Rusting Steel in Post Bases Risks and Fixes
Recently, we took a look at a patio that was built off the side of a building. The patio has a rooftop above that is supported by a set of posts. An area of the concrete slab had been installed after one of the posts. A different area of the concrete slab had been cut to allow the other post to be installed. Both of these posts happen to be made from steel instead of wood. Both of the posts are rusting near the base which can lead to accelerated deterioration and shortening of the lifespan of the posts.
Overall, we’ll examine the components of this construction in a two-part series. Today, we will start by discussing some of the framing elements. Then, in this coming week we’ll take a look at the issue of steel post oxidation and accelerated deterioration.
In most cases, here in Washington DC, particularly for residential construction, we will often use wood posts. In some cases, steel is a better alternative though. Steel is generally lighter weight, but has better options for connection to other elements of steel framing, in most cases. Also, in some cases steel posts can be configured to attach strongly to wood framing elements, as well.
The picture below shows a custom fabricated channel at the top of the post which allows for a wide positioning bolting pattern to connect to the heavy wood timber used as a girder. The layout of this type of installation is very similar to a typical deck construction. The framing at the underside of the awning roof is similar to framing you might expect to see in a typical backyard deck.
For most decks, a support may be installed back at the building. From there, a ledger board can be attached, generally bolted directly to the building facade. The side rim joists and the majority of the other joists in the deck framing will also run perpendicular to the building facade, in most cases.
The joist will generally terminate away from the building, where the ends of the joist will be connected with a perpendicular rim joist. The support for the portion of the backyard deck away from the facade can be supported near or in line with the rim joist. In most cases though it makes more sense to bring that girder in from the end, just a foot or two.
This leaves the last foot or two extending outward in a cantilever type configuration. The majority of the weight will still bear directly on top of this girder, at the exterior most side of the deck. It helps to offset the girder placement slightly because it reduces the amount of load required on the individual main deck joists.
Even though this is an exterior roof system, not an actual deck, the framing is very similar. Here, because the roof is intended to convey water away from the building, a gutter has been installed. The gutter attaches to a fascia board at the location where you would normally find the exterior rim joist. A rim joist generally serves multiple purposes. It ties together each of the individual joists, adding rigidity to the structure.
Here though, instead of using an actual rim joist for this purpose the connections from the joists to the girder have been reinforced with additional steel connector ties. In the picture below, you can see the bolts at the outer corners of the steel channel. Spacing bolts farther apart allows for greater strength. Not all connection points though have the size or span to allow for sufficient or improved spacing in the layout of bolting patterns. It’s generally a better idea to not install fasteners at the end of wooden boards.
Wood has a tendency to split when a large fastener is inserted near the end of the board. The individual grain elements in wood are weakest near the ends. Also, by installing fasteners close together it can increase the chances of splitting. Several things can be done to decrease these chances of splitting, when the framing elements or configuration provide few alternatives for better spacing. One of the most common methods to reduce the chance of splitting is to pre-drill areas of lag installations.
Legs are a type of screw, and they require the area of the wood to not be drilled so large that they are loose. The threads of screws must be able to bite into the wood. Being able to have this interface requires the hole to be about the size of the shaft of the screw or smaller, but not larger than the threaded section of the screw. In fact, we would more often recommend a pre-drill not be larger than the shaft of the screw.
As an alternative to screwing, in cases of beam to post connections, carriage bolts or similar types of bolting fasteners can also be used. Bolts and screws are different from one another. Bolts require not just wood for the threads to lock into, but they require an additional element at the opposite side of the screw head, from the fastener.
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
