Keep a Storm Door From Rusting During Winter
Tom Silva gives advice on how to keep storm doors from rusting in the winter
I replaced an entryway storm door that rusted because ice had formed frequently on the inside of the glass panel. The following winter, ice formed on the inside of the new door, and this time it was ½ inch thick. What can I do to stop this from happening? —Anthony Vallone, HowelL, N.J.
You need two things to make ice: cold temperatures and a source of moisture. Moisture vapor leaking into the space between the door and the storm door might cause some icing, so make sure the main door is weatherstripped around its entire perimeter. If the weatherstripping is in good shape, it might be that the storm door is -actually too tight and not allowing trapped moisture to get out. The solution in that case is to drill four 3⁄16-inch-diameter holes through the door's rails—two about ½ inch from the top of the door and two about ½ inch from the bottom. This will allow air to circulate and moisture to escape without reducing the effectiveness of the storm door.
But ice as thick as what you describe makes me think that water is somehow leaking in from above and freezing on the glass. To stop such a leak, first check the door for missing weatherstripping, particularly at the top. Also, make sure that metal flashing is over the top of the door casing and that caulk covers the joint between the side casings and the siding. There shouldn't be any caulk along the top of the flashing. Speaking of caulk, check to see if there's any caulk between the storm-door frame and the door casing. If there isn't, remove the frame and run a bead of butyl caulk behind it before putting the door back. I prefer butyl in this situation because it stays soft and pliable against metal.
Finally, inspect the siding and windows above the door to make sure they're weathertight. If water is getting in through an open joint around a window or a crack in the siding, it's sneaky enough to work down to the door and leak in just where you wouldn't expect it to.
— This Old House general contractor Tom Silva