This shows a mount using the smallest conduit with a strap on the bottom and one screw in the top. The strap is lined up so it screws into the bird house floor. Use a fairly large screw in the top. Screw it in and make a note of how far it sticks in the inside, back it out and cut to length. It is difficult to bore the hole in the conduit, but placing it between two pieces of 3/4 boards makes it a little easier.
Using conduit makes it difficult for predators to climb. Cut to 7 ft, drive in ground and then mount the house.
Note that the roof should be flush with the back in order to mount on post, building or tree.
Bottoms of the houses should have holes or the corners cut to allow for drainage and air circulation. Examples of both in this photo.. It doesn't hurt to have a crack up one side like the top one.
Side view of the above houses. One opens on the front and the other on the side.
Couple assembly notes.
When you bore the entry hole stack the front on the back with the tops lined up. Bore enough for the pilot to make a mark in the rear. Complete the entry hole with a piece of scrap under it. Bore a smaller hole in the back at the mark made by the pilot bit. This way the upper mounting screw can be tightened with a long screwdriver through the entry hole. The above is for mounting on a tree, wood post or a building. I do all mine this way and can mount with the conduit or on a post etc
Make sure you line up hinge holes on the hinge sides.. Stack them and bore through both at the same time. The door should be just a little narrower than the opposing side.
For circulation you need to bore 3 holes in the front and back. Note the one on the right has only two, but you can see the additional vent at the top. You could make that vent about 3/8 and not have to bore the holes.
I made these 6 last week and screwed up on the bottom left. It overlaps on the back and i had to do a fix. It just cannot be mounted on a building or a post that reaches above the roof.... Will work fine on conduit or a 2x2. Looks pretty good the way I fixed the front.
Chimneys are just pieces of oak and once the houses age will look kinda neat...
Note: That I bored holes in the rear partition to match the mounting screw holes. Just in case longer screws are needed.
Since bats need the rough surface to cling to. Options are to rough the surface with a utility knife, cut saw kerfs or use rough cut material for the interior surfaces. I used the saw Kerf method and mounted two saw blades on my radial arm saw with a spacer about 3/8" thick. The partitions were ran through the stacked blades, reversed, ran through again, flipped and the process repeated. Next, I moved the saw head out 1" and repeated. This resulted in both sides being grooved/kerfed. The front and back panels were ran through. One side only. This photo shows the kerfs/grooves and the ventilation holes in the partition. 
For the exterior landing area supports, I took a piece of 1 x 12 pine and cut the grooves on one side. This board had a lot of heart pine in it and should last for years. After kerfing, I ripped to 3.5" width. This photo was taken with them on top of the partitions. Click the photo for detail.
I made these 6 last week and screwed up on the bottom left. It overlaps on the back and i had to do a fix. It just cannot be mounted on a building or a post that reaches above the roof.... Will work fine on conduit or a 2x2. Looks pretty good the way I fixed the front.
