Exterior wall sheathing Wall sheathing is the base material attached directly to the studding. The finished siding and trim are nailed to the wall sheathing and brick or other masonry material is applied over it. As well as forming a base for these materials, wall sheathing also provides the structure with some degree of rigidity and insulation. There are several types of materials used for wall sheathing. The type used may depend on the exterior finish of the house, that is, whether it is to be of vertical or horizontal wood, composition siding, or brick or stone veneer. The climatic conditions also affect the sheathing used. Some types have a greater insulating value than others. Fibreboard Sheathing This type of sheathing is made from compressed wood fibre or wood pulp. It comes in sheets that are 1200 mm wide, 2400, 2800, or 3000 mm long, and from 12 to 20 mm thick. Most types are treated on the outer face to make them water-resistant. Some are impregnated with an asphalt base material to make them still more impervious to water. The main advantage of fibreboard sheathing is its high insulation quality. This is due to the fact that it is loosely compressed, porous, and made up, to a large extent, of minute air spaces. This also makes the sheets lightweight and easy to handle and cut. Another advantage of fibreboard sheathing is that it costs less per square metre than most other types of sheathing. There is also considerably less waste, as the sheets can be purchased in lengths to correspond with the height of the wall. There is less labour involved, as most of the cutting required will be around the wall openings, if the studs are properly spaced. Since fibreboard is not affected by shrinkage, it makes a tighter job than solid wood sheathing. For an example click Here! Particleboard Sheathing A material similar to fibreboard isparticleboard, a more tightly compressed composition board made from wood chips. It is somewhat heavier than fibreboard, and has less insulation value, but, like plywood, it has better nail-holding ability and is stiffer and more rigid. Gypsum Board Sheathing Another type of sheathing made in sheet form is gypsum board, manufactured in sheets of 1200 mm x 2400 mm with a thickness of 12 mm. it consists of a gypsum core sandwiched between 2 moisture-resistant layers of heavy paper. Gypsum board makes a rigid sheathing but has a much lower insulation value than fibreboard. Plywood Sheathing Plywood sheets are extensively used for sheathing and, when properly nailed, make a very rigid wail that does not require sway bracing. An unsanded sheathing-grade plywood 8 mm thick is generally used. It is extensively used for prefabricated homes. Plywood has the advantage of providing a surface strong enough to nail most types of siding to, while still being lightweight, easy to apply, and economical. Sheathing that is made in sheets or panels can be applied vertically, with the long side of the sheet parallel to the studding however, for a stronger, more rigid wall, plywood sheets can be applied horizontally, with the long side of the sheet parallel to the plate. When sheets are used horizontally, girths should be placed between the studding, as all edges should have nailing support. Gypsum board is the exception to this rule, as the long edges have a groove on one edge and aVon the other, making it unnecessary to use short 38 mm x 89 mm girths between the studs at the joints. These sheets are always applied horizontally. Vertical joints should be staggered where possible. For an example click Here! Solid Wood Sheathing When solid lumber is used as sheathing, the individual boards are generally 19 mm thick and 64 to 184 mm wide. They should never be less than 17.5 mm thick nor more than 300 mm wide. The wider the individual piece the more shrinkage will take place, and shrinkage will affect the appearance of the finished siding. Solid wood sheathing is generally made from matched lumber with either a tongue and groove or shiplap edge to make a tight, solid surface. Solid wood sheathing may be applied either at right angles to the studding or diagonally to it. When the sheathing is applied horizontally, the joints should be staggered and should always occur over studding for nailing support. Two 60 mm nails should be used in each stud, 3 nails if the boards are 150 mm wide or wider. When the sheathing is applied diagonally, no sway bracing is needed, as the diagonal sheathing provides the same bracing effect. The ends of all pieces must be cut at a 45° angle to be fully supported on the studding.