Advanced Framing

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Optimal Value Engineered (OVE) or Advanced Framing techniques are framing techniques that use less lumber than conventional framing, yet are just as structurally sound. Using 5 to 10 percent less lumber is cheaper and faster because it uses 30 percent fewer framing pieces,21 which equates to a direct reduction in lumber package costs. But, as important, these methods also present one of our best opportunities to improve the thermal performance of the structure.

Remember, thermal performance is one of our primary goals. Because Advanced Framing uses less lumber, this leaves more space in the cavities to allow for higher levels of insulation, resulting in better thermal performance. In fact, Advanced Framing results in a 75 percent improvement in thermal performance22 over standard 2 × 4, 16-inch-on-center framing.  e lumber cost savings can add up to enough to cover the additional costs associated with improv- ing the thermal performance, including the cost of adding insulated sheathing to reduce thermal bridging through the wall assembly.

This is definitely a case of “less is more,” in that using less lumber saves trees and uses less money in your budget, with the added bonus of leaving more room for insulation, giving more thermal performance.  ink about that because it represents significant improvement in your building performance for minimal additional construction costs and lowers your long-term utility bills. So if you are planning a framed structure, you should make certain that your framing contractor has been trained in and practices the methods discussed here.

Many computer-aided design (CAD) programs can be set to a grid of either 16 inches or 24 inches on center (the distance from the center of one framing member like a wall stud or ceiling joist to the center of the next) to allow for ease of designing to these two basic spacing criteria. Providing these Advanced Framing details in your architectural plan sets can assure that you bene t from those cost savings and performance benefits. Better efficiency, improved comfort, and reduced costs are all achieved in each of the following methods:

Framing 24 Inches on Center: Exterior wall studs, floor joists and roof rafters can be spaced at 24 inches on center (as opposed to the conventional 16 inches on center). Depending on the load bearing on walls, framing lumber may require 2 × 6 studs rather than standard 2 × 4 framing. Note that the total cost (material and labor) for framing with 2×6 studs spaced 24 inches on center is about the same (since 30 percent fewer studs and only a single top plate are
required) and o en less than what it would have cost for 2 × 4 studs spaced 16 inches on center. Because there are fewer studs to cut, there is less waste.  is also saves labor for both your electrical and plumbing contractors, who now have to drill fewer penetrations for mechanical runs.

However, with most types of cavity- ll insulation (depending on climate R-value requirements), it may cost more to  ll a 2×6 cavity than to  ll the same structure framed with 2 × 4s.  is is not only due to the increased depth of the studs but also to using less framing materials overall, so it will take more insulation material than it would have for the same depth, regardless. In addition, the added two inches of wall thickness will require extension jambs at all of the windows unless drywall returns are used.

In-line Framing: Aligning the floor, wall and roof framing members directly above one another so the loads are transferred directly downward, requiring no additional structural support, can save considerably on structural engineering and framing costs. With in-line framing for improved load stability, double top plates can be eliminated because the load is distributed evenly through the remaining single top plate. Note that studs that are 24 inches on center are placed in direct alignment with floor joists spaced 24 inches on center and directly below roof trusses spaced 24 inches on center.  e structural concept is to align all point loads to carry the weight directly down to the ground.

Headers Sized for Actual Loads: Structural headers are o en over- sized or installed over all window and door openings, regardless of whether or not they are structurally necessary. When the size of the window used is specified in conjunction with in-line framing, headers are not necessary because no studs need to be cut. If walls are not load bearing, no headers are required over window or door openings. Having your structural engineer specify which areas will require headers, as well as the size of each header required, will save both materials and money.

In most cases right-sized headers can be pushed to the outside of the framed wall assembly, allowing for insulation on the inside of each header cavity, which not only improves the overall thermal performance of the wall assembly but also eliminates thermal bridging at the headers. Note that it is possible and now required by code to insulate headers by using foam sheathing as a spacer in place of plywood or oriented strand board (OSB), either between or on one side (preferably the exterior side) of doubled headers.  is technique uses scrap foam sheathing to reduce thermal bridging through the wood header.

Two-stud Corners (California Corner) with Drywall Clips:  is method of corner framing uses only two studs, saving material and providing space for additional insulation in the corner. To attach drywall in a two-stud corner, drywall clips are fitted onto the edges of the drywall before being attached to wood or steel studs.  is eliminates the need for an additional stud in the corner to attach the drywall.

