Framing as a Safety System
By: Amanda Campbell
Updated: August 13, 2010
After the foundation, the most important part of your home is the framework itself.
The primary force that drives all of us to find a home is the desire to provide shelter for our loved ones and our possessions. You should think of the frame as the backbone of your house, the anchor for the shelter you're building for your family. The frame is a system of features located all over the house that depend on one another to form a united structure. Let's start from the ground up to take a look at some ways to tie those features together so you can protect your house from the damaging forces of nature & keep your family safe.
The Frame as a Safety System - Our segment featured framing elements at our Project House that tie the house together, foundation to roof, for greater structural integrity & greater resistance to extreme weather conditions - conditions which could tear apart a house that does not include these safety features in the framing process. Forces of nature tend to rip a house apart (negative pressure caused by tornadoes & hurricanes makes a house want to literally "explode" outward, wind can lift a roof off a frame, rain pouring into a hole in the roof can ruin a house in minutes, etc). We'll demonstrate how a tied-together system of safety features combats those forces.
Anchor BoltAnchor Bolts - We've mentioned in past episodes that tornadic forces can sweep a foundation clean of any evidence of a structure. Anchor bolts can help the frame of a house resist these forces. Anchor bolts are placed in a foundation before the concrete is poured. Once the concrete sets, the bolts stick out above the foundation. Framers build the walls and drill holes in the base plates (the bottom piece of wood on the exterior walls). The entire wall is then lowered onto the bolts, and secured to the foundation with a washer and a nut. This creates a much stronger structure than simply nailing base plates into the foundation, as some builders do. If a wall is simply nailed into a foundation, a strong wind could place a tilting force on the wall and loosen nails like a claw on a hammer can.
2x6s vs. 2x4s - Experts recommend 2x6s as the main structural elements in the walls of a solid frame. 2x6s cost more to a homebuilder up front, but since they're larger structural members, they contribute to an overall increase in the strength & stability of the frame compared to 2x4s.
Consumer Tip - 2x6s may cost more up front, but since they allow for more and better insulation, they'll quickly pay for themselves in lower energy bills.
OSBCorners wrapped in OSB - Louisiana-Pacific provided the Oriented Strand Board for our Project House.
Once the four walls of the frame are built, the next step is bolstering the strength of the corners of the frame. This is done using sheets of Oriented Strand Board. OSB is an engineered wood product made of narrow strands of wood fiber that are oriented lengthwise and crosswise and bound in resin for increased strength. The corners of the frame are "wrapped" in OSB, top to bottom, and extending out at least four feet from the corners. The "box" of the frame can now resist shearing and twisting forces better than it can without the reinforcement at the corners. In our segment, Michael held a common cardboard box that he twisted with his hands to demonstrate the shearing or twisting forces on a frame that wrapped corners counteract and resist.
Wrapping corners in OSB is a minimum safety step. Michael recommends you wrap your entire frame in OSB, so your house is solid like a tank against the attack of severe wind & weather.
FramingRafter Clips or Hurricane Straps - Strong winds can easily get under the eaves of a roof and lift it off the frame. If a roof is simply nailed to the top of the walls, the wind can pull those nails out like the claw of a hammer can pull nails out of wood. Hurricane Straps or rafter clips form a stronger connection between the walls and the roof to resist those forces. If a rafter is simply nailed into the top of the wall, the forces of a strong wind could lift the rafters off the wall like a claw on a hammer removes a nail.
All these features form a System - Now we have a cohesive and unified system to strengthen the entire frame. Anchor bolts secure the walls to the foundation. OSB wrapped around the corners ties the entire wall to the base plate, which is anchored to the foundation. Hurricane straps anchor the roof to the walls, completing the system top to bottom. All the individual features work together to fortify the frame against destructive forces.
Before you start to build your new house - that's the time to do what you can to beef up the strength and integrity of your house. Chances are most of us won't ever have to face the kinds of weather extremes that can tear a house apart, but there's no reason to take chances. A minor initial investment now could mean the difference later between comfort & catastrophe. It's never too early to think about safety when you're building your new house.
Consumer Tip - The up-front cost of these safety system tools is minimal & infinitesimal compared to the cost to repair severe weather damage.


