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Published on 24 February 2016 13:48

NLU - U-value Calculations and Condensation Risk

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Key Learning outcomes
  • The importance of understanding the characteristics of different insulations.
  • Why thermal comfort should be the priority.
  • Thermal conductivity, thermal resistance, and how they relate.
  • How U-values are calculated.
  • The importance of U-values being calculated competently.
  • Why condensation occurs and the importance of ventilation.

Research into the performance gap has highlighted that improving knowledge is a key part of tackling why ‘as built’ performance does not match ‘as designed’. And when it comes to insulation, U-value calculations and condensation risk, there can be many misconceptions.

You might think an insulation manufacturer talking about thermal performance is going to be nothing but hot air; an excuse to say, ‘look how good our products are’. Well, we’re happy to admit that this CPD is hot air – but not for the reasons you might think.

Specifically, it’s hot air that everyone pays for: from the fuel into properties, to the boiler burning the fuel, to the building fabric keeping the hot air inside. Insulation manufacturers can’t do much about fuel prices and boiler efficiency, but their products have the biggest role to play in achieving better performance from building fabric.

This article aims to raise levels of confidence and understanding. Demystifying issues around building fabric is important for everybody, whatever their role, because the principles are fundamental. By understanding how insulation works and what factors affect the calculation of U-values, we can make a step forward in seeing buildings perform in reality as they do on paper.

1.0 What we insulate with, and why

There are MANY insulation types, some more commonly used than others, including:

- Polyurethane (PUR), polyisocyanurate (PIR) and phenolic foams
- Bio-sourced (woodwool, cork, straw etc.)
- Cellulose
- Foamed glass
- Mineral wool
- Multi-foils
- Vacuum Insulated Panels (VIPs)

The main reason for specifying insulation is to resist the transfer of heat, and this article concentrates on thermal performance. However, it should be remembered that there are constructions/applications where it is inappropriate to directly swap one material for another. Different insulations offer different performance characteristics – acoustics, compressive strength, moisture tolerance, for example – all of which should be kept in mind when specifying and using them.

At the same time, it can be possible to create solutions using a combination of products to utilise the best characteristics of each.

Why do we insulate?
Because of targets set in Building Regulations, people often ask, “What’s the minimum I can get away with?” when considering insulation. While there are legitimate reasons for asking, it’s interesting to wonder whether homes and buildings would go uninsulated if that option was available. If people only see insulation as red tape, it is hard to communicate the benefit of using it.

And there are genuine benefits. Insulation products can directly tackle two-thirds of the heat that would be lost from an uninsulated home. Thermal insulation, correctly installed, reduces heating demand and means the boiler doesn’t have to fire as often.

Because the boiler burns less fuel, insulation is helping to reduce the carbon footprint of the individual building. Despite government scrapping various ‘green’ initiatives throughout 2015, the UK still has a legal obligation to reduce total carbon emissions by 80% by 2050. On a personal level, nobody is probably that invested in helping the government achieve their targets. But if reducing heating bills isn’t enough motivation, what will spur people on?

Comfort, not legislation
Why do we turn up the heating in winter? Or open a window in summer when rooms get hot? Because we like to feel comfortable.

If new buildings are built well, or existing buildings are refurbished carefully and thoughtfully, that kind of comfort can be a permanent feature. Imagine not having annoying draughts that make the back of the neck feel cold. Imagine having rooms that don’t overheat and become stifling in summer. Insulation has a huge role to play in achieving that, and comfort should be the message.
Comfort doesn't have to be at the turn of a thermostat, but in many properties - including the very newest houses from the nation's biggest housebuilders - that is unfortunately the norm.
Comfort doesn't have to be at the turn of a thermostat, but in many properties - including the very newest houses from the nation's biggest housebuilders - that is unfortunately the norm.
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