 80 years for the ali clad version.
 

[Barney12]

The "warranty provision" clauses you refer to are pretty standard fare for all manufacturers of built environment products. You will only achieve one thing by studying them carefully; raising your blood pressure! 

The reality is that if you've reached the stage of relying on T&C's its probably already gone too far! Remember that most big companies will certainly be able to afford better lawyers than you! You'd be better finding a long standing manufacturer with a good reputation who you can "trust" (and thats not a legally binding term) to support the customer. 

The only real option for you if you want to have real visibility of materials and quality is to find an artisan maker who you can go and touch and feel. But be prepared to pay for it! 

As for BS standards, trade bodies and groups. Well just remember who funds them! 

Sorry thats all a bit dark but after 16 years linked to the building products industry you learn a huge dose a realism. 

and........look on the bright side. You could be specifying uPVC windows and thats FAR more murky in terms of quality/service/repair.

[beenthere]

Ta guys. We've looked at Rationel Dave, and at others in a similar space. Having somebody fit supply only windows is possible, but supply and fit is more the norm in this market for replacements. Unlike possibly in the UK where the opposite (?) may be the case. It's possibly that way because finding a trained and capable installer of scandinavian windows (bearing in mind that with timber windows correct installation is a huge factor in determining longevity) who will reliably work to supplier specs is likely to be a bit of a crap shoot here.

Price isn't so much the issue for us either (there's competitive quotes about) - it's more that at 60 years of age we don't want to find ourselves with rotting windows in 20 years. Agree 100% that trust/reliability of the supplier and product is the point Barney - the aim is to get it done right first time as diving for the paperwork is indeed futile. It's a given that the fine print is going to be one sided, and there's probably even reasons why it needs to be so. e.g. people playing silly buggers over a final stage payment.

With that in mind the core issue my original post tried to prompt some discussion on is that most of the mainstream 'scandinavian' suppliers seem recently to have deserted the double vacuum impreganted pine heartwood route in favour of flow coatings (reputedly much less penetrating) and witches brews mixing heart and other cuts of wood. One fine print I have commits only to using 'scandinavian softwood' - which theoretically could be any old mush.

These presumably cost reduction driven moves may well be fine, but it's tough to establish what is likely to be delivered in practice by way of durability of the resulting timber. If nothing else it's very new, so historical data won't mean much. 80 years per brochure claims (the fine print anyway excludes brochure claims from forming a part of any contract) is a big ask.

BS EN 8417 (good data or not - it claims to be based primarily on test data and experience) reportedly says that exterior window joinery (use/hazard class 3) for a 60 year service life requires at minimum timber classified as durable (class 2) in BS EN 350-1. e.g. http://www.timberinconstruction.co.uk/features/different-class

The trouble with this is that the various pines (even top quality slow growth heartwood) seem to range from class 4 (slightly durable) to class 3 (moderately durable) - so highly effective impreganation or at least preservative application processes seems to be essential to get whatever is being used now up to class 2 and the claimed 60 never mind 80 years service life.

The Danish makers as above claim compliance with DVC (Danish Window Control) standards, but I can't find a way to cross reference them to the BS/EN wood durability classes which at least are European/international.

I mentioned Nordan because they are an option, and seem still to use the proven double vacuum impregnated pine heartwood - wondering if anybody has hands on experience with them?

 

Edited July 22, 2016 by beenthere
typo

[beenthere]

To reduce the topic to specifics.

 

Some of the Scandinavian window makers seem to have backed away from the traditional double vacuum impregnation of slow growth pine heartwood to e.g. use of some heartwood on external surfaces (potentially a tiny amount overall), and flow coating/surface application of preservatives. Which may deliver durable timber, but could amount to an increased dependence on the paint film remaining intact, and a reduction of water resistence/stability and an increased tendency to stain and rot. i.e. be mostly be about cost reduction.

 

Judging by the restrictive fine print and warranty conditions they're certainly not betting the farm on timber from the new (and presumably unproven) processes being bulletproof.

 

Nordan for example still seem to use the more traditional approach.

 

I'm wondering does this (and the possibility that it delivers more durable timber) account for the latter company's success in Scotland, or whether anybody has any standards, industry or real world based views on how the two processes compare?

