The purpose of the Structural Engineering Services inspection was to visually examine the timber-framed decks extending off the front of the home at the second and third levels and provide a report including findings and recommendations. With approval from the homeowners, areas of the soffit at the underside of the deck were removed during the inspection in order to perform the inspection.

The structure is a three-story detached timber framed structure most likely founded on shallow concrete footings. At the second and third levels, timber decks extend off the front of the structure, above the driveway below. The floor level height of the first deck is approximately 12½ feet above the driveway’s concrete slab, while the height of the second level, directly above, is approximately 21½ feet. At the front end of the deck, Laminated Veneer Lumber beams (LVL’s) with dimensions of approximately 3½ inches by 11¾ inches provide the support at each level, while at the end of the deck adjacent to the home, the support is derived from the connection to the house’s framing. The deck’s floor joists span from the connection with the house to the LVL beams, approximately 9 feet maximum, and cantilever over the LVL beams by approximately 2 feet 3 inches. The LVL beams (2 per level) are supported by 6×6 columns of preservative pressure treated (PPT) dimensional lumber extending to concrete pedestals below. At both deck levels, a 2×10 dimensional lumber ledger is attached to the front face of the house and the deck’s joists are attached to this ledger using steel joist hangers. The overall width of the two story deck is approximately the same width as the house, approximately 40 feet, and the total length the deck extends from the front of the house is approximately 11 feet maximum.

Several framing details key to the structural adequacy of the deck were investigated. A few areas of the soffiting below the deck was removed in order to view an example of these details and get a clear idea of the workmanship and structural soundness of the assembly. The area of soffiting removed was limited to the right side of both the first and second levels. The following framing and connection details are key to the structural function of the deck and were investigated during the inspection:
- Connection of the deck to the house (ledger board condition and connection)
- Column to beam connections
- Connection of the deck joists to both the ledger board and the supporting beams
- Span lengths of structural members
- Railing post connection details

These typical details as well as member sizes must adhere to certain codes and specifications and/or be designed for appropriate loading conditions. These details, as observed from field investigation on this deck structure, are described below.

The connection of the ledger board to the structure in a timber framed deck, especially for a deck that is not free standing, is an extremely critical connection, and can lead to failure if not adequately designed and constructed. The ledger board in the case of this particular deck is of 2×10 dimensional lumber, not preservative pressure treated (PPT). The ledger board is attached to the front of the house, which overhangs the foundation below. The home’s overhang is supported by metal plate connected wood trusses (MPCWT’s), which support a portion of the second level floor, and cantilever over the 2×6 front load-bearing wall at the first level. This overhang varies from approximately 2 feet 3 inches to approximately 4 feet. The second level’s MPCWT floor framing supports the front exterior stud walls of the second and the third levels at the end of their cantilever span. The ledger board of the first level deck is fastened to the home in the area of this cantilever. The first level ledger board is connected through a combination of lag bolts and nails. Two different sizes of lag bolts appear to have been used, ½” diameter and 3/8” diameter. The soffit and structure’s sheathing at the underside of the overhang (right side only) was removed in order to investigate the ledger connection to the MPCWT’s. Of three lag bolt connections viewed, two of these connections were solely into the OSB (orientated strand board) sheathing. One lag bolt appeared to be connected to the end of a MPCWT. The average lag bolt spacing seen was approximately 16 inches on center. The deck’s second level ledger board was observed at the right side. 3/8 inch diameter lag bolts were used and extend through the OSB sheathing of the house. The actual connection of the deck’s second level ledger board to the structure’s framing cannot be inspected unless the interior finishes are removed and the area be investigated from the inside the home.

There are serious issues concerning the current connection of the deck’s ledger boards to the front face of the house. The deck’s first level ledger board in many instances is simply connected to the OSB house sheathing with ½-inch and 3/8-inch diameter lag bolts. This connection is extremely inadequate due to the relatively low strength of the OSB to resist pull out and bearing of the lag screw. Typically, a special detail is required when connecting a deck ledger board to a MPCWT floor system. These details usually include special bridging within the bays between the ends of the trusses and a specific lag or through bolt spacing based on the length of the deck joists. An alternative to the special bridging may be a 1-inch thick Structural Composite Lumber (SCL) or 2x dimensional rim board. Neither of these details is present in the existing deck connection. In addition, 3/8-inch diameter bolts are typically undersized, as ½-inch diameter lag and through bolts are usually specified for ledger board connections. The lag or through bolts should be connected to the MPCWT floor system using a staggered pattern, as to avoid splitting along the grains of the ledger board. The current bolting pattern observed at the right side of the deck is not in a staggered pattern. The ledger board itself should be comprised of PPT lumber, however the current 2×10 ledger board is not PPT. There are several standard details available based on studies and tests conducted by the Virginia Tech Department of Wood Sciences and Forest Products and Washington State University Wood Materials and Engineering Laboratory. These studies and tests have been adopted by the 2007 Supplement to the 2006 International Residential Code (IRC). These documents should be used as a guideline when designing deck ledger connections. Prior to this supplement, the connection of the ledger board to the structure should be adequately designed to resist vertical and horizontal loading. It appears as if the current ledger connection at the first level is not strong enough to properly resist vertical and horizontal loading. The deck’s second level ledger connection was not observed except for the lag bolts present, which appear to be 3/8-inch diameter.

In addition, attached decks are typically not to be supported by the overhang of a structure unless the framing supporting the overhanging portion was designed to support the additional load of the attached deck. In this particular instance, the MPCWT’s that cantilever off the front wall must be designed to support the loads associated with both decks, the first and second levels. Original drawings and the original truss design should be checked to verify that this loading was considered. Otherwise, the trusses may be overloaded.

