Dimensional Timber

Having learned about the characteristics and production techniques of the timber products that we work with, it’s important to understand the standard shapes and sizes that are available from the builder’s merchant. Here we will look at an extensive list of the “off the shelf” materials that are commonly utilised in construction, with pertinent information about the specific shapes and sizes of each material. This list is organised from the smallest to largest materials in terms of width and thickness. It will also be categorised into a few different selections. 

Before we begin, we should briefly look at the standardised strength grading scale that is applied to structural softwood timber products, as observed in the UK and most European countries. This scale is known as the “C rating” and is applicable to all “off the shelf” structural softwood timber components. The C stands for “Coniferous” and is followed by 1 of 4 numbers: C14, C16, C18, C24. These numbers are an indication of strength within each member, as assessed through meticulous testing of the visual appearance (how many visible defects) in conjunction with mechanically tested load resistance. The higher the number the stronger the timber, with C24 grade timber being the standard requirement for use in structural applications. The other commonly available grade is C16, with the other two categories being far less common. Deciduous hardwood timber also has a similar scale, the “D grading system”, though this is not relevant knowledge within general UK site construction. These categories are D24, D30, D40, D50, D60 and D70, though they are not applicable in scale to the similar numbers of the C rating scale. The grading systems mentioned here are highlighted in the BS 5268-2 and BS EN 14081 regulations. 

Another thing to note about the wholesale of standardised timber is the length of each board. Off the shelf materials are sold in 300mm increments of length, starting at the low end of 1.8m(depending on the merchant), and working their way up. Some materials and mouldings will be sold in a select number of these 300mm increments, with most versatile timber products being available in a larger range of lengths. The most common “off the shelf” lengths are 2.4m, 3m, 3.6m, 4.2, and 4.8m. The maximum length for off the shelf timbers is typically around 6 metres.  

Additionally, as we begin to look at specific measurements and dimensions, now is a good time to gloss over a metric to imperial measurement chart. Construction products that are sold in the UK are described via both metric and imperial measurements. The US primarily uses the imperial system, with Europe typically favouring the metric system. Understanding the conversion between these measurements is useful and not complicated to understand.  

Treated timber

19mmx38mm batten (¾”x1½”)

This batten is very thin, typically used for packing strips or in counter battening applications. This batten is too thin to be used as roof battens, with the minimum required thickness of batten being 25mm. This batten is treated, and comes in a variety of lengths, often 3m as well as 4.8m lengths. It's a good choice for timber grounding applications in scenarios where keeping the packing to a minimum is a consideration. Individual lengths can be purchased, though they are also sold in bundles of 6, 8, and 10. This is true for most varieties of batten.

25mmx38mm batten (1”x1½”)

This batten is a typical material used in roofing and is the smallest allowable off the shelf batten that can be used for roof tiling. Beyond roofing, this batten is only really used for timber packing and doesn't have many other applications in general construction. It comes in standard lengths of 3m and 4.8m. 

2”x1” batten (50mmx25mm)

This type of batten is the most widely used within construction and has many applications. It is often used to batten out roof systems for tiles but can be used internally in an array of scenarios. It is a great choice for layout rods, as well as throw away props or temporary railings. Internal applications include first fix boxings and counter battening. Most ladder frames for boxings will be made from this type of batten. This timber, unlike other larger imperial sizes, is true to its shelf name in size, being exactly 2”x1” in width and thickness. Lengths of this timber can be purchased in most increments of 300mm, up to around 5.4m. Battens like this, as with the other smaller batten types will often be dyed a certain colour to identify the supplier. This type of batten, like most of the other types of batten, can be purchased as treated Spruce for external use, as well as Planed All Round (PAR) Pine.  

2”x1½” batten (50mmx38mm)

This type of batten is not generally used in roofing applications, as it is on the thicker end of the batten spectrum. Uses for this timber include boxing material, packing material, as well as being the standard requirement for use in cladding applications. It is used to counter batten surfaces ready to receive cladding in external scenarios due to the appropriate depth of fixing provided, as well as appropriate depth of airflow for ventilation. This batten comes in most standard lengths, up to about 5.4m. 

