Why Wood Notching – Tips and Benefits

Notching wood for the purpose of making more durable joints has been around for a long time, but for beginners, it can be hard to understand in full the benefits if not laid out. We see various kinds of notching throughout our daily lives, and while some are outstanding works of craftsmanship, others are simple and even sloppy. You might wonder if one is better than the other or if they each serve their own individual purpose in an equally efficient manner.

Although it can look beautiful as well, notching is often primarily to give structural support to wooden members where hardware such as screws and bolts alone are insufficient. They are often used in conjunction with each other as alone, neither are good enough, but together, they form an almost unbreakable joint. Where visible, techniques such as blind nailing/screwing and the utilizing of aesthetically pleasing hardware and even wooden pegs become important. (See my article on blind nailing.)

On the other hand, where not visible, such as attics and wall framework, notching is purely structural and therefore doesn’t need to look good. In this case, looking sloppy does not equal sloppy, as its purpose is being served without compromising the structure. Various techniques are incorporated in such “behind the scenes” locations to compensate for imperfect wood, such as sandwiching slivers of plywood between boards to bring one up etc.

In fact, if you were to crawl into your attic you’d most likely be able to inspect the various structural members that make up the bone frame of your house. Upon closer inspection you’d probably also notice the various notch work – even “sloppy” ones – that help ensure the integrity of the many joints. There are many different notch profiles used that each have their individual strengths. When notching one must first determine what kind of load the notch will be countering.

Take a 2 by 4 column with a 2 by 4 beam crossing its center, making the shape of a cross. Now, you could just hammer a big fat 75mm nail where they meet and call it a day, but think about it…it has almost no resistance against rotation, and the one nail is the only thing keeping it from sliding downwards. Sure, you could hammer in a second nail and space them both apart evenly – heck, riddle the thing with nails if you want to – but because the area where the 2 boards meet is small, the nails won’t be stretched out far enough to effectively counter any substantial rotating force. And remember that each nail is essentially puncturing a hole in your wood, reducing its strength, so although some are necessary to provide adequate friction, too many will cause the wood to split.

Solution: Notch it. And remember, notches don’t have to be deep. Again, they do not have to be deep! At least not in most cases. In the above example, notching the vertical 2 by 4 even a quarter-inch would sufficiently lock the horizontal one in place, and with an additional screw or two, you have yourself a pretty solid joint. This joint can now withstand most rotational forces, as well as those in the up-down directions.

The obvious times when you would probably need to notch deeper is for major structural members. If a horizontal beam were to support something like a second floor for example, you would either have to lay it OVER the vertical columns(as in resting on the top-end of the columns), or notch it a couple inches. The exact depth would depend greatly on the expected load as well as the timber cross section you have to work with. Naturally, as the load increases, so will (or should) the second moment of area. (See my article Second moment of area made easy for more information on this.)

One thing to be careful about when notching is the depth of notch in relation to the position of the notch on the board. Bear in mind that depending on position, a board is only as strong as its weakest, or should I say thinnest point. Say you wanted to join two 2 by 4’s in the above “cross” fashion, and wanted to notch it so as to make the joint flush on the outside faces. This would require you to notch both 2 by 4’s halfway and slot them into each other.

While this is perfectly fine for non-structural uses, this kind of notching would not be recommended for structural members of any kind. As far as the structure is concerned, these are no longer 2 by 4’s but 2 by 2’s. While you may have a nice flush joint, half your 2 by 4 is notched out and gone, rendering it unsuitable for any project that requires the full strength of a 2 by 4. In any case, it’s better to sacrifice looks than safety.

If you’re bent on having this kind of joint intersection, you would need to use timber that is double the cross section you actually need so that after notching, you’ll still have the full strength needed. This is one reason you often see overly large columns and beams used in rustic construction where the framework and joints are visible. Obviously it looks pretty damn good, but the structural members must also be compensated due to the notch work.

Comments are closed.