Solar orientation
In Northern United States, the Ideal orientation of a home is to have the side with the most window area exposed in a south-south west direction. This ideal assumes that the area is adequately protected from winds out of the west, either by trees or the lands topography. If the home is not protected from westerly winds, then south facing homes are the ideal. There are three main considerations for passive solar heating, when building a home, they are orientation, solar protection and exterior finish.
Orientating a home with a south-south-west exposure, you can expect solar gains during the winter of up to 550 Btu per square foot of area from your southward facing windows during the peak sunlight hours (about 1:00pm to 3:00pm). However, you still need to protect yourself from this hot sun during the summer months when heat gains of over 1500 Btu per hour are possible.
Designers tend to use one, or both of the following solar protection methods. First, by planting deciduous shade trees within about 20' of the south wall of the home, which will fill in with leaves during the summer and block the sun, while shedding the leaves in the winter permitting sunlight to enter into south facing windows. The second method is to utilize a roof overhang or eave. This overhang, as a rule of thumb, should be about 2.5 times less, in width, than the total height of the window, including the header (beam over the window opening), for which it is overhanging. This will give plenty of shade protection during the summer months when the sun arcs higher in the sky, than in the winter, when the arc of the sun is much closer to the horizon.
The exterior finish will also have an impact on the ability of the building to absorb or retain heat. Although minimal, you should try to stick with a rough surfaced siding or brick, which is of a darker color. This will allow your exterior walls to soak up as much of the suns radiation instead of reflecting it, raising its temperature enough to help slow the rate of heat transfer through the walls. Interior finishes should be smooth and lightly colored, to reflect radiant heat back into the room as much as possible. Avoid flat paints if possible. This is also true for the roof assembly with the use of darker shingles and light colored, smooth interior ceilings.
And if you want to take solar gain to an extreme, you could also consider shaping the profile of the land on the south side of your home, into a cup shaped reflector, so that the reflected solar rays, bouncing of the winter snows surface, concentrate into the southern exposed windows.
Air and Vapor Barriers
We utilize two types of membrane barriers in modern construction, the air barrier and the Vapor barrier.
The air barrier is located on the exterior side of all wall assemblies that are constructed of wood. Attics, as of yet, do not require the use of one. This includes the outer side of strapped basement walls and the underside of floor joists in homes built on piers. It has two main functions. Primarily it acts to prevent the passage of free water from the exterior side of the insulated cavity into the wall or floor assembly, which would cause structural wood, rot, and saturate the insulation. But at the same time, the barrier allows water, in the form of vapor, which would otherwise remain trapped in the wall cavity, to escape to the outside, thereby reducing moisture concentration within the wall components. A secondary purpose of the air barrier is to prevent the passage of air, through wind or differential pressure, which would disperse the heat trapped in the air pockets of batt insulation much more rapidly. The air barrier also helps to add to the thermal resistance of the building, by as much as R-2.
The vapor barrier is installed on the interior side of insulation, and is used to slow the passage of water, in the form of vapor, entering into insulated spaces. This vapor, in turn condenses in the insulation or on structural members, saturating the insulation and rotting wood components. The vapor barrier is applied to the interior side of the building and is almost always installed as a polyethylene sheet (clear plastic sheets), which come in rolls 9' wide and stapled in place. The joints between sheets are treated with acoustical sealant or 2 stud overlaps to ensure a continuous seal. The tighter the vapor barrier is sealed the better, so it's a good idea to pay special attention to all joints, and any penetrations or holes.
One thing you may want to consider is the application of non-porous paints (oil based) to the interior finishes, as these perform much in the same way as vapor barriers, and add to their effectiveness. Caulking and sealing the finishes at the joints, such as floors and ceilings, prior to application of the interior trimwork, also adds to the overall effectiveness of the painted barrier. On a final note, I would not recommend the use of exterior sheathing materials such as plywood's or aspenite. These materials effectively act as a vapor barrier on the outer wall surface, and traps moisture passing through the interior vapor barrier, within the wall cavity, where it condenses and rots structural components.
There are three main materials used as air barriers, they include saturated building papers, extruded foamboard, and a new product made of spun glass paper.
