This article was originally published in the January/February 1996 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online January/February 1996
Adding Efficient Living Space
by David Connelly LeggDavid Connelly Legg is an energy consultant and trainer in Auburn, Massachusetts.
By paying attention to the building shell, remodelers can make sure that the energy bills don't grow faster than their home.
A house's worst energy problems often develop because of how it is enlarged. Fortunately, there are many ways to add on to a house economically while adding as little as possible to the energy bills. Many of the techniques described also apply when retrofitting a house that has been remodeled.Remodel It Right-
Make It Tight Many homeowners complain that converted rooms are the coldest parts of the house in winter and the hottest in summer. This is partly because these spaces were not initially designed to be lived in. Remodeled rooms may have inadequate air sealing and improper insulation, as well as heating system problems such as contorted or leaky duct runs. In addition to excessive heating and cooling costs, enlarged houses often have problems involving moisture control and air quality.
As remodelers and homeowners add new living space, the framing elements and heating and cooling systems of the house often become more complex. The complex framing can lead to more voids in the insulation and more bypasses for air leakage.
Some of the worst problems are what weatherization professionals call key junctures. Key junctures are openings in the frame of the building, often hidden from view at intersections between walls, porches, floors, and ceilings. Typically far more air and heat escape through key junctures than through more obvious leakage points such as doors and windows.
Remodeling can present opportunities for energy savings wonders as well as wasteful blunders. It can be a good time to do a full energy remodel, insulating walls and sealing air leaks while the workers are at the house anyway. It is usually easier to access key junctures during a remodel, as interior walls go up and as cavities are opened to extend electrical and mechanical systems to the new space. If these are attended to, the remodel can improve the house's overall energy performance.
Align the Boundaries
One must go beyond the well-known energy-saving measures. It is not enough to insulate walls, floors, and ceilings. The key junctures between those components must be sealed and insulated too or the insulation won't work as expected. To get the best performance, air sealing and insulation must be coordinated to ensure that the pressure boundary and the thermal boundary are continuous throughout the house. The pressure boundary is the barrier (such as framing, Sheetrock, or sealant) that prevents infiltration of outside air and exfiltration of inside air. The thermal boundary is the border between the conditioned area and the unconditioned area of the house. The pressure boundary should be on the warm side of the insulation, which should be positioned in line with the thermal boundary.
Remodeling presents an excellent opportunity to insulate thoroughly and to create an effective air barrier (pressure boundary) in walls, ceilings, and floors. Techniques for retrofitting the walls are similar for conversions and room remodeling. It is best to install insulation into inadequately insulated or empty exterior walls before new Sheetrock, wall covering, or siding is installed. This cuts costs, because the installers won't need to remove and replace siding. They can drill through the existing siding or plaster, and they won't need to plug the holes, since these will be covered later anyway. High-density cellulose is the best choice, because it insulates and seals the wall in one shot. The insulation crew should use fill tubes and pack the key junctures. The material should be blown to a density of 3.5-4 lb/ft3 to resist air flow and avoid settling over time.
Wooden framing makes up about 20% of a typical framed wall or ceiling. Although there may be insulation between the studs, the wood itself has a moderately low R-value. A layer of rigid board insulation under that new siding or Sheetrock will improve overall wall R-value considerably and cut down on conductive heat loss through the wall studs. This may be cost-effective only in more severe climates. When using fiberglass to insulate open-framed exterior walls or ceilings, cut, fluff, and fit the batts to fill the cavity completely. Fiberglass cannot resist air flow and will perform poorly if there are any voids or bypasses, such as when the top of the wall cavity is not sealed off.
Prevent Moisture Problems
Applying a polyethylene vapor barrier on the warm side of the insulation will retard moisture and air movement into wall cavities and attics. That will keep heat and moisture inside and will help to prevent fungal jungles in walls and attics. The vapor barrier should be overlapped and sealed at all seams with tape or caulk. To be effective, it must be continuous; therefore it must extend onto adjacent walls, floors, and ceilings. Try to maintain at least 12 inches of overlap at all seams. Press the sheeting tightly into corners and take care to install it smoothly so it will not interfere with the installation of finishing materials.
