When to use an Engineer

Using the span tables, rules of thumb, and help available from this site you can do much of the structural workup for your own building projects. So when do you need to talk to an engineer and how do you use their time most effectively?

First some perspective...

Standard plans and most beam and span tables are engineered for the DOWNWARD loads that are at work on a building for 99.9% of its lifetime. Some of these loads (such as snow loads) will go on and off the structure but are fairly easy to design for.

Then there are the big dynamic loads - especially the sideward and up and down motions that come with unusual events such as hurricanes and big earthquakes. These are forces that are both much more complex (and to some extent) unknowable.  

However, after every earthquake or hurricane, engineers pour over the wreckage assessing what did and did not work to hold things together. They then use these tricks and revised analytical models to predict how future buildings can be inexpensively made to withstand such forces. Nothing is certain but death and taxes, but your engineer can provide your house with a kind of security blanket.

The real question is, is your project subject to such unusual forces? If so, an engineering review by a practical and up-to-date local engineer is good insurance. (Workups on most of my own local projects cost about $300.)  

If you do work with an engineer, have them check the beams and joists (the easy part), and also do a lateral analysis based on the wind and shear loads that local buildings are currently being designed to withstand.

Here are the conditions that can make an engineering review either a good idea, or a requirement of your local building department:

How to make the engineers job easier (and perhaps eliminate the need for one entirely):

In summary, an engineering review can carry a lot of the burden of convincing an inspector to approve your building permit. And it will help you sleep better as well.