Window and Door Placement: By aligning at least one side of each window and door to an existing wall stud, use of an additional jack stud is not necessary. If the window or door width does not completely  ll the cavity and align with the next stud, you can attach the other side to the next stud with a metal hanger.  is eliminates the need to frame additional studs to support the load transfer around these penetrations in the wall assemblies.

Interior Partition Walls Intersecting with Exterior Walls (T-walls): Traditional framing addresses T-wall intersections by adding studs at each side of the partition solely for the purpose of providing a surface for attaching drywall. Ladder blocking between the exterior studs behind the partition wall uses two-foot scraps of lumber to provide the same supporting structure and allows for much better wall insulation and reducing thermal bridging. You can use scrap wood for ladder blocking, reducing the additional lumber you need to purchase.

Building Shading Devices

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Direct sun exposure on walls, especially west- facing walls (and south-facing walls in the summer) can significantly increase the loads on your cooling system—roof overhangs and porch roofs to the rescue! Many types of external shading de- vices that can keep heat from entering the building are o en recommended in lieu of prescribed low solar heat gain coefficient windows on southern exposures in passive solar design. These can include pergolas, awnings and patio covers.

Shading a window on the outside of the glass is twice as effective at reducing heat gain as doing so inside of the house.  is is the best strategy for reducing cooling loads and lowering energy costs. Individual awning structures mounted directly above windows can provide more protection, being closer to the window, than an over-hang that is several feet above. Of course, the projection factor, or the ratio of the depth of the overhang or awning to the height above the sill of the window be- low it, will influence its effectiveness in shading all or portions of the window over the cycle of the sun’s path between the solstices. By using the projection factor formula, we can design the shading device to precisely control which months the sun is allowed to shine into these windows. Even in the north, you don’t need solar heat gain in July.

Never underestimate the benefits of any shading devices. As was previously mentioned, they also serve to protect exterior doors and windows during major rain or storm events. However, if external structural devices are not possible, trees can provide shade, either continually or seasonally. If your site does not have trees, neighboring buildings or other existing features can provide the desired shading on the east and west sides of your home.

Building - Passive Solar Design

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Wherever you live, you can embrace design strategies to further manage the sun’s heat loads on the structure. As we mentioned in Chapter 1, in the northern hemisphere the sun is always either in the southern sky or directly overhead. In North America, the sun rises at due east on the spring equinox, April 21, and fall equinox, September 21, and sets at due west on the same dates. On June 21, the summer solstice (the longest day of the year), the sun crosses at its highest path across the sky overhead, rising and setting well north of due east and west. Each day a er June 21, the sun’s path starts and ends further toward the south of due east and west and lower toward the southern horizon until it reaches its lowest path across the sky on December 21, the winter solstice (the shortest day of the year), and then the process reverses. Knowing the seasonal sun path across your site allows you to design to manage solar heat loads to your benefit. Take time to research your location’s latitude.  e closer you are to the equator (like in the southern US), the more days you will need air conditioning rather than heating. You want to minimize the amount of solar heat gain on the structure, so, as mentioned in Chapter 1, you want the short walls of the house to face east and west; since these two walls have the least amount of wall area, they will absorb the least amount of solar heat into the home.

Interestingly enough, if you live in a predominantly cold climate area like the north (with more days needing heating than air conditioning), you should still design your home with the long walls of the rectangle running east and west.

Regardless of your latitude, you want the south-facing windows to be completely shaded at noon on June 21 and completely un- shaded at noon on December 21.  e key here is the design of the overhangs. In this case they must keep the sun o  the glass when the sun is high in summer and let it in when the sun is low on cold winter days.  at means that we design to control the amount of heat gain through the south wall and windows. We can use ex- tended roof overhangs, covered porches and other shading devices (like awnings) to shield windows and walls on the south side of the house from the hot summer sun.  is improves the cooling effects of passive ventilation strategies in the summer. These same windows on the south side of the home can provide passive heating of the living space when the sun’s path is lower in the sky in the winter.  e result is that overhangs help to lower our mechanical heating and cooling costs.

As you can see in the drawing above, the lower the sun is in the sky and the shorter the overhang length, the further the sun penetrates into the house.  e farther north you are, the lower the sun’s path across the sky, and the farther south you are, the higher in the sky it moves.  is fact will affect the length of your overhangs and how you build to take advantage of or avoid solar heat gain in you home. All three of these things—length of the overhang, height of the overhang above the window, the angle of the sun in the sky— impact how much solar heat gain you will reap (or keep out, as the need may be).

