Home Star Engineering

Making the Critical Measurements

What we need to compute your optimal roof layout are the following pieces of information:

Your Latitude

• One tool you can use to determine your latitude and also (most likely) the orientation of your roofline, is Google Earth, which is a free downloadable program. Assuming your house has existed for a few years, you can locate it by address and zoom in to see details of your house and yard. There is more than one way to find your latitude and longitude in Google Earth. I will describe one way.
  • Start by making sure the needed tools are available. From the Menu bar at the top, go to View, and make sure that Toolbar, Sidebar, and Status Bar are checked. Also under View go to Show Navigation and in the sub menu select Always. The other settings are optional, for our purposes. On the side bar under Layers it might be helpful to select Roads, Borders and Labels, and Terrain. There are many other options you can experiment with at your leisure.
  • In the top left corner of the window, on the Sidebar, there should be a search box. Type in your address and hit Enter. The view should move to your location and zoom in. This should take you to your house, but sometimes addresses are estimated, especially on country roads. Locate your house from landmarks. Use the "Hand" cursor to move the map around. If you have a wheel on your mouse you can use it to zoom in and out. Otherwise, you can zoom using the navigation tools in the top right of the window. In the unlikely event that Google Earth can't locate your address, you would have to zoom in and find your house by landmarks alone.
  • A good way to locate your latitude and longitude is to put a placemark on your house. You can do this from the toolbar, or under the Add menu select Placemark. Placemarks look like pushpins. When you first set a placemark you can move it around. Along with the placemark will be a popup window that gives the precise latitude and longitude of the tip of the pin. Mark your house with a placemark, then write the numbers down.
  • Once you have identified your house with a Placemark, go to the File menu and select Save and in the sub-menu select Save Place. It will save as a .kmz file. You can also email the placemark .kmz file (File, Email, Email Placemark) which allows others, us for instance, to locate the exact spot you have marked. It is a good idea to email us the Placemark file as a backup to your measurements.
• To find your latitude and longitude from a website that does not require downloading anything, try Geocoder. Geocoder will give you latitude and longitude in several alternative formats based on your street address. Other mapping websites may or may not give latitude and longitude.
• You can also use a GPS. If you have a GPS navigation system in your car, park the car in the driveway, out from under any car ports or other shelter, and give the GPS several minutes to establish a good reading. Consult your manual to find out how to read the latitude and longitude of your current position.

Orientation of the Roofline

• The official name of the angle we are looking for is the "azimuth" of your roofline. This is the angle, looking down on your house from above, measuring clockwise from true north to your roofline. If you measure counterclockwise from true north, the angle is negative. To make sure there is no confusion you might want to add a note with a verbal description of your measurement, such as "runs from NE to SW." This is another reason it is good for you to send us your Google Earth placemark as a backup.
• If Google Earth shows your house, you can determine the azimuth of your roofline using tools in Google Earth.
  • First make sure the map is oriented due north. In the top right corner of the window you will see the Navigation Tools, which include a circle with an N surrounding a disk with arrows and what looks like an eye. The "eye" is actually supposed to be a joy stick that controls the tilt of the view. If the view of the terrain appears to be at an oblique angle, click and drag the joystick down and hold it until the view levels out. You want to be looking straight down on your house.
  • Now drag the N around the circle and watch as the map orientation changes. If the map was set to anything other than North Up, letting go of the N will cause it to automatically set itself upright. Moving it again will rotate the map. Moving it again will cause it to snap back to North Up. Every other movement of the N will result in North Up. Move it several times to get used to its behavior.
  • Zoom in on your house. Under the Tools menu select Ruler. The Ruler is accompanied by a popup box that has two tabs: Line, and Path. Select Line. Notice the labels Length and Heading. Set the unit of length to feet. The cursor turns to a box with a cross in it. Place the cursor over the more southerly end of the roofline, then click and release the mouse. Now move the mouse to the other end of the roofline. Click again. The ruler box will tell you the distance and the "heading" which is equivalent to the azimuth we are looking for.
  • While you're at it, use the ruler to measure the length and width of your house. These don't figure directly into our analysis, but they allow us to construct a more realistic image of your house with the optimal plane for the solar panels.
• If you don't have access to Google Earth, use a city map and a protractor to determine the orientation of the street in front of your house. Often your roofline will be parallel or perpendicular to the street.
• Another method is to sight along a magnetic compass. Be careful not to have any iron object (such as a belt buckle) near the compass. Once you have a reading, you will have to make an adjustment from Magnetic North to True North. This is called magnetic declination, which can be found on topographic maps or at this website.

Pitch of the Roof

• To measure the pitch of your roof directly, use a carpenter's level and a tape measure. First measure the length of the carpinter's level. We call this the "run." Now, standing on a ladder at the edge of the roof, set the level and use a ruler or tape measure to measure the "rise."
• Another place to measure the pitch is under the eaves. Again, use a level and a ruler or tape measure to measure the rise and the run.
• A third way to make the measurement is stand a large distance from the house in line with the roofline and take a digital picture. It is important to aim the camera horizontally, as though you were taking a picture of a person your own height standing by the house, except using a wide enough field of view to show the roof or the eves. What you want is for the image plane at the back of the camera to be vertical and parallel with the wall you are facing. Display the picture in imaging software to measure the pixels over and up.

... or send us a kmz file with a Placemark on your house and a digital picture taken as described above, and we will do the measurements for you. (We charge an extra fee for doing this extra work, but if you are not comfortable making the measurements yourself you might find that preferable.)