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. 

Stress grading 

This is an added expense but one which may saw money in the long run by allowing the use of smaller sections of timber. Stress grading adds in excess of 7.5 per cent for GS grade timber to over 20 per cent for SS grade timber to the basic cost of timber, however, the cross-section of the timber also affects the cost on a modestly sliding scale. 

Grade of sheet material 

There are many different board and sheet materials on the market. A large number of them might be described as, say, plywood. However, there is a vast difference in price between a sheathing plywood, a Douglas Fir plywood and a hardwood veneered plywood for decorative work, or between one where the glue is graded water and boil proof (WBP) and another graded moisture resistant (MR). 

Similarly, there are many different types and grades of particle board, lamin board, blockboard and so on.  

Pre-treatment 

This covers treatment with chemicals against insect or fungal attack or for increased fire resistance. The treatment may be applied with a simple brush, in vacuum/pressure plant, etc. Note that sheet material can be pre-treated as well as natural timber. Currently pressure impregnation against fungal or insect attack with copper chrome arsenate (CCA) salts-based preservative adds around L20-£25 per cubic meter (second quarter of 2002) to the basic cost of timber. The smaller the cross-section of the timber treated, the greater the amount of preservative fluid used and so the higher the costs. 

Machined timber 

Timber may be supplied regularized or wort rather than off the saw, or may be swan to a special shape. 

It is impossible to say what percentage to add to the basic timber cost for regularizing or machine planing, since the act of machining the surface of a rectangular shape is much the same whether the cross-section is 38 x 38 mm or 100 x 100 mm. What does vary of course is the proportion of waste produced to the remaining processed timber. Fora section 38 x 38 mm (1444 mm;, fully wort surfaces will mean that the timber will end up as 32 x 32mm (1024 mm maximum. This represents a loss of 420 mm2 or 29.09 per cent. The 100 x l00 mm timber (10 000 mm2) will end up as 94 x 94 mm (8836 mm2). This represents a loss of 1164 mm2 or 11.64 per cent. If the timber is 200 x 200 mm, the loss will be 5.91 per cent. The following are typical costs of these timbers as quoted by timber suppliers in the second quarter of 2002.

Timber sizes and costs 

The raw material, whether for direct use on site or for prefabrication, may be purchased by the meter. Usually the price quoted is for 100 m of a specific cross-section. More rarely timber is purchased by the cubic meter, but generally this is by the shipload and without conversion or processing between unloading and delivery. 

Timber is supplied in a range of cross-sections. The following common names are approximately in descending order of cross-sectional area: balks, half-timbers, flitches, planks, deals, boards, strips, battens, squares, slating battens and scantlings. 

Timber is also supplied in one of four conditions: sawn or off the saw; regularized or surfaced, i.e. machined to a constant cross-section; wrot or dressed, i.e. machined to a Constant cross-section and a smooth finish suitable for joinery work; and moulded, i.e. work and with a shaped cross-section. 

BS 4471, 'Sizes of sawn and processed softwood', gives the sawn sizes of softwoods together with the reduction in overall size when the timbers are regularized or wrot. Note that flooring boards are treated differently and are the subject of BS 1297, 'Grading and sizing of softwood flooring'. Material from which UK sawmills machine flooring boards is specifically sawn for that purpose at the original sawmill before being shipped to the UK; the contractor buys the machined boards. BS 5450, 'Sizes of hardwoods', gives sawn sizes and processing allowances for planing, etc. 

As well as standard cross-sectional sizes, softwoods are supplied in standard lengths. The shortest length normally supplied is 1.8m. Standard lengths increment by 300 mm from this basic length. The range of sizes continues therefore as 2.1, 2.4, 2.7, 3.0m, etc. 

If these lengths do not fit the work required of them exactly, there is a maximum wastage of 299 mm to cut the next largest size down. The bulk of timber is purchased in the range of lengths from 3 to 6 m. If the wastage of 299 m is taken on the average length of 4.5, it is equivalent to 6.64 per cent. Many authorities quote 7.5 per cent allowance for wastage, which has also to include pilferage and damage. In the examples here we will take 10 per cent on timber, 7.5 per cent on manufactured units such as trusses, and 2.5 per cent on manufactured units such as doors and windows. 

Although supplied in such a wide variety of sizes, natural timber is generally priced per cubic metre fora range of sizes and finishes. Pre-treatment is also costed out on a cubic metre basis. Prefabricated work (manufactured units) is generally purchased on a unit basis, i.e. per door, per flight of stairs, per kitchen unit, per trussed rafter, etc. 

As in all the other trades. the estimator must ensure that delivery costs to site are included in any quotes or must make an appropriate allowance. Unloading on site is most often done by having a mechanical off-load (MOL) facility on the delivery truck, or by having rough terrain fork-lifts to cope with banded or pelleted materials. A fork-lift would be priced in the preliminaries section. 

