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Proper Insulation in Modern Construction

A major factor in the performance of the building fabric is not simply the amount of insulation you install, but how it connects with its other components and the other insulated elements within the design.

One great Myth of modern home construction is the "U-value" measurement used for insulation. U-values have been sold to consumers for so long they have taken on "Chiselled-In-Stone" status. The saddest part of this myth is that the U-value by itself is almost a worthless number, as it is impossible to define insulation effectiveness by this number alone.

What would the U-value of insulation be after it has been submersed in water or had a 20 mile per hour wind blowing through it? Would the "Effective" U-value of fibre insulation go to zero? Uvalues are meaningless unless we know the other important factors! Take a wall construction for example: you may achieve very good U-values by adding more insulation; however the majority heat loss will not be through insulated areas, it is estimated that up to 30% will occur at wall & floor junctions, ceiling junctions, reveals, and other areas where the sections meet.

The use of U-values as the only criteria for insulation has to be questioned!! Insulations which quote low U-values when not properly sealed will allow the wind to travel through it as if there were no insulation at all.

U-values are a result testing the loss of heat through material in a sealed test fixture under controlled laboratory conditions e.g. AIRTIGHT; but these conditions are not even remotely associated with the real world of installed performance of insulation. What really matters is the "effective" U-value when insulation is subjected to these real world conditions!

Dense fibre insulation is generally assigned low U-values, yet it can only achieve these values when tested in an absolute zero air-movement and zero moisture environments.

In addition, water vapour from the atmosphere, showers, cooking, breathing, etc. constantly moves back and forth through the walls and ceilings of our homes.

If a building is not properly ventilated on a fibre insulated home, the water vapour generated inside a house will very quickly semi-saturate the insulation above the ceiling and in the walls. Even small amounts of moisture will cause a dramatic drop, as much as 50 percent or more, in fibre insulation's performance.

Correct insulation performance should be tested on:

1. Conduction (Thermal Conductivity, Thermal Resistance, Effective Conductivity etc)
2. Heat Transfer (Heat transfer coefficient for forced convection, Natural convection etc)
3. Thermal Radiation (Emissivity, reflectivity, diffusivity etc)

U Values will prove Conduction & Heat Transfer in an Airtight environment, however will not consider Heat Transfer where air convection exists or for Radiation. When choosing correct Insulation you must ensure not only good U-values but also the Air & Vapour tightness of the insulation, otherwise you are only getting part of the picture.

Sprayfoam Insulation on tar based felt roofs

The use of SEALECTION® 500 insulation against the underside of the roof sheathing in an unvented application has long been validated as an extremely beneficial method of gaining energy efficiency in the structural envelope. Our applicators have a great amount of experience in the use of the foam against various substrate materials including asphaltic felt material. This empirical data is based on nearly two decades of use without any problems including adhesion or migration of chemicals between the substrate material and the foam. Demilec approves the application of our foams against the asphaltic felt material - download the original document