Cracks and gaps in existing walls and ceilings should be sealed to provide an effective air barrier. Make air barriers or vapor barriers continuous by sealing them right up to windows, electrical outlets, switch boxes, and any pipes and wires that pass through the walls and ceilings. A practical option for new electrical wiring boxes is to install them inside airtight plastic boxes such as those made by Lessco.
Seal all Bypasses
Plumbing pipes and chimneys often pass through ceilings. The openings cut by plumbers around pipes can be sealed with foam or caulk. The chimney will often have a 2-inch gap framed all around it that allows conditioned air to escape through the ceiling. That gap can be sealed with sheet metal and high temperature caulk. Key junctures can be sealed with high-density cellulose or rigid materials and sealant. Rigid materials may be at hand already on the remodel project. Pieces of plywood, rigid insulation, and Sheetrock all work fine for this.
When properly used, a blower door is a good tool to identify air leakage and test for the location and continuity of the pressure boundary. Blower door tests before and after the work can help to determine that the house is not too tight and that there is adequate air for combustion appliances. Inadequate air supply may lead to chimney backdrafting and carbon monoxide production. Carbon monoxide and other pollutants can have serious health consequences and may even be fatal. It is very important to conduct blower door tests and safety tests of heating and hot-water systems and gas stoves, especially when tightening a whole house using these techniques (see Combustion Safety Checks: How Not to Kill Your Clients, HE Mar/Apr '95, p. 19 and Building Tightness Guidelines: When Is a House Too Tight? HE Mar/Apr '93, p. 13).
Determine Heating and Cooling Needs
One important decision the remodeler will make is how to heat and cool the new living space. The existing heating and cooling systems will often be adequate to condition the new space, if close attention is paid to air sealing and insulation. Weatherizing the rest of the house will reduce the load on these systems. Extending a forced-air system to the new room may involve running new ductwork, and the HVAC technicians should seal duct leaks throughout the distribution network while they are there. If additional heating and cooling is needed in the new space, remember that electric heating is usually expensive to run. (Look for an article on choosing a heating system in the next issue of Home Energy.)
A Troublesome Juncture
One aspect of a porch conversion that is often overlooked is the juncture of the porch roof and the house wall. Builders in the old days, and some today, didn't install any wall sheathing on the section of the exterior wall adjoining the porch roof cavity (see Figure 1). This doesn't show and it saves money on lumber, but it certainly doesn't save on heating and cooling. Conditioned air in that wall cavity can readily flow into the space between the porch ceiling and the porch roof and escape undetected. The problem is especially bad in balloon-framed two-story houses, where the joist cavity between the first and second floors is open into that same space. It's like having a river of heated or cooled air flowing straight to the outside.
This will continue to be a big energy loser even if the wall is insulated and the rim joist is insulated-which is rarely done anyway-because fiberglass batts or loosely applied cellulose can't stop the air flow. The first step in treating the problem is to gain access by removing a section of the porch ceiling. The juncture can be sealed with rigid material and sealant or packed with fiberglass stuffed into heavy-duty plastic bags or dense-packed cellulose. If rigid materials are used, they in turn must be insulated on the cold side; otherwise they could become cold air barriers that will trap condensation and lead to moisture problems in the wall. Rigid insulation used for this purpose should be at least 1 inch thick in moderate climates and thicker in severe climates.
Fastening Floor Insulation
Improper floor insulation is another common problem in porches, which often have wooden floors. Unless there is a slab below or a full basement, the underside of the porch floor should be insulated with batts or blown-in insulation. The insulation will work most effectively if placed in direct contact with the flooring.
A common mistake is to fasten batt insulation to the bottom of the floor joists using staples and the kraft paper insulation backing. Not only does that create an air space for heat to flow past the insulation, but the paper and staples often fail to keep the insulation in place more than a few years. (It also means that the vapor barrier is on the cold side in heating climates, which could lead to moisture problems.) Spring steel bars that span between the joists typically fall down after a few years too.
