Weatherization

This whole section is “energy tips” from the professionals.

• Maintain the fit, sealing, and closure (alignment) of exterior doors to minimize air leakage. Adjust the closing mechanism as applicable.
• Kids that leave the door open or ajar all the time? Install a spring-type door closer.
• Interior blinds with a shiny, white exterior-facing surface are best for summer because they reflect much of the light back outside.
• Capillary action: the ability of water to move through almost any material from high-moisture to dry areas.
• Replace garage doors with thermally insulated doors to reduce the heat loss through that part of the building shell. The garage is not heated or cooled; however, an insulated garage tempers the temperature of the wall abutting the house.

 Where does the heat go?

• 25% Roof
• 35% Uninsulated walls
• 20% Windows
• 15% Infiltration
• Virtually all wood-frame buildings have a thermal bridge at the floor-wall junction around the perimeter. The R-value of wood is half that of fiberglass batt insulation, so a lot of heat flows through that junction.
• Any conducting element that passes through a wall/floor/ceiling assembly is a thermal bridge: mechanical fasteners, structural elements, the geometry between a wall and floor or ceiling, and other edge-architectural elements.

All of which have a lesser R-value than the overall building envelope.

• An entry “airlock” foyer reduces energy lost through the doorway.
• Air is a good insulator if it’s static (i.e., there are no convection currents to allow heat to move up or down), in a narrow space, and if the air space isn’t perpendicular to the thermal envelope.
• Install a door sweep (weather stop) in the garage door.
• Thermal bypass refers to a thermal bridge in an otherwise insulating building element. For example, an empty wall cavity in which air movement occurs, transferring heat up and down by convection, thereby dramatically lowering the overall R-value of the wall assembly.
• Blow through happens when air passes through an otherwise insulated part of the thermal envelope. This is a thermal bridge of the worst kind, following a path with zero R-value.
• Foundation slabs should be insulated, properly drained, and sealed against water intrusion.
• Replace window screens with storm windows.
• Build a solar room or “conservatory” on the south side of a house for some extra heat in the winter.
• Be sure walls and floors over or next to an unheated space (garage, attic, basement) are well insulated.
• Be careful with foam-type insulation because it can cause walls to expand outward and pop sheetrock nails, forming a bump in the wallboard.

 16.1 WALLS

An integral part of “wall assemblies” is the vapor barrier, which also stops air infiltration, both for moisture and temperature.

Install batt insulation with a reflective aluminum facing (a radiant barrier) with a one-inch gap between the facing and the gypboard. That gap increases the amount of thermal energy reflected back into the house.

The thermal conductivity, k, of steel studs is 310 versus 2 for wood. Use wood for framing all exterior walls!

Drywall can be an air barrier when sealed with caulk, glue, and/or gaskets.

Fiberglass batts for wall insulation do little to slow the convective motion of air, reducing the R-value of the wall assembly.

Cellulose or fiberglass can be blown into uninsulated walls by an insulation contractor via two sets of holes drilled from the outside (one high and one low). Closed-cell foam insulation needs only a small hole, but it’s much more expensive (but twice the R-value).

Passive solar retrofits increase window areas (mostly on the south exposure, for winter sunlight) and also increase the thermal mass of the walls op

 16.2 WINDOWS

New windows are rated on the label for air leakage: cubic feet of air per minute per foot of crack. Values range from 0.1 to 0.3. The lower the leakage, the better.

Close outdoor shutters at night and in foul weather.

 The most solar heat enters through these windows:

• East & west exposure
• South with no roof overhang
• Large windows
• Skylights and sloping glass

Don’t have thermal curtains for those cold winter nights? Heavy blankets will do the trick.

Replace window screens with storm windows.

Insulated shades on a sidetrack-guide (which seals the sides) add R-4 to the window assembly.

Put super-insulating windows in the busiest rooms of the house. Regular double-pane windows are fine for everywhere else, e.g., upstairs bedrooms where you keep the blinds or curtains closed most of the time anyway.

Every window has a Solar Heat Gain Coefficient (SHGC) that rates how much solar energy transmits through a window assembly. (The SHGC is never 1.0 because the rating includes the frame.) Very hot climates want a low SHGC, while cold climates seek to max out the solar heat gain (aim for at least 0.8 or 80 percent).

