Insulation and designing to reduce heat loss
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In effective residential design we utilize several factors in Northern United States, to reduce the overall loss of heat. The major considerations include: Solar Orientation, Air and Vapor barriers, ...
In effective residential design we utilize several factors in Northern United States, to reduce the overall loss of heat. The major considerations include: Solar Orientation, Air and Vapor barriers, and Insulation.
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.
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