Timber Frame Knee Brace Layout

How to layout a timber frame knee brace correctly.

The knee brace is the fundamental element of a timber frame structure. Although it looks simple at first glance there are many ways to get off track when laying out your knee brace to cut. From inconsistent rough sawn material to the geometric complexities of noses and mortise and tenon joinery, it can prove daunting to the novice.

Here we explain how to overcome all of those hurdles with solid carpentry principles and good guidance. Please download our drawing and instructions on how to accomplish the basic timber frame task correctly. The download goes into how to begin with rough sawn or surfaced timbers all the way through correctly laying out the knee brace joinery and making sure it is correct in irregular rough sawn material.

Knee Braces and Timber Frame Raisings

The Joint and Peg team recommends that you typically always have the knee braces of a timber frame suspended from the beam when you are flying the beam during a raising. We find that most do not do this. Here is what we suggest: First of all, always have as much of an assembly as possible already connected before raising. However, when you do need to fly a beam, such as a wall plate to connect some frames, we recommend that you rig the beam, and then lift it off the ground slight enough to insert the knee braces into their corresponding beam mortises. We also recommend always labeling the knee brace tenon on the downhill side so that you can see the labeling during this procedure. Now, you don’t connect the knee brace to the beam with the peg, you use a smaller diameter rod or peg that allows the brace to sloop just a bit from its in situ angle. Or in other words, it allow some play in it. Once you have the knee braces suspended from the beam you can go ahead and fly the assembly to its place to be installed.

Here is the primary reason for always flying the knee braces with the beam:

The person there to make sure all the joints go together can usually use the suspended brace to align and guide the rest of the joinery to be connected. First, they can see that the knee brace has the correct label, such as A1+ or A2-, then grab the brace and guide the whole assembly into place as he/she pushes the brace up into the post mortise as the beam comes down.

So much easier than guiding the beam with your hands.

Providing proper feeding (chamfers) on joinery according to proper raising procedure helps with this process as we will discuss this in another post.

Find the Center of the Circle or Circular Arch

You are probably in the field and someone has poured a circular slab. However, the didn’t leave you the origin of the circle. You could also be wanting to create an arch and you need to find a spot on the shop floor to use your trammel points (large compass) to create the proper radii on your rough stock.

Fear not fellow tradespeople, follow the instructions below.

Also helpful for drafters, architects, and whoever else is trying to find that elusive center of a circle.

While we are at it, and because we LOVE geometric design based on arcs and radii. Have you ever seen a hypocycloid? Leave a comment if you can figure out what is going on with it. Think dynamic movement.

Timber Frame – No Plywood

Do you need plywood for your timber frame?

The short answer is No. However, it is true that modern day panel products such as OSB and plywood do provide a measure of lateral strength when analyzing enclosed timber frames. In most cases, the desire to build the timber frame without the need for plywood becomes an issue when someone wants to build a timber frame structure that is not insulated. Insulated timber frames typically (not always) will have a panel good product as part of the insulating enclosure composition. However, when someone wants to build a true and authentic timber frame barn, for example, the last thing they want to do is see plywood from the inside.

Now it must be considered that different areas of the country will need more lateral stability than others. For instance, along the Gulf Coast and south Atlantic seaboard, timber frames will need to withstand extreme wind loads. Another instance is out West. There is a great deal of seismic zones and areas that will need that additional lateral strength when designing timber frame structures. Relatively milder areas of our country, and continent, might not need the additional lateral strength. In these milder areas, your typical 3′ leg knee braces might be sufficient for lateral strength when coupled with, for sake of an example, 4x level nailer girts at 4′ centers, with rough sawn board and batten siding. If this is the case, wonderful; but let’s look at the areas where this nailer and siding arrangement will not be adequate.

The High Wind Zones

If wind is a factor in creating stability of your frame design, and you don’t want to use a panel product, what are your options?

Better Bracing

A typical timber frame knee braces usually has a 3 foot leg in the vertical direction and a 3 foot leg in the horizontal direction. When we need to gain more lateral strength bigger and longer brace members can help. Your typical knee brace only reaches a small portion down or up your post. In order to gain more strength, we need to get at least half way down, or up, the post. Even better, take a bay and dedicate it to bracing and run the brace more than 50% of the post. Be sure to make sure your post is big enough to with stand the additional bending forces it will be subjected to.

Considering that this brace bay will not be useful for any Rough Openings, I like to go ahead and celebrate it with perhaps some X-bracing. Also called St Andrews Cross this type of configuration can create a much stronger bracing effect. Enough, in most circumstances, to alleviate the plywood in those engineered timber frame drawings. Below is a project that our founder, Moyer Fountain, designed and built that incorporates X-bracing and timber frame stability in a high wind zone, without plywood.

Please CONTACT US if you need our expertise. We can get your project going and completed for you.

This timber frame barn was built for a location on the coast. The exposure loads were great considering it is very close to the coast. Designed, Engineered, and Built to withstand 150 mph winds for 3 second gusts. The barn is the monitor style with two flanking sheds on either side of the main frame. There are also two lofts on each end of the frame. The cupolas were also designed and built by us. This frame consists of rough sawn Cypress timber. The structure was built of traditional mortise and tenon joinery with oak pegged connections. Other components in the structure are iron tie rods and X-bracing on the gable ends to withstand the heavy wind loads of the site. We love traditional barns projects!

Wood: Where to Begin?

“Pet the Cat”. It is an entirely accurate analogy for wood working. If you aren’t paying attention to the grain, then you are going to find you work less pleasurable and less successful.

All aspiring woodworkers, carpenters, timber framers and those that work wood should start with hand tools in their hands. Power tools have no place in the novice’s toolbox. Hand tools give you feedback when working wood. If you don’t cut straight, your saw binds and your effort and results are less than satisfactory. If you push your block plane, or jack plane, across a face in the wrong direction, the chatter and results are rather unsightly. Proper woodworking takes less effort. Know thy material! Once you have an appreciation and understanding of how to approach your work, by learning from hand tool work, then you may graduate to the power tools.

Let’s go over some hand tool methods, next week.

Timber Frame Biergarten Event Space

The Bower at Edmunds Oast was designed in house. We built and raised the structure in November of 2014. The frame consists of second growth Cypress from the Sandhills of NC. There is also some elaborate metal work to resolve tension in the trusses. There are four open air bays and two enclosed bays. There is also a prominent timber tower to locate the entrance to the area. 1081 Morrison Charleston, SC

We will explain more about how we raised this timber frame, the plan behind it, in an upcoming post!