Glossary of Common Terms (R – Z)
What exactly is a U-value?
The final post in our glossary series aims to supply you with a quick and easy definition of a U-value… along with R-value, Y-value and other common industry terms for that matter! (FYI – Kappa value, Lambda value and Psi value are all covered here.)
If you want to delve a little more in depth on the subject of U-values then do take a look at our other posts on the topic.
Think we’ve missed something? Let us know in the comments and we will do our best to help.
Hint: Use CTRL + F to search for a specific term!
Retrofit – The installation of insulation over pre–existing building elements or insulation.
RH – Relative Humidity is a percentage that measures the relationship between the actual moisture content of the air and the saturated moisture content of the air.
R–Value – This demonstrates thermal resistance of a material in relation to its thickness. It is measured in units of m2K/W where ‘m’ represents the thickness of the material in metres which is divided by its value.
SAP – Standard Assessment Procedure which measures the energy performance or efficiency of a domestic building. It covers the energy consumed in relation to the floor area, a fuel–cost–based efficiency rating, and CO2 emissions. The procedure follows the structure of BREDEM (BRE Domestic Energy Model).
Sarking Board – Rigid boards, such as timber planks, plywood or OSB used above rafters in a pitched roof. The use of sarking boards is most common in Scotland, where traditionally sarking boards comprised softwood sawn planks fixed to the upper face of the rafters.
SBEM – Simplified Building Energy Model assesses the energy efficiency of a non–domestic building. The software is used to measure the CO2 emissions of non–domestic buildings and whether they comply with building regulations and standards.
SIPs – Structurally Insulated Panels are a combination of insulation and structural elements such as timber facings in one board. An example is the Kingspan TEK Building System.
Soffit – The underside of an architectural component, for example an arch, beam, staircase or underneath car park decks. Insulations for this type of building element include Kingspan Kooltherm K10 FM Soffit Board and Kooltherm K10 PLUS.
Tanking Membrane – A waterproof membrane used to prevent moisture ingress further into a construction. Products of this type are often used in basement wall or floor constructions. A variety of materials ranging from membranes to liquid applied systems, with both bituminous, cementitous and synthetic plastic products all being available in the market place.
TER – Target Emission Rate, which is based on a ‘notional building’, concurrent specification, which differs based on the country in which you are building (eg England, Wales or Scotland).
TFEE – Target Fabric Energy Efficiency is an additional standard in England presented alongside the TER. Thermal bridges are channels through which heat can be lost when a material has a higher thermal conductivity than adjacent building elements. They can also be referred to as Cold bridges or Heat bridges. The three main types of thermal bridges are:
- Repeating thermal bridges which develop in a regular pattern, for example where there are timber studs in walls. U–value calculations take account of the effect of repeating thermal bridges e.g. a 15% timber bridging fraction might be taken for studs in a timber framed wall.
- Non–repeating / linear thermal bridges occur in an irregular pattern at junctions between building elements eg around windows or between walls and floors.
- Point thermal bridges are used as adjustments to the U–value of a building element. They take account of thermal bridging at fixings, fasteners and beams.
Thermal Conductivity – The measure of thermal conductivity used on materials in which heat transfer occurs through conduction, convection and radiation.
Thermal Mass – This is how well an element absorbs, stores and releases heat per metre squared (see Kappa Value).
Thermal Resistivity – As with thermal conductivity, this measures a material’s ability to resist heat transfer through conduction, convection and radiation in relation to the material’s thickness or surface emittance (see emissivity).
Thermoset – A type of insulation that sets permanently after cooling. If the insulation is reheated it will not change shape. Thermoset materials will not run, melt or drip when exposed to fire. Examples include Kingspan’s Kooltherm and Therma ranges.
U–Value – The sum of the thermal resistances of the layers that make up a building element (i.e. walls, floors, roofs etc.). It includes adjustments for any fixings, air gaps etc. This value shows in units of W/m2K the ability of an element to transmit heat from a warm space to a cold space in a building and vice versa. The lower the U–value, the better insulated the building element is. Our U-Value Calculator is a helpful tool for calculating U-values.
Ventilation – The process of “changing” or replacing air in any space to remove excess moisture or other pollutants, such as carbon dioxide or ground gases such as radon and replaced with external air (see MVHR).
Water Flow Reduction Layer – A membrane such as Kingspan Aquazone typically utilised within inverted roof constructions where it is laid above the thermal insulation to aid in minimising the cooling effect associated with rain water draining beneath thermal insulation. These products typically compose non–woven, spun–bonded polyolefin with micro–perforations which allow the escape of moisture vapour while preventing the majority of liquid water from peculating further down into the construction.
Wind Uplift / Wind Load Calculations – Wind can apply a positive or negative force onto objects depending on the construction detail, its orientation to the direction of wind, and the difference between internal and external air pressures. Wind load calculations are particularly important for systems restrained to the outside of a building, such as warm or inverted flat roofs and external wall insulation systems such as EWI render and rainscreen systems. A wind load calculation considers a number of factors, such as the location and altitude of the building plot, local topography (i.e. geographical features, valleys, hillside etc.), adjacent structures which may shelter or funnel wind towards the building, also the construction type, its height from ground, and position on the construction in relation to the prevailing wind direction.
XPS – Extruded Polystyrene has high resistance to condensation damage and has a high thermal resistance. Kingspan Styrozone is a rigid extruded polystyrene.
Y–Value – An approximation of a specific building’s heat loss via its junctions. It is calculated by dividing the HTB (overall thermal bridging coefficient) by the building’s total exposed area (see HTB).
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