Strong Connections for Your Deck and Pergola
A few weeks back, we looked back at a pergola that is mostly made with a Western Redwood Cedar, and although it is primarily made from wood, there are lots of metal connectors used in the entire assembly. We discussed several details and looked at several different angles of this pergola in this past week’s blog. Today we’re going to show additional details that help make this pergola, and similar backyard deck assemblies, strong. The pictures below show the upper portions of the pergola and how those elements are interconnected.
Often in deck and pergola construction, shouldering is often used to connect horizontal elevated beams to vertical posts. Shouldering is cutting out a portion of the post so that the post or column so that beam can be seated into that cut out recessed. When installed in a shouldered fashion, the beam is seated in a much much stronger position. We’ve looked at structural dynamics of deck construction and pergolas and another backyard carpentry type elements, in many of our past blogs. However, this particular issue of beam connection is one of the areas we haven’t discussed deeply before. We’ll take a much closer look at this specific issue, of beam engagement, in an upcoming future article.
Connecting posts and beams in deck and pergola construction requires good fasteners. ‘Good’ can be measured by the right balance of the following characteristics:
- Strength
- Installability
- Durability
- Cost
Strength is not necessarily just measured in one context, but two of the most common measurements of strength of a fastener are its tensile and shear strength. The way we’ll explain this is definitely an oversimplification, but you can basically think of the difference between tensile strength and shear strength as looking at the tensile strength as the resistance to pull out.
When a fastener is set into a substrate, it has a strength to retain objects that it’s mounted to. In most cases elements are mounted to connect two different elements. In this case we’re talking about a beam connected to a post. That’s one of the most common and simple type of connections in deck and pergola type construction. Those two elements are sort of pressed together by a bolt or a fastener. In a sandwich type assembly. The fastener’s tensile strength holds them to each other.
The number printed on the bolt in the picture below indicates that it is a stainless steel material. Specifically, the ASTM A182 UNS S30400 is a specification of requirements mandated for a type of stainless steel. You can see that under the head of this bolt, a washer is placed the expand the area of force of the head. The same assembly is applied at the nut side at the other end.
In contrast, the shear strength is the resistance to snapping. Imagine if the post and beam move in the opposite direction from one another, the two different sides of the business will be pulled in opposite directions, almost like snapping or bending the fastener. At some point, at some level of force, the fastener will actually break or snap. The ability to resist that pressure or force is the fastener’s resistance to shear mechanics or its sheer strength.
Some of the most common options for types of connecting hardware includes bolts (lag bolts, carriage bolts), screws (deck screws, structural screws), nails (hot-dipped galvanized, stainless steel, copper), and structural hangers / ties.
The material choices for these connecting hardware elements will impact the overall performance and the criteria we discussed above (ie: strength, installability, durability, and cost). Stainless steel offers one of the highest performance levels of corrosion resistance but is simply expensive. Hot-dipped galvanized provides decent protection due to its better adhered zinc coating, while electro-galvanized is cheaper yet has way less corrosion resistance. Copper has corrosion resistance and is naturally antimicrobial, but is generally very costly, will discolor over time (which may be desirable), and is generally much weaker.
In addition to the basic metal fasteners, there are also some alternative approaches like some types of mortise-and-tenon joints that do not rely on hardware. This option though may require significantly more expensive wood materials and extremely specialized labor options.
The picture below shows the flashing location where a copper screw has been installed, not for structural purposes, but instead to attach the copper flashing on top of elements of the pergola.
In other locations, even in the same overall assembly, copper nails have also been used for the same purposes.
Use a contractor who understands and cares about doing things right. Always, feel free to reach out to us here at Dupont Decks and Patios. We are happy to help with almost all steps of the deck building and design process. A backyard and outdoor space should make a significant, positive impact on both quality of life and home value. We can help with more than just decks, we also build patios, pergolas, ramadas, awnings, gazebos, arbors, and privacy fences.
Let us know about your ideas and talk to us if you have questions about possibilities. We are happy to participate in improving your outdoor space and quality of life! You can call us at (202) 774-9128. You can find us online at https://dupontdeckspatiosdc.com and you can email us there as well at https://dupontdeckspatiosdc.com/contact-us
