Solar Housing

Many roofs could benefit from a solar thermal application, but as I said before some roofs are more suitable than others. The importance of heat storage and heat insulation have also been discussed so we should be able to move on to a topic that few builders are concerned with, namely solar heat gain. 

Most of us live in standard rectangular houses with ridge or truss roofs. Any deviation from traditional house designs seems to make real estate agents cringe. Change is always difficult, but growth can only take place where there is change. For now I’d like you to put down your hammer, grab a piece of paper and pensile and design a practical energy independent home of your own. Use your personal experience tempered with the things you've learned about solar heating. The examples presented are about houses at latitudes between 35 and 50 degrees. 

Ranch houses with a low pitched roof are still popular. Attic space is sometimes used for central air conditioning, but hot attics with temperatures beyond 160⁰ F are not the best place to lose heat. Low pitched roofs maximize heat gain in summer when extra heat is more of a problem than a blessing.

The south facing surface area of a 50 foot long roof like this is 787 sq. ft. If a solar thermal roof were installed over this roof all the hot water needs of a family of four could easily be met but winter heat gain would be minimal.

What would happen if we optimized the pitch of the roof for solar heat gain during the day with the least amount of sunshine, December 21?

December 21 may not be the coldest day of the year but it is the day with the least available sunlight. To maximize heat gain our roof must be perpendicular or almost perpendicular to the rays of the sun for the best part of the day. A roof designed to maximize heat gain on Long Island for this day would have a pitch around 64 degrees and cast a mean shadow.

What would Santa say about a roof like this?

I bet Rudolf would have a word or two on the subject.

Carpenters would throw down their hammers in disgust and say: “2x6’s don’t come 34 feet long.”

And building inspectors would just say “Forget it fool! The roof’s too high. Take it down.”

It’s a difficult roof to build even if it were allowed. How about changing a light bulb in the second floor ceiling? Is there anything good about a steep roof like this? Sure there is. Think about the 1700 sq. ft. of solar thermal roof heat gain on December 21. In just three hours a roof like this could harvest the fuel oil equivalent of 9.5 gallons of # 2 fuel oil. After December 21, the roof angle would of course no longer be optimized and by the end of January when wind chill factors plummet below 0⁰ F you might be wondering if you chose the best pitch for your roof. A few million BTU’s could make all the difference between energy independence and another year of fossil fuel dependence.

How would it be if we: moderated our tilt angle a bit to meet the height concerns of the building department, let carpenters use the kind of lumber they are accustomed to using and also favor those winter months when heat gain is needed most?

A roof angle of 55⁰ should keep everybody happy, but I still think we could make better use of construction materials as well as double the living space with a little more effort. What do you think?

TRREE STORY HOUSE WITH SOLAR THERMAL ROOF

This three story building has about 3,000 sq ft of living space compared with 1,200 sq. ft. for the others. If you’re planning a second floor addition you might as well go all the way as long as you keep the inspector happy by keeping the height under  30 feet. An extra floor doesn’t necessarily mean more money.

If you can live without an antiquated truss or ridge roof that wastes valuable construction materials you should be able to build a three story house for about the same cost as a two story house.  The south facing roof is ideally suited for winter heat gain and the north facing shed roof is suited for PV panels tilted south. In this way the entire surface area of the north and south facing roofs connect with the sun.

You’re probably wondering what you’re going to do with all that space.
If you have no children to come home and roost you might consider stuffing plenty of sound insulation between the floors and renting the entire house out to four sets of strangers. Oh I forgot to mention the finished basement.  A properly designed basement with adequate ventilation can provide additional living space. Your tenants will love the accommodations and you won’t have to worry about heating bills with a 4,000 gallon heat storage vault under the solar greenhouse. A 10KW array of PV panels on the shed roof  might even eliminate your electric bill and if you need more power there’s always the possibility of a  solar thermal engine that runs on heat from the heat storage vault. More about that later…

Now it's time for you to design your own energy independent house and create a JPG of your house design and upload it to the Bulletin Board forum Solar House. Use the image function of the bulletin board to upload images.