Armchair Builder

Manufactured Floor Joists and Fire Protection

Manufactured Floor Joists

If you are thinking about building a new home or addition, you will probably take a look at manufactured floor joists as an alternative for structural support.  Manufactured floor joists can replace traditional 2×10’s and 2×12’s in new construction.  They have some advantages over traditional dimensional joists but there is a recent code change you should know about.  Here we will discuss the advantages to using them and talk about how the recent code change may affect your budget.

Advantages to Using Manufactured Floor Joists

Manufactured floor joists, sometimes called I-joists, use a top and bottom flange that is separated by an oriented strand board (a.k.a. OSB) web.  There are some real advantages to using I-joists for floor systems.  Here are the major benefits…

  • Greater Spans – A designer creates the floor system using I-joists to fit each particular plan.  The joists will span greater distances by using a taller web, beefier top and bottom cord, and by spacing them closer together.  Traditional dimensional lumber has a rather limited span compared to manufactured floor joists.  This greater span potential helps create more open floor areas in new homes.
  • Stable Pricing – Dimensional lumber typically has a higher price volatility than i-joists.  Because dimensional lumber is more of a commodity, the price fluctuates based on mill output and demand.
  • Lighter – One of the benefits for workers using I-joists is that they are quite light in comparison to traditional dimensional joist lumber.  An I-joist can be picked up and easily moved by one carpenter.
  •  Knockouts – Many of the I-joists on the market have knockout holes to allow mechanical trades to easily run wiring and piping through them.  This can save time and money.
  • Floor Squeaks – You get fewer squeaks because manufactured floor joists have a wider flange to nail into and the material is straighter and moves less has the house settles.

Traditional Dimensional 2x10 Joists

Code Change for Fire Protection

A new code change requires fire protection on the underside of manufactured floor joists.  Apparently fire fighters have been hurt in house fires because the rate of burn on the I-joists is faster than traditional joists.  These fire fighters have fallen through the floors because the structure has weakened more quickly than with traditional floor framing.  So by requiring fire protection to be installed under these I-joists, the code people hope to slow down the rate of burn.  This change has been added to the 2012 International Residential Code and will affect any new construction projects covered by this code.  Check with your local building department to see if this change will affect you.  Here are the details of the code change…

  • Section R501.3 Fire Protection of Floors
  • Requires 1/2 inch gypsum wall board or 5/8 inch structural wood panel to be applied to underside of manufactured floor joists

Exceptions Where Protection is Not Required:

  • If area below is protected by automatic fire sprinklers
  • If the manufactured joists are located directly over a crawl space not intended for storage or fuel burning appliances

You will want to review the new code to see all of the details and exclusions.  If you do decide to go with the manufactured floor joists, you will want to add the additional labor and material costs to your budget to comply with the new code change.  If you are finishing the basement of your new home with a drywall ceiling, this change won’t add any additional costs to your project.  For more information to help choose between traditional 2×10’s versus manufactured floor joists, check out this article, Floor Joists:  Use Manufactured or 2x’s?  If you are thinking of building a new home and want to know what options you have, check out this video, Building a New Home.

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