What is a Flitch Beam?

Dan Cavallari

In construction and renovation projects, it is sometimes necessary to reinforce or strengthen a beam that will bear weight. There are several methods for doing so, and few are more versatile and effective than using a flitch beam. This is comprised of two wooden beams joined together by a steel plate--called a flitch plate--to reinforce and multiply the strength of a singular beam. While the use of these beams has largely been replaced by composite lumbers that are just as strong but cheaper and easier to install, they still has many uses and are a common technique, particularly in renovation projects.

A flitch beam can bear a much heavier load than a simple wooden beam, so it is a good choice for roof construction.
A flitch beam can bear a much heavier load than a simple wooden beam, so it is a good choice for roof construction.

In situations that call for a beam that can transfer load over longer distances,a flitch beam can be particularly useful. The construction of a roof would be an example of such a situation. A flitch beam can bear a much heavier load than a simple wooden beam, so it is a good choice for such applications. It is also lighter than a steel beam, which adds to its advantageousness in home projects. Because the beam is made of wood as opposed to metal, it can still be connected to existing wooden structures using screws or bolts with less effort than would be the case with a steel beam.

To construct a flitch beam, two beams must be cut to length. Then, a prefabricated flitch plate is sandwiched between the two beams. Finally, the three parts of the composite beam are bolted together, which can be done off-site or on-site, depending on the size of the project and the availability of resources. One of the drawbacks of this technique is that the plate often has to be prefabricated; if it is not, it can be something of a chore to install on-site, though it is by no means impossible. Some experts have moved away from flitch beams because of the high labor costs associated with installing them, opting instead for engineered composite lumber studs and beams to accomplish the same goal.

The flitch beam is a versatile method, too, because the strength of the beam can be increased by adding more flitch plates and wooden beams. The more plates and beams are added, the stronger the beam will be. Again, this is particularly useful in renovation scenarios where an existing structure must be reinforced. Further, because this type of beam is stronger than a normal beam, the flitch beam requires less depth than a regular beam.

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Discussion Comments


@Animalz – I think you should use flitch beams in the rafters of the gazebo. I renovate “fixer upper” houses with a friend of mine on the weekends, and use flitch beams in all of the roof renovations. I use a lot of them in roof truss construction because they’re so much stronger than simple wood beams.

It’s not the normal way to do things, because it’s so time consuming, but when I build a new truss for a project, I use flitch beams for every part of the truss. I replace broken or warped rafters with flitch beams, too.

When my friend and I show off one of our finished houses, we always stress how the flitch beams make the roof sturdier. The buyers are usually happy about that. It seems like they’re willing to pay more money because they feel that the house is strong.


@Animalz – I’m only a hobbyist carpenter, but I find that flitch beams are able to bear 1.5 to 2 times the weight of traditional wood beams. If it looks like I’m going to need more strength than that when I’m designing a project, I usually add another metal plate and wooden beam to my flitch beam. After that, I often have to change my design a little bit in order to accommodate the extra beam width, but the results are worth it.


I have a question about flitch beam design. I understand that sandwiching a steel plate between two wooden beams makes the final beam way stronger than wood is by itself. But, exactly how much stronger is a flitch beam than a regular wooden one? I’m building a gazebo for my backyard and want to do the calculations right.

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