Why You Don't Caulk Under Clapboards


Clapboard siding was the standard for wood frame construction for over a century and is still used today for rustic construction. With its overlapping boards it is an American icon on farm houses and homes in small towns across the country, especially in New England. With proper care and maintenance, a well-built wood frame house can last well over a century.

Clapboard design

  • Clapboard siding is designed to overlap, each board being laid on top of the top edge of the board below. This provides a weathertight seal that sheds rain, snow and ice, keeping the interior of a clapboard house dry.

History of clapboard

  • Originally the clapboards were split in wedge-shaped lengths from logs, creating a board that is thinner on one edge -the top- and thicker on the other- the bottom. The name comes from a German word meaning: to split, "Klappen". Another process uses a saw that cuts half the depth of the log, the log being turned 5/8 inch every time to provide the clapboard bevel.

Care of clapboard siding

  • While hardwood clapboards can last for decades without any finish, a good quality paint job is the best way to ensure longevity. Proper preparation and priming are essential for best results. Be sure to scrape and repaint chips and peeling as soon as it is noticed.

Differences from modern clapboards

  • Modern clapboards are made from a variety of materials, from PVC to concrete. Due to increased regulation in the building industry, modern building codes mandate plastic vapor barriers under the siding that keep the inside of walls dry. Not so with older construction.

Dangers of moisture in clapboard walls

  • Unlike the vapor barrier sealed walls in modern construction, older wooden homes need to breathe. Left unsealed the gaps along the bottom edges of wooden clapboards provide an excellent method of ventilation. The boards will naturally swell as moisture builds keeping rain safely out, but allowing humidity and condensation to escape. Sealing clapboard siding with caulk can lead to moisture-related issues from rot to mold. Excess insulation inside these older walls can also carry the same catch-22, without the moisture barrier, restricting airflow in these walls may not be worth the risk.

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  • Photo Credit Image by Flickr.com, courtesy of sue
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