Sealing a shed door involves placing weather stripping around the door casing so that the door seals weather, dust and insects out when it closes. This stripping can be purchased at a home improvement store and is applied to the casing by removing a paper strip from the adhesive side of the stripping. Stripping can be placed along the top, bottom and two sides of the door casing. Sealing the door also keeps the shed warmer in the wintertime and cooler in the summertime.
Push on the door while it's closed to see how big the gap between the edge of the door's face and the door jam is. Measure this gap with a tape measure. Write this measurement down and use it at the home improvement store to determine which thickness of weather stripping you need to buy.
Open the shed door as wide as it can be opened.
Measure the inner-dimensions of the door jamb. The jamb is the area where the outer edges of the door face come into contact with the door frame when closed. Measure the top, bottom and sides. If the frame is square the top and bottom should be the same length and the two sides should be the same length. Use a tape measure to do this. Write these measurements down.
Unroll the weather stripping and place the end of it on the inner edge of the door casing and close the door. Look to see if the width is of the stripping is thick enough to provide a nice seal between the door and the jambIf it's too loose take it back to the store and get a thicker one.
Unroll the weather stripping and cut it using the utility knife to the four length measurements
Peel the backing off the top piece and apply the sticky side of the stripping to the inner edge of the top of the door casing. Close the door after this piece has been applied to check the seals tightness. If you have to slam the door to shut it then the stripping is too thick and you'll need to remove it and buy a thinner roll of weather stripping.
Open the door and place one of the side pieces of stripping. Close the door to test the seal. Apply the second side and then the bottom. Close the door each time a new piece of stripping is applied to test the seal. Use the utility knife to trim up the corners if the pieces of weather stripping are overlapping each other.