14. Save Energy on the House Exterior

Building Envelope

A menagerie of ideas from the experts on improving the building shell:

  • Tight, well-insulated houses lose heat very slowly after the power goes out. If you set back the thermostat, you can coast through a cold spell, all bundled up in sweaters and long johns.
  • Wood stoves need an outdoor combustion air vent to draw makeup air from outside (instead of inside) the house.
  • An enclosed front porch can buffer the airflow into and out of the house every time the front door opens. Storm doors help keep the heat in, too.
  • New home construction standards should strive to exceed the “energy standards” by 50 percent.
  • Windows on the south side of the house should be 10 percent of the floor area. Any more and the house can overheat even in the winter.
  • Airtight construction is essential for super-insulated buildings. Otherwise, internal humidity created by the occupants (bathing, washing dishes, breathing!) transports moisture through any cracks or gaps in the building envelope. Why? Because of vapor pressure. A higher vapor pressure inside forces vapor through the walls until the inside and outside vapor levels are equal.
  • Chimneys cause a negative pressure in the house because they exhaust air from inside the building shell.

Finding air leaks (on a windy day)

  • By feeling, works well for localized leaks and in very cold weather.
  • Small flames, from a candle or barbecue lighter.
  • The pros use test smoke, which works well for leaks leaving the house but not leaks into the building shell.
  • Tissue paper dangling near the leak site.
  • Lightweight ribbon on the end of a stick.
  • Infrared thermograph imaging using a hand-held device.
  • Smart vapor barriers are breathable materials that change permeability with the humidity. Permeability is higher in the summer, so moisture trapped in the fabric dries out and causes no physical damage. Smart vapor barriers work for either roof or wall assemblies.
  • Light-gauge steel framing (made from recycled steel) can be used for interior walls.
  • Put casement windows (which are ideal for funneling air into the house for ventilation) on the side of the house facing the prevailing winds.
  • The EPA standard for air-tightness in the United States is 0.35 Air Changes per Hour (APH). That means one-third of the air in the house is replaced with fresh air every hour. Or three hours for a full air change with outside air.
  • If water pools in your basement, either fix the source or get a sump pump. Standing water eventually ends up as humidity inside the building envelope, and that’s not good.
  • Basement ventilation lets fresh air inside and lowers the humidity level.

This same principle applies to crawl space ventilation.

Where are the air leaks in your average house?

