Woodwork Carpentry - First Fixings

The rationale behind the layout and structure of the rules of measurement in SMM7 has done away with the work section/trade headings which have been so familiar in the past. The versatility of wood and wood products and of the carpenters and joiners themselves now means that the rules of measurement for their work are well scattered through the new document. However, in this and the following chapter a selection of items and rates for these traditional trade divisions is presented in an order similar to that of SMM7. 

Special requirements 

In dealing with any woodworking items the estimator will be on the lookout for the fol-lowing information, which will denote something additional or unusual and therefore possibly expensive! 

Species of timber 

Hardwoods are generally more expensive than softwoods, and in either classification there is a wide range of cost due to what might appear to be a diversity of factors. These, however, generally all boil down to scarcity of a suitable supply of timber. It is also true to say that timbers are more expensive when required in larger cross-sections and/or long continuous lengths. These latter factors can be overcome using machine jointing and modem synthetic glues; the joint is often stronger than the raw timber but the jointing process does add to the cost. However, if timbers in excess of 5.4m long are required this will add around 12.5 per cent to the basic cost of timber. In excess of 7.5m long an addition of 25 per cent or more would be quite likely. 

Asphalt work

Introduction 

It is perhaps unfair to refer to any particular trade as special, for every operative in the industry demonstrates skills which are unique to the craft he follows. However, asphalt work is generally referred to as a specialist trade because it encompasses some unique features and is practiced by a relatively small number of craftsmen employed by a relatively small number of companies. To further emphasize this specialism, contracts for this type of work are normally let as a subcontract and most commonly to a nominated subcontractor. 

The most unique aspect of the trade is the material used. Unlike every other trade, the material, mastic asphalt, is handled by the operatives while it is hot, generally between 200 and 220 °C. Pitch mastic is laid at the lower temperature of 160 °C. 

This has two consequences. The first is that the work is dangerous; protective clothing is essential and safety procedures must be adhered to. 

The second is that a relatively rapid pace is needed in the application of the material, as it sets by cooling to ambient temperature. As soon as the material is drawn from the cauldron or mixer it starts to cool. When it is applied to a surface the rate of cooling accelerates for two reasons. First, the base surface is at ambient temperature and a base of masonry presents an enormous heat sink. Second, as the material is spread out,' more of it comes into contact with this cold base and with the cool air over it. 

Perhaps as a consequence of the specialist nature of the work there seems to be no well-defined procedure used by estimators for building up rates for measured items of work. Therefore the data and examples which follow are given only as a guide to one possible approach to achieve comprehensive financial cover for all expenditure. 

Before commencing examples it is proper to consider the logistics and practice in the trade. 

Roof coverings part 03 - Lead sheet coverings and flashing

Lead sheet coverings and flashings 

Milled lead sheet is manufactured to BS 1178:1969 'Milled lead sheet and strip for building purposes'. A range of six sizes of lead sheet, defined by thickness in millimetres, is provided for in this Standard (see Table 9.5). A colour coding system is used to enable easy identification of thicknesses. 

Lead sheet is supplied by the manufacturer cut to the dimensions required, or in large sheets, the largest sheet size being 2.4 m wide by up to 12 m long. Lead strip is defined as cut to widths from 75 to 600 mm. 

Lead strip is supplied in coils and is the most common form of lead sheet used, being convenient for flashing and weathering applications. 

Fixing accessories for external leadwork 

The following accessories are normally associated with the fixing of lead sheet in the traditional manner.

Copper clips 

Copper clips should be cut from copper sheet not less than 0.6 mm thick and conform to BS 2870.

Nails 

Nails should be copper clout nails with jagged shanks conforming to BS 1202 Part 2, Table 2. They should not be less than 25 mm long or 10 SWG shank diameter. 

Screws 

Screws should be of brass or stainless steel to BS 1210. They should be not less than 25 mm long or 10 SWG. 