2”x2” batten (50mmx50mm/45x45mm)

This type of batten does not often see use in roof covering applications; however, it is often used for drip edges or packing in flat roof construction. It can be used for a variety of internal applications such as boxings, as well as packing/battening in certain bespoke scenarios. Due to its thickness, it is a good choice of material for small bespoke gates/fences that are not due to take much load. This batten can come from the merchant in a full square edge 50x50mm billet, as well as a smaller 45x45mm rounded edge variation. This is important to note, as they are both sold as 2x2 if care isn't taken to specify. All standard lengths can be purchased off the shelf. All off the shelf batten varieties are likely to be milled from spruce timber. Once again, most of these varieties can be purchased as PAR finished timber as well as treated external timber. 

Cladding boards

Cladding/fencing boards come in a variety of different shapes/profiles and sizes. They can be treated or untreated, with each different moulding providing a different aesthetic and functionality. Common profiles include feather edge board, shiplap board, and tongue and groove board. These can be purchased at common widths of 100mm/4” wide and 150mm/6” wide, as well as a range of other custom sizes. Common lengths include 2.4m, 3.6m, as well as the less conventional 4m lengths - the latter of which suits a 400mm batten layout. Specialist cladding can be purchased in a variety of different materials. These boards are used to clad buildings, sheds, as well as in fencing applications. The thickness of the different boards varies between mouldings and suppliers, though they are typically going to be somewhere between 10mm and 20mm. 

4-12”x1” timber backer treated

This type of timber is primarily used as a timber fascia backer in roofing applications, though it is sometimes used in specific packing scenarios. It can be purchased off the shelf up to around 8” in width, though larger widths can be purchased from specialty suppliers. This variety of timber is treated for use in outdoor applications. The thickness of this timber is exactly 25mm/1”. It can be purchased in a variety of lengths, with 4.8m being the most common. 

4”x2” (45mmx95mm) treated timber

This type of timber is one of the most used within the construction industry, forming a basis for many structural tasks. Stud walls are the most common application of this material, though there are many bespoke scenarios in which 4”x2” timber is called for. The finished thickness of this material comes out slightly under the full imperial dimensions stated, typically with rounded edges and a smooth surface finish. The finished dimensional width and thickness of this timber is around 3 ¾”x1 ¾” (95mmx45mm) respectively. It can be purchased off the shelf in all the standard 300mm increments, all the way up to 6m in length depending on the supplier. The material is often spruce. As an aside here, whilst the timber is often sold with the supposed correct dimensions, for example 95x45mm, due to swelling of the timber its common for these sizes to be slightly larger - 97mmx47mm. The exact amount can vary though depending on the exact storage conditions and moisture content of the timber. All these exact figures are going to vary between merchants, though for all intents and purposes, these minor variations are negligible in relation to the tolerances of structural carcassing tasks.  

5”x2” (120mmx45mm) treated timber

This type of timber is not tremendously common within construction and serves most of its purpose for building height in flat roof curbs and specific thickness stud walls. For example, a 5” (120mm”) kerb will receive standard 120mm insulation within a flat roof assembly, allowing for the sheathing material to sail seamlessly over the two. It finds other applications internally as well within similar packing scenarios. It can be purchased in all the standard lengths.  

6”x2” (145mmx45mm) treated timber

This timber is commonly found in applications such as roofing and joisting, as well as many other structural tasks. This is commonly the minimum requirement in depth for rafters and joists and is also a requirement for the construction of external timber structural stud walls. These timbers come with rounded edges like all the other 2” timber and are most commonly milled from spruce wood. They come in all the common 300mm increments.  

7”-12”x2” treated timber

All these timbers mostly serve the purpose of rafters and joists, with the variety of sizes being called for in relation to specific structural calculations. These timbers are similar to the other types of 2” timber and can be purchased in all of the standard lengths. Deeper timbers such as 8”x2” are often called for in the construction of hip ends as well as long spanning joists. 

Furring strips

These timbers are relatively thin strips of timber that are used in the creation of flat roofs to give them a consistent run. Furrings come in a selection of different sizes, tapering from thick to thin along their length. The width of the furrings is typically 2”, in order to allow them to be placed directly on top of 2” timber joists. Off the shelf furrings ordinarily taper to nothing and can be purchased with a thicker end of 2” (50mm), 3” (75mm)), and 4” (100mm). These thicknesses can be purchased in different lengths, typically 3.6m and 4.8m, which changes the severity of the slope, with the longer lengths making the fall of the furrings more gradual. This timber is treated for use in exterior scenarios. In most instances, the “off the shelf” precut furrings have an approximate fall of around 1 degree in relation to the level plane of the main portion of the roof. This minor fall is adequate to redirect rainwater in a specific direction.  

