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  • Writer's pictureNorthern Timber Crafters

Curved Beams and Arched Timber Features

Updated: May 13

One thing that separates us from other timber framers is our ability to create curved beams and arched timber features. In fact, this is one of our specialties.


Most large timber truss producers will shy away from curved beams because they cannot be produced with automated CNC machines. We handcraft our curved and arched features with a blend of specialty tools and traditional techniques.


This ability to craft curved features allows homeowners to create one-of-a-kind homes. Curves add interest and individuality versus solely using straight beams.


Some of our most popular curved features include arched trusses and knee braces. Additionally, curved common rafters can be used to create domed or arched ceilings.


Example of arched bottom truss. See more trusses.


Example of curved knee braces. See more knee braces.


Example of curved ceiling. See more ceilings.


In this blog post, we will discuss the design and building process of several curved timber features that we have crafted over the years.


Designing with Load in Mind


The first question when designing a curved feature is what amount of load does the feature need to support? Sometimes these elements are purely decorative, and sometimes these elements need to carry a significant load. The load requirement on these elements will largely dictate how they are designed and ultimately built, but we also integrate the client's aesthetic desires. We usually start by drafting several options for our clients and then make adjustments as needed.


Example of straight versus curved patio cover.

 

Curved Glulam Beams for Significant Loads


When a curved beam will be under significant loads then there are really no other options than using a curved glulam beam. Glulam beams are commonly used in commercial buildings like hotels and office spaces. They are also commonly used in residential projects with long spans, usually over 40' long.


To create a glulam beam, multiple layers of wood are glued together with the required radius. Once dry, the end product is an extremely strong and ridged curved beam. These curved glulam beams should be manufactured by a certified APA-member. An APA certification is granted from The Engineered Wood Association and is the toughest and most comprehensive wood quality auditing program in the industry.


The drawback to using a curved glulam is primarily cost and aesthetics. The multiple layers of wood will always be visible but the impact can be negated with different finishing techniques like adding a resawn or hewn texture.


44’ long curved glulam used for bottom chord of extra large timber truss

 


Solid Beam with Arch Cuts for Medium Loads

 

When a project calls for a medium load on a curved timber then oversized solid timbers can be used to produce curved beams. Other factors to consider are the span (length) and radius (curve) of the design.


For example, if a customer wanted a truss made of solid members, we would start by designing a curved bottom beam. We would take an oversized solid beam and make radius cuts on top and bottom to produce the desired beam.

Example of solid timber with proposed radius cuts to produce curved beam.


When part of a larger feature, special consideration should be given to reduce the radius of the arched cuts in order to maintain a greater structural capacity for the beam. Less curve = more structural support.


Using free of heart timbers for these arched beams is necessary in order to prevent detrimental checking. Managing the moisture content of the beams is also important since the radius cuts will expose a large amount of fresh end grain that might want to quickly expel any remaining moisture.


Example of truss with radius cuts in timbers to create curved members

 

 

Solid Beam Glue-Up for Light Loads

 

When a large curved beam is desired, but the structural capacity of a curved glulam is not necessary, then the only option is to glue several timbers together in order to create the curved beam. This is typically necessary when a beam is more than 18" tall.


This method is only for decorative and light load applications since the radius cut will expose end grain which would be the typical failure point under enough load.


In order to improve the alignment and strength of this beam we will typically embed dowels into the glue joints as described below. The length and size of these dowels can very significantly depending on the application.

 

 Solid cedar beams were glued together to create this large arched beam

 

Process to Glue-up Timber Beams


Even though this is only used for light load applications, there are a lot of variables that will contribute to the strength of the finished curved beam such as quality of seams, type of glue used, width of timbers, quality of timber cuts, and moisture content management after cutting the radius cuts.


Polyurethane glue should always be used when gluing timbers due to the moisture content in timbers. Since timbers typically have a moisture content AFTER being kiln-dried of around 16-17%, yellow glues such as Tightbond might not ever cure.

 

Exposed pockets and dowels before glue-up.       



 Shape of glue-up before the radius cuts are made.


Curved beams that resulted from the glue-up process above.


Conclusion

We love working with clients to design and craft timber features. Curved beams and arched trusses are among some of the most extraordinary projects we have crafted. Reach out to us today to get a quote and get started on your next project!


Curved Beam on Patio

 


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