  • 30% gaps in siding
  • 30% doors & windows
  • 15% floors
  • 15% walls
  • 10% ceiling
  • Exhaust fans should have a backdraft damper (to ensure airflow is one direction only) where the exhaust duct exits the house so that outside air can’t enter the house.
  • Orient a house so that the south wall of the property faces within thirty degrees of true south for optimal use of passive solar energy.
  • Sealed combustion heating appliances (furnace, wood-burning stove, clothes dryer, water heater) vent toxic products of combustion directly outside through a sealed pipe. Sealed combustion exhaust is essential for any appliance located inside the conditioned space.
  • When you see the phrase “gas-fired space heater,” you should think, “Crack open a window nearby for combustion air.”
  • Very “tight” houses need a CO2 sensor to monitor indoor air quality.
  • Wind washing, air leaking through fiberglass insulation, reduces the rated R-value by 15 to 50 percent.
  • Most air leakage originates in the garage, attic, crawl space, and basement.
  • Dropped ceilings and recessed light fixtures are infamous for infiltration and exfiltration issues.
  • Look for dirty spots in the ceiling paint of the topmost floor and repair cracks with caulk.
  • The more “pressured” a house (from exhaust fans or clothes dryer exhaust), the more pressure asserted on all envelope penetrations to leak like a sieve.
  • Seal any leak near a heat source (furnace, chimney) only with fire-resistant materials.
  • Use rigid Styrofoam to seal large openings. Hire a qualified carpenter if it’s in a highly visible area.
  • The colder the climate, the more insulation you need—everywhere.
  • Cold air can enter a house three ways: wind, fans, and the stack effect, which refers to air moment through chimney-action (wind siphoning air out of the chimney).
  • Fifty million American homes are under-insulated if you compare them to building-code standards. The number is twice that if you go by energyefficiency standards.
  • In cold climates, the vapor barrier is on the heated side of walls, ceilings, and floors. In warm climates, it’s on the unheated (outside) surface.
  • Many kinds of building materials act as a vapor retarder: tarpaper, 6-mil plastic, plywood with exterior gluing, and plastic-coated exterior foam sheathing all qualify as vapor barriers. (Plastic is the most effective.)
  • Vapor barrier paint or primer (with a therm rating of less than 1.0) qualifies as a vapor barrier. It’s great for bathroom walls.
  • Any vertical surface in still air has an R-value of 0.5 to 1.0.
  • Air supply registers should not discharge air directly onto the interior surface of a window or exterior wall, destroying the insulating value of a static air layer on that surface. That airflow increases the temperature differential across the window or wall, increasing the heat transfer rate.
  • Maximize the shading and reflectivity of the roof, walls, and windows to lower seasonal cooling loads.
  • Install a ground vapor barrier over any bare soil in a crawl space or basement to mitigate moisture problems.
  • If a door is not used at all, seal it closed permanently. Be sure it won’t be needed for emergency egress.
  • Thermal shutters are a type of moveable insulation to add R-value to windows and skylights at night.
  • Low-emissivity window coatings that face the interior of a building reflect the long-wavelength infrared radiation that is emitted by the warm interior. This reduces heat loss from the room in wintertime.
  • Install a suspended, insulated ceiling to lower the heat gain/loss from the ceiling and the top part of the walls plus even more savings if the existing ceiling has no or little insulation.
  • Reduce the window area of large expanses of glazing with insulating panels or transparent insulation.

Technically, the “building envelope” consists of the roof, floor, and walls—the physical boundaries of the air-conditioned space. The Roof & Attic discussion didn’t treat that part of the structure as an element of the formal building envelope because, for the most part, it excluded the ceiling of the structure and its insulation. That made it possible to focus more on the heat transfer aspects of the roof-attic assembly, introducing you to the concepts of ventilation and heat transfer in a familiar context.

The discussion to follow also applies, retroactively, to the attic-roof, even though I’ll now focus mostly on the exterior walls and their main elements, doors, and windows.

15.1 ARTIFICIAL SHADE IS BETTER THAN NO SHADE AT ALL.

In HVAC engineering, any shaded exterior wall is a north-facing wall. Northern exposures have far lower thermal loads than east-, south-, or west-facing walls. Trees are the best way to shade, but awnings make shade, too. If you have a west-facing porch, thatch roller shades can block out the summer heat and let it inside in the winter.

15.2 OPEN THE GARAGE DOOR IN THE SUMMER. 

The garage can get very hot in the summer if the folding garage door is closed. Assuming the back wall of the garage abuts the house, heat from the garage will migrate through that back “partition” wall and into the house. Get some ventilation going through the garage: Open a side window and crack open the garage door a few inches. The opposite is true in the winter: Seal the garage tight to keep the heat in and the drafts out.

15.3 SHRINK–WRAPPED HOUSES ARE THE NEW FAD.

Many builders install a plastic house wrap barrier as the second line of protection (after the exterior cladding) instead of tarpaper. Both products are water- and airresistant and form a quality vapor barrier. House-wrap manufacturers claim their product is easier to install (in almost half the time) than tar paper and is more forgiving to any damage done during the construction process (tar paper tears easily).

