The Shell:

Efficient heating and cooling starts with a shell (walls, floor, and ceiling) that will prevent the movement of heat out of the building in winter, and into it in summer.   That shell must also be equipped to protect itself from the inroads of unwanted moisture.

Here, we paint with a relatively broad brushbrush, describing cost-effective "systems" for walls, ceilings, basements, doors, and windows.  

Exterior walls above grade:

In the United States, most houses built in the last 30-35 years have 4-inch walls filled with fiberglass insulation.  There is also a vapor barrier in place that helps to keep moisture out of the walls.  That 4" cross-section supports your heating/cooling system much better than the walls of yesteryear.   It keeps occupants more comfortable, and saves fuel. 

However, the 4-inch wall is not good enough for tomorrow.   There are a number of "tomorrow" wall designs on the market, and many of them will prevent heat transfer  better than the 4-inch.

Of these newer wall designs, the simplest and most cost-effective is the 6-inch wall, framed with 2 x 6 studs, rather than the conventional 2 x 4s.   It is as simple as the 4-inch, stronger, with 60% better resistance to heat transfer, and it costs little more than the 4-inch. 

If your builder insists that 6-inch walls cost more than 4-inch, simply point out that most modular houses, under tighter cost controls than site-built, are built with 6-inch walls. 

In the 6” wall, the studs have increased from today's 3.5 inches to tomorrow's 5.5 inches, reducing wall heat loss or gain by about 40%.  Also, in tomorrow’s wall, the larger studs are 24 inches on center, instead of the 16" spacing used with 4" studs.  As a result, a higher percent of the wall is filled with fiberglass, which is a much better insulator than wood, so the wider spacing improves the wall's resistance to heat transfer by another 8 or 9 percent.

There are two plastic skins that are very important in the construction of today's wood-frame buildings.  A 4-mil film of polyethylene is fastened to the inside of the outer-wall studs before the sheetrock or other decorative paneling is mounted.  This membrane greatly reduces the movement of warm, moist air into the colder outer wall.  Not only does that cut down on condensation against the back of the outer sheathing, but it saves most of the heat energy that went into evaporating the moisture in the first place. 

The electrical boxes installed in inner walls are openings in that barrier.   They allow warm moist air to penetrate the wall, where it condenses, wasting heat and causing paint to peel.   As soon as the electrician signs off, install leak-stoppers behind the cover plates. These are 3 x 5 foam pads that can be bought at any hardware or lumber-supply store.

On the outside of the frame, a 4-mil film of Tyvec (or its generic equivalent) is stapled to the plywood before the final covering is applied.  This membrane does an excellent job of reducing the penetration of cold air. If new clapboards or shingles are being installed over the old covering, Tyvec or its equivalent can, and should, be applied first.

Ceilings and Roof:

The top ceiling is, of course, part of the shell.  Though protected from the weather by the roof, that uppermost ceiling is the element that stops the heat loss or, in summer, the heat gain.  In a ranch or Cape with less than 9 inches of ceiling insulation, and with double-glazed windows, about 30% of the heat loss is through the ceiling. 

In the simplest case, a 24-foot wide ranch will have 6" ceiling joists, and the builder will install six-inch batts of fiberglass.   That is not enough, when the heating expense over thirty years is considered.

Considering that many ranches are converted to two-storey after a few years, it might be wise, when building a new 24-foot ranch, to install 8” ceiling joists at the outset. (10” if span is over 12 feet).   That makes 9" insulation practicable, and the added cost of the stronger joists would be recovered by energy savings in a couple of years. 

If the builder does use 6" joists, a layer of 3-inch fiberglass, without any backing, should be laid crosswise on top of the six inches that are installed between the joists.   

Avoid penetrations in the uppermost ceiling. They cause energy waste because they allow moist heated air to escape and, because, when that escaping warm, moist air hits a cold surface in the attic, the moisture condenses and damages property.

Exhaust fans for kitchens and toilets should be ducted horizontally to caps in the outer wall, instead of into or through the attic.  Ceiling insulation should be on top of the duct. To appreciate the cost of losing "moist heated air”, check out Condensation.  Avoid, also, installing recessed light fixtures in the uppermost ceiling.

In the warmer months, heat builds up in the attic. That heat radiates into living space. It is uncomfortable, and adds to air-conditioning load. Your building code may already require attic venting. In any event, install vents in the soffit. Put shields over the ends of the attic insulation to assure good airflow, and specify a vent the entire length of the roof peak, covered by a rain cap.

In addition to venting (or “instead of” for an existing building), install a “whole-house” fan in the roof or gable end.  This fan should be able to exhaust the whole house in an hour or less. In the evening, when the sun is no longer beating on the roof, open the door or trap-door into the attic, turn off the AC, open a couple of doors or windows on the lowest floor, and see if that fan will pull enough cool air through the house to make it comfortable without AC in a little while. See Air Conditioning for more detail.

Slab Floors:

In some areas, soil conditions require a slab floor, which can creep or sag over time. A soil report and recommendation from a certified soil engineer could save you expensive reconstruction in the future.

The Basement:

Where a full basement is called for, many building codes require that the main floor, over the basement, be fully insulated.   This is to reduce heat loss from the primary living area.   The code that calls for insulation of this floor may offer the option of insulating the inside of the concrete walls. 

There are several reasons for not insulating the main floor, thereby isolating the basement.  The heater and the distribution system are apt to be in the basement, and the heat that leaks from them will be lost through the upper two or three feet of the basement wall.   The basement provides a great deal of space, useful for laundry, workshop, or home office.  If that space is isolated from the warm living area, it will be too cold to be useful. 

The money spent on that floor insulation usually would be better spent on insulating the outer walls of the basement itself. Adding one inch of extruded polystyrene or polyisocyanurate to a 10-inch concrete wall satisfies most code requirements.  With the insulation on the basement wall, instead of overhead, the basement space will be warmer, and much more useful.