When a porch doesn't have a fully enclosed foundation, the porch floor insulation will need protection from the elements. Exterior grade plywood fastened to the bottom of the floor joists will protect and hold the insulation in place and allow the use of blown or batt insulation. Housewrap, such as Tyvek, will protect it from wind. Another method for securing batt insulation is to use plastic mesh or chicken wire stapled to the floor joists every 6-8 inches. In either case the floor joist cavity should be filled completely with insulation. These methods of insulating floors often work very well for additions as well, since they are often built over crawlspaces. If there's an enclosed crawlspace foundation with a dirt floor, the floor should be covered with plastic ground cover to control moisture.
Remodelers often overlook the need for an effective air barrier on the warm side of floor insulation. The easiest and most effective place to position the air barrier is on top of the existing wooden porch floor. In most cases plywood underlayment will be needed to provide a smooth surface for carpet or other floor covering. Plywood that is rated for exterior use can be used as a combined air and vapor barrier. Seal all the joints in the plywood with caulk including the joint where it meets the walls. Another option is to lay a plastic vapor barrier on the floor, seal all the seams with tape or caulk, and then cover the plastic with plywood or hardwood flooring.
What To Do with Windows
Comfort problems related to windows often show up in converted porches. This is partly because enclosed porches usually have many windows. The windows are usually leaky, too, since all they had to do for the porch was keep out rain and snow, not heat or cold. Unless the windows are very energy-efficient, provide a terrific view, or face south (in a heating climate), it may be best to eliminate some of them. This will provide more usable wall space and avoid the comfort problems that are posed by a room loaded with windows. In cold climates a large area of cold glass leads to heavy conductive heat loss and can also steal radiant body heat, making the room feel far colder than it is. In southern climates it can lead to unwanted heat gain.
The remaining windows should be evaluated carefully and considered for repair and weatherstripping or replacement. Often a good way to save money up front is to weatherstrip the windows, assuming that they can be weatherstripped, and install airtight low-e storm windows (see Selecting Windows for Energy Efficiency, HE July/Aug '95, p. 17).Converting a Garage In garage conversions and porch conversions, it can be difficult to extend the existing heating distribution system to the new room. Electric heat is cheap and easy to install, and it is often chosen for these spaces, but it's expensive to operate. When electric heat is planned for the remodel, it is best to beef up on insulation in walls, ceilings, and floors and even consider superinsulating by building an additional stud wall.
If a separate heating system is needed for the converted room, one option is a compact and efficient sealed-combustion space heater that burns gas, propane, or kerosene. Unlike unvented space heaters, many new models vent exhaust gases through the wall and also take combustion air directly from outside. Another issue to be aware of when converting a garage is the need to provide adequate outside air for combustion if the existing house furnace or water heater is in the garage.
Garages never have adequate windows, so people usually add them when converting a garage to living space. It makes sense to spend the additional money to get windows with a high R-value, especially if electric heat will be used. The heating of the garage can be planned with an eye to solar sources. If one side faces south, windows can be installed there. If a large area of glass is added, some form of window insulation for cold winter nights may be needed. Beware of inexpensive aluminum sliding glass doors; they are prone to air leaks and have a very low R-value.
Slab Floor Options
Garages typically have concrete slab floors, which can serve to store daytime solar gains. Sections of a slab used as thermal mass should be tiled, not carpeted, and the slab should be insulated on the outside perimeter. Slab insulation involves some digging, however, and this may be impractical, due to the terrain or the placement of driveways, sidewalks, and landscaping.
