Sometimes a capping of concrete is installed over the sub-floor, to allow for the installation of tile, or radiant floor heating pipes. It is through this assembly that the forced air system ductwork will be installed, as well as miscellaneous plumbing and electrical lines.
There are three main types of floor structures, generally used in modern construction. These include framed, truss floors and manufactured joist systems.
Of all, the most commonly installed visit here system are framed floors. They consist of dimensioned lumber, bearing on exterior and interior load bearing walls or beams called “floor joists”. Generally the floor joists are installed, spaced 16″ apart. Installing rim and trimmer joists, to which the floor joists are nailed, finishes the perimeter. Bracing, usually in the form of bridging, but often installed as strapping, prevents the joists from turning in place. One other method used to prevent this type of turning is to glue the sub-flooring to the joists, as the sub-floor is placed. All joists must extend at least 1-1/2″ on to a bearing assembly, of either a beam or full height wall, unless metal hangers are installed to provide proper bearing support against other structural components. Beams, which support the floor joists over greater spans, are constructed in the form of laminated joists often referred to as built up beams, or one piece solid load bearing beams, cut from logs or manufactured. Electricians and plumber may often cut or drill into the joist work to install utilities, and this is accepted, so long as they do not remove more material than what is required by codes. This type of floor system is usually the cheapest to install.
Truss floors are simply that. They are constructed from small dimensioned lumber, interconnected in a webwork pattern by the use of metal or wood plates. Occasionally, the trusses will be built on site, utilizing plywood plates to connect the webwork together. Generally they are installed 24″ apart, either suspended on bearing walls or beams, or installed with plywood trim or rim joists around the perimeter. Strapping is installed on the bottom side, to prevent turning in place, which is a common ailment for deep truss components. In the case of long span truss work, bearing lengths of at least 3″ are quite common. Trusses span greater distances than framed floor assemblies and can be designed to span the entire building, eliminating center load bearing supports. They are moderately more expensive than framed floor assemblies, but provide a remarkably strong floor with little deflection or “bounce” to it. Another advantage to this type of structural system, is that utility installations can be run between the webwork components. Never allow trades to cut or drill into the members of a truss, for they are manufactured precisely for the loading conditions they will undergo during the life of the building.
The manufactured joist, which is a relatively new product, is often manufactured from low cost materials in the shape of an I beam, similar to steel beams in larger buildings. What this means is that the joist is constructed with a thicker top and bottom edge, and generally interlocking aspenite vertically spanning between the two. These systems are very strong, often capable of spanning the entire width of the building. One drawback is that this type of floor requires special hanger systems designed for the joists, to enable them to be hung from each other or against beams/bearing walls. Manufactured joists are becoming a popular flooring system, for they are relatively cheap, reduce labour time and provide adequate support. However, builders need to familiarize themselves with its installations, for poor installation can cause severe structural damage to the joists. A good example is a three point, center bearing joist, left with the top chord uncut, which can potentially fail or pull apart, over the center bearing point.
There are three main types of sub-flooring installed to cover and span the floor structure. It is over this that the finished floor will be placed. The sub-flooring types include raw sheathing, interlocking and strip. It is utilized not only to provide a surface for the interior finishes to be placed on, but also to prevent twisting or torque forces placed on the building. The sub-floor also allows load sharing within the joist framing system. Often the sub-flooring is glued to the joist work to eliminate creaking floors and to prevent the floor joists from turning.
Raw sheathing comes in 4’x8′ sheets, most often installed as 3/4″ thick plywood panels. This type of sheathing is adequate for spanning joist work spaced up to 24″ apart. The sheathing is lain with the joints staggered in such a matter, that no two edge joints line up with adjoining sheets. It is very easy to install, requiring the least amount of labour. The sheets are fastened with either 1-1/2″ flooring screws, or 2-1/2″ nails, spaced about 8″ apart. Although not required, it is a good idea to provide backers or supports under the joints, between sheets which run perpendicular to the framed floor assembly.
Most commonly installed are interlocking sheathing panels. This type of sheathing is generally 5/8″ thick, and manufactured as either plywood or aspenite (commonly referred to as “chipboard”) in 4′ x 8′ sheets. The sheets come with the long edges designed to interlock with a tongue on one edge, and a grove on the opposing edge. They are installed by simply pushing or pounding the sheets together, and nailing or screwing them to the joist work, in the same manner as raw sheathing. It is often the cheapest to install.
Strip floors, were once the most popular type of sub-floor installed. But with the introduction of manufactured sheathing products, it has become less utilized. Strip floors consist of 1″ by 6″ or 8″ boards, placed diagonally over the floor joist framing system. It is slightly more expensive to install, and requires experienced tradesmen. To install such floors properly, the lumber should be non-kiln dried, with a relatively high moisture content. This may seem odd, but in reality, as the wood dries out, it will shrink. This shrinking action pulls the floor together, adding strength to the overall system. The advantages of this type of sub-floor are its strength and durability. One important note, homeowners are often disturbed by the small 1/4″ wide gaps, generally left between the individual planks after the wood dries out. Although disturbing to see during construction, upon completion, the spaces are not noticeable, and really have no impact on the sub-floor components at all. Strip floors are designed to be interlocking, through lapping or spacing of joints.