 15.4 THE EVER–READY WEATHERIZER BUNNY.

Weatherization is the buzzword for sealing all the small leaks in the building envelope to minimize infiltration by cold/hot air as well as moisture. Siding is caulked up and down the seams. Weatherstripping around the doors and windows can dry out, get torn off, or otherwise stop sealing correctly. Outside faucets and electrical outlets that penetrate the building shell should be caulked, too. Large openings can be filled up with expanding insulation, a foam application in a can. Sealing all those penetrations keeps the bugs out, too. (Details in the Weatherization chapter.) Once the caulking or sealant is dry, paint your work to match the walls.

 15.5 SOME AIR INFILTRATION IS ESSENTIAL. 

You don’t necessarily want to make the house completely airtight. All human activities require oxygen. The carbon dioxide we exhale must be exhausted.

A densely populated space like a classroom must have the complete volume of air in the room replaced with outside air three or four times each hour. Your house also requires this replacement cycle, if at a lesser rate. Usually the building envelope (shell) is air-permeable enough so that wind/open windows/traffic in and out, and so forth. keeps the air fresh.

A shrink-wrapped house, on the other hand, may form such an impermeable barrier that outside air must be ducted into the house at the air-handling unit to ensure a healthy environment within. If you have many people in the household or experience what you think is bad indoor air quality, ask a contractor to test the air with a CO2 meter, or purchase one yourself for a modest sum. Share the device with your friends, coworkers, and extended family!

 15.6 NEGATIVE PRESSURE IS THE KEY CONCEPT.

Whenever you exhaust air from the bathroom or kitchen, it creates a mild negative pressure in the house overall. Outside air creeps in through cracks around siding, windows, outdoor faucets, doors, and down the chimney. This infiltration continues until the pressure equalizes, inside versus outside.

Voila: fresh air in and stale air out. If you have a fireplace, a breeze naturally draws air up and out the chimney (unless you have a seal-tight wood-burning stove insert).

 15.7 THE V IN HVAC IS SUBTLE, BUT VERY IMPORTANT. 

It’s called Heating, Ventilation, and Air Conditioning. Ventilation is ubiquitous with air conditioning, as suggested by the previous examples. Ventilation via exhaust is how you purge extra moisture before it puts an additional “latent load” on the HVAC cooling coils or condenses inside the walls.

Ventilation is needed to eliminate carbon dioxide, replacing the CO2 with fresh, oxygen-rich outside air.

 15.8 HEAT FLOW CALCULATIONS–A LITTLE SCIENCE. 

Heat flows from point A at T1° F to point B at T2° F at a rate based on the temperature difference (T1-T2). The actual heat flow (Q) is a function of area (A) and the insulation value (U) of the partition between A and B: Q = U*A*(T1-T2)

Where Q = heat flow, U = insulation value, A = Area, and (T1-T2) = Temperature difference.

For a given amount of ceiling insulation, the amount of heat that flows (always from the higher to the lower temperature) out of the air-conditioned space is directly proportional to the temperature difference:

Without a ventilation fan: Q = U *A * (150°F – 80°F) = 70*UA

With a roof ventilation fan: Q = U*A * (100°F – 80°F) = 20*UA

Roughly four times less heat flows from the attic through the ceiling into the house when the vent fan is running.

The vent fan stops saving energy when the energy used to operate it is greater than the air conditioning energy saved. Practically speaking, most contractors set the temperature “set point” of the vent fan at 100°F to 110°F.

 15.9 OPEN THE WINDOWS AND TAKE A DEEP BREATH!

In a residential setting, you can throw all the windows open when there’s a cool, dry breeze outside. It’s an excellent opportunity to get all the stale, high-CO2 air out of the house and replace it with healthy, fresh, high-oxygen air. A house does fine with a fresh-air flush once a month, weather allowing.

Theoretically, a well-designed house never needs to be flushed out like this. Leakage through windows, opening/closing doors, and exhaust fans (clothes dryer!) introduce a regular amount of fresh air.

However, in my humble opinion, you can never have enough fresh air. Plus, temperature and humidity permitting, an open house is a real pleasure. Better yet, if you time it right, you can cool down the home a bit in the summer and warm it up in the heating season.

