Got questions? Answers just a click away

The National Frame Building Association is a vital clearinghouse for information on post-frame. NFBA members receive free technical, legal and market information and advice from experts who are uniquely knowledgeable about post-frame.

As NFBA Technical Advisor, I am charged with coordinating technical and research initiatives and responding to technical questions about post-frame.

NFBA has been engaged in several technical projects since I began serving in this capacity. One of our most important recent accomplishments has been the development of a model specification for post-frame building systems in three-part CSI format.

Anyone may download the model specification from the NFBA web site at www.nfba.org.

We plan to make an interactive online version of the form available for use in the near future.  The development of this specification was key to further expanding post-frame into the commercial construction market, in accordance with the NFBA’s Post-Frame Market Initiative to grow the industry. There are hundreds of technical articles and other resources available to NFBA members only online.

As NFBA’s marketing efforts have delivered more traffic to NFBA’s web sites (along with more business referrals to members), more people are now posting questions on the “Ask an Expert” module on the NFBA web site.
Anyone may go to www.fnba.org and visit the “FAQ” section to post a question on one of two categories:
Below are questions and answers to technical questions posed within the past few months.

Question 1: Help with posts
I am interested in building a 40×60 post-frame building with 14’ side walls and a room in attic (40psf live load) engineered truss (6/12 pitch).

How can I determine the correct size for the posts (6×6, 6×8?) and header size (double 2×10, double 2x12s?) as well as the post spacing.

I live in southwestern Michigan. Thanks for the help.

Answer
Post-frame buildings are engineered systems. The post sizes depend on many factors including the building site, the intended use for the building, and structural detailing. To determine the correct sizes and spans of structural components, a qualified engineer should perform the necessary design analysis and calculations. You can find a qualified design professional near you from the “Find a Designer” links on NFBA web sites.

NFBA offers in-depth seminars for professional engineers about how to engineer post-frame structures at our annual convention and trade show, Frame Building Expo. For more information, visit www.nfba.org/Expo. 

Question 2: Condensation

Are there any industry standard solutions/details to prevent condensation on the underside of the roof system in an unheated post-frame facility housing animals? We are considering pinching a vapor barrier and batt insulation between the roof purlins and the metal roof panels, but are concerned about this causing the roof panels to bulge at the pinched locations and look “wavy.” Thank you.

Answer

There are two primary ways to prevent condensation on the underside of the roof system of an unheated animal facility: good ventilation of the underside of the roof and/or insulation of the underside of the roof. Good ventilation minimizes the potential for the moisture laden air from the animal facility to accumulate near the roof; insulating the underside of the roof keeps the temperature of the lower side of the roof above the dew point (the temperature at which condensation begins to form on the underside of the roof surface). Good ventilation of the roof area is beneficial whether or not the roof area is insulated.

An old, but still good, reference on environmental control of animal facilities is the Midwest Plan Service, Structures and Environment Handbook. This reference recommends an R-value of 6 for unheated, naturally ventilated animal facilities.

Additional information on heat and moisture control in animal facilities can be found in the latest editions of the ASHRAE’s Applications Handbook, especially the chapter on agricultural buildings. ASHREA’s Application Handbook, the 2006 International Building Code, and the 2006 International Residential Code provide sound information regarding control of condensation for commercial and residential structures.

If you apply insulation to the underside of the roof, it is important to install a vapor barrier to the
 underside of the insulation or to have a vented airspace between the top of the insulation and the bottom of the roof surface. Without one of these details, airborne moisture can pass through the insulation and condense on the lower roof surface.

Of course, once this occurs, the insulation and roof framing will become wet and with that occurrence all kinds of problems, such as ineffective, sagging insulation and deterioration of framing members, ensue.

Question 3: Post-frame home

I am going to build a house from post- frame. Is there anything that I should know about insulation, ceiling, concrete slab floor?

Answer

It is usually easier to insulate post-frame houses to high R-values than many other construction types because the wall cavities are thicker (6-inch minimum to 10-inch) and wall frame spacings are wider (4-ft minimum to 12 or 14 feet). Thus, there are fewer breaks in the insulation.

In addition, where breaks do occur, there is a 6- to 10-inch thickness of wood which has significant thermal resistance. Thus, the potential for thermal bridging in post-frame buildings is lower than for many other building types.

The 2006 International Residential Code provides recommended levels of insulation for residential buildings. ASHRAEs Fundamentals Handbook and Applications Handbook also have good recommendations for insulation of buildings.

Many of the builder and supplier members of NFBA could help you out with details of insulation levels and installation for your geographical area. Just use the “Find a Builder” or “Find a Supplier” online business referral system on www.nfba.org.

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