Saturated building papers are basically paper, which is impregnated or saturated with tar, or a similar substance, making it water-resistant. It generally comes in three or four foot wide rolls, which is stapled with a horizontal 6"-12" overlap. Of the three types, this is the cheapest and probably the oldest means of applying exterior air barriers.
Extruded foamboard is an ideal material as it can be applied as both insulation as well as acting as an air barrier. Care must be taken in this approach, for all the joints need to be sealed with vapor tape, which is quite expensive, although easy to apply.
Spun glass fiber sheets are a relatively new building material (often referred to as "sheathing paper"). It is primarily manufactured from glass that is spun, combined with other materials, then pressed to form a paper like continuous sheet. This type of barrier generally comes in a roll 9' wide and is quite easily applied.
Insulation
Insulation works by trapping air in pockets, which slows the rate of heat transfer through the reduction of conducted and convected losses. The use of reflective materials such as foils or smooth, light colored surfaces also slow radiant heat losses. It is important to remember that we can only slow the rate of loss, not eliminate it all together. Industry commonly measures the ability of materials to slow heat loss by referring to the "R-value" or resistance value of materials. There are practical limits to insulating, and a good design takes into account the payback time that balances the cost of construction with total energy savings. A good guideline to follow is to compare the overall cost of adding the insulation, which would include the higher cost of wider structural components (for example 2x8 wall construction instead of 2x6) against the length of time you expect to be living in the home. As well you should consider the projected rise in cost of the fuel used by your heating sources.
There are three main types of insulation available on the market today. They are spun glass fibers, rock wool, polystyrene and ureaformaldehyde.
Spun glass fibers are most commonly produced in either batt or crushed fiber type for installing in homes. Batt insulation is glass that is spun into threads and woven into a thick mat of fibers of varying thickness with an approximate R-value of 3.2 per inch of thickness. Crushed fiber insulation is basically the same as batt insulation, but it is crushed at the plant and separated for insulating in horizontal locations such as ceiling or floor assemblies. It can be placed either by blowing the crushed fibers through piping using mechanical equipment, or pouring it out of bags, then spreading with a pitchfork or similar tool. Blown glass fiber insulation provides an average R-value of about 2.6, while pouring and spreading is a slightly higher thermal resistance of R-3.1.
Rock wool is similar to glass fibrous insulation, except it is manufactured from rock, instead of glass. It comes in both batt-type and crushed fibers, with batt insulation offering higher R-values than glass of 3.6, blown values of R-2.9 and poured placement totaling R-3.2.
Expanded polystyrene is one of the best insulation's available, but also one of the more expensive. It comes in three main types; Extruded polystyrene, expanded polystyrene and polyurethane or ureaformaldehyde foam. These types of insulation are ideal for areas where they will be exposed to wet conditions such as basement foundations, for they maintain insulative values even when immersed in water. As well, expanded polystyrene can be used effectively for an exterior air barrier, required by codes in Canada, so long as the joints are sealed with appropriate vapor tape.
Extruded polystyrene (often referred to as "foamboard" or by the tradename "Styrofoam") is generally blue or pink in color. It is manufactured by pushing freshly expanded foam through a mold, in effect extruding it through a template, or by injecting the polystyrene into individual molds. Generally the edges are designed to interlock to ensure a continuous thermal break, and help to seal the joints between the panels. They are manufactured mostly in 2'x8' sheets and offer very high Resistance values of about R-4.7 per inch of thickness.
Expanded polystyrene (sometimes referred to as "beadboard" or "cut cell polystyrene), is cheaper than extruded foamboard and is generally white in color. It is manufactured from billets or chunks of expanded foam, which is then cut into slabs of varying thickness, most often without the interlocking joints like the extruded polystyrene. This type of expanded foamboard is most often manufactured in 4'x8' sheets of varying thickness'. Unfortunately, beadboard lacks the high resistance values of extruded polystyrene, with an average R-value of only 3.6.
The most expensive of the foam insulation's is the ureaformaldehyde or polyurethane foams which are placed by injecting or spraying chemically expanding foam into cavities or over surfaces. This type of foam has seen a lot of controversy over both its off gassing of chemicals into the buildings, ands its lack of consistency in placement. It does, however offer the highest R-value available for foamed insulation, which is only slightly higher than extruded polystyrene with a resistance of R-4.8.
