As a designer, every moment of your time is valuable.  You can save a considerable amount of time in your design process by selecting the correct design parameters at the beginning of the design phase.  In fact, you can even eliminate the risk of redesigning an entire job simply by setting up your job with the correct general overall settings. Even for a design pro, these may be valuable ‘refresher’ steps.
Step 1: Review the construction documents.
The very first step is to carefully review all the construction documents that have been submitted with the job package. These documents will either provide detailed design specifications to follow, or prompt you to select correct job settings. If the construction documents do not contain job specification or job descriptions, ask your customer what type of structure you will be designing trusses for. The more you know from the start, the quicker you can get the job done!
Step 2: Set up your job defaults.
Once you have reviewed the job documents, you are ready to start setting up your job defaults within the MiTek® 20/20® Engineering software. To do this, start a new job by clicking on ‘File > New Job’. Provide a name for the job and click OK. At this point, you are presented with the JOB BASICS dialog window. This is the location from which you can save considerable time by setting up the proper information. Start by entering the default information for your job, such as basic span, slope, overhangs, heels, etc. Once those basic criteria are entered, click on the DESIGN INFO button in the lower left hand corner of the dialog window.
Step 3: Define your Design Info.
In this dialog window, you will define the Occupancy Category and Building Code required for your job. Occupancy Category refers to the type of structure you will be designing. The options are Residential, Commercial, Agricultural and Essential. The Building Code field is where you select the required building code for you job.
A few Building Code explanations:
There are two main design codes that have been adopted all over the country. They are the International Building Code (IBC) and the International Residential Code (IRC). While the IRC is limited to designing one and two family dwellings and multiple single-family dwellings (townhouses) not more than 3 stories in height with separate means of egress, the IBC can be used to design basically any type of building, commercial or residential. So if the construction documents do not specify a building code and they are titled “Customer Residence”, then the IRC may be an appropriate choice. But if the documents are titled “Acme Office Building”, then they would fall outside the criteria for the IRC building code, and the IBC would be the appropriate choice.
The International Code Council (ICC) issues new codes in 3 year intervals. There are 3 to date, starting with IRC & IBC 2000, followed by the IRC & IBC 2003, and the most recent IRC & IBC 2006. You can visit the ICC’s website: ( and view each state’s adoptions, as well as download State and jurisdiction adoption charts, and purchase your states edition of the ICC codes.

Once you have selected the Occupancy Category and the Building Code for your project, click on OK. This will return you to the Job Basics dialog window.

Step 4: Set your Loading defaults.

From this location, click on the LOADING button (next to the Design Info button) in order to setup the loading defaults for this project. You will now be faced with the Loading dialog window. From this location, you will define the loading defaults to be used throughout the job.

Start by setting the Top and Bottom loads as defined in your job description. Then click on the Wind Tab to define the wind loads to be applied to your project.

Once you have selected the appropriate Wind Design Method for your project, select the SNOW tab and select the correct snow design method for the job you are designing:
[In this example, we have not addressed any of the factors that are shown on the Wind or Snow tabs, but only shown how to select the Design method referencing the corresponding version of ASCE 7. (Note: For the wind example, the focus is on the ASCE 7-05 method. Although hybrid wind was selected, MWFRS or C-C may have been appropriate, as long as they were ASCE 7-05.)]
A quick reference guide for Building Code/ASCE/TPI could be shown as:
         IBC/IRC 2000                                IBC/IRC 2003                           IBC/IRC 2006
ASCE 7-98 wind and snow           ASCE 7-02 wind and snow       ASCE 7-05 wind and snow
  ANSI / TPI 1 – 1995                        ANSI / TPI 1 – 2002                  ANSI / TPI 1 - 2002
It is important to have the correct design methods chosen because the different editions of ASCE 7 use different calculations for wind and snow design. These very possibly will yield different designs, and in addition, TPI 1 -2002 has many new enhanced plating checks, different deflection criteria, and unbalanced load check requirements that are not included in TPI-95.
While there are still many factors left to consider, these are the basic design methods that will be used in the truss design for the job.
Step 5 – Start Designing!
Questions? Call our Chesterfield office at – 1-800-325-2556
Stay tuned for future articles in which we will review the critical details of wind and snow loading parameters.

 This page last modified on 11/27/2007