The web is ablaze with green building ideas. Does anyone really know what ‘green’ is? Let me tell you. ‘Green’, is equal amounts of yellow and blue! All kidding aside, green building is creating or renewing a sustainable efficient building product that affects the environment with less impact, from inception through manufacturing and delivery, to installation and beyond.
OK, what is an example of an green building product? How bout wood? The most sustainable building product on the planet. Wood in it’s natural state is wonderful. Problematic is what we do with wood. So what is my solution? Here’s one.
Most trusses are built to mimic standard roof rafters. They start from the plate or wall line, and rise to the ridge. Are they green? Not as green as they could be. Remember the rule. “Renewing”. So, lets renew the ‘Truss’. We know the truss ‘rises’ from the plate to the ridge. And most roofs with more than four inches of rise in twelve inches will have enough height at the ridge to allow enough insulation to code. My insulation in my attic is well over twenty inches deep. But what of the plate, or wall line? On a truss, the rafter and the ceiling joist meet at the wall line and are joined together with a metal gusset. For short roof spans, they are commonly built from two by four stock. From the bottom of the ceiling joist to the top of the rafter vertically, the total height is four and one quarter inches. This only allows for (at best) R-11 insulation directly above the exterior wall. But wait; In standard framing practices, an eve vent is installed about every six feet. This takes the effective insulation value down. Also, the eve vent needs to have clear space in between the rafters, so a wood or paper baffle is installed to keep the air way clear. In other words, No insulation every six feet at the wall line. Depending on the size of the home, the configuration of the roof ( gable or hip) this can be a substantial loss. Winter or summer. What’s the green fix? The ‘Stand-Off Truss’
Here’s where we go green. We have a product (trusses) that is already manufactured for the housing industry. It is sustainable. It is renewable. To make a more ‘green’ product from this example would be to modify the manufacturing enough to create more initial and long term efficiency. How do we do it? By adding a vertical leg in the truss between the ceiling joist and the rafter directly over the exterior wall line. The Stand-Off Truss.
This accomplishes many things.
- Allows for deeper insulation directly over the exterior wall.
- Reduces radiant energy from entering the conditioned air space
- Removes the baffle that hinders insulation at the eve vents.
- Allows a stronger frame to roof attachment when sheer wall is installed
- Allows for an optional built-in soffit at the eve line. (Continuous venting for the WUI codes)
And the benefits are increased when the roof configuration is a hip roof. Then the application is continuous around the structure.
The example is the roof frame of one home. If entire subdivisions were to be build with this one example, the energy savings would be significant for the community. This is ‘Green’.
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