|D&D Design/Remodel of Irving, Texas, left the 4/12 roof pitch of this 1957 Dallas ranch home but created a 6/12 pitch for the master bath ceiling.|
An 8-foot flat ceiling can make a home feel cramped and uniform these days, as higher ceilings, both flat and vaulted, take over the housing market. Forty-two percent of builders responding to a 2002 NAHB survey said their homes had 9-foot first-floor ceilings, and 15 percent claimed ceilings of more than 9 feet. In a June 2005 AIA survey, 51 percent of residential architects said they use increased ceiling heights, two-story entries and vaulted ceilings to add volume to their homes.
Creating a cathedral ceiling in a ranch or split level home is one of the easiest ways to break out of the box, architecturally speaking. Cathedral ceilings can open up a house, adding a more spacious feeling to just about any room.
On the other hand, rooms with cathedral ceilings can be difficult to heat and cool. Homeowners may love the appearance of their newly remodeled room, but find that it is uncomfortable to live in.
Proper design, planning and building techniques will make the new ceiling look and function better. With access to the roof structure, you can boost insulation and air sealing — two important aspects of better energy performance and indoor air quality. By including skylights or larger windows that extend into the cathedral space, you introduce more natural light, saving on energy that was used for artificial lighting.
In any cathedral ceiling project, remodelers should take five factors into account:
- The type and configuration of the existing roof framing;
- the current state of insulation and how to improve it;
- the current state of roof ventilation and how to improve it;
- the location and distribution of HVAC, plumbing and wiring; and
- the existing finishes, such as paneling, gypsum board or paint, and whether to change or improve them.
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If the house was built before World War II, the wood-frame roof structure may consist of ceiling joists, separating the room below from the attic space above, and roof rafters. This construction method affords a cathedral ceiling the maximum volume and permits the selective removal of some of the ceiling joists, which further opens up the space. Newer construction, on the other hand, is more likely to use prefabricated roof trusses, which do not permit much useable attic space, and therefore offer less volume for a cathedral ceiling.
With ceiling joists and rafters, remove the insulation — usually batt — between the ceiling joists and the ceiling surface, which is usually gypsum board. This will expose the framing. Consult a structural engineer about which joists can be removed without undermining the integrity of the structure and how remaining joists should be fastened. By code, lateral horizontal ties must be no more than 4 feet on center.
You might want to install new wood or steel rod horizontal ties and remove the ceiling joists altogether. These ties can be located about a third of the distance up from the roof plate at the top of the wall and the ridge. This will result in a more spacious feeling.
Next, you will need to install new insulation between the roof rafters. Install insulation between the wall studs if the new space includes a side or gable wall. Roof rafters of 2 by 10 inches or more will be sufficient for the installation of kraft-faced, 8-inch-thick R30 compressed batt insulation, with a 1.5-inch airspace above it for venting (Figure 1).
|PATH suggests different insulation techniques for cathedral ceilings depending on the framing of the existing roof structure. Figure 1(top) Figure 2 (bottom)|
Ventilating the rafter cavities prevents ice damming in cold climates, which can lead to moisture problems and mold growth. Install soffit vents under the eaves and ridge vents at the top of the roof to encourage sufficient ventilation through the rafter cavities. If the roof rafters are less than 2 by 10 inches, a 2- by 2-inch or larger member can be nailed along the lower edge of the rafters to increase the depth.
With its new insulation and vent space, the ceiling plane will be ready for gypsum board or another finish material. If you want to use wood paneling or sheathing such as bead board, install it over the gypsum board, which will help air-seal the home.
Trusses, normally spaced at 24 inches on center, call for a slightly different approach. Remove the existing ceiling materials and insulation to expose the trusses and the underside of the roof decking. Depending on roof span, pitch, and other factors, strong-back lateral bracing may be installed. In this case, consult an architect or engineer.
The truss top chords are normally no more than 2 by 4 inches. Because of their minimal depth and the complications introduced by the truss web members, some of the insulation may need to be installed above the existing roof. This will require stripping the roofing shingles to expose the plywood or OSB roof decking. Over this, you can add 4-inch-thick insulation panels (Figure 2). Other thicknesses can be used depending on the required R-value.
Structural insulated panels, prefabricated foam insulation "sandwiches" sheathed on both sides with OSB, can also be used. SIPs are easy to install using long screws that penetrate the full depth of the material into the existing roof decking. Roof SIPs typically have a rating of about R-4 per inch. The existing roof trusses should be sufficient to support this additional load, which is about 3 to 4 pounds per square foot. To gain higher R-values, install additional rigid insulation boards on the interior side of the roof decking between the truss top chords.
Applying 1-by casing to the sides of the truss top and bottom chords creates a more finished appearance and eases installation of the ceiling finishes by covering the gap between the finish material and the truss top chords (Figure 2).
The method described above is for a non-cavity assembly where ventilation is no longer required. However, air sealing remains critical to prevent interior air from moving up through material seams where condensation and resulting moisture problems may occur.
Installing insulation panels or SIPs will increase the depth of the roof structure, so you will need to reconfigure the soffit and fascia. Because of the increase in depth, this method will work best where the resulting roof surface terminates against a gable or comprises the entire roof surface.
To increase the amount of reflected light inside the new cathedral ceiling, finish the underside of the roof slope and the trusses themselves with a light-colored paint. To soften this slightly industrial look, encase the sides of the exposed top and bottom chords in trim sized to cover the gang-nails typical of most truss member connections.
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|The vaulted ceiling made room for two custom windows that increase natural light. Photo by Vaughn Creative Services|
The approach to mechanical systems and lighting in either kind of roof framing is virtually the same. HVAC equipment, ducts, pipes or wiring located in the attic will need to be relocated. Perimeter soffits and coffers may provide alternate locations.
PATH suggests avoiding recessed lights in sloped ceilings, as they create large voids in the insulation, which can cause air leakage. The best choice for new lighting is surface-mounted fixtures or lights installed on the collar ties or truss chords to up-light the underside of the roof.
Installing skylights between the roof rafters or trusses will increase the sense of space and light. Some skylights are specifically sized to fit between the top chords of the trusses. North-facing skylights provide the best quality light. Avoid placing skylights on south or west roof slopes, especially in hot climates, since the additional heat gain and glare may be difficult to control.
If spaced correctly, skylights can reduce the need for electrical lighting, especially in a room with few windows. Ultimately, spacing depends on factors such as glazing type, design of the skylight well and skylight size, but a rule of thumb is to set them apart 1 to 1.5 times the height of the ceiling. Total skylight area should not exceed 5 percent of the floor space for a room with many windows and 15 percent of the floor space for a room with few windows.
Adding a cathedral ceiling should have negligible impact on energy costs and positive impact on energy performance and comfort, if you follow the principles outlined above. These methods will also prevent future moisture and comfort problems that can arise from air stratification and leakage — two problems that are never easy to fix after a project is done, no matter how much money the homeowner invests.
The Partnership for Advancing Technology in Housing (PATH, www.pathnet.org ) is administered by the U.S. Department of Housing and Urban Development.