Building Stack Ventilation System

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One of the basic principles we work with is that warm air rises. As this occurs, the area below is left under slightly lower pressure, so there is a suction effect. As the hot or warm air rises, windows located high on the opposite wall, or in an open upper-story area (like a stair-well, clerestory, cupola or monitor), can exhaust warm air out of the house while drawing cool breezes in. Any time we can use these passive ventilation strategies, we increase the velocity, and thus the effectiveness, of even the mildest breeze. Whole-house fans can intensify this effect. These devices are especially useful in areas where summer nights are relatively cool, exhausting warm air that builds up during the day and drawing in cool nighttime air for passive ventilation. If we can provide cool, comfortable air without having to use our mechanical systems, we save energy and money.

Building Cross Ventilation System

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It is important to design your home with operable windows on the prevailing breeze side of the house (east or south sides, in Figure) and on the opposite side of the house for the purpose of supplying passive ventilation.  e prevailing breeze creates pressure differences from one side of the house to the other. Strategically placed windows on the prevailing breeze side of the home and the opposite side work to draw the breeze through the living space. We can actually increase air ow through the space by opening more windows on the negative pressure northwest (downwind/leeward) side than on the positive pressure (southeast/ windward) side of the home. When wind currents travel through a constricted opening, the velocity increases (the Venturi effect).  e Bernoulli principle determines that as the air speeds up, its pressure drops, causing it to create suction and drawing in even more air.

The same principle can be applied to the architectural layout of the structure itself, using a vernacular breezeway or dogtrot design to channel breezes into the living space. To increase the breeze’s effective cooling, the alignment of the building sections can be o set at an angle. In this way, we can use smaller windows or openings on the windward side of the dogtrot and larger windows or openings in the dogtrot on the leeward side to pull air through the structure. Windows on the side walls of the dogtrot are used to channel that increased volume of air into the living space of each building.

Building Passive Ventilation System

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Repeat again: ventilation. We tend to believe that all windows should be operable. Regardless of where you live, there are times of the day and times of the year when the outside temperature and humidity are comfortable. Fresh air can provide numerous health benefits, and the sounds and smells allow us to be a little closer to nature, even as we stay inside our sheltered home.

We talked about the importance of determining the direction of prevailing breezes and selecting a building site that could take advantage of passive ventilation strategies.  These strategies should be a part of every good green home design. But for those breezes to really provide cooling for the home, the design must incorporate elements to promote air circulation through the building.

Windows, depending on location, can be used for cross ventilation, circulating natural breezes throughout the home, and stack ventilation, exhausting heat out through stairwells, monitors, cupolas or upstairs rooms. However, prevailing winds can be impeded by a number of factors, including  adjacent structures and topography that either block the air ow or change its direction at window level. But if we can get above the obstruction, we can use our roof design as a scoop to channel the wind back down into the building. Wing walls can also accomplish this at ground level, if we can capture the breeze coming around the neighboring impediment and direct it back toward our other architectural features that are designed to capture it. Investing in these kinds of architectural details will pay o  over the long run by reducing your mechanical cooling costs. We can also use natural ventilation strategies instead of running our air conditioners, thereby lowering our utility costs. Open windows can reduce our need to use mechanical ventilation appliances, like bath and kitchen exhaust vents. Opening the windows can also improve indoor air quality by exhausting stale, contaminated air, allowing us to temporarily shut o  our mechanical fresh air systems. Opening the laundry room windows can provide a source for make-up air for the clothes dryer, preventing negative pressure that might bring in air from unwanted sources.

It is important to note, however, that operable windows should not be considered as a replacement for mechanical ventilation systems.  ink about how o en you actually open your windows or how many days each year passive ventilation is a viable option for you. We will discuss indoor air quality and how to manage indoor air pollutants in your home. Mechanical ventilation is a necessary component of healthy indoor air quality. More than that, mechanical ventilation is a mandatory requirement in the 2012 International Residential Building and Energy codes.  e paradigm is to build them tight and then ventilate them right! We will have more to say on the equipment to use and how to provide ventilation in the different climate zones in our country in Chapter 6. Yes, climate makes a big difference in how ventilation should be done.