A passive solar house utilizes natural heating and cooling through design features that cost about 10-15% more than conventional homes, yet can save their occupants 20% or well up to 60% or 80+% of the cooling and heating energy requirements, depending on how well it is designed and built. The house itself becomes the solar collector and saves utility costs for the lifetime of the home.
I have an ebook you can download free at the bottom of this page for designing a passive solar house.
Design features of a passive solar home typically includes:
1) 7% of net glazing facing solar south (if in the northern hemisphere–faces true north if in southern hemisphere)
2) The envelope is superinsulated
3) House has a proper glass-to-mass ratio, meaning that inside the house is adequate thermal mass to absorb and release heat to maintain a near-constant temperature
4) Roof overhangs are designed based on latitude so they keep sun out in summer and allow it into the windows during winter
It is important to remember that as long as *any* house has windows, it qualifies–at least in theory–as a solar house, because sunlight can enter the home; however, to technically qualify as a passive solar house it needs to follow those basic rules above. Many solar homes are either designed by an architect and built by a building contractor, or they are designed and built by owner builders.
I was playing around with some paper one day and decided to just cut and tape some simple shapes together to represent a model of what a passive solar home might look like, and to compare it to a conventional “standard construction” home. Here is what I came up with.
The above design shows a gable roof for the conventional building, whereas high clerestory windows in the passive solar home allow sunlight to the back half of the building. The image below shows a side view of that same split-shed style roof. This is only one simple design of many for a passive house with solar design.
Thermal mass should be placed on interior walls and floors, but can also be part of built-in furniture like benches/bancos, stone fireplaces, half walls, cabinets or other permanent fixtures, or even a thermal mass rocket stove. Floors should be darker colored if they receive direct gain from the sun. Interior walls are more effective than mass floors, however, for absorbing and releasing heat. Cement slabs become inefficient if too thick (over 6″).
Other thermal mass materials for INTERIOR walls and floors can include brick, adobe block, cement/concrete, cob, rock, tile, slate, cement block, plaster, stucco, or other materials that can absorb and release heat.
This is contrasted with insulating materials, which should be in your EXTERIOR walls only, and should be avoided on the interior, such as: wall insulation, wood products (siding, waferboard/OSB/plywood, wood flooring, 2x4s/2x6s/etc.), gypsum board/drywall, carpeting.
Having thermal mass inside the home is the main difference between standard or conventional housing and passive solar design that makes a huge difference on the utility bills. Allowing sunshine in to heat the thermal mass, or the overhangs to keep sunlight out of the house during summer (keeping thermal mass cool), is what stabilizes the temperatures within the house. Insulating the envelope ensures there is no heat loss or heat gain from or to the outside.
Passive solar design, then, is a system that works with nature and just sits there passively and does its work without any effort on your part outside of it being designed and built correctly. This can save you money for as long as the house exists!
You can download my passive solar home design ebook for free here.