The connection of the LVL beam to the 6×6 PPT column is achieved by notching the top of the column to receive the beam in full bearing. The column is then face bolted to the LVL beam using 3/8” diameter lag bolts. The column supporting the second level deck simply bears on the plywood decking of the first level deck. It appears as if a small piece of 6×6 PPT column has been placed below the decking in this area in an attempt to transfer the load of the second level column to the first level column below, however the blocking was loose during the inspection and the plywood decking supporting the second level’s column was sagging under the column’s load. In addition, it appears as if the first level column was cut slightly short, and the 2×4 used to connect the soffit to the underside of the deck was partially supporting the blocking.

Typical details for the connection of the post to a deck beam usually require ½-inch diameter through bolts. This can be verified within the “Prescriptive Residential Deck Construction Guide” published by the American Forest and Paper Association. In addition, the column support to the second level deck is inadequate due to the blocking condition between the top of the first level column and the bottom of the second level column. The second level column bears on the plywood decking and a sag can be seen in the plywood decking. The 6×6 piece of blocking placed within this location is currently loose and does not bear on the column to beam connection below.

The deck joists are comprised of 2×10’s of dimensional, non-PPT lumber and are spaced at approximately 16 inches on center. The joists’ main span (from house connection to LVL beam) is approximately 9 feet maximum and the cantilever span from the LVL beam to the end of the deck is approximately 2 feet 3 inches. The joists are connected to the ledger board using steel face mount hangers, Simpson Strong Tie, Model LUS 210Z. The joists rest upon the top face of the LVL beam and are toe nailed into the top of the beam. The deck joists supporting the second level deck have been ripped in order to provide a positive slope away from the structure.

The deck joists appear to be properly fastened to the ledger with steel joist hangers. It appears as if corrosion resistant fasteners have not been used in the toe nailing of the deck joists to the top of the LVL beam. Also, the connection between the joists and the LVL beam may require the addition of brackets connecting the joists to the beam. A proper bracket will assist in the bracing of the LVL beam, thereby restricting the possibility of lateral movement, or buckling. Typically, manufacturers design their engineered lumber products for continuous lateral bracing at 24 inches maximum.

The main span of the LVL beams is approximately 18 feet 3 inches. The LVL beams cantilever at each end between approximately 8 inches and 1 foot 2 inches. The main span of the deck joists is 8 feet 3 inch maximum (7 feet minimum) with a 2 feet 3 inch cantilever overhang.

Calculations were conducted to check the span lengths of the LVL beams as well as the deck joists. Since the manufacturer’s stamp of the LVL beam was not visible, a reference modulus of elasticity and bending strength were assumed based on literature from a common manufacturer. The LRFD method was used to verify the beam’s strength, using the 2005 National Design Specification guidelines published by the American Forest and Paper Association (AF&PA). The LVL beam appears to be strong enough in bending and stiff enough for allowable deflection based on these referenced values. The maximum span of the joists were cross referenced with The Prescriptive Deck Construction Guide, which is based on the 2006 IRC, and is published by the AF&PA. It appears as if the main span of the joist (from the front face of the house to the LVL beam) is well within the allowable span length for a 2×8 joist of hem fir species spaced at 16 inches on center. However, the allowable maximum cantilever span is typically the main length divided by 4. This would result in a 1 foot 9 inch maximum cantilever overhang length. The cantilever span of the joists present is 2 feet 3 inches, which would signify an over-spanned condition, and would require a design for this specific case.

The railing posts of both levels of the deck are comprised of 4×4 PPT dimensional lumber and in some instances extend through the floor decking and in other instances are simply nailed to the top of the decking. The right side posts were inspected from underneath and it was found that no posts were fastened to the deck framing with through bolting. Of the four posts investigated, two extended through the deck and two did not. The two posts that extended through the deck seem to be simply toe nailed to the right end joist and rim board. The first level railing posts at the front and rear of the second level’s right column do not extend through the plywood decking and appear to be simply toed into the plywood.

Typically, the standard detail for connecting railing post to the deck framing should include ½-inch diameter through bolting to the deck joists. In several cases, it was observed that the posts did not even extend through the plywood decking, making them susceptible to detachment.

Due to the severely deficient structural conditions observed, it is recommended that access to the deck be restricted until such time that the deck can be strengthened. The process of strengthening the deck will require the strengthening of the connection with the house, strengthening the connection between the columns and the LVL beams, strengthening the connection of the railing posts, and possibly converting the deck to a freestanding deck if the home’s MPCWT floor system was not designed to support the additional weight associated with the two deck levels. It is also recommended that the connection of the second level ledger with the house be investigated by removing interior finishes such as drywall and insulation in this area. The structural condition of the second deck connection cannot be fully surveyed unless the inner connection is visible. It is recommended that details be provided for making the deck structurally adequate. Much of the need for redesign may be eliminated if original design plans can be located. If the deck was designed properly, it may be simply an issue of improper construction, and the original design details may be reused.

An additional noted area of concern is the water-tightness of the soffit and capping. Trapped water in the underside of the soffit was released when the soffit was removed. Since very little of the lumber used in the framing of the deck is PPT, the prevention of water from contacting the timber members is important. Minor water staining to several timber members could be seen during the inspection. It is recommended that drip edges or channels be introduced at the flashing present at the fascias of the decking. It is also recommended that the overall soffit construction be inspected for water tightness.

Note that the opinions, recommendations, and conclusions presented in this report or discussed during the inspection are based on my observations and engineering experience. They are based on visual symptoms or lack of symptoms of structural problems common to this type of construction. No destructive inspection or material testing was performed, thus this report is based on the visual inspection of accessible and visible areas only.