Step 1
Measure the space around your log cabin's windows from the outside. Note the height and width of the window jamb, which will serve as the inner dimensions for your exterior frame.
Step 2
Select lumber to use for your window frame. Pick material that either complements or contrasts the design of your cabin. You might prefer rough, hand-peeled logs with one hewn, or flat, side, or more finished wood with an attractive grain pattern.
Step 3
Lay each piece of lumber across a pair of sawhorses. Measure the size of one side of the exterior window frame and cut it to length with a hand saw. Repeat the process for all four pieces of lumber.
Step 4
Put on a pair of heavy work gloves. Press foam insulation, by hand, into the gaps and indentations between the logs that form your log cabin's walls near the window.
Step 5
Locate the piece of cut lumber that will form the bottom edge of your exterior window frame. Hold it against the window jamb. Lay a carpenter's level on top of the wood to ensure that it's level.
Step 6
Hammer 3-inch galvanized nails into the bottom piece of the frame at a downward angle. Drive them through the window frame and into the logs that form the wall below them. Space the nails about 4 inches apart from one another.
Step 7
Nail the sides of the window frame into place, angling the nails outward so they go into the log walls rather than the window jamb. Nail the top of the frame into place last, nailing at an upward angle.
Step 8
Press foam insulation into any gaps created by the corners of your window frame, especially where the lumber doesn't create a flush seam against the other parts of the frame.
Step 9
Apply chinking compound with a putty knife around the seam where the inside edge of your frame meets the cabin's window jamb. Spread the compound evenly around that seam and over any visible gaps where you inserted insulation.