What’s the cost of swapping for cheap?

Mark Hickox
Mark Hickox

Thinking of swapping out IGU components for cheaper alternatives? Thermoseal Group’s sales director, Mark Hickox, warns that the numbers need to add up before you do, otherwise it could cost you dearly.

One customer recently told me they had been offered a cheaper product, which they were considering.

They said that as long as it looks like Thermobar/Thermoflex, that their customers can’t spot the difference, and that they will save money, then it would be difficult to refuse.

Swapping out products, or components of products, happens all the time in the construction industry, and there is nothing wrong with it, if the customer is not left in a worse position than before the change.

In the case of the glass and glazing industry, the focus tends to be on the energy efficiency of the final window. So, I pointed out to my customer that his customer – the window fabricator or installer – would have calculated the U-value or Window Energy Rating (WER) for the windows they supply.

This is usually by way of a simulation using the verified performance figures of each component part. And if the thermal performance figures for the new spacer bar are worse than the Thermobar or Thermoflex it replaced, then the overall window may no long meet the thermal requirements expected of it.

In a worst-case scenario, the customer is not informed of the component swap, and only finds out when the company issuing the rating certificate visits a property to check the compliance of the installation.

Only then do they find that the IG had used an unknown worse-performing spacer bar. At best, this would require free-of-charge replacements. But, given the shift to tighter building regulation restrictions, we could see claims of mis-selling like we have seen in the automotive industry or finance sector. ‘Are installed windows what they claim to be?’ It’s a chilling prospect.

But, if my customer can prove that the thermal conductivity of the new spacer bar is equal or better than the Thermobar or Thermoflex it replaced, then there is no foul.

But what does that proof look like?

In recent years, it was agreed in Europe that a test method proven by IFT Rosenheim would be the only type used, so that all types of warm edge spacer can be compared fairly.

These test reports show indicative values in certain ‘standard’ frame types, plus the sealant type value and warm edge value used to calculate the window value. The combined sealant and spacer bar value is referred to as the ‘two-box method’ value for comparison.

Therefore, both the window manufacturer and IG manufacturer need to see a copy of the original IFT conductivity report, and confirm the sealant does not perform worse than the one used in the calculations (HM 0.24W/mK, Ps/Pu/Silicone 0.40W/mK).

Most calculations default to the value used for two-part sealants, and hot melt value is only used if specified.

BFRC will validate all IFT reports before allowing any figures to be used in registered BFRC window performance documents.

The component supplier and IG producer should confirm to the window installer that the claimed ‘interchangeable spacer bars’ have the same dimensions. The highest performing spacer tubes are all 6.5mm high x air space width, which is the same as traditional aluminium systems. Most metal hybrid spacers or poorer performing plastic tubes are 7mm high. These cannot be substituted into WER or U-value calculations without re-simulating if the original spacer used has a 6.5mm height.

If it’s a Thermoflex foam rubber or thermoplastic rubber product, then the same conditions apply and the claimed conductivity value must be compared. The most common size used in the UK is 4.8mm thick x airspace for flexible foam. Thermoflex has a value of 0.125W/(mK), so it can be substituted into any WER/U-value calculation for any other foam rubber spacer system, but it’s not possible to substitute the others into a Thermoflex simulation without re-calculation.

This can make a big difference when comparing a window with and without laminated glass. Substituting Thermoflex for an alternative could see a window with a laminated unit drop from an A to a B, which if not identified at the outset, could lead to false claims.

It is possible to interchange warm edge tubes, flexible foam and thermoplastic spacers by comparing the total dimension of spacer and sealant combined, calculating the conductivity value for each ‘box’ arriving at a two-box value for comparison.

If the new Future Homes Standard requires specific values for each window, which will be recorded on the customer’s paperwork, it will be classed as a declaration of performance. As a result, window companies and IG producers could be asked to prove how they arrived at those figures, and if they used the components specified.

Thermoseal Group Limited
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