Giovanni Valle is a licensed architect and LEED-accredited professional and is certified by the National Council of Architectural Registration Boards (NCARB). He is the author and managing editor of various digital publications, including BuilderSpace, Your Own Architect, and Interiors Place.
Today, there are many different types of building construction systems available to home builders. One of the most popular is post and beam construction. Post and beam construction consists of heavy timber components assembled in both an upright and horizontal orientation.
Post and beam construction is a derivative of classic timber frame construction. It uses vertical structures (posts) and horizontal structures (beams) to create a framework that allows for expansive flooring and flexible wall structuring. It gives the building strength and a rustic appearance.
This article will help you understand everything about post and beam construction, including giving you an overview of this construction system and its design considerations. You’ll also learn about the difference and similarities between post and beam and timber frame construction.
What Is Post and Beam Construction?
Post and beam construction is a building system that involves using vertical and horizontal timber structures to create a frame for a building. These vertical and horizontal structures are called posts and beams, respectively.
If you’ve ever been to a construction site where this type of design is being used, you’ll notice the builders laying a concrete floor, erecting timbers on that floor, and laying other wood members over the vertical ones.
Unlike the dimensional lumber used in light wood framing, post and beam construction uses heavier lumber or structural components. Other materials that can be used as posts and beams include steel and concrete.
This type of construction dates back to the 16th century when timbers were modified manually and joined using hardwood pegs. They were also sometimes joined by removing a part of timber so it can slide over another. These days, however, gusset plates and other mechanical fasteners are used to join adjacent timbers in post and beam construction.
Design Considerations in Post and Beam Construction
As simple and flexible as the post and beam construction is, it cannot be taken for granted. From the anchoring of the posts to the floor, the connection of the beams to the posts, and the finishing you choose, it’s important that you understand what fits what and how to achieve your desired result.
We all know that any structure’s strength depends, to an extent, on the strength of its foundation. Erecting a building depends on posts and beams because they make up the building’s skeletal part and require a foundation that suits their connection type.
Post and beam construction can be used on any foundation type because of its characteristic point-specific load-bearing nature, mostly at the erected posts. However, other important considerations should be made, such as the pier.
The pier is a concrete structure that holds the post anchor. It is embedded in the foundation and can be of different shapes. The shape of the pier you choose is mostly determined by the type of soil your foundation is laid in.
Generally, circular or round piers are costlier than other pier shapes. However, it costs less when used to improve the rigidity of post and beam construction. Another factor that determines the shape and size of the pier is whether it will be visible or not after the building is completed.
The post is a vertical timber structure that supports the beams to form the building’s framework, and it is held in the post anchor. Similarly, the post anchor is held in the pier.
The post anchors can be custom made or generic and are made of steel. Since posts come in square or rectangular shapes, post anchors come in these shapes too. A large part of the post anchor is not visible as they are embedded in the concrete to hold the structure together.
Usually, you can choose if you want the remaining part of your anchor to be visible or concealed.
The floor slab is done in layers. The first layer is made of crushed rocks. The base of the foundation is filled to a shallow level with bits of rocks. After this layer, the rigid insulation is installed, and the slab follows it.
The concrete slab is the upper layer of the floor and is likely not the final finish of the floor, depending on your choice. You must know before-hand what your floor finish material will be. The thickness of your floor finish material will determine the height and dimensions of the slab and piers.
Beam-to-Post Connection in Post and Beam Construction
Post and beam construction is so named because of the constituents that make up the structure. The beams need to be attached to the posts to make them stand. Apart from this connection, other connector hardware is used to fasten beams to posts and create a more rigid framework.
Here are some of the fasteners and hardware employed in beam to post connections.
- Braces: Braces are supports and fasteners that hold a beam to a post. They are usually placed diagonally between a post and a beam to share the load between them.
- Mortise and tenon: This connection is one of the strongest in woodwork construction. This connection technique involves creating a hole (mortise) in the timbers that will serve as beams and tongue (tenon) on the lumber that will serve as posts. This method of connecting beams and posts has been around for a long time.
In post and beam construction, the beam to post or beam to beam connection is usually either exposed or concealed.
Concealed connections are made in such a way that they are embedded into the posts or beams. Exposed connectors are just that. They are visible and are left that way mainly because they serve an aesthetic purpose.
Differences Between Post & Beam and Timber Frame Construction
Post and beam structures are often mistaken for timber frame construction despite the apparent differences between them. The main difference between these two construction systems is in the connection that exists among their parts.
In timber frame construction, posts and beams are joined using timber joinery. In most cases, the mortise and tenon are held in place with pegs. This design is usually more costly because it requires precision and intensive, highly skilled labor.
In contrast, post and beam construction uses steel pins and steel plates cut in square and rectangular shapes to hold beams and posts together. These pins and plates can either be concealed or exposed. Due to the modified fastening, it requires lesser-skilled labor and also reduced labor cost.
Another difference is that post and beam structures can be built with engineered wood, while timber frames mostly require solid timber. However, current construction practices have seen timber frame structures use engineering wood such as glulams.
Similarities Between Post & Beam and Timber Frame Construction
Despite the differences in the joinery, they share some similarities in the visual element that gives them their class.
If you look at buildings constructed using the post and beam method or timber frame method, the rustic appearance is what catches the eye. The structures, made of wood, are the basis of both construction types. Also, their skeletal framework, timber upon timber, timber into the wood, is similar.
Pros of Post and Beam Construction
- Rustic appearance: The beauty of the post and beam construction is the exposed wooden skeletal frame. The timber used in this construction, polished and solid, gives a naked beauty to its interior.
- Construction time: Compared to other building construction systems, post and beam structures take less time to construct.
- Fire resistance: The wood used in this type of construction is usually denser than in other building systems. As a result, they are usually more fire-resistant.
- Building strength: This construction type provides rigidity and strength to the building, helping it withstand the harsh treatment of the elements and natural disasters.
- Reduced skilled labor cost: The cost incurred in erecting a building using post and beam construction is reduced mainly due to the modification made in connecting posts to beams.
Cons of Post and Beam Construction
- Rot and rust – Modifications made in the joinery used in timber frame; steel pins and steel plates now used in post and beam construction is susceptible to rust. The steel can begin to rust when moisture condenses on it. Also, the beams can rot after some time as they are often exposed to the outside of the building.
- Material incompatibility – Metals and wood aren’t the most compatible materials. When metals are fastened to woods, they cause fast deterioration when they begin to rust.
Post and beam structures are one of the most stable construction systems that exist. If you’re looking to build your new home with posts and beams, it could very well be a great fit. Apart from strength, post and beam construction offers large living space and an open floor area and makes the building more aesthetically pleasing.
- Designing Buildings Wiki: Timber Post and Beam Construction
- Timber Haven: Post and Beam Construction; Introduction – Part 1
- Houzz: Know Your House – Post and Beam Construction Basics
- Carolina Timberworks: What’s the difference? Post and Beam and Timber Frame Construction
- Hendricks Architecture: Timber Frame vs. Timber Post and Beam Construction
- Hunker: Advantages & Disadvantages of Post & Beam Construction
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