 15.10 THE TECH EDGE VERSUS THE TRUTH. 

Excuse me, but couldn’t I have just saved you the last few pages of science and said, “Open the windows when the weather is nice outside”? Sure, but then you wouldn’t know why. You might do it when it’s incredibly humid outside and not suffer the consequences.

As an aside: Since most of America lives in areas with terrible air pollution, do people avoid opening the house at all?

 15.11 THERMAL MASS COMPLICATES EVERYTHING, BUT IN A  GOOD WAY.

It might make perfect sense to open all the windows, say in the fall, to (figuratively) sleep under the crisp, starry night sky. There’s nothing like piling on the blankets and the feeling of cold air on your face. If it’s chilly inside the next morning, that’s what the central heat is for, right?

Small problem: When you maintain your home at, say 20°F below your comfort range all night, much more than the air is cooled down. All the furnishings, walls, appliances—everything inside the building envelope is cooled down, too. The following morning the heater must heat the air plus all the interior items in your home.

It’s better to (1) flush out all the air in the whole house for thirty to sixty minutes, then (2) close all the windows in the house except your bedroom. That way, with the central heat turned down all night, the heavy mass only falls a couple of degrees (instead of 20°F), and the heater doesn’t have to work nearly so hard the next morning.

All that solid matter—furniture, floors, books, walls, furnishings—is called thermal mass, a kind of thermal momentum to your house’s temperature-state. It’s like taking your foot off the gas going down the interstate: It’s a whole lot easier to get back to speed from 45 MPH than from a dead stop!

The air inside a structure is part of the thermal mass, too. Also, the humidity in that air.

 15.12 HOW INSULATION WORKS.

The fiberglass insulation in walls or the attic has an R-rating. The thicker the batts, the higher the R-value. The amount of heat flowing through a roof/wall/window is directly proportional to the temperature difference on either side.

Any time there’s a temperature difference, heat will flow. Insulation on a water heater tank, for example, doesn’t stop the flow of heat but only slows down the process. A “slower process” means less heat escapes over a given amount of time.

Fiberglass insulation works by blocking the movement of air. For example, in a wall with no insulation, the air is free to move up and down via natural convection (“hot air rises”). Block that free movement of air, and it’s harder for heat to flow through the wall.

In other words, when there’s insulation in place, the hot/cold outside surface conducts heat to the air trapped in the fiberglass until the temperature equalizes. But the air can’t move away now! For heat transfer to continue, the heat trapped in the fiberglass must move away by conduction, which is much slower than convection, hence the higher insulating value.

Take, for example, a large sliding glass door. In the winter, cold air cascades down the glass and flows out onto the floor in a steady stream of cold air. In the summer, hot air streams upward and heads for the ceiling. Venetian blinds interrupt this airflow, to the extent that when kept at a 45° angle to horizontal, a double-pane window assembly has the equivalent R-value of a storm window (triple panes). Curtains, especially heavy, insulating curtains, help even more.

Thermal flow in the heat equation depends on temperature difference: The higher the temperature difference, the greater the heat flow. When a wall or window has zero insulation, the air is heated/cooled, it moves right away up/down by convection, and more air (with the high-temperature difference) replaces it, and the process continues ad infinitum.

Notice that the difference between R-13 and R-30 fiberglass insulation is the thickness. If you squash the batts to fit into a space, down to half the natural thickness, the R-value drops to half its design value.

My faux-wood plantation blinds salesperson said the wood increases the insulation value of the window assembly. Very minimal. The enhanced insulation value comes from stratifying the airflow across the surface of the window.

15.13 VAPOR PRESSURE: IT NEVER GIVES UP!

You don’t need air movement for moisture to go from one place to another. Not even solid walls can stop moisture. If the vapor pressure is higher on one side of a wall (outside, after a hard rain) than on the other (inside your cool, dry house), the moisture migrates right on through the wall. It won’t stop until the humidity is the same inside as it is outside.

