manuals/databases supplied with modelling tools such as DOE-2 and ESP-r.
The thermophysical properties are determined from experiments adhering to national standards. It is noted that the data provides steady-state thermophysical properties, for example BS EN 1745 uses a square-guarded hot plate method at fixed temperature and moisture content for determining thermal conductivity. Clarke et al., [122], also reports limited data for some materials only allows for their use in steady-state heat loss and condensation assessment.
The data supplied for materials that allows for dynamic thermal assessment has been used in this investigation. Clarke et al. offers the most comprehensive data on building material thermophysical properties in [122]. The data were used to provide expected properties of materials used in structures as identified via building regulations.
Variation in material properties, resulting from evolving technology for material manufacture and varia-tion in the raw materials used for producing building materials [6], was not accounted for. Uncertainty in material values is not considered by the modelling work of this thesis.
4.2 Building Controls for Identifying Structural Component Prop-erties
Having established a source for the thermophysical properties of building materials, an account of the construction of building components was needed. As empirical surveys had used periods of construction for grouping energy performance of a building stock, a similar approach was intended in the probability simulation model. Without carrying out large scale intrusive and potentially destructive testing on existing ND buildings, control laws were considered as an alternative solution for establishing ranges in building component construction.
A review of historical building controls showed efforts were made to standardize building control in UK Parliament from 1844 onwards. Model by-laws were introduced which local authorities were to use in controlling building construction. Little adherence to these controls was recognised and the laws were regularly changed with improved understanding of building requirements. A period of stability and greater national acceptance of the model by-laws occurred under the Public Health Act 1894 and London Building Act 1894 [13].
Based on an expected instability in building control prior to 1894, the building controls were only used in consideration of buildings built after this date. In doing so the existing building stock is not fully considered by the model. From the NDBS Project’s evaluation of the Valuation Office Agencies data on building age, 75% of the ND floor space is accounted for between 1900-1994 [20]. A similar study [1]
conducted ten years later showed a similar proportion post dating 1900.
4.2.1 Building Control Periods - Pre Building Regulations 1894 - 1965
Prior to the introduction of official building regulations as an instrument of building control, by-laws and British Standards were used to regulate building construction. For wall construction, wall thickness charts were used.
Three construction control periods were identified for the model as:
(i) 1894/1915 - 1938 [13]
(ii) 1939 - 1952 [123]
(iii) 1953 - 1965 [124]
The earliest period can be used to represent load bearing structures built from 1894. Building by-law controls for reinforced concrete and steel frame structures were only established in 1915 [39]. The use of these controls (depending on treatment of framed structures pre-1915) can therefore be applied to the ND building stock as far back as 1894.
The 1936 Public Health Act resulted in revised wall thickness charts and general building by-laws used up until the (government issued) 1952 Model Byelaws - revised in 1953 [123, 124].
It is recognised that up until 1952 the central government issued by-laws were subject to change under local authority guidance [125]. Introduction of standards and Codes of Practice in [124] made it possible for other methods to be used to determine required structural composition. These techniques for deter-mining structural performance allowed introduction of new materials and building techniques, increasing diversity in building stock form.
The sources identified for determining wall structure between 1894 and 1965 can only be considered as guides. Uncertainty exists due to regional variation in adherence to the by-laws. The study of (and use of) regional building laws is an area of further research for developing the probability model.
4.2.2 Building Control Periods - Introduction of Building Regulations 1966 - 1984
The Building Regulations of 1965 (coming into force in 1966) were introduced by the Minister of
Pub-regulations introduced control of thermal performance of the basic building envelope (walls, floors and roofs).
In 1972 a new Statutory Instrument of Building Regulations were brought out. The only noticeable change is the use of metric (S.I) units, rather than imperial units. This results in minor differences from rounding up or down of the converted values.
The oil crisis of the 1970’s resulted in further tightening of building thermal efficiency regulations, that were introduced in the 1976 Building Regulations (coming into force in 1977).
Based on the minimum required standards set out in these regulations, wall structures of varying (yet common) material and construction method are given.
Three periods of control were identified for the ND building stock probability model as:
(i) 1966-1971 [126]
(ii) 1972-1976 [127]
(iii) 1977-1984 [128]
The regulations of these periods only state dwellings (i.e. not commercial buildings) needed to adhere to the thermal regulations. Other reports [113, 129], however, show commercial buildings applying thermal performance concern to building construction as a result of the 1970’s oil crisis. The regulations have therefore been applied in determining ND building structure.
4.2.3 Building Control Periods - Post 1984 Building Act (Part L Energy Regulations)
The 1984 Building Act restructured the building regulations. Part L was introduced to regulate energy performance (by structure and efficiency of building services) - titled Conservation of Fuel and Power.
This structure of regulations are still in use today.
Focusing on structural thermal efficiency requirements, the building components are regulated by mini-mum U-values . Review of Part L, showed changes to these regulations occurred in 1991, 1996, 2002 and most recently in 2006. For structural thermal regulations, there is no change to regulations for the 2002 and 2006 regulations.
Four periods of structural thermal control were identified for the model as:
(i) 1985-1990 [130, 34]
(ii) 1991-1995 [35]
(iii) 1996-2001 [36]
(iv) 2002-Present [37, 38]