Weathervanes are traditionally mounted on the highest point of a roof, although there are a few different ways to install a weathervane. You can attach a weathervane’s spire to the ridgepole, which is the vertical member between a roof’s two end rafters.
You can attach it to the top of a cupola, if your house has one, on a support from the inside. You can attach it to the wall with a mounting bracket or the top of the roof with a bracket. A weather vane can also be attached to the top of a pole in your garden.
Unless you are used to working at heights, and have adequate safety equipment (extension ladder, non-slip safety shoes, safety harness), then either hire a professional to install the weathervane or use the garden pole mounting method. For this, steel mounting poles are available wherever weathervanes are sold.
A hole is dug a couple of feet deep and 12 inches in diameter, similar to digging a fence post hole. The hole is then filled with wet concrete mix and the mounting pole is placed in the concrete; you may need to support with pole with guide wires or strings tied to stakes until the concrete hardens completely, which is around 3 days typically. Check that the pole is at a 90 degree angle to the ground with a carpenter’s level.
Follow the manufacturer’s instructions for mounting the actual weathervane; you may have to assemble some hardware, and will need a compass to orient the directional indicator to North. After all, what is the purpose of a weathervane? It is to know which way the wind is blowing.
Of course, to get the best reading, the wind vane needs to be well above the ground and away from buildings, trees, and other objects that might cause deviations from the wind’s true direction.
Rooftop installation should be in the ridgepole rather than on a mounting bracket attaching to the roof, which requires drilling holes through the roof covering, which can cause leaks. The minimum size ridgepole you can reasonably install a weathervane in is 1 ½ x10 inch. If it’s on the thin side, you can reinforce it by adding sister boards either side of the ridgepole in the attic in the area the vane’s spire will be.
Using an electric drill with a long shanked bit the same diameter as the mounting rod, drill a hole down into the center of the ridgepole to a depth an inch or so from it’s bottom surface; you don’t want to drill a through hole.
Place the spire or mounting rod of the weathervane into hole so it reaches the bottom. Use a carpenter’s level to check for vertical orientation of the rod; you may have to enlarge the top of the hole and shimming to get the pole straight up and down, but it is important to do so or else the vane will not spin properly in the wind. Do not force the spire or rod. When you have ensured the mounting rod is positioned properly, seal the hole with a good quality exterior silicone caulk around the rod.
You can then assemble the remaining parts of the weathervane onto it’s mount, following the manufacturer’s directions. Use a compass to point the directional letter N to true north. You may also want to coat the bearing surfaces with grease where they rotate.
If you live in an area that has lots of electrical storms, consider installing lightning protection to your weathervane. If you have a lightning rod or some form of grounding equipment already, you may be able to just connect it up to that, depending on how it is designed; consult a lightning protection specialist.