What happens if it’s more humid inside the house than outside? Humidity migrates toward the outside and condenses on the inside of the tarpaper. Over time, that can create an environment favorable to the growth of mold inside your walls.

Note: This is for a warm climate, where the vapor barrier is on the outside of the wall assembly. (This is the standard in the whole book.)

 15.14 FELT (TAR) PAPER TO THE RESCUE. 

We saw how felt paper in the roof assembly (underneath the shingles or other roofing material) collects water and allows it to drain off the roof. Once it stops raining and the water drains, the roof paper evaporates the remaining moisture back into the atmosphere.

The overlapping layers of asphalt tarpaper on the exterior walls make an ideal vapor barrier. If water gets behind the felt paper, the tarpaper absorbs that water and then slowly allows that moisture to evaporate back into the air (when the humidity is lower, e.g., in the afternoon).

15.15 MOLD IS THE SILENT KILLER. VERY DANGEROUS TO THE  HEALTH. 

Water vapor (alias humidity) equalizes across any given barrier. Exterior walls, by law, have integral vapor barriers to retard this process. Eventually, the external vapor pressure equalizes with the interior.

In humid climates, it’s paramount to maintain separation (closed windows, well-maintained exterior walls, and adequately-caulked joints or penetrations throughout). Absent a uniform vapor barrier, then, over time, mold grows inside the walls, causing an enormous amount of damage to the structure.

15.16 HILLBILLY ENGINEERING: REMOVABLE INSULATION.

The original owners designed my house in the Appalachians as a three-season second home. (Atlanta is only a few hours away.) There are tons of windows (with a nominal lake view when the leaves are down, but otherwise just trees). All that glass exposure makes the place feel very chilly in the winter, even when the thermostat says it’s toasty warm inside.

Cold glass is hard to explain. The best I can do is to say it’s the opposite of a fire-hot fireplace. The actual heat from the hearth is secondary to the “radiant heat.” An expanse of cold glass is like radiant cold, absorbing warmth from the room.

The same room at the same temperature feels much colder in the winter than it does in the summer. Cover up the cold glass (close the blinds and curtains), and the room feels much warmer. I did even better than that:

I wrapped two-inch solid Styrofoam boards in burlap fabric and stuffed them into half of the windows in my house. The batts fit nicely between the window glass and behind the plantation blinds. It looks pretty redneck from the outside (who cares?), but inside, I close the plantation blinds over the insulation so you can’t see the burlap facing. I have a whole new house to live in, full of cozy winter spaces.

Half the windows are still there, and I get plenty of daylight. Many of the “radiant cold” windows are gone and replaced by windows with an insulation value better than the walls. (Call it my stealth house.)

I also put the batts in the windows for one month in the summer when it’s hottest outside

The year-to-year graphic printouts I get from the power company show just how much electricity I save. I do even better than the empty houses in the neighborhood, where the heat runs just enough to stay above freezing.

15.17 MORE CREATIVE INSULATING TECHNIQUES. 

Most buildings in the United States are code-compliant, but the “Green New Deal” proposes spending trillions to make businesses and houses even more energy efficient. However, just because your building is “current with the current building codes” doesn’t mean you can’t do better.

High ceilings are well suited for hot climates. The thermal layers of static heat form layers at the ceiling. Recall that heat flows in proportion to the temperature differential. Warmer stagnant air at the ceiling means less heat transfer from the attic above. My downstairs has ten-foot ceilings. Those rooms remain delightfully refreshing in the summer (heat rises) but are chilly all winter. Insulation between the floors (in the downstairs ceiling) helps a lot, both with heat transfer and noise.

A good builder puts insulation in the walls separating the living area from the sleeping quarters. This reduces noise transmission. It also lets you open bedroom windows in the winter to “sleep under the stars” but to not chill down the whole house in the process. Some contractors also put a moisture barrier around the bathroom walls.

