Now that you are familiar with the role the engineer provides to the public and the construction industries, we can explore the various scenarios where an engineer may be needed or required.
The building codes don't always identify exactly when an engineer is required. That decision can be left up to the chief building official in the building department, he has the power and decision making ability to decide how the codes are to be enforced. He usually has enough leeway that he MAY let an architectural firm be responsible for the engineering work on some projects, even though they aren't actually engineers. But this would most likely be because he is familiar with the firm, it's principles, and track record.
But remember that building department officials do tend to be cautious, after all it's the nature of their business to be forever vigilant for potential problems. Add the fact that negligence suits against building departments aren’t exactly uncommon and you can begin to see why the man behind the counter may want more documentation on a new and unique style of building compared to a traditional design.
One reason you may be required to get an engineer to sign off on your project is based in state law. Usually it's the states that are the actual adaptors of the model building codes, and when the code is adapted it is entered into the law of that state. The state law cannot be so easily over ridden by the local building officials. If your state’s laws govern when an engineer is needed you may want to check for exceptions. Often single family structures, (for example for building not higher than 2 stories and basement), or garages, or farm buildings are exempted, If you feel the need to avoid the use of an engineer at all costs, your challenge will be to make your project fit the available exemptions.
Another way engineers may be required is by inference
An example of inference is when the building code states, “Any method of construction to be used shall be based on a rational analysis in accordance with established engineering principles”or “Sufficient strength must be demonstrated by structural calculations".
It’s most probable that your local building codes and regulations will identify when a structural engineer is required, by some similar phrasing. In many jurisdictions the deciding factor may come down to whither the building has a beam over a specified length, or a wall over a certain height, which will then require an engineer’s approval.
Another area you could potentially run into a request for an engineer’s certificate is in the case of welding work. Without the certificate of compliance to ascertain that the welding work was done as shown on the plans, you MAY find yourself with a building department ruling that will allow for only ½ the allowable maximum strength of your welds. It's up to the building dept. how hard nosed they want to be, so be nice to them.
As you can see by the number of times the word MAY has been used in this chapter so far, there are a variety of possible times and reasons you will need to call upon an engineer to assist you with your container home plans.
When you do need the verification of an engineer to get the permit, you should be sure to file a written record of the computations he used to justify the design. Each drawing and written computation should be signed by or stamped by an engineer licensed for the type of service performed.
By code a wood framed structure's size is limited by its fire resistance. The area and height can only be increased beyond a certain point if fire resistance increases. Because of the way the fire rating regulations are written, the typical single family residence can be built from wood, but as the floor plan grows larger fire walls and other measures meant to mitigate fires spreading add to the cost. For this reason in larger residential and most commercial construction, steel has become the material of choice. The large commercial structures, such as shopping malls and other structures that can hold a large number of people, are almost always exclusively some combination of steel and concrete, primarily for their fire resistant properties.
Unfortunately, when some used shipping containers are converted into a residence the building department is likely to evaluate it like any other steel buildings. Because of the fire ratings issues mentioned, in the eyes of the building department a steel building will automatically be assumed to be a more complex structure than the typical wood framed residence, calling for a more stringent review.
This can complicate things if you aren't able to talk the talk of the engineers at the permit counter. While a wood structure of the same size would avoid the need for structural drawings of the wood framing by relying on the free engineering which is readily available from the included charts and tables in the code book. These standards for sizing rafters, floor and ceiling joists, floor girders, roof and floor sheathing are readily accepted by building departments. However, steel construction, from the building department’s perspective, is a whole different animal, each steel building is generally given more scrutiny, rightly, or wrongly.
Your presentation and level of preparedness are going to play a crucial role in how far you can get with the building department. If you keep your project “simple/stupid”, as the saying goes, you may even be able to get permits without getting an engineer involved. The further your design grows into a radical departure from the designed and intended use of the container, the more likely you are to need the assistance of an engineer. If that becomes the case this section should provide you with enough knowledge to have an intelligent conversation with your selected engineer and building department.
Because it's so unusual to see so much steel in a residential construction the building department will almost certainly deem it worthy of a second look, and perhaps even a third look, just be prepared for a lot of meetings.
Ideally, if everything goes you way, the building department will be satisfied with the dead and live load calculations and your structural plans. And again, I can't stress enough how much depends on the local environment. Trying to maneuver a container home project through the building department of New York City or Los Angeles is completely different from doing do so in a small town or county in Texas for example.
Technically, if the load calculations relevant for your area are up to code and all other aspects of the project are up to code, your project passes and a permit should be issued. But, If the man behind the counter has personal issues with you, or your attitude, or even with your project, you may expect to jump through some additional hoops, "No rubber stamp today sir, sorry".
The bottom line is; you'll never know the exact situation in your jurisdiction until you apply for the permits. There is more information on the permitting process in the construction section.
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