Fastenings and adhesives 

Fastenings and adhesives are not generally measured separately. Nails are deemed to be included; all other fastenings are given in the item description. There is a wide range of fastenings available, each suited to a particular application. 

Nails can be manufactured with round flat heads or bullet heads, and from round or oval wire. The materials range through mild steel, stainless steel, brass, copper, aluminium, galvanized steel, zinc plated steel, sherardized steel, etc. Shanks can be plain or jagged, or can have an annular ring barb to improve holding power. An old form of nail which was punched out of steel sheet has enjoyed a revival in recent decades, as it has been found suitable for direct fastening into autoclaved aerated concrete blockwork and no-fines concrete. These nails were known as cut nails and were produced in a variety of patterns, one of which was specifically designed for fastening flooring boards. Others were designed for anything from general carcassing to fine cabinet and upholstery work. Nails are well illustrated in BS 1202. Wood screws are manufactured in a similar wide range of materials and finishes, and with a variety of heads (countersunk, round, pan, etc. as well as slotted, Phillips, Posidrive, etc.) and thread forms. Wood screws are fully specified in BS 1210. In addition there is a range of bolts, lag screws, fastenings for attachment to masonry, patent clips, hangers, hold-down straps, etc. far too numerous to mention here. Manufacturers' catalogues give details of proprietary fastenings. 

Glues can have several different prime sources, including animal bones, hooves and horns, fish, milk, cellulose and various synthetic rubbers and resins. Glues based on animal, milk and cellulose products are generally classified as being from unmodified natural materials. 

Since the late 1940s there has been a rapid growth in products based mainly on synthetic materials, and these have provided the industry with adhesives which cover every requirement. BS 5442:Part 3 gives guidance on the suitability of all the glues mentioned above for use with wood. The synthetic materials are classified as synthetic thermoset resins, elastomers and thermoplastics.
The carpenter and joiner is expected to fix items of ironmongery ranging from simple hat and coat hooks through complex items securing doors and windows, patent fasteners and openers for sashes and doors, to control gear for large industrial doors. The range of ironmongery is too extensive to list here, and manufacturers' catalogues and :instructions should be consulted.
Round wire nails in plain steel are the most common method of fastening for general carcassing work. Galvanized round wire nails are used when simple rusting would be a problem. Under the rules of measurement, plain steel nails are the norm and are deemed to be induded. Galvanized nails have to be given in the item description, the bill headings or the preamble. Similar provisions apply for nails in other materials and finishes, and for other more complex (and more expensive) forms of fasteners.

Labour constants 

In general terms, hardwood is more difficult to work with than softwood. Various authorities quote labour constants for softwood, and show multipliers ranging from 1.5 to 2.5 to be applied to these constants for working with hardwood in general. Others give multipliers for specified hardwoods, recognizing that not all hardwoods have the same physical hardness or ease of cutting and machining.

Of course neither are all softwoods the same. Some of the so-called softwoods are harder and heavier and more difficult to machine than the majority of hardwoods; for example, pitch pine (Pines pulustris) is quite dense and very resinous, which makes it difficult to work with hand tools. Modem construction practice tends to utilize pines, spruces and firs specially grown or selected from natural stands for their easy working capabilities and a general uniformity of quality. This obviates any need to differentiate between varieties as far as labour constants are concerned. The estimator must beware, however, of the occasional use of some unusual material in carpentry work. Many Far Eastern and South American exporters are promoting the use of unusual hardwoods for carpentry work in the face of an environmental movement in Europe concerned about the felling of rain forests! 

Table 1 gives a range of labour constants per linear metre for various carpentry timbers based on their cross-sectional area. Table 2 gives a further range of constants per cubic metre for general dassifications of carpentry timber(s). Both tables assume general softwood pines, spruces and fin. 

Table 2 must be treated with caution. It is not feasible to convert these labour hours for 1 m3 directly into hours per metre fora particular cross-section of joist, plate, etc. Table 3 shows the results of such a conversion for sleeper joists using a figure of 20 hours/m3. Comparison with the figures in Table 1 shows how the labour for floor timbers has been overestimated. Similarly, Table 4 shows calculations for roof timbers on the basis of 30 hours/m3. Again these overestimate the constants per metre. 

So why bother with hours for 1 m3 of timber? Well, it is convenient for pricing works where there are no detailed quantities and no time to produce them. The inaccuracies will even out if the job is large enough, but the total result can only be an approximate estimate and not an accurate prediction of cost. Therefore costings based on ITO of timber must be treated with care. In the examples here, constants based on individual cross-sectional areas will be used.