Floor Construction Methods

Learn all about the different types of floor construction.
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©2007 Dorling Kindersley Limited

©2007 Dorling Kindersley Limited

©2007 Dorling Kindersley Limited

©2007 Dorling Kindersley Limited

©2007 Dorling Kindersley Limited

©2007 Dorling Kindersley Limited

©2007 Dorling Kindersley Limited

Photo By: DK - Do It Yourself Home Improvement ©2009 Dorling Kindersley Limited

Photo By: DK - Do It Yourself Home Improvement ©2009 Dorling Kindersley Limited

Photo By: DK - Do It Yourself Home Improvement ©2009 Dorling Kindersley Limited

Photo By: DK - Do It Yourself Home Improvement ©2009 Dorling Kindersley Limited

Photo By: DK - Do It Yourself Home Improvement ©2009 Dorling Kindersley Limited

Photo By: DK - Do It Yourself Home Improvement ©2009 Dorling Kindersley Limited

Photo By: DK - Do It Yourself Home Improvement ©2009 Dorling Kindersley Limited

Photo By: DK - Do It Yourself Home Improvement ©2009 Dorling Kindersley Limited

©2007 Dorling Kindersley Limited

Photo By: DK - Do It Yourself Home Improvement ©2009 Dorling Kindersley Limited

©2007 Dorling Kindersley Limited

Platform Framing and Foundation

Since the 1930s, the most common type of floor framing in the U.S. has been platform framing, also called “western” framing. Joists, studs, rafters and plates are the members that are used to construct platform framing. Each floor is constructed as its own unit, helping to prevent fire from spreading between floors. Platform frames are started with a sill plate attached to the foundation, and joists run perpendicular from the sill plate. A joist header attaches to the end of each joist. The studs are then attached to the joists, running the ceiling height of the floor. The subflooring is installed on top of the joists. A sole plate is then installed on top of the subflooring material.

Platform Framing and Upper Floors

The details in upper floor framing are similar to the ground floor. No firestopping is required, as the construction method provides a joist hanger, which is a built-in firestopping and structural system. The height of the studs for each floor are determined by the desired ceiling height for that particular floor.

Balloon Framing and Foundation

Introduced during the mid-1800s, balloon framing is no longer a popular framing system. Balloon framing uses the same type of members as platform framing, but with more substantial sized material for studs. Studs in a balloon frame run continuously from the sill all the way to the rafter. The second floor joists are supported on a ribbon instead of a joist header. Firestopping is added to the spaces between the studs, which provides a space for mechanical system installation. The foundation for a balloon frame is constructed the same as in the platform framing method. There is a sill plate attached to the foundation, and joists run perpendicular from the sill plate. The studs are then attached to the joists, and run the entire height of the house. The subflooring is installed on top of the joists.

Balloon Framing and Upper Floors

The details of upper floor construction are different in balloon framing. Each floor’s joists are run off of the same stud members that continue through the height of the house. In order to hang the joists, ribbon members are installed to the studs. This type of construction provides great stability. Firestopping is included in the stud bays.

Sawn Timber Joists Method

In this traditional floor construction, the ends of joists or beams are built into the walls of a block building, and are therefore directly supported by the wall structure. Sometimes joist ends rest on wooden wall plates secured to the wall surface. Old lumber joists secured within a wall may eventually become damp, and might need replacing over time. Joist size can vary according to the floor span, and this is an important consideration when building a new house or creating an addition. Shown here, the joists are braced using herringbone struts and blocking, and are covered using straight-edged or tongue-and-groove boards.

Joist Hanging Method

In modern buildings, metal joist hangers are often used to support the joists. Joist depths, widths and designs vary, so there is a wide range of hangers available to match. It is also an option to use joist hangers when renovating an old floor as these do not require large holes in walls and are straightforward to fix. Metal lateral joist straps are used to brace joists in position. One end of the strap is attached to the exterior wall, and the other end is attached to joists (either across or in line with them), to secure their position. Lateral joist straps are mainly used in new building projects. Shown here, the joists are attached to the wall using joist hangers, and the joists are braced with lateral restraint straps and metal herringbone struts.

Concrete Floors

Ground floors made from concrete have been common for many years in residential construction, but as concrete grows in popularity as a building material, upper floors also are being constructed from concrete. If you build an upper floor from concrete, you will most likely use concrete beams and blocks, as opposed to the slab we commonly find in basements and ground floors of homes without basements. When preparing a bottom floor for concrete, it is essential to insulate and prepare the floor for moisture control. Your floor will need compacted fill, possibly a drain tile, vapor barrier, and perimeter insulation (see below) to effectively combat potential moisture problems. Vapor barriers not only help keep the house sealed from moisture, but they also help speed the curing process of the concrete. A 6-mil polyethylene vapor barrier is laid over any mechanical systems, but the connections need to be accessible and above the finished floor level. Pouring in the concrete and leveling it off by “eye” is possible, but it is far more accurate to create some shuttering within which a level floor can be laid. To achieve a smooth surface, concrete floors are usually covered with a topcoat of screed. Screed is a 3:1 mix of flooring sand and cement, and ready-mixed screed is available. The structure shown here is suitable for renovating or replacing an old floor. However, this type of structure is also used in new properties. In this case the damp-proof membrane would be lapped into the main wall structure.

Wood Floor Construction Materials: Wood Joist

Floor joists are supported by exterior walls as well as interior load-bearing walls. The floor surface is constructed by laying wooden boards or chipboard sheets across the joists. The wood joist is made out of solid lumber and vary in size. They are typically 2 x 6 inches (50 x 150 mm) or 2 x 8 inches (50 x 200 mm) in cross-section.

Engineered Joist

Modern versions of sawn lumber, joists are made of laminated layers of wood, and are lighter than sawn lumber.

Wooden Boards

Rather than using plywood, these are the traditional covering for joists and are available with flat edges and with tongue-and-groove edges.

Chipboard Floor Sheet

This is available with tongue-and-groove edges and in moisture-resistant forms.

Joist Hanger

Joist hangers attach directly to the wall face.

Brick or Block Hanger

This hanger’s top section is installed into the mortar.

Joist Hanger

This type of hanger is designed for use with joists.

Lateral Restraint Straps

Used for bracing joists and floor structures.

Wooden Bridging

Used to brace floor joists by adding diagonal support.

Sawn Lumber Connector

Used to connect two joists together in order to give greater support.

Metal Bridging

This modern version of a wood strut is used to brace floor joists.