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Glossary of Terms

Below is a glossary of terms

Term Definition
U-value [W/m²K] This is the steady state heat flow through the element per unit degree of temperature difference between the internal and external environmental temperatures per unit area. Note that this quantity may differ from other U-values quoted as it does not take account of thermal bridging and is sensitive to the values of surface thermal resistances used.

A measure of the resistance of building materials and structures to the flow of heat or the thermal resistance of a material; the higher the R-value the better the substance is as thermal insulation.

Thermal Conductivity

Thermal conductivity is a measure of the rate at which heat passes through a material. The units are watts per unit thickness per degree temperature difference across that unit thickness.


Originally defined as the quantity of heat needed to raise the temperature of 1 pound avoirdupois of air-free water 1°F under a constant pressure of 1 atmosphere starting at the temperature at which water is most dense, 39.1°F. This is about the amount of energy released when the tip of a kitchen match burns.                                                              Mean Btu.     =       1055.87 joules

Compressive Strength

Compressive strength measures the pushing force that one needs to break a material. When the limit of compressive strength is reached, materials are crushed.   Concrete Blocks are manufactured in various compressive strength depending on application.

Load Bearing Wall

This is a wall that bears some of the building’s weight in addition to its own weight.

Non-Load Bearing Wall

This is a wall that does not support any gravity loads from the building, hence doesn’t bear any weight besides it’s own.



Llay Rd, Llay,
LL12 0TL

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