This information is the most common for how to comply with the energy conservation requirements for your new home, addition or sunroom/conditioned garage and is not representative of all the conditions you may encounter.
DEFINITIONS
Consider the following definitions when complying with the energy conservation requirements of the Virginia Residential Code.
- A conditioned space is an area within a building that is heated or cooled or has a fixed opening (no door or closable window) to an area that is heated or cooled.
- A basement wall is more than 50 percent below grade and encloses a conditioned space.
- Glazing is windows, skylights and glass doors.
- An R-value is a measurement of a material’s thermal resistance (the higher, the better).
- A U-factor measures the ability of a material (glass) or assembly (window) to transfer heat (the lower the better).
- A sunroom is a one-story structure attached to a dwelling with a glazing area in excess of 40 percent of the gross area of the structure’s exterior walls and roof.
*See section R301.2.1.1.1 2021 Virginia Residential Code for sunroom category definitions.- Category I, II, III sunrooms are unconditioned.
- A Category IV sunroom and attached garages are permitted reduced insulation and fenestration requirements, however they must meet all of the following conditions:
- Sunroom/attached garage is served by separate and independently-controlled heating and/or cooling system.
- Closeable exterior doors and windows separate the sunroom/garage from the rest of the dwelling.
- A Category V sunroom must meet all of the same conditions for the main dwelling
DESIGN VALUES
The table below provides the R-value and U-factor requirements for insulation and glazing, respectively. Higher insulation R-values are permitted provided their dimensions properly fit in the intended cavity without compacting its thickness. Glazing with lower U-factors than required are also permitted.
Minimum R-Values for Walls/Floors/Ceilings
| Element | New Home, Addition | Sunroom/Attached Garage |
|---|---|---|
| Ceilings8 | R-491 | R-491 or R-196 |
| Walls (wood framed) | R-15 or R-13+1" continuous2 | R-15 or R-13+1" continuous2 or R-137 |
| Walls (concrete, CMU) | R-8/133 | R-8/133 |
| Floors | R-19 | R-19 |
| Basement Walls | R-13 or R-10 continuous4 | R-13 or R-10 continuous4 |
| Slab-on-grade5 | R-10, 4 feet down or into heated space under slab | R-10, 4 feet down or into heated space under slab |
| Crawl Space Walls6 | R-13 or R-10 continuous3 | R-13 or R-10 continuous3 |
1 R-38 can be substituted for R-49 with a raised heel or energy truss where the full height of the insulation is maintained over the entire ceiling footprint and the exterior wall; see Figure (1) below.
2 The first value is cavity insulation; the second value is continuous insulation. “13+1” means R-13 cavity insulation plus R-1 continuous insulation.
3 The second R-value applies where more than half of the insulation is on the interior of the mass wall.
4 Use R-15 when applied continuously against the wall; use R-13 when applied between studs or furring strips.
5 Insulation must extend from the slab edge to a length of 48 inches vertically and/or horizontally; see Figure (2) below.
6 Category IV sunrooms/attached garages may use a reduced ceiling R value when all requirements are met.
7 Category IV sunrooms/attached garages may use a reduced ceiling R value when all requirements are met.
8 Fairfax County is now recognizing the ceiling R value from the 2024 Code. This will reduce the R value in ceilings from R-60 to R-49.
Maximum U-Factors for Glazing
| Element | New Home, Addition | Sunroom/Attached Garage |
|---|---|---|
| Window1 | 0.30 | 0.45 |
| Doors1 | 0.30 | 0.45 |
| Skylights1 | 0.55 | 0.70 |
1 Windows, doors and skylights shall have a maximum solar heat gain coefficient (SHGC) of 0.40.
Figure (1)
Figure (2)