 

 

Edited July 25, 2016 by beenthere
clarification

[Monty Gerhardy]

For a comparison of the processes I’d refer you back to BS 8417: 2011+A1:2014 and the footnotes to Table 4 “Preservative recommendations as given in Table 4 are based on penetrating processes (see 6.5.3) for which laboratory and, where appropriate, field tests and service experience provide a high degree of confidence in performance.....Developments in treatment techniques using superficial processes….. might justify the use of such processes” (my italics). Hardly a ringing endorsement for superficial processes such as flow-coating.

 

Further, observations by Joran Jerner of SP Technical Research Institute of Sweden can be found here http://www.svanemerket.no/PageFiles/9770/Background%20_windows_consultation_proposal.pdf… but for a taster he states “ It is naive to think that a high share of heartwood can compensate for permeation.”

 

Regarding desired service life data. You second post referenced BS 8417 in relation to a 60 year service life – “requires at minimum timber classified as durable (class 2)”. This is taken from table 3 and is for untreated timber. Table 4. for timber treated using preservatives in accordance with BS EN 599-1, asserts that permeable wood (softwood& heartwood are indistinguishable) with penetration to class NP3 (6mm lateral, x10 longitudinal) will provide for a 60 desired service life. In other words slightly/moderately durable timber such as Pinus sylvestris is good for 60 years with the appropriate treatment. Without that level of preservative penetration then 15 and 30 year maximum service lives are suggested depending on the treatment. “30 years before maintenance” sounds ridiculously optimistic. Any window or door should be inspected at least annually - and more frequently in exposed environments. At a minimum hinges will need to be lubricated.

 

DVC standards are designed for the Danish market …and Danish conditions. BS Codes of Practice (such as BS 8417 Preservation of wood. Code of practice) have been developed with the specific requirements and experience of the British market and the climate/geography of the British Isles in mind. It’s a similar situation with security testing of windows and doors – the UK maintains a requirement for additional forced entry testing - PAS24 - in addition to the EN 1627 standard to accommodate the techniques typically used by UK burglars. The move towards superficial preservative treatment processes (such as flow coating) has been driven primarily as a cost-cutting exercise (and to a lesser degree by workplace elf n’safety factors). It is a lot quicker (cheaper) to make windows if you eliminate the vacuum impregnation process. With the minimal preservative penetration (≤1mm) achieved by flow-coating the durability and continuing integrity of the surface finish is extremely important.  In such circumstances even the sanding of the frame can reduce the preservative depth.  As Rationel make very clear in their O&M manual ( http://www.rationel.co.uk/media/1620007/om-manual_2014_sept14_web.pdf ),  “Any cracks in the paintwork or timber, will allow moisture to penetrate into the product and over time cause decomposition of the timber” (my italics).  

 

I’d treat the Wood Window Alliance claims with a degree of caution. The kernal of their durability claims are based on academic studies conducted on vacuum impregnated windows of a specific design.  They have ‘carried over’ the results from these studies  – as you have noticed – to any generic window that their (paying) membership produce that complies with some basic guidelines.  Those guidelines do not have a requirement for vacuum impregnation. The excellent TRADA book Wood windows: Designing for high performance (Patrick Hislop) notes that there are numerous designs of timber windows never mind the range of constructions that are described as ‘composite’.

 

In the real world the preservative treatment is essentially a safety net. A well designed & constructed window, correctly installed with interface details suitable for its environment should shed the water that will facilitate rotting and have a service life of 60-70 years if not longer. The presence of Pine heartwood is certainly no guarantee against rot – remember at best it is only ‘moderately’ durable.  Furthermore, heartwood is difficult to penetrate with preservative treatments. Nordan make good windows (SW Norway actually gets more rain there then we do in here in Ireland, never mind the sepearte arctic climate further north) hence their popularity with our Caledonian cousins. UK manufacturers are moving towards flow-coating on cost grounds. Penetrating processes would still be common amongst Norwegian and Swedish window manufacturers – the rest of continental Europe is flow-coat or dipping. Preservative treatment is just one factor in assessing the quality of a timber window but I would suggest that for anybody considering installing timber windows in areas of severe, or very severe, exposure it would be imprudent not to use a vacuum impregnation preservative.

Good luck with whatver you choose. It will look a lot better then plastic and should last a lot longer if looked after.

Edited August 5, 2016 by Monty Gerhardy