When should you hire an engineer to observe the construction of your project?

First, the legal background: The Building Inspector "inspects" construction. Engineers "observe" construction. What's the difference? Only the attorneys and the insurance companies know for sure, but "inspection" implies more detailed scrutiny than "observation".

The building code allows typical wood framed buildings to be constructed according to certain standards that have proven adequate over the years. Most carpenters have memorized these standards and apply them to the houses they build, which results in houses that meet the building code requirements for "conventional light-frame construction."

Complex modern custom home designs can prove extremely complicated from an engineering standpoint. Building codes require a "complete load path" that will transfer wind and earthquake forces to the building's foundation. This load path is almost never a direct route. Most custom homes feature stairwells, offset first and second floor walls, large expanses of windows, changes in floor levels and other architectural features that make their design so appealing from a visual perspective. These features can break the load path, and the engineer must address each break so the structure will carry loads around it to the foundation.

If your project required engineering, it is beyond the ordinary. Engineered designs include special requirements that will assure a complete load path. These may be as simple as adding a few more nails than the building code's "conventional framing" requirements call for, or as specialized as welding steel beams and columns into a rigid frame to carry forces around a wall full of windows. Structural features such as increased wall connections to the foundation, additional rows of blocking, long steel straps to "collect" forces and carry them to shear walls, shear wall tie-downs and the like may show up in a custom home design.

But I paid building permit fees so the Building Inspector will make inspections—why do I need the engineer to come out, too?

Even though municipal building inspectors are experts in a wide variety of construction fields, they typically cannot provide a thorough structural inspection of a house. This is because they have limited time allotted to each inspection. Forty-five minutes would be a generous time allotment for an "F-E-P" inspection (which means Framing, Electrical and Plumbing). The inspector might allow up to 30 minutes to inspect a house's structural frame. For residential construction the inspector will usually look for commonly found problems and construction that does not comply with the latest changes in the code. The inspector may not have time to become familiar with special structural requirements shown on the plans.

The structural designer can provide the most thorough and focused attention to a building's structural system. No one besides the person who designed a home is more familiar with all the structural requirements of its design. If the construction does not meet the plan requirements, then the person who can authorize changes to the plans is right there to provide alternative construction methods. Work does not have to stop while the municipal inspector waits for an approved change from the designer.

What stages of construction should the engineer come out to see?

The following list covers almost all phases of construction where structural observation could be beneficial. (Hardly any project involves all items on the list.)

Footing excavations completed, formed ready for placing of reinforcing. (To check for required footing dimensions and locations, etc.)

Footing reinforcing bars in place. (To check for proper size and location of reinforcement, tie-down anchors, sill anchor bolts, etc.)

Slab on grade reinforcing bars in place. (To check for proper size and location of reinforcement, tie-down anchors, sill anchor bolts, etc.)

Concrete placing operations. (To confirm proper concrete placing techniques, etc.)

Note: Items 2, 3, and 4 above can usually be combined into one observation visit.

Wood framing completed but not closed in. (To check for specified shear wall sill and stud sizes and end post size and anchorage, post and beam sizes and locations, special framing connections and steel straps, etc.)

Floor sheathing nailing completed but not covered. (To verify typical sheathing nailing and special nailing requirements at shear walls or drag-ties below, etc., which will be covered by subsequent wall construction, concrete floor topping, etc.)

Wall and roof sheathing nailing completed but not covered. (To verify special nailing requirements at shear walls or drag-ties below, steel straps, etc., before they are covered by roofing.)

Welding operations. (To confirm that a Special Inspector will inspect the welding, or that shop welding is done in an Approved Fabricator's shop.)

High-strength bolting operations. (To verify proper tightening of bolts.)

All structural work completed. (To check any other special building conditions.)

Which construction operations require Continuous Special Inspection?

Special Inspection is more formal than structural observation. Special inspections may be performed by the engineer or a qualified inspector selected by the engineer.

Grouting of concrete block walls when grout lifts are more than two feet high. (To confirm that block cavities are free of debris before grouting, and that grout is properly vibrated and revibrated, etc. Note: If walls are designed using only one-half of the strength that is otherwise allowed by the Building Code, then no observation is required.

Concrete placing operations for structural slabs and concrete walls. (To assure that reinforcement conforms to the Plans, and that concrete of the specified mix and consistency is properly placed and consolidated, etc.)