If thermal mass is not to be used, carpeting may be adequate for insulation in a moderate climate. In cold climates an uninsulated slab floor will be cold and uncomfortable. If exterior insulation won't work and the slab won't be used for thermal storage, a wood floor can be built. One cost-effective approach is to lay 2 x 4 framing down flat, place 112-inch-thick sheets of extruded polystyrene insulation in between the framing members, and then add a plywood subfloor. If the slab is sloped toward a central floor drain, it will be necessary to either build a sleeper system of floor joists or pour concrete to level it off first. To keep rain from damaging that new floor and the insulation, a drainage gully may be needed in the driveway just outside the garage wall (where the garage doors once were).Adding a Wing When adding a wing to a house from scratch, it is easy to incorporate all of the energy-efficient measures that can be done in new construction. The remodeler can plan the framing and insulation to create a tight space that is well-protected from the elements. Unfortunately, several problems often occur in these new spaces.
Vaulted Ceilings Make High Bills
Many one-story additions built today have vaulted (cathedral) ceilings. Three significant insulation problems are common in these ceilings. The first problem involves the slope of the vaulted ceiling. Typically styrofoam proper vents (white sheets of 2 ft x 14.5 inch styrofoam) are used to maintain a ventilation air space above the insulation in the sloped ceiling. Unfortunately cold air often blows into soffit vents and creates windwashing in the insulation. This diminishes the R-value of the slope insulation and often causes cold spots that can lead to mold and mildew formation or moisture damage in the slope cavity. One solution to this problem is to use a second layer of plywood sheathing or sheets of rigid insulation in the slope, with wooden strapping between the layers, to create a strong, tight air space under the roof deck for ventilation. That space should extend all the way from the soffit vent at the base of the slope to a ridge vent at the peak.
A second common problem is the gable wall of the vaulted ceiling that adjoins the house. Often this gable wall adjoins an unconditioned attic where insulation was placed on a flat ceiling. That means the gable end wall is at the thermal boundary and should be insulated-but it often isn't. Also, insulation is prone to fall out of the wall, since it is open on the attic side just like a kneewall. Insulation there should be well secured, using plastic mesh, chicken wire, house wrap, or furring strips. In severe climates, a second layer of insulation batts can be stapled or secured with furring strips to the studs and the gable end wall. For the best results, vertical insulation can be covered with house wrap such as Tyvek.
The third problem in vaulted ceilings is recessed lighting, which is quite common. In the typical vaulted ceiling even the best fixtures rated for insulation contact-the ones that don't have air leaks-still don't permit enough space above the fixture for insulation. As a result the top of each light is completely uninsulated. Track lighting is one alternative (but use efficient-compact fluorescent or halogen-fixtures). Specially designed vaulted-ceiling trusses that add more depth to the ceiling cavity offer another way to deal with this problem and increase the R-value throughout the ceiling.
The Leaky Common Wall
On numerous occasions I've encountered houses where the biggest problem was the common wall between the house and the addition (see Figure 2). It's not unusual for infrared scans to reveal this interior wall as the coldest wall in the house. Why? It's very often open to the attic at the top, uninsulated, and loaded with wires and pipes that were punched through during remodeling.
In most cases the addition wall is actually two walls with a space in between them. That space can usually be sealed at the top with foam sealant or rigid materials or packed with high-density cellulose. It should be sealed in line with the ceiling of the addition or the ceiling of the old part of the house or both. In some houses (like the old farmhouse I grew up in) the space may be big enough to walk through. Even dense-pack cellulose is no use then. It takes some smart carpentry (dirt and sweat too) and durable rigid materials like plywood and Sheetrock fastened with nails or screws, as well as foam caulk, to seal a space that large.
Problems like these are commonly encountered when remodeling old houses that have grown many times. It may take some exploratory surgery with a saw to find them. Remodeling is the best time to fix these problems, and the remodeler often has the carpentry skills to do it.An Investment
That Pays Off Remodeling provides an opportunity to improve the energy performance of a home by air sealing and insulating. When done correctly, these treatments can be an excellent investment. They increase energy efficiency, pay for themselves, add value, and improve comfort. They even keep a home quieter and inhibit rodents and other pests from coming in.
Does it cost more to remodel right? R.S. Means (a leading cost information company) estimates costs for an addition at over $70/ft2. Insulation and air sealing account for a small fraction of those costs. The cost difference between just adding insulation and properly insulating and air sealing is only pennies more per square foot. Those pennies can bring big benefits.
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