Revitalizing an Old Deck The Next Steps
This past week we started taking a look at the deck shown in the pictures here below. We pick up and continue with this topic today, and specifically this week we are looking closer at the structure underneath of the deck boards which shows the framing elements, the structural connections, load path, distribution of those load path and structural elements of the deck.
In the past blog, last week, we looked at several examples of the post connections above the deck itself. Several of those posts were connected with base plates which nailed around the perimeter of the bottom of the post. In most cases, post for connecting the guardrail will continue all the way from the footing or at a base plate above the footing up to the height of the guard rail. In this unique case, the deck was built as a continuous near horizontal platform, And it was later modified to have the guardrail added.
That type of circumstance is not common and is somewhat unique. Essentially when the post is extended or spliced with a separate portion, the separate portions have a relatively weak connection because connecting two elements in-line interrupts the continuous structural fiber of wood members. Unlike Steel and many other different types of materials, the axis of strength in lumber and framing elements comes from the wood grain.
Wood grain, goes back to the nature of the trees from which the wood comes from and even though there are many different types of species of wood, almost all of them grow in a similar type of manner. The wood green grows vertically up a trunk of a tree or near horizontally through the branches of a tree in a longitudinal type of direction. That grain direction provides the axis of strength.
cellulose microfibrils, embedded in a matrix of hemicellulose and lignin
Cellulose, a long-chain of polymers of glucose, which forms highly ordered crystalline microfibrils. These microfibrils, align parallel to the cell’s long axis, provide exceptional tensile strength due to the strong covalent bonds within the cellulose chains and the extensive hydrogen bonding between them. When a load is applied parallel to the grain, these microfibrils effectively resist deformation by distributing the stress along their length, because of that fibrous structure.
In the pictures above and in the pictures below you can see that at the underside of the deck, the wood framing is basically built with a series of 2x dimensional wooden joists. Those joists are pressure treated lumber and relatively strong for a floor deck type support when installed in this type of series of framework.
When a typical deck is built off the rear of a building such as a typical Washington DC rowhome, often there’s just a single girder that runs parallel to the rear wall the building. The rear wall of the building will generally support a ledger board and the girder will be installed in parallel several feet away from the building. Here though, this deck has a very large span and a girder is installed near the center and at each far side to provide additional support in a large or long span.
At each connection point where each joist connects to the girder, the individual smaller joist is connected with a joist hanger, a special type of steel hardware used to provide a firm connection between a ledger or girder and a connecting joist.
Another picture below shows those joist hangers as each of the joists where they connect to the girder. This deck was built decades ago and built relatively well and it’s held up pretty well considering. However, today a connection between a girder and a post would be made with shouldering, a rabbet cut the entire size of the joist or with specialized hardware to make the structural connection. In this case though the boards of the girder are simply mounted to the sides of the post and that would not be sufficient by the building code requirements today, in most cases.
In this coming week, we’re going to take a look at different pictures of an old deck that examine the guardrail around the perimeter of the deck. In the process of looking at these details, we will discuss the building code requirements and the typical standards for guardrail construction.
We recommend building and homeowners here in Washington DC use a contractor, like us, who understands and cares about quality, deck and patio longevity, snd simply doing things right. Always, feel free to reach out to us here at Dupont Decks and Patios, you can give us a can or just drop us a line. We are happy to help with almost all steps of the deck and patio building and design process. Let us know about your ideas and talk to us if you have questions about possibilities. 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
