The Building Conservation Directory 2020

BUILDING CONTRACTORS 2 49 C AT H E D R A L C O MM U N I C AT I O N S T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 2 0 tops of horizontal timbers are also sometimes protected by lead flashings which are turned up behind the render coat. Where the panels have been rendered the vertical timbers often have a rebate cut into the reverse face, when the render was applied this was forced into the rebate thus concealing any edge shrinkage and minimising the risk of water penetration. There are variations but in general the principal rafters, tie beams, corner posts and sill beams have similar dimensions to the earlier timber frames although the depth of these timbers is normally restricted to between 100 and 150mm. The remaining posts and rails are typically around 50mm deep, and from 125 to 200mm wide. In some cases the interstices created by the frame are filled with an arrangement of vertical studs covered with timber laths or expanded metal lathing, this is then rendered over. Behind this there may be a solid brick wall or a secondary stud wall that is set back from the timber frame to produce an effective cavity. In many cases the frame is enclosed in a solid striking elements of the earlier frames and multiple jetties are quite common, particularly in urban settings. It is also common to find that the ground floor is constructed from solid masonry, while the upper storeys are fully or part timber framing. Understanding the method of construction is vital when trying to anticipate how the building might perform when defects develop, and when designing repairs and alterations. Original construction drawings may sometimes be available, but a detailed physical inspection should always be undertaken as there can be considerable variation in the construction methods. MATERIALS The palette of materials available to the builders of post medieval timber frame walls was restricted to what was locally available: essentially this was timber, earth daubs and lime plasters. By the end of the 19th century advances in building technology and the introduction of new building materials meant that the new generation of timber frame buildings included a much wider and more sophisticated range of materials. Structural frame members (often limited to principal rafters, tie beams, sill beams and collars) are generally oak, which tends to be used straight from the saw with little or no surface finishing. Pegs for securing the joints are also oak and sizes vary but contemporary specifications for houses built at Port Sunlight village prescribe pegs of one and one eighth inch (29mm) diameter to project one and a quarter inches (32mm) from the face of the framing. Non-structural posts and braces are generally oak but not exclusively and softwood was also used. Various species of timber plastering laths were used and from the late 19th century expanded metal lath was used, especially in the formation of covings. Ferrous metal fixings are common and these tend to be ungalvanised iron or steel. Infill panels are commonly rendered. Depending on the type of construction this may be applied over either solid brick or lathing. The type of render varies but ordinary Portland cement (OPC) was used extensively, sometimes in the form of a hydrated lime putty mortar gauged with OPC. Rendered panels are sometimes pargetted, the quality and complexity varies enormously from simple incised patterns, to allegorical figures or semi erotic scenes executed in high relief, both styles were completed using lime- and cement-based renders. Where solid materials have been used to fill the panels, brick is the most common, but several other materials have also been recorded. These include brick veneers and hollow terracotta blocks as well as ‘Terrawode’ blocks produced by Jabez Thompson and Sons Ltd of Northwich, Cheshire. CONSTRUCTION The precise method of construction varies from one building to another. Although architects and builders are likely to have shared their ideas and superficially many of these buildings may appear very similar, anomalies in the construction are to be expected. The following is an outline of the type of construction that is likely to be encountered in buildings constructed during the late 19th and early 20th centuries. A familiarity with 16th and 17th century timber frame buildings is certainly helpful when looking at late Victorian and Edwardian half-timber buildings, but there are a number of significant differences that set most of these buildings apart from their predecessors. The fundamental difference between the earlier timber frames and the timber frame revival buildings is the thickness and composition of the load bearing walls. Typically the walls of 16th and 17th century timber frame buildings rarely exceed 150mm, whereas timber frame revival buildings typically have an external wall thickness not less than 225mm (nine inches – the length of a standard brick) and sometimes considerably more. As a consequence, many but not all of these buildings have partially composite load bearing walls built from a variety of materials. Although some of these later buildings were designed and built using the earlier techniques, cost considerations and the requirement to maintain a minimum wall thickness of 225mm in order to prevent water penetration meant that in most cases the timber frame does not extend through the full thickness of the wall. There are exceptions and in some cases full thickness framing has been used throughout the building, or may occur in certain parts of a building, although this is normally concealed by plaster. Problems of water penetration around the panels of the earlier timber frames was clearly considered by the Victorian architects who were normally careful to include drips on the underside of any projecting beams to prevent water running down the face of the wall. The A late 19th century jettied upper storey which had deteriorated due to inadequate design and timber decay The dismantled timber frame showing new longer jetty joists bolted to existing floor

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