Insulation in the interior walls of guestrooms or other areas that see infrequent use isolates them thermally. The HVAC supply vents can be partially closed, maintaining a different temperature from the rest of the house. It’s not a good idea to close the vent(s) entirely because you still need some airflow for moisture control.

 15.18 THE PAINFUL TRUTH.

Windows make up 10-25 percent of your heating and cooling costs. Single-pane windows are horrible (R-1). If you can’t afford to replace them with double-pane (R-2 or better), you can improve their thermal value with curtains (any curtains will do, but heavy insulating ones are best), Venetian blinds, or both.

Not all windows add the same thermal load on the HVAC system. North-facing windows are the least problematic, followed by south facing, then east, then west. Your window contractor can do simple annual loads analysis (or use my spreadsheet in the “Energy Audit” chapter) for the exact values on your house and at your location.

Given limited funds, replace the most critical windows first, usually those facing west, then south.

 15.19 TO LOW–E OR NOT TO LOW–E?

Single pane windows are a crime, even to manufacture them. But what about energy-saving coatings? Low-e coatings don’t increase the insulating value. Their thermal advantage is how they block some of the sun’s high-energy UV rays. Hint: a window on the north side of the house that never gets any direct sunlight will not benefit from a low-e coating.

“Passive heating” is the art of using the sun’s energy for space heating, especially when the sun is far to the south in the winter. Forget about that warm sunlight if the windows have a low-e coating. Sure, you want to keep those rays out of the house in the summer (west-facing windows in the afternoon). Blinds, shades, and curtains do a good job of that (trees, too).

 15.20 DON’T FORGET THE FLOOR.

If you have a slab foundation, there’s not much you can do to save energy there, although, in very cold climates, you can insulate the exposed edges of the slab. Any home with a crawl space benefits from insulation in the floor rafters, either fiberglass batts or open-cell foam spray insulation (which also acts as a vapor barrier).

If you live in a freezing climate, you’ll know that the foundation has to extend below the frost line to prevent foundation heaving. (Frozen ground expands and can ruin a foundation.)

It’s worth noting that in a narrow crawl space, there is a thermal interlocking between the ground and the bottom floor: They track roughly the same temperature, even with ventilation. This is good news because the ground is always cooler than the air in the summer and warmer than the air in the winter.

Note: Observe that even if the ground is frozen, 32° F is warmer than the outside air when the daytime highs don’t get above freezing.

 15.21 ARE TWO BY SIX EXTERIOR WALLS WORTH THE EXTRA COST?

The universal standard for residential frame construction is two by four walls. You can also frame with two by six lumber (which also increases the cost of windows and doors because you need deeper frames). The extra material costs for the two by six framing is roughly $1 per square foot of the total house area. There are also additional labor costs because framing crews are used to working with two by fours, which are a good bit lighter.

Two-by-six framing makes the structure much stronger, and the extra insulation also helps with sound-proofing.

It’s common to assume that two-by-six framing is cost-effective but only in

very cold climates. Anecdotally, even in Michigan, two-by-six framing adds $3,000 or so to the cost of an average 2,200 square foot house, but only saves about $50 ayear on heating and cooling bills. That’s a fifty-year payback. Hence it’s not worth the effort, at least for thermal efficiency alone.

You’re better off spending that $3,000 on something with a better payback. For example, you could use open-cell foam insulation instead of fiberglass insulation in the two by four stud walls to double the overall R-value of the wall assembly. (Don’t use closed-cell foam because it’s not vapor-permeable; water trapped between it and the vapor barrier wouldn’t have anywhere to go.)

Note: Calculations like this assume that energy costs remain constant during the fifty-year payback period. That may be a stretch if the politics of climate change ever gain traction.