Roof coverings Part 02 - Tile roofing

Tile roofing

Roof tiles are manufactured from clay and concrete to a wide range of colours and profiles suitable for pitches from 17 to 45 degrees. Greater pitches up to vertical cladding are achievable but require additional or special fixing. Roof tiles are generally sold by the thousand in crates or strap banded to be stored on site pallets.

Clay plain roof tiles

British Standard BS 402 provides for tiles of nominal or work size 265 x 165 mm. Table 1 of the Standard gives maximum and minimum deviations for manufacturing size. Also detailed are requirements for tile manufacture, colour, nibs, thickness etc. Where tiles 280 x 175 mm are required fora project, but otherwise comply with BS 402, then such a requirement should be stated when ordering. BS 402 recognizes that plain tiles of different specification are manufactured, and although the Standard is not intended to provide for such tiles it does not rule out their use. 

Plain tiles are laid using the double lap principle; this ensures that there will be at least two thicknesses of tile covering any part of the roof.I 

Roof Coverings

Slate roofing The main sources for roofing slates in Britain are Cumbria, Cornwall and North Lancashire in England, and Bangor, Portmadoc and Caernarvon in Wales. There are no longer large scale quarries in Scotland; therefore the main source of Scottish slates is from demolition for use second hand. On the British market there are also roofing slates from European countries such as Spain and Portugal. Roofing slates are said by the tonne or by the thousand depending upon the source. 

British Standard BS680 Part 1:1944 (imperial) and Part 2:1971 (metric) details geological formations of true slate rock from which roofing slates can be quarried, together with characteristics, grade tests and sizes. The labour outputs given here are for standard site slates in accordance with BS 680 Part 2 Table 1 'Standard lengths and widths of slates'. Sizes of randoms and peggies can be obtained from Table 2 'Range of lengths for randoms and peggies'. The labour outputs in Table 9.1 are based on a squad of two slaters and one labourer, and allow for carrying and fixing in position. Unloading, holing and dressing of slates are highlighted as required in the examples, which follow.

Underpinning

Introduction 

Underpinning is the transference of the load of a building to a lower stratum of the ground. This is done for several reasons: 

• To permit the construction of a new basement within or adjacent to the existing foundations which are above the level of the new basement.
• To provide a new foundation at a lower level than the existing, where the existing has failed due to, for example, shrinking clay or subsidence.
• To increase the load bearing capacity of the existing foundation.
• In extreme cases, to allow the whole building to be mechanically moved by installing a ground beam.

There are a number of ways to carry out the underpinning operation; the choice depends upon the stability of the existing structure. Except in the most simple cases and where the structure is in good condition, the work will be carried out by a specialist contractor. This contractor will employ stabilizing techniques such as the drilling of ground anchors and/or the construction of ground beams.

For a straightforward operation on a stable structure the contractor will price the work described in the bills of quantities. The constants used will be based upon those for the ground work, in situ concrete and masonry sections. 

Brickwork and Blockwork

Introduction 

Bricks can be obtained in a number of sizes and various compositions, strengths and shapes, to mention only the more obvious factors. The appropriate British Standards give details for clay, concrete, sand-lime and other bricks. 

To give examples of rates using all of the different types of bricks would be impossible in the space allocated, as well as highly repetitive. Therefore the examples in this chapter will concentrate on a metric brick with dimensions 215 mm long, 102.5 mm wide and 65 mm thick. Whether the brick is solid, hollow or perforated, or has single or double frogs, will make no difference to us here, although in theory the different weights of bricks could affect the laying output per man and other factors.

Mortar 

If bricks have no perforations or frogs, are absolutely rectilinear, are laid on a bed of mortar 10 mm thick and have each end jointed 10 mm thick, then 1000 bricks require the following volume of mortar: 

1000[(0.215 x 0.1025 x 0.01) + (0.1025 x 0.065 x 0.01)] = 0.287 m3