Doors and Windows - Sealing up a home made door?

I just purchased a house once I resolve some other major issues. I need to take care of this one. I have a detached garage. I am using it to store my project car. It is an older garage and it needs some work. The door is home made using solid wood boards. It seems pretty strong and I don't have plans or money to replace it now, but I would like to seal up the gaps in between the boards and paint it, so that the garage is a little more sealed. I'm not sure what to use to seal up cracks. Is wood putty ok for outdoors, and colder NJ winters? after its puttied. After I fill the gaps I just want to paint it white. Any advise is much appreciated.

Can't tell if this is the man door or the main door of the garage, or type board juncture (butted, lapped, etc).

Butted wide & deep gaps: poke in backer rod (expanded foam in the shape of rod) fill last 1/8” with good grade oil base caulk. Prime with oil base, paint with latex. Lessor gaps & cracks – omit backer rod.

Man Door options: using sheet metal form a cap |_| shaped for the boards. Install, legs down, across the top of the door. Using sheet metal form two drip caps L shaped (approx). Install one above the door across the opening. Install the other one on the exterior face of the door near the bottom. All of the former help retard water, ice, and snow penetration.

Garage Door - I won't even guess what it looks like.

If the gaps aren't too large, you could probably use a good quality caulk, then prime and paint it. After it dries, look into sealing the closure with something like foam strips. If the gaps are too large, then either backer rod and caulk or overlay battens to cover the cracks.

this is a side door to walk in, not the main garage door to get a car in. This is my first house and I don't really know that much about doing these kinds of things. I am not familiar with backer rods and sheetmetal form? I am going to see if I can get a picture of the door up today, when i get home from work. It is like 2x4 or 2x6 boards going across and there bracing behind it on the inside part of the garage. I would say the gaps are maybe 1/8 or an inch, some smaller some a little bigger, but you can see light through them. Thanks for the help, I really appreciate it.

You can seal 1/8" gaps with caulking alone [backer rod is a filler to make large gaps caulkable] Depending on how much your door expands/contracts with humidity changes - caulking might fail in some areas. A more permament fix would be to either cover the gaps with lattice strips or the entire door with metal or thin plywood.

I googled lattice strips. I didn't find anything that really explained them that great. Are they jsut thin strips of wood? Should I caulk then put the lattice strips over the gaps? How do you fasten the strips, screws?

A lattice strip is a thin piece of wood, approximately 1.5" wide and .25" thick. I usually make my own by ripping a 2x on a table saw.

It wouldn't hurt to both caulk and nail up strips. Use a 4 penny galvanized nail.

Thanks to everyone who posted , I am going to get on this asap.