Triple-glazed south-facing windows get the most out of the southern exposure and keep that heat in when the sun goes down.

 Considerations for replacing a window:

• Annual rainfall
• Orientation versus wind, rain, and sun
• Distance of the top of the window from an overhang

 The more exposed the window is to the weather, the more critical waterproofing (and replacement, as the case may be).

A storm window over a new double-pane window can cause serious overheating problems in the summer and cause the window seals to fail.

Condensation on the inside of windows can be a problem in cold climates, causing rot and other issues. If you get new windows, select ones with a high condensation resistance factor. (Hint: the better the R-value, the less condensation you get.)

 16.3 FLOORS AND BASEMENTS

Don’t insulate floors over heated basements.

Insulate the floor over an unheated space (garage or basement) with R-20 or greater. Be sure to stuff fiberglass into the rim joist, the opening at the end of the joists that support the floor.

Install a 6-mil polyethylene (thick plastic) vapor barrier over the unfinished or dirt floor to stop moisture infiltration.

Install a vapor barrier for basement walls on the side of the wall facing the living space.

Foam boards, which don’t absorb water, are suitable for insulating basement walls.

 16.4 MOVEABLE INSULATION: AN OLD IDEA WITH A NEW PRIORITY.

Passive solar homes have a considerable glass exposure on the south side—sometimes a full wall of glass—to allow direct sunlight into the house. That thermal energy accumulates in a massive wall (stone, concrete, filled with sand, or even stacked water containers). When the sun goes down, the system extracts the stored heat for space heating.

What about all that exposed glass, with an insulation value of R-2? Won’t all that valuable heat be lost to the cold night air?

The solution is moveable insulation. For example, fixed wood panels with integral insulation to cover the exposed glass when there’s no sunlight. The panels can be inside (on a track like pocket doors) or outside (hinged, tilt up and down as needed).

In the ideal situation, a thermal storage Trombe Wall, the massive wall is only a few inches from the glass. Close proximity maximizes exposure to direct sunlight. That air gap is a perfect location for moveable insulation panels, which retract into the adjacent walls during the day (on floor, ceiling tracks, or both).

16.5 THERMAL CURTAINS AND “FOLDING BLANKETS.”

Windows are great for daylighting. They also let passive thermal energy into the house. Still, they have such a low R-value that “moveable insulation” is a great way to increase their insulating value at night and otherwise. Here are a few applications:

• An insulated, hinged outside hurricane shutter to close over the window to increase the insulating value from R-2 to R-20.
• Exterior, insulated roller shutters to lower over large expanses of glass like a sliding glass door or a wall of “lake view” windows.
• Afraid your solar water-heating panels will freeze? Install a spring roller to cover the panels with a heavy fabric on frosty nights. This simple assembly brings the panels into the thermal envelope (the roof), just like plants near the house don’t get as cold on those sub-freezing nights.
• An insulated roll-down shade inside a sunroom or greenhouse covers large glass walls to trap heat inside at night.
• Line your heavy curtains with bubble wrap (like they use to insulate pool covers) to increase the R-value.
• Attach individual “pop-up” assemblies over windows with Velcro strips or magnetic tabs.
• Insulated bi-fold shutters over large skylights or roller blinds inside the skylight, a custom, foam-insulated box cover outside, hinged to close over the skylight expanse.
• Insulated Roman shades.
• Heavy, insulating curtains with an aluminum-foil inside surface to reflect hot sunlight back outside before it heats up the house. (No more aluminum foil taped over the windows.)
• A sliding shutter over clerestory windows.
• Insulated garage-type doors over patios, screen porches, and “lake view” window walls.
• Rolled-up insulation “blankets” to cover sloped glass walls of a greenhouse or sunroom.
• A hinged shutter that insulates a glass greenhouse wall at night then opens up during the day. It has a reflective inner surface that deflects more sunlight through the glass, like a solar collector.

Future Tech! 

16.6

Building inspectors should have thermal-bridge architectural and structural flaws corrected in the construction stage.

16.7

A transparent gel in the gap of double-pane windows can double the insulation value (and not double the cost, like other solutions) and not affect the visual field.

 16.8

Closed-cell foam insulation has twice the R-value per inch as fiberglass batts. It’s more expensive. However, widespread use could bring the cost way down. Closedcell foam provides greater protection against water and moisture flow through the wall assembly.