Monday, June 6, 2011

Conventional Construction: What Is It?

History and Definition

Builders, designers and city/county plans examiners are all familiar with the term 'conventional construction', but what exactly is it? Long before the first building codes were written, builders had accumulated a lot of knowledge about light-frame wood construction. Buildings that stood the test of time (or didn't) demonstrated what worked and what didn't. The first building codes incorporated the materials and methods that worked best into a section on 'wood-joisted dwelling construction'. That term evolved into 'conventional construction'. Looked at another way, conventional construction is prescriptive structural design; "if you follow these rules, your building won't fall down". The review and update cycle continues today. In California, for instance, the 1989 Loma Prieta earthquake was a real-world test of conventional construction. Study of failed structures led to changes in the next code edition's structural design rules.


Reference works on conventional construction have been hard to find. The ICC (formerly ICBO) has published one book, updated with each new code version. The new edition, called Conventional Construction Provisions of the 2009 IRC: An Illustrated Guide, won't be available until July so we don't yet have an up-to-date guide to current codes. The latest published edition of the book is titled Conventional Construction Provisions of the 2006 IBC: An Illustrated Guide. It's still useful on most topics, but I'm hoping the new edition will be more complete. This book, and its predecessors, have been my primary guides to conventional construction. Conversations with G.C. Scott Milrod and Jim Heaney, building plans examiner at Santa Cruz County, have also been helpful.

Study on the subject of conventional construction is further complicated by the fact that so-called "model codes" such as the old Uniform Building Code (UBC) and the current Uniform Residential Code (IRC) comprise only the base layer of local requirements. California has its own rules, contained in the California Building Code (CBC). Although based on the model codes, the CBC contains many differences, so the ICC books must be used with caution. Thanks to the Internet Archive website, you don't have to buy a copy of the CBC-modified IRC. A viewable/downloadable copy of the document is available, titled Title 24, Part 2.5, 2010 California Residential Code.

Three Layers of Codes

More layers, sitting on top of the CBC, are local building codes which vary from one city or county to another. These take the form of amendments to the CBC, and are contained in documents such as the Santa Cruz County Code. The County Code is viewable online, but is currently not very helpful. The online version has not yet been updated to the current (2010) CBC.

This series of posts will attempt to provide some answers to questions about conventional construction. Next: What is it good for?