The Ins and Outs of Caulking: How Tos for the Homeowner

Are your windows and doors caulked? With winter approaching, the homeowner may be thinking about this task. The Ins and Outs of Caulking by the late Charles Carll will tell you everything you need to know.


Painted redcedar lap siding butting tightly against a window casing without caulk. Photograph taken summer 2005 on a single-story home built in 1940.

Caulk is sometimes used in residential construction to inhibit rainwater intrusion where wall cladding interfaces with windows and doors (fenestration units) and is commonly used where utilities (such as pipes, vent hoods, and electrical conduit) penetrate the wall. Prior to development of modern caulks, caulk typically wasn’t used at the interfaces of wood siding and fenestration units. Although not assumed to be watertight when subjected to windblown rain, these interfaces nevertheless usually did not leak noticeably. Fenestration units were designed to shed water at sills and drip it beyond the exterior of the cladding (siding) system. Siding pieces were tightly fitted to jamb casings and were shingle-lapped with sills with head flashing or drip cap at heads or both.

Different styles of buildings call for different techniques in caulking, as the photos below show.


Wood siding shingle-lapped with an outwardly sloped wood window sill without caulk. Photograph taken in summer 2005 on a 1½-story home constructed in 1916.


Wood drip cap, atop window head casing, installed in shingle-lap fashion with redcedar trim and without caulk. In this example, there is no metal head flashing over the wood drip cap and behind the siding. Water intrusion between the drip cap and the siding could be expected if this detail were exposed to significant wind-blown rain. A modest 0.3 m (12 inch) roof overhang on this single-story home evidently provided adequate shelter from wind-blown rain. This is the same window shown in the second photo on this post.