April 29, 2010

How to build a ‘stress-free’ wood building

Stodola

The information in this article is a culmination of research and experience I’ve gained over the last 22 years in the wood-framing field. I’ve combined a simple new framing technique with a simple fastening and drywall system to create “stress free buildings.”

It doesn’t matter if you are building a single-family home or a 350-unit mixed-use complex, this system works! By top plating all the bearing walls with standard 1.5-inch dimensional lumber and reducing the interior non-bearing wall top plates by 0.75-inch, we eliminate inadvertent loading of building components, which causes expensive damage to the finished materials and the need for continual door maintenance.

By providing an air space between the joist and non-bearing walls, we also greatly reduce noise transfer, especially when used in concert with wood I-joist, floor-cavity insulation, and the two new products I’ve designed for deflection and sound transfer reduction.

It is still common practice to make bearing and non-bearing walls the same height. As a veteran carpenter, I went to great lengths to make the first level of all structures as flat as possible in an attempt to limit the telegraphing of foundation inconsistencies through the buildings. It wasn’t until I became a superintendent and took projects through from ground breaking to completion that I became aware of short- and long-term building issues that cost so much time and money.

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Exxel Pacific is using the Deflector fastening system and the stress-free building concept on the Othello Station project in South Seattle.

At a one-year warranty walkthrough with an owner, the most costly issues usually are drywall stress cracks, screw/nail pops, associated repainting and door adjustments resulting from structural settlement.

Imagine a structure having a floor system spanning anywhere from 10 feet to 20 feet from bearing point to bearing point, with interior non-structural walls in any number of configurations in between. If you are able to get your concrete perfectly flat, the tops of the walls should be flat also.

Now, picture those joists spanning over a door opening not designed to take any load.

A typical I-joist at 16 feet has deflection of 0.25- to 0.38-inch calculated into the design. However, there is no room for the designed deflection! The loading issues are compounded as you go up in levels; high spots on slabs and uneven foundations contribute to the problem. With no room for deflection, any weight put on the upper floors directly loads the non-bearing door header and surrounding non-load-bearing walls on the lower floors.

By the time we get to the roof structure on a three- to five-story wood-framed building, the loads on the non-load-bearing walls are alarmingly high. This is when we attach our drywall, set our door frames and install our latching hardware. If you have been in the business long enough, you will drywall from the top down on taller structures to “load” the building in an effort to eliminate some of the drywall stress cracks. This puts even more stress on the lower non-bearing door headers and walls.

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Traditional metal connectors can split wood on I-joists, causing floor squeaks.

A wall under this much stress is going to move and cause a multitude of issues over the life of the building, which until now we just accepted as the way it was.

Watch out above

Roof systems pose a different challenge in relation to deflection. When you load a roof structure, the pressure pushes down on the walls below and, in some extreme cases such as tile roof systems, this pressure can ruin the trusses, walls or the joist below the walls because there is no room for deflection. Even if the roof trusses are designed to carry the load, they still need room below to load properly and carry the weight. This problem is rarely addressed until it is way too late.

Once a roof is loaded we drywall, attaching to sheetrock backing nailed either to the top of the interior walls or hung off the trusses themselves. Next, we insulate the attic space, covering the bottom cords of the trusses and keeping them insulated.

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Leaving a gap and using Deflector fasteners between I-joists and non-load-bearing partition walls allows the I-joist to flex without loading the wall below. The fastener can move up and down inside the wall cavity.

The top cords of the trusses are in the open attic environment and react differently than the insulated bottom cord. On very hot days with high humidity, the top cords absorb moisture, heat up and expand. Conversely, on extremely cold winter days, they react in the opposite manner. These two actions cause the bottom cord to flex up and down, cracking drywall and popping screw/nail heads. In some cases, the actions can lift walls off the floors.

The solution

By lowering the elevation of the non-bearing walls 0.75-inch, using the Deflector fastening system (http://www.fastcap.com/deflector) with our joist and roof systems, and installing the Deflector F corners, we eradicate the issues related to deflection. The F corners allow for slight movements in the roof structure without the resulting drywall cracking.

We save an amazing amount of time during construction, reducing extensive blocking and backing systems, and the one-year warranty walks are amazingly painless. The material savings help the budget and the reduction of wood products help with green building concepts. The sound transfer benefits are embraced by everyone, especially our acoustical engineers.

Structural engineers can design buildings using this new concept without worry of how the structural components will affect the cosmetic features of the building. Architects, owners, carpenters, general contractors, sheet rockers and door installers will all benefit greatly.

I hope you find the new “stress free” building concept the answer to as many of your construction issues as we have.

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