There are probably as many different types and styles of decks as there are houses. However, from an inspection point of view, your main concern should be safety rather than appearance. When inspecting a deck, you should begin with the supporting members underneath the deck area. If the deck is more than a few feet above the ground, it will typically be supported by wood or metal columns, on appropriate piers or footings. When the deck is closer to the ground, and does not have a roof structure, it may be installed on shallow pads or footings.

Treated lumber should be used when wood will be in contact with soil. Dampness normally associated with this soil will promote deterioration in wood. Supporting columns should not be installed in a situation where they could absorb water into the bottom of the posts. Concrete that does not collect water is acceptable. Cast aluminum standoffs, called plinths, are usually used to raise the columns above a moist condition. Posts, columns, pads and footings should be plumb, secured properly at the top and bottom, without deterioration or cracking that may impact the integrity of the deck structure.

Most decks are supported or attached to the house on one side, without any vertical supporting posts. The most common method of deck attachment is to attach the stringer joist or ledger board to the structural components of the residence with through bolts and large washers or lag bolts. It is important that the through bolts or lag bolts are long enough to penetrate into the floor framing of the residence, or completely through the foundation walls. Supporting of the ledger to the band joists of the house with nails, either through the ledger and into the ends of the joists or toenailing is not sufficient. Any movement of the ledger away from the band joists severely weakens the load-bearing capacity of the deck.

It is important that the joists be properly supported, either by metal joist hangers fastened to the band joist, or is placed on a cleat or ledger strip. The metal joist hangers or stirrups are the preferred method of attachment. When evaluating the attachment, it is important that nails be placed in all holes in the joist hangers.

There should be approximately 1/4-inch space between the decking. This space allows rainwater and melting snow to drain away from the deck and helps to prevent deterioration. If steps lead to the deck, the treads, stringers and handrails should meet typical stair requirements. The stringers for the steps and support posts should rest on a concrete pad, rather than being placed on or in the soil. When the deck is more than 30 inches above grade level, a guard rail should be installed around the perimeter for safety. The balusters in the guard rail must meet the 4-inch maximum spacing requirements. The guardrail, as well as the hand rails to the stairs, should withstand a 200-pound load applied at any point and from any direction to the railing.

Today, most decks are built with pressure-treated wood. This wood is treated with an arsenic compound to render the wood resistant to wood-destroying insects and deterioration. There are 3 levels of treated lumber. Foundation grade (FDN) can be used in the ground. Ground Contact (GRD CNT) can be used in contact with soil. Custom grade is treated lumber, however, it has minimal protection characteristics.

The pressure treating of the wood does not increase its weather resistance. In fact, unless the pressure-treated material is appropriately sealed, the material will usually crack and splinter very rapidly. Most manufacturers suggest that the treated wood be finished with a semi-transparent stain rather than with paints. Water-repellant treatments are also good. To identify pressure-treated lumber, look for the green tinted stain. Pressure treated lumber is properly stamped or end-labeled. If the labels are not accessible or visible, then the material should be reported as standard grade lumber or at least qualified.

Standard grade lumber is also used for the construction of decks. This material should be treated or coated, either with paint or stain, to prevent water damage or deterioration. The material is also susceptible to wood destroying insect infestation. It is important to keep in mind that materials such as cedar and redwood are not pressure-treated lumbers and are standard grade material. Although cedar and redwood, to some extent, are naturally resistant to wood destroying insects, they are prone to water damage and deterioration.