HWL’s non-glass bonded R9 window passed PAS24 last month. Graham Howatson, our Sales Director, argues that Part Q approval makes the case for R9 frame-only supply, compelling.


HWL Trade Frames’ decision to supply R9 in a non-glass bonded form, has ‘rocked-the-boat’. R9 was and is, a still largely glass bonded system. The IGU in this case delivering additional structural integrity and security in an otherwise mechanically jointed product.

Where HWL has delivered a step-change, is in its decision to offer sashes unglaze ( in addition to glass bonded options).

The reason that it can do this is Timberweld®. This allows HWL to replicate the aesthetic delivered in a 90° mechanical joint in a welded sash, delivering a significant increase instructural strength, which HWL argues means the glass bonding of the sash is no longer a requirement in most configurations.

“We have and continue to manufacture R9 as a glass-bonded system”, says Graham Howatson, Sales Director, HWL Trade Frames. “The reason that we do that is where customers specifically want a glass bonded window or where the specification requires it, we need an offer.

“If, however, you give an installer the option on the supply of a glass-bonded or unglazed frame, they always choose unglazed because of the wealth of advantages that it delivers. And we can give them that option because of Timberweld®”,Howatson continues.

This follows six-figure investment by HWL in new Urban machining and cutting centres and welders last year. “It’s not just the pay-out on machinery but the investment we have made in its optimisation and our process, which has allowed to bring a very competitive offer to market”, he adds.

HWL’s unglazed R9 window is the product of an 18-month long R&D programmed delivered in partnership with the Residence Collection

The arguments for buying-in R9 ‘unglazed’ are the same as for any other PVC-U system. You aren’t joined-at-the-hip to your fabricator and can buy glass locally – and in most cases at lower cost.

Handling is also that much simpler. R9 is a heavy-weight system in more ways than one, so taking out weight through frame-only supply makes installation easier, while fixing points are more easily accessed, also making it quicker and lower cost to fit.

The third reason, according to HWL is repair. “If you’re installing R9 glass-bonded and there’s damage to the glass in installation or there’s an imperfection, you need to take the whole sash out”, says Howatson.

He continues: “Theoretically you can cut out the unit but in our experience and that of our customers, it’s an absolute nightmare.

“If it’s damaged later down the line, you can be looking at whole window replacement because sashes will have weathered and replacement with a new sash against an older frame often stands out to the point that you have no choice but to replace it.

“There are efficiencies and savings in installation but also a very strong message to the consumer. If I had the option on a glass-bonded window or a window which is glazed in the same way as everything else on the market, I know what I’d choose.”

If the case for ‘R9 unglazed’ is compelling, what are the arguments against it? Well, as Howatson acknowledges, R9 unglazed won’t necessarily be right for every installation, although he reiterates that it will be ‘for most’.

So is through-life performance compromised? “We offer the industry standard 10-year guarantee on the all of frames that we supply, regardless of whether they’re supplied glass-bonded or Timberwelded. We don’t draw a distinction”, says Howatson.

HWL has also gone to lengths to establish and evidence product performance independently, through a rigorous test programme. The first results coming in in with BS6375 – 1 Weather Testing, delivered in March this year and in partnership with the Residence Collection.

These returned a series of top passes with an Exposure Category rating of 1600, a 9A Class rating on water-tightness, a Class 4 wind load rating and Class 3 air-tightness rating.

Buying-in R9 unglazed can cut installation costs by as much as a third.

Perhaps more significantly, however, HWL has now followed that with PAS24 and Part Q approval. Put through its paces under PAS24 at the beginning of May by independent testing house, Exova,  testing returned a series of clear passes under PAS24 test requirements for mechanical load and manual intervention testing.

This is in addition to the regular weld tests that HWL conducts as part of its manufacturing process. This reveals that the Timberweld unglazed R9 head weld consistently stands up to up to 11 bars or 1100kN/m2of pressure. This is consistent with a standard inline welded product which ranges from 9-12 bars (900kN/m2 – 1200kN/m2).

“What’s really good is that at its most fundamental level, PAS24 is about strength testing”, says Howatson. “We knew that we had a very strong window. We’d put it through load testing as part of development and we test weld strength as part of our in-house quality checks.

“Nonetheless, it’s always reassuring to see that confirmed independently. And the same goes for our customers. It’s not just us saying it, independent tests have proved the performance of the product, the Timberweld manufacturing process and ultimately the supply of R9 unglazed.”

PAS24 features a series of three-minute manual assaults on all fixed locking points, hinges, glass and beading. Mechanical load tests replicate the bi-directional loading that you would get if someone was using a pry-bar to force the sash or hinges.

Howatson explains: “You’re essentially trying to force the window. The unglazed product stoodup to absolutely everything that was thrown at it, which is an indication of the inherent strength that we can achieve through Timberweld.

 “This for me is a key point. Timberweld has been around for a few years now and it’s a proven manufacturing process across multiple systems. What you get with R9 is slightly thicker profile and internal walls, so it’s ideally suited to Timberweld manufacture.”

“It wasn’t a technology available to us when we first started  manufacturing R9, which is why we – in  common with other fabricators – glass bonded.

“Now – and in common with other systems – R9 can now be supplied and fitted unglazed. The test results are there, as is the commercial return and competitive advantage buying in R9 on a frame-only basis is delivering to our customers.”

For more information email sales@hwlwindows.co.uk, call 0113 2449006