From Farmhouse to Modern Passive Solar, Part 2
This is part 2 of a 2 part series. In this article, we see the current features of the passive solar house.
Part 1 shows a photo progression that took place in the transition from a small farmhouse to a modern passive solar home.
The passive solar house has a window wall that faces south. It has been constructed so that the sun can shine directly onto the materials with thermal mass during the winter. The window wall also has an overhang that creates shade that keeps the thermal mass cool in the summer by blocking the summer sun. Because of its design, it simply, passively sits where it is built, so that the house is warm in the winter and cool in the summer without any extra electricity. The clerestory windows located at the top of the house naturally allow hot air to leave the building, while cooler air is drawn in from the lower windows.
The overhang that provides the summer shade extends two feet from the house. During the winter solstice, the sun shines into the sun room and 5 feet up the brick wall. On the summer solstice, however, very little direct sunlight enters the building.
This picture was taken during the springtime in May. One can see by looking at the floor tiles that sunlight only enters a depth of about two feet into the house.
The shade from the overhang (seen in the picture above) keeps the higher summer sun from entering and heating up the house.
On the summer solstice, only about an inch of direct sunlight enters the southern facing room. This, along with built-in convective air channels, sometimes referred to as an ‘envelope’ feature, help to keep the dwelling cool in the summer.
The Thermal Mass
This photo taken from another angle, shows the thermal mass that was added during the remodel of the house. The house has thermal mass in the tiles on the floor (with a concrete slab underneath) and a two story brick wall, both added for their inherent heating and cooling attributes.
The house is two stories in height and open, with a series of decks and staircases leading to different sections of the house.
No air conditioning has been installed. When asked about the temperature range in the house, they said that the hottest temperature that the house reaches is around 80 degrees near the end of a hot summer day.
(Whereas I’m currently in my hot stone house, getting pounded by the sun, trying to write this post in a temperature hovering around 92 degrees. A lesson: If thermal mass is shaded, it will stay cool. In my case, with the sandstone blocks on outside of house, it is the opposite of what is desired in a passive solar house and since it is outside, it absorbs and releases (or radiates) the heat energy inside. Since I cut the trees to get ready for the retrofit project, the house really gets hot in the summer and stays hot for hours after the sun goes down. It is better to use thermal mass in smart design so that it can help warm the house when it is wanted.)
In the winter, they relayed the information that the upper story stays around 60 degrees.
Convective Air Channels
They designed and built in a feature called an ‘envelope’ within the house. This technique utilizes convective air movements through the creation of air channels that move temperatures through the house.
When it is warmer in the summer, the windows and doors on the west and east sides of the house on the lower level are opened. This pulls air into the house.
The thermal mass is shaded by the overhang and stays cool, helping to cool the air moving over it.
A spiral staircase installed and located near the back of the house acts as a chimney that pulls the cooler air from the bottom of the house through back of the house.
As the air moves through the house, it picks up heat and rises. Through these natural convective air movements, the warmer air exits through the clerestory windows located at the top of the house.
By opening the venting windows in the cooler evening and early morning, the house naturally remains cool in the summer without a need for mechanical air conditioning (hence the term passive solar design – the building sits there and is cool in the summer and warm in the winter).
The clerestory windows are accessed by a collapsible folding ladder. When not in use, it retracts and tucks into the deck above.
The Open Design
The passive solar house features an open plan.
The second story bedrooms are also open without a ceiling that allow for the air to circulate.
They found that while this allows for greater air circulation, it also impacted areas where it’s usually not expected, in the closets. This made the clothes dusty, so they installed recycled plate glass ceilings over the them.
Always curious about utility costs that could be saved in a retrofit project, I asked about what they pay for utility bills.
They guessed that they were paying about 30 dollars for natural gas in the summer and about 55 dollars in the winter. Natural gas also heats the hot water and the ground floor.
In regard to electricity use, the house’s heat is supplemented by electric baseboard heaters located on the second floor. They estimated that they were in use about 30 nights out of the year. Because the house is located in the countryside, electricity is also utilized for the water pump and a portion of the electricity also goes toward their community’s rural street lights. They estimated that they use about 500 kW of electricity per month, whereas the average house in the area uses approximately 600 – 700 kW.
During the remodel, only one window was added on the north side of the house, located in the bathroom on the second floor. (The other two windows were part of the original house.)
The Thomas’ have really been pleased with the house. Jim Thomas as the owner-builder, drew up the plans. As a teacher, he had the summer to work on the house and hired a crew of the shop teacher, and four others. They proceeded to pour a concrete slab foundation, tear off the previous roof, and build the new structure and roof it in one month.
They expressed that they would have done a couple of things differently. Jim wished that they would have rented a crane to put the beams in place. Instead, they rigged a pulley system and placed all the beams with the teamwork of 5 men. He also wished that they could have used SIPS (Structural Insulated Panel Systems). He said that back then, that kind of technology was just beginning to be utilized. Because of this, the county, being unfamiliar with SIPS, did not approve of their use.
Over the course of two years, Jim finished the dry wall and electrical work.
They have a perennial garden in front of the house that it is established and watered about three times a year. See the progression of how it changed from a farmhouse to its current state.
The Thomas’ house
Designer / Builders – James and Nancy Thomas
Time – Main conversion – One month, Inside finished in 2 years
Square Feet – 2430
“Natural gas also heats the hot water and the ground floor.”
So, tell me why you would heat hot water. And, why not make hot water by heating it in the sun?
Every build is a little different because the land that a home is built on is different and with this case, they were converting a previously built structure into a passive solar one.
I can’t speak for them, but they were able to convert the house and get it enclosed in one summer – that’s a huge undertaking for an owner-builder! Projects that are done in manageable steps are the ones that get completed, and the ones that are written about here. I do know that they recently installed active solar panels, so perhaps it’s in the works.
Just learning about passive solar energy. Hoping to build home on property in next few years. It will mostly be a rectangular home with a few walls jetting further out. Plan to have back side of home with lots of windows. It will not be directly Southern exposure…more south-eastern exposure to take advantage of property views. Dealing with high wind coming from West (west central Ohio) so no windows on west and only front door on North side of house. I have read a few of your articles and see 2′ mentioned as the overhang for southern exposure windows to protect from overheating in summertime. Is there an amount of an overhang that is too much – that nolonger benefits us in wintertime or the sunlight in summertime? I had hoped for a larger overhang to have part of the patio covered for our bbq and aging/super young guests to avoid the sun.
Thanks for your help. Please email response to me as I may have trouble finding this article again – I have bookmarked so many!