Specification performance variables with secondary glazing
Performance requirements are an intrinsic part of any building works. And where there is a specification there will also be a verification process to show where it is met or falls short. Some requirements, however, are easier to meet than others. Consider the following three cases.
Case 1
If there is a requirement to supply a 7kw heater then it is easy to verify conformance as the requirement is entirely within a single component. The heater would be an off the shelf product with a defined rating, so it could be categorically confirmed that the requirements are met.
Case 2
If say the requirement was to heat a room to 20 degrees Celsius, then this would be more difficult to verify conformance but, still possible. For this, an assessment would have to be made of the heat loss of the building fabric. Once known an engineer could calculate the energy required to maintain the temperature, a margin of error could be applied, and a suitable heater could be used with thermostatic controls to maintain the temperature. So long as the heat source can always provide more energy than is lost then the performance can be met.
Case 3
But what if the requirement for the room was at the limit of any available heating method. Then verification becomes less clear. Assessments can still be made but there can be no certainty that the requirements can be met as they could be adversely impacted by any the variables which exist within. This is exactly what happens time and time again with secondary glazing.
Performance and secondary glazing
The two most common reasons for specifying secondary glazing are for noise and thermal insulation.
Often the requirement is for the performance to be the best possible. But the requirement for “best possible” is subjective, it could be the best product on offer, it could be the best within a budget, or it could be the best within the laws of physics. With no specific requirement, the purchaser is entirely in the hands of the supplier.
But what if the requirement is specific and set at the limit of typical performance, as is regularly seen with noise reduction and heat loss. Then compliance becomes far more difficult and maybe even impossible to verify. Unlike the 20 degree room you cannot apply a margin of error and over specify equipment which is already at the limit of its performance.
The impact of variables
The impact of the variables for any secondary glazing treatment is significant. For both noise and thermal insulation, the overall benefit is drawn from the combination of the primary and secondary window.
It would be difficult enough to assess the secondary alone given all the different sizes, configurations and glass options, there are so many variations it would not be possible to have tested or assessed them all.
Then there is the primary window size and make up; are they timber, steel, stone or leaded light? And the operational performance; are they leaky and drafty? It is rare that the primary performance is known so some form of assessments needs to be made but realistically these can only be very generalized.
Timber framed windows, stone reveals, metal framed windows
There is also the relationship between the primary window and the secondary window, what is the cavity or air space and what is the reveal construction and material.
With so much to consider, verifying conformance to a specific requirement is not always possible. The application of known data will only ever be as good as the ability of those applying it. It is possible to spend a lot of money carrying out assessments of performance to a specification, which in truth can never be verified, only to end up with the “best possible”. Sometimes you need to put yourself in the hands on someone you trust, work closely with them and take their best advice. And on a final note, never underestimate the power of an installed sample.
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Timber framed windows, stone reveals, metal framed windows
There is also the relationship between the primary window and the secondary window, what is the cavity or air space and what is the reveal construction and material.
With so much to consider, verifying conformance to a specific requirement is not always possible. The application of known data will only ever be as good as the ability of those applying it. It is possible to spend a lot of money carrying out assessments of performance to a specification, which in truth can never be verified, only to end up with the “best possible”. Sometimes you need to put yourself in the hands on someone you trust, work closely with them and take their best advice. And on a final note, never underestimate the power of an installed sample.