Tilt fillet

Tilt fillet is a sawn type of timber, typically 2” thick, with a right angled triangular through section. The purpose of tilt fillet is to soften the angle of felt as it laps up vertical surfaces. For example, where a flat roof meets a solid wall, a tilt fillet should be installed along the intersecting 90-degree angle, in order to soften the lap up of the lead/ felt, or other roof covering. By softening the lap, the felt will be less prone to cracking over time due to exposure to weather. Tilt fillet is also used to surround a flat roof assembly in order to guide water towards an appropriate outlet. Tilt fillet is treated for exterior use and is typically milled from spruce. Tilt fillet can be purchased in most of the common lengths. 

Arris/Cant rails

These lengths of moulded timber form the structural members within a bespoke fence panel. Typically placed horizontally spanning from the post on one side of the panel to the other, these shaped timbers provide support for the vertical boards to attach to. They are typically milled from spruce and then treated, giving them great resistance to weather conditions, though different species of timber are available from specialist suppliers. They are moulded in an aesthetically pleasing way and come in many varieties to allow for a custom finish. These mouldings also help to match existing fence panels for repair work. 

Planed all-round/untreated timber products

4-12x1 untreated

This type of timber is used in a similar way to the treated 1” timber, in that it is fitted to the ends of the rafter tail plumb cuts as a fascia board. However, this untreated, much smoother planed timber, is better suited for being painted. Appropriate weather resistant paint must be applied to this timber for use in external applications, but this type of timber creates a very nice timber aesthetic within a roof system. This application is used without a uPVC fascia capping. This timber comes in mostly 3m and 4.8m lengths. This type of timber is also appropriate for replacing damaged old-style floorboards, as finding exact matches can be difficult. 

Lining material

Lining material is a type of planed, untreated timber similar in appearance to that of the above untreated 1” timber. It differs in width however, with a selection of specific widths available for the creation of interior door linings. The widths can vary between suppliers, though generally speaking there is a standardised selection of widths to accommodate specific applications. The most common widths that are used are 108mm/4 ¼”, 120mm/4 ¾”, and 132mm/5 ³⁄₁₆”. Regardless of the width, the material can be bought in lengths or purchased in pre-housed door lining kits. The long lengths of material are used for bespoke interior applications, such as forming custom door linings. The door lining kits are sold with a head and two jambs. The heads of these kits have housings cut on either side, with each side housed out for a different specific width door. The most common off the shelf sized lining has housings for a 30” door on one side, and a 33” door on the other. Custom order kits can be purchased for smaller or wider door arrangements, though it's typically easier to make them from lining material. When the linings are assembled out of the kit, the jambs are fitted into the housings in the head to form a lining that will accommodate a full height door when placed on the finished floor/subfloor level. Lining material can be purchased off the shelf from specialty suppliers in several finishes, such as pre primed as well as veneered, or in hardwood material. Some lining kits come with door stops pre-cut to the correct length inside the shrink-wrapped packaging.  

Here we will briefly look at the most common widths of lining material and their applications.  

●       The 108mm lining is intended for use in thinner 3” CLS timber stud walls.  

●       The 120mm lining is intended for internal CLS stud walls and is ever so slightly proud either side of an 89mm stud wall sheathed with plasterboard. This allows for 2 coats of plaster to be feathered into the lining, giving a perfect finish - 89mm stud + 25mm (2 thicknesses of plasterboard) + 3mm (4 coats of plaster - 2 each side) = 119mm.  

●       The 132mm lining is intended for modern interior blockwork walls (100mm thick), that are hard walled/plastered either side. The thickness of the render on either side of the wall brings the finished plaster out to the lining. This type of lining is well suited to being fit into structural openings that have been cut into existing traditional masonry walls, as these walls are typically around 130mm in width, allowing for a fresh coat of plaster either side to be feathered into the lining.  

●       The 155mm lining is suitable for wider existing imperial interior masonry walls that are dry lined either side. 

●       A smaller 145mm can be used in the same above scenario where the walls are hard walled and plastered instead of dry lined. 

