The floor/ceiling influences the level of thermal isolation between a building’s storeys. Three basic categories were identified as ground floor, inter-storey and top storey ceiling/roof. For each category two sub-categories were defined as:
(i) Ground Floor - Solid/Suspended (concrete/wood) (ii) Inter Storey Ceiling/Floor - Wood boards/Concrete slab
(iii) Top Storey Ceiling - Ceiling to roof void/Roof to external environment
In each instance the thermal bridging associated with joists was ignored for simplification of construction for the DSM.
4.5.1 Ground Floor Construction
The two methods of construction (solid and suspended) were identified as possible in all of the considered building periods (1894 to present day). The building controls and regulations set minimum standards for each method. For suspended floors with exposure to external air, thermal regulations were applied in the 1965 Building Regulations. For solid flooring thermal regulation was introduced in the Part L regulations following the 1984 Building Act.
Table 4.8 summarises the dimensions associated with solid and suspended floor construction prior to thermal regulation. These are minimum values found in by-laws and regulations. Consistency in the controlling laws prior to the introduction of the 1965 Building Regulations is evident.
Table 4.8: Basic floor construction identified in regulations - without thermal regulation (1894-1990).
Control Period Type Concrete Base Thickness (m) Suspended Floor Height (m) 1894-1938
*Construction required if not thermally regulated (i.e. not exposed to external environment by more than the required amount of ventilation for moisture control).
For suspended flooring exposed to external air, table 4.9 shows the maximum expected U-value for each period, along with expected construction identified in the building regulations. In all instances the airspace is considered as an unventilated air cavity with constant thermal resistance, R, of 0.18 m2.K.W−1.
For later control periods insulation levels are related to floor area and perimeter dimensions. Tables from Part L building regulations that control the insulation levels for ground floor construction are summarised in appendix C. The data given here and in appendix C was used in the logic of the probability model to determine the floor construction.
4.5.2 Inter-storey ceiling/floor construction
The level of thermal transmittance associated with inter-storey flooring is only considered in regulations post 2001. For earlier periods a consistent construction was assumed for both timber flooring and concrete slab flooring. Thermal bridging effects were ignored with construction layers representing the ceiling of the lower storey and floor of the upper storey.
Table 4.9: Floor Construction - controlled by thermal transmittance: regulations post-1965).
Tongue & groove timber ! 0.016m Joist
Concrete Thickness ! 0.150m Density " 650
kg/m3
The required insulation is dependent on the floor perimeter to area ratio. The tables provided in Part L building regulations are summarised in Appendix 4B.
0.45 All Ground
Gypsum plasterboard was a recognised building material for all considered construction periods, see [6].
It has been applied as the initial layer for all ceiling constructions.
For later regulatory periods, inter-storey floors have a specified U-value according to Part L Building Regulations. The values of required insulation thickness to meet overall U-values are calculated by taking into account bridging effects of floor joists. In the regulations the joists are assumed to account for 12% of total floor area. As bridging effects are not accounted for in the constructions of the DSM, the insulation levels were recalculated to obtain the same U-value as stated in the regulations2 (see appendix C).
4.5.3 Top Storey Ceiling and Roof
The top storey ceiling is either connected to the external environment (as a flat roof construction) or to a roof void. No account of pitched roof with sloping ceiling was made.
Table 4B-17 in appendix C summarises the insulation levels accounted for by building regulations from 1966 onwards. Pre-1965 building regulations, the basic construction is considered with no insulation.
For pitched roofs pre-1965, only tiled roofing was considered.
4.5.4 Thermal Properties for steady-state and dynamic consideration
The harmonic response function (Admittance Method) was used to investigate the dynamic thermal response of the two basic categories of light and heavy weight floor/ceiling construction. Table 4.10 shows the results for each building control period’s modelled ground floor form3.
The calculation procedure did not include external surface resistance as the ’external’ floor surface is considered in full contact with the ground (external environment). For the suspended floors no ventilation is considered and an air cavity thermal resistance, R, of 0.18 m.K/W was applied (as the default applied in esp-r).
The data in table 4.10 shows an increased U-value from pre-Building Regulation control periods to the periods between 1966 to 1990 when comparing like-for-like ground floor construction. This results from a reduced requirement in concrete base thickness that reduces dynamic response factors and time leads/lags.
Stability in U-value and Y-value appears in the later periods between the solid (heavy weight) ground floor and suspended (light weight) floor. This is a result of layer order, where insulation layer is on the upper side of concrete floor slabs and lower side of suspended wood flooring. Though not stated in the regulations as the required order (as U-value will be the same regardless), all examples found in the regulations use this order.
For simplification in the probability model, a fixed order of construction layers for flooring and ceiling (as given in construction examples in building regulation documentation) was used. In all instances in the model only one insulation material was applied. It is recognised that this simplification does not consider the potential difference of dynamic thermal behaviour of different insulating materials or layer order. Insulation material and layer order demonstrated in examples within regulatory documentation were used4.
2This procedure was carried out for all structural components with implied thermal bridges in calculating U-value.
3Each form example resulted from study of regulatory or bylaw documentation.
Table 4.10: Ground Floor Construction - Thermal properties for minimum standards set by building
Thickness = 0.025m Thickness = 0.025m
Thickness = 0.1524m
Thickness = 0.2286m Thickness = 0.1524m
2.7 3.3 1.1 0.6 0.8 -2 -0.6 1.8 2.7 1.1 0.7 1.5 -2.5 -0.7
Thickness = 0.025m Thickness = 0.025m
Thickness = 0.1016m
Thickness= 0.2667m Thickness = 0.1016m
2.7 3.3 1.1 0.6 0.8 -2 -0.6 1.9 2.7 1.1 0.7 1.4 -1.9 -0.7
Thickness = 0.025m Thickness = 0.025m
Thickness = 0.1000m
Thickness = 0.2775m Thickness = 0.075m
0.6 2.5 0.9 0.8 3.5 -3.3 -1.2 0.6 2.5 1 0.8 3.4 -2.7 -1.2
Thickness = 0.025m Thickness = 0.025m
EPS Thickness = 0.038m EPS Thickness = 0.031m
Thickness = 0.1000m Thickness = 0.2775m
Thickness = 0.075m
0.45 2.5 0.9 0.8 3.5 -3.3 -1.2 0.45 2.5 0.9 0.9 3.7 -2.8 -1.2
Thickness = 0.025m Thickness = 0.025m
EPS Thickness = 0.049m EPS Thickness = 0.051m
Thickness = 0.1000m
Thickness = 0.2775m Thickness = 0.075m
0.25 2.6 0.9 0.9 3.9 -3.7 -1.3 0.23 2.6 0.9 0.9 3.9 -3.5 -1.3
Thickness = 0.025m Thickness = 0.025m
EPS Thickness = 0.091m EPS Thickness = 0.121m
Thickness = 0.1000m Thickness = 0.2775m
Thickness = 0.075m
Different insulation materials have different thermophysical properties. In the regulations the thickness of insulation required is dependent on the material’s conductivity, κ , and desired U-value. In a dynamic thermal process, however, the thermal storage (dictated by density, ρ , and specific heat capacity, cp ) may vary. Table 4.11 demonstrates this dynamic thermal variation (by the admittance method) due to different insulating material, whilst U-value remains constant for a suspended floor construction that adheres to current regulations (see table 4.10).
Table 4.11: Suspended hardwood floor of differing insulation material but with the same U-value.
Insulating Material (Conductivity)
U-value Admittance (Y) Decrement Factor (f)
0.23 2.81 0.43 0.81 3.32 -9.93 -1.34