A home with good insulation but leaky windows will still feel drafty near the glass. Quality windows installed in walls with gaps in the air barrier will underperform because conditioned air escapes around them. And even a tight, well-insulated envelope won’t help if the heating system is undersized for the space.

This matters in Virginia because our winters, while not extreme by northern standards, include enough cold snaps to test how well a home is built. In the Smith Mountain Lake area, temperatures regularly drop into the teens during winter, and single-digit nights aren’t unusual. A home that performs well during those stretches will be comfortable year-round.

This article walks through the major components of a home’s building envelope and explains what we include in Ellis homes and why.

Traditional construction uses housewrap as an air and weather barrier. It’s installed in sheets that overlap and get taped at seams. The problem is that housewrap depends heavily on installation quality. If tape fails, if sheets get torn during construction, or if seams aren’t properly detailed, gaps develop. Those gaps let air and moisture through.

ZIP System sheathing works differently. The weather-resistant barrier is built into the structural panel itself rather than applied as a separate layer. Seams are taped with a specialized adhesive designed to bond permanently with the panel surface. The result is a continuous barrier with fewer opportunities for installation errors.

Insulation that’s compressed loses R-value. Insulation with gaps around electrical boxes or plumbing lets heat bypass it entirely. These installation issues are common in production building where crews work fast and supervision is limited.

For context on what R-values mean in practice: R-48 in the ceiling (what we specify) reduces heat transfer to about 2.6% of what would occur with no insulation. R-15 in the walls reduces it to about 6.7%. The ceiling matters most because heat rises, which is why Virginia energy code requires higher R-values there.

Low-E (low-emissivity) glass has a thin metallic coating that reflects radiant heat. In winter, it reflects heat back into the room rather than letting it escape through the glass. The practical effect is that the interior glass surface stays warmer, which reduces condensation and makes the area near windows more comfortable.

During sustained cold, with temperatures in the single digits for several days, window quality becomes obvious. Homes with basic single-pane or low-quality double-pane windows develop condensation, frost on the interior glass, and noticeable cold zones. Quality Low-E windows maintain more consistent interior surface temperatures.

Modern heat pumps are significantly more capable in cold weather than systems from 10 or 15 years ago. Our standard systems are rated at 14.3 SEER2, which reflects current efficiency standards. But the efficiency rating is only part of the story.

The air handler (the indoor unit that circulates air through your home) matters just as much. We use variable speed air handlers, which adjust their output based on demand. A basic single-speed system runs at full blast until the thermostat is satisfied, then shuts off completely. It cycles on and off repeatedly, creating temperature swings and wasting energy.

Variable speed systems run longer at lower speeds, maintaining more consistent temperatures with less energy. During sustained cold, when the system runs for extended periods, the difference is significant. The home stays at a steady temperature rather than swinging between too warm and too cool.

In older, leakier homes, fresh air enters through gaps and cracks throughout the structure. That’s inefficient for heating and cooling, but it does provide air exchange. A well-sealed home eliminates most of those leaks, which means ventilation has to be intentional.

Moisture is the primary concern in winter. Cooking, showering, and even breathing add moisture to indoor air. In a tight home, that moisture has nowhere to go unless it’s actively removed. High indoor humidity can cause condensation on windows, musty smells, and conditions that promote mold growth.

Controlled ventilation also matters for indoor air quality. Stale air, cooking odors, and off-gassing from furnishings and finishes need a path out of the home.

Our foundation system starts with 9-foot poured concrete walls, which provide more strength and water resistance than block construction. But the concrete itself isn’t waterproof. Water will migrate through it over time unless there’s a barrier.

We use the complete Tuff-n-Dri system on every home: spray-applied waterproofing on the exterior walls, Warm-n-Dri insulation board over that, and Drain-Star perimeter drainage to direct water away from the foundation. The Warm-n-Dri board provides R-5 insulation to the basement walls and protects the waterproof coating from damage during backfill.

This system comes with a 30-year written warranty from Tuff-n-Dri against water penetration. It’s one of the strongest foundation warranties available in residential construction, and it transfers to subsequent owners if you sell the home.

Heat escaping through the roof warms the underside of the snow, causing it to melt. The water runs down toward the eaves, which are colder because they extend past the exterior wall (there’s no heat below them). When the water reaches the cold eaves, it refreezes. This creates a dam of ice that traps subsequent meltwater, which can back up under shingles and leak into the home.

The primary defense is proper attic insulation and ventilation, which keep the roof surface cold so snow doesn’t melt from below in the first place. But ice and water shield provides a secondary defense at vulnerable areas.