 15.22 DOUBLE THE WALL THICKNESS.

Hard-core energy conservationists recommend a retrofit to houses in cold climates by adding two-by-four framing on the outside (or inside) of the existing walls, filling the extra four inches with insulation, and finishing out the siding.

It seems like a reasonable idea. However, since we just discovered that adding two inches of insulation isn’t worth the cost, adding four inches (at a much greater cost in time and materials) is unlikely to have an acceptable payback.

 15.23 THERMAL BRIDGING IN EXTERIOR FRAMING WALLS.

When HVAC engineers do a thermal analysis of outside walls, we don’t use the R15 value of the four-inch fiberglass insulation batts. The wall has a two-by-four wood stud every sixteen inches. Wood doesn’t insulate as well as fiberglass, so the overall R-value of the wall assembly isn’t R-15 but closer to R-11.

Many commercial buildings are made with steel studs. Far from being a weak insulator like wood, steel is a conductor. A wood stud wall lowers the Rvalue 15 percent below that of the insulation; a steel stud wall lowers the R value over 50 percent, down to almost R-7. That’s why steel framing is usually six inches, getting you an overall R-value of 8 (versus R-16 for a two-by-six wood frame wall).

 15.24 THE THERMAL BENEFITS OF EXTERIOR CLADDING.

If you think brick siding adds insulation value to the exterior shell of your house; well, the insulating value of a four-inch brick is R-1. The half-inch space behind the brick façade (for drainage) has almost that much insulating value.

What about the brick’s thermal mass value? It’s helpful to look at the daily thermal cycle of the wall:

During the day, the brick heats up with the outside temperature. Walls with direct sun exposure heat up even more. When the sun goes down, the wall stays warmer than it is outside. This is good in the winter but bad in the summer.

By midnight the wall is at the outside temperature and tracks that value until sunrise, at which time the outside temperature rises, but the brick temperature lags. This is good in the summer but bad in the winter.

So, in the course of a year, you gain some thermal value and you lose some, for a minimal net annual benefit.

The best place to have your brick wall is inside the insulated frame walls. In summer, the wall reduces the heat that gets through the wall assembly, and the brick wall slowly absorbs that heat, so that it’s many hours before there’s any need for cooling inside the house.

When the outside temperature falls to lower than the t-stat setting, the direction of heat flow reverses. Now the heat moves in the opposite direction, toward the exterior, and the outside heat never even reaches the interior. Vice-versa happens in the winter, again reducing the thermal load on the heating system.

That’s why it’s so helpful to have thermal mass on outside walls—bookshelves, heavy furnishings, or a brick façade.

In my last house, several exterior walls in the kitchen were brick on the inside, except it was a façade. They literally cut bricks in half and mortared the half-inch piece on the wall assembly (1940s construction tech). These days they make fourby-six foot panels with a brick veneer-looking finish—very realistic—that can dress up your wall and add a little thermal mass, too.

15.25 OLD–HOUSE INSULATION ISSUES.

You live in an old house, but the heating and cooling bills are killing you. You hire a contractor to do an infrared scan of the house to see where all the heat is escaping. He tells you there’s no insulation in any of your outside walls!

A good contractor can drill small holes at the top of the walls between each stud, insert a small tube, and fill the space with expanding foam. Open-cell foam is R-3.5 per inch, and closed-cell foam is R-6.5 per inch, versus R-2.5 per inch for fiberglass batts. So, you’ll end up with two or three times the insulating value as fiberglass batts, and excellent sound-proofing against their teenager’s violin practice.

They can also drill larger holes and blow in cellulose insulation, which has a lower R-value than expanding foam but is a lot cheaper.

15.26 SOUND–PROOF WINDOWS HAVE THEIR PLACE UNDER THE SUN.

Live near a highway, airport, sports stadium, railroad tracks? Noise can be very stressful, especially if it’s out of your control. Most of the sound entering your house comes through the windows. They’re on the expensive side, but they do make “sound-proof” windows that let a lot less sound through.

