'U' Value definition?
A 'U' value is the measure of heat flowing through a structure W/sqm.K
Examples of materials used in a house built in 1920;
Single glazing = 5.6 Solid 9” thick wall 2.0
The Heat Loss through 10sqm of a 9” wall assuming
inside temperature of 21C and outside of 1C
= Area X Uvalue X Temperature diff = 10 X 2 X 20= 400W
Compare this with a better insulated wall.
Each material has a resistance to heat flow and the overall U value = 1divided by the sum of resistances
Watch our Uvalue calculation video
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Calculation of resistances for an insulated wall
| Item | Thickness (m) | Thermal Conductivity (W/mK) | Thermal Resistance (m2.k/w) |
| Iside surface e.g. wall paper / paint | - | - | 0.12 |
| Plaster | 0.015 | 0.170 | 0.09 |
| Block | 0.100 | 0.230 | 0.43 |
| Insulation | 0.050 | 0.035 | 1.43 |
| Brick | 0.100 | 0.860 | 0.12 |
| Outside surface | - | - | 0.06 |
| Total | - | - | 2.25 |
U Value = 1/2.25 = 0.44 W/m2K
Heat loss for 10sqm of wall = 10 x 0.44 x 20 = 88w
i.e. An insulated wall is 5 times more efficient as a 9 inch wall (Buy insulation products)
NB: Thermal conductivity factors can be obtained from the product manufacturers
To test a U Value, watch our video on testing a U value