Decks – Improper construction could be hazardous

By: Rob Parker, RHI, CMI, CHI

A deck may accommodate a large number of people; because of this, it can be subject to bare a lot of weight. Unlike your interior floors that usually have direct bearing points for the floor joist, a deck may be supported only by connectors, at the house and/or supporting posts. In addition to problems associated with weight bearing, it is quite common to have the ledger board attached directly to the house, with no flashing or spacing to prevent water infiltration. This can lead to rot at the sill plate, bandboard, ledger, and/or siding. Water can also pocket which can freeze over the winter months, and cause damage to the siding, even vinyl and aluminum. There are some recommended methods to prevent this. One solution is a flashing cap. The flashing should go up under the siding at least several inches, angle out on top of the ledger, and bend down over the face of the ledger. This will force the water to run off and away from the siding. Another acceptable method is to space the ledger from the house, and fill the bolt holes with silicone or some other sealant prior to inserting the bolts. This will allow the water to drain between the deck and siding

Another serious problem involves the potential for rotting of supporting posts and/or footings. When support posts are put into the footing, and even the ground, they are prone to rot. Even pressure treated posts, may completely fail within a few years. The problem occurs when the post is put into the ground, and concrete is poured around the post. Once the concrete has set, the post has established a pocket in which water can collect. The water is absorbed into the post and cannot dry out. In colder climates the water freezes and can crack the concrete. Additionally, the deck should be bearing on top of the footing and not in it. One method to prevent posts from rotting is to pour the footing either level or above the grade. Then using a positive connection, such as a galvanized anchor base, the post should be bolted to the anchor which is embedded in the concrete. This will elevate the post off of the ground, and out of the footing. This will prevent the wood’s capillaries from wicking up water. In addition you will have direct bearing on the footing. It is also acceptable to pour a footing below the frost line, at least 8 inches thick; then sit the post on top of the concrete and tamp (pack) fill dirt around the post. This will allow the water to drain away from the post.  Some soils have a high acetic content or moisture level and may still cause the post to rot, so the post needs to be routinely monitored.

Other items to visually check for are a positive connection at the top and bottom of the stairs, to the deck or landing. The connections are often inadequate. With notched stringers it is imperative to have the bottom section of the stringer, which is solid, to be connected to the deck. If you draw a parallel line with the top edge of the board, the connection, should fall in the solid section of the board. Otherwise this connection is prone to failure if the grain should crack or fail.

The railing and pickets should also be secure. Ideally, the railing posts should be through bolted and the railing should be bolted to the deck frame securely. All pickets should be secure and on higher decks and care should be given to ensure the pickets are close enough together to prevent a child from falling through. A high deck with decking running perpendicular to the joist may be susceptible to shaking back and fourth. This may be due the lack of proper triangulation. A board fastened to the bottom of the joist from the ledger to the outside bandboard, can help stabilize the deck. Alternatively, decking running on a diagonal can add triangulation to the deck.

If you’re considering the purchase of a home, you should know that decks are included in a general home inspection. Your inspector will be able to provide information concerning the deck’s condition at the time of the inspection.