Note that there is a wide array of different widths that are available. A measurement should be taken of the width of the surface that receives the lining to determine the correct width. In some instances, custom widths must be made from 25mm sheets of plywood, or ripped down from wider lining material, depending on the existing width of surfaces. In renovation scenarios, existing walls that have an irregular makeup, such as layers of lathes, or double board etc can make finding an off the shelf width difficult.  

4” (89mm) x2” (38mm) CLS

Originally manufactured in Canada in accordance with strength regulations and engineering practices set out by the Canadian Lumber Standard, this type of timber grew widely in popularity and soon became a standard form of structural timber. Originally intended for the creation of timber frame houses, this type of timber is used in many applications in modern construction. It can be purchased treated and untreated and is typically used for interior applications in this country. It is planned to have a smooth finish with rounded corners for ease of transportation as well as safe handling. The CLS available in this country is normally graded as C16 on the C scale and is untreated. The most common application for this type of timber is internal stud partitions. These timbers can be configured within a wall assembly for structural applications. For the most part, this timber is typically a cheaper option than other types. It can be purchased from most suppliers in standard 2.4m and 3m lengths. Smaller widths and thicknesses of this timber are available for lighter duty tasks, such as 3”x2” CLS. The actual thickness of this timber is less than the full-sized imperial measurements it is named after.  

Skirting/Architrave

Traditional timber skirting and architrave are lengths of timber that are moulded and shaped with specialist hand tools to several different standardised profiles. In modern times these mouldings are formed using power tools to speed up the manufacturing process and reduce costs. There are many different standard profiles for both skirting and architrave that we will look at later in the book in more depth. Skirting is a moulded covering, also known as baseboard in some parts of the world. It is intended to smooth the visual transition between the floor and the bottom of walls and gives a nice aesthetic to any room or house. Architrave within a house is used to outline a door lining or window frame, and gives a nice, finished aesthetic. Both of these mouldings are used to cover the edge of the plaster line as it meets the door lining and floor line. Typically, the profile of the skirting in a house will match the profile of the architrave. Different mouldings can be purchased in different lengths, but for the most part most standardised 300mm increments can be purchased. 

Doorstop

Doorstop is a purpose specific interior planed batten that is used for the door stop portion of an internal door lining. Whilst this type of batten can be used for other interior finishing jobs, it is universally understood and sold as door stop. It is made of softwood and has been planned to a smooth finish. It is sold in a variety of lengths, and the finished size is 12mmx32mm, or around ½”x1¼”. The longer lengths that can be purchased are long enough to cut 2 legs and 1 head for a single lining out of it. This type of batten can also be used for lightweight airing cupboard shelf construction.  

Mouldings

Mouldings/beads are a type of finishing trim material that can cover seams/joins and give nice, finished edges to work pieces, as well as a range of other finishing applications. They are ordinarily used at the end of a project to bring different components together, and to get over any problems that may have occurred during the build/renovation. Mouldings come in many different profiles to allow for a greater variety in their usage. They can be purchased off the shelf in both softwood and hardwood, as well as in primed MDF. There is no true standard size for the length of these mouldings, though 2.4m and 3m lengths can be commonly found. We will look further in depth at the different profiles of these beads later in the books. We will look at how to install them and where the different mouldings come into use.  

MDF skirting & architrave

MDF skirting and architrave comes in many different sizes and mouldings to allow for a great variety of finishes within a house. The skirting boards are typically somewhere around 4 metres in length, though many off the shelf sizes are available, especially shorter lengths to allow for repairs and patching work. The architrave typically comes in longer lengths, around 4.4m, to allow for 2 legs and a head for one side of a door to be cut. Both of these types are pre primed with white primer to allow for easier installation and decoration. We will look in depth at the sizes and different mouldings of skirting and architrave later in the Second Fix chapter of the book. 

Window boards

Window boards can be purchased in a few materials, namely MDF and pine, though there are plenty of specialty suppliers that offer specific hardwood varieties to allow for a greater choice of finish within a home. These specialty varieties can be ordered to width and length from the supplier, though off the shelf varieties are standardised between the different merchants. The thickness of window boards is typically 25mm/1”, though some exist in 18mm and 30mm varieties. They can be purchased in a whole array of widths to allow for different scenarios. These widths range from around 100mm all the way up to around 400mm, with varying increments in between. The most common off the shelf widths are around 225mm/9” up to around 300mm/12”. The MDF variety of window boards are similarly primed with white primer to allow for quicker installation and less work for the decorators.