You may need to only replace one or two windows, on the noisy side of the house, or in the room where the noise bothers you the most.

A cheaper method might be a noise-canceling electronic device. My Jeep Wrangler has noise-cancellation technology (Wranglers are notorious for road and engine noise.) The system pipes “white noise” through the stereo. It helps quite a lot.

 15.27 TWO–ZONE HVAC SYSTEMS FOR LARGE HOUSES.

Some floor plans are well suited to having two heat pumps with two thermostats, or a single system with two zones. A two-zone system requires a damper, controls, and a small computer panel, but it can save a lot of energy in the right situation.

Both zones share the same return-air path, making it a kind of hybrid system.

My two-story house has a two-zone system, one for upstairs and one for downstairs. I set different temperatures for each floor all year. I mostly live upstairs in the winter. If I’m downstairs in the office, I wrap an electric blanket and work away (peddling on my little eccentric cycle gizmo, which keeps me warm, too).

 15.28 INSULATE BETWEEN THE FLOORS IN A TWO–STORY HOUSE.

Usually, the bedrooms in two-story houses are upstairs, and the kitchen, living room, and dining room are downstairs. My house is on a hillside, with a walkout basement, so it’s set up the exact opposite: two bedrooms downstairs and the main living areas upstairs. Most people wouldn’t think of doing it, but insulating between the two floors is an excellent idea.

That inter-floor insulation helps with soundproofing, too. It separates the two zones of the HVAC system so that I can keep the two floors at different thermostat settings. In an existing house, you can still add expanding-foam insulation between the floor rafters, just like was explained for outside walls, between the rafters.

15.29 STORM WINDOWS AND STORM DOORS.

A “storm window” is a second glass panel attached to the outside of the existing window during the wintertime. The assembly creates a layer of static air, increasing the R-value of a double-paned window to that of a triple-pane window. The storm window also eliminates drafts from strong winds, further reducing the heating bills.

The same principles apply to storm doors, a second glass door outside an existing door. You might be tempted to keep the storm door on all year so you can open the main door and let some light into the house.

15.30 LONESOME WINDOWS.

If you have windows that you never, ever open, then why not screw them shut and caulk around the edges to nix all possible airflow? This is especially helpful for second-floor (and higher) windows, where the pressure effects from wind are more significant (e.g., increased infiltration).

15.31 DON’T FORGET THE BASEMENT.

A basement is a part of the building envelope, even if it’s not heated or air-conditioned; it’s still a thermal load on the lowest floor of the occupied space. Insulating the basement walls and ceiling reduces that HVAC burden. Absent wood framing in which to stuff fiberglass batts, you can apply spray-on insulation. Open-cell foam has twice the R-value of fiberglass per inch and is vapor-permeable. Closed-cell foam has three to four times the R-value of fiberglass batts and isn’t vapor-permeable (don’t use closed-cell foam if there’s already a vapor barrier in the wall or floor assembly).

If you have gas-burning appliances in the basement (furnace or water heater), be sure to keep a sizeable opening for fresh air to enter the room for combustion.

 Future Tech! 

15.32 The building envelope is the chapter most concerned with the actual materials that comprise a house: framing, siding, roofing material, foundation, etc. All of these materials need to be sustainable, as per the “green building” criteria. This should be the design standard for all new houses everywhere.

 Green building basics

  • Energy conservation
  • Indoor air quality
  • Conservation of natural resources

15.33

Using reclaimed lumber keeps the wood from deteriorating and sending all that captured carbon back into the atmosphere. All lumber should be reclaimed and reused.

15.34

Basements are greatly neglected by the codes and standards. All slabs should have two inches of rigid foam insulation underneath and along the sides. This applies in all climates, even if it’s most beneficial in cold climates.

15.35

Concrete for all aspects of construction should be made with fly ash, a byproduct of coal power plants. It’s abundant, cheaper than Portland cement, and makes a more durable concrete that Portland products.