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Mildew and algae

Causes of moisture issues in historic homes

Wood rot from water damage
Central Chimney and vegetation on Sconset cottage
Indoor plumbing
This past winter snow blew through gaps in overhang, through stud cavity and six feet into the structure where it melted and dripped through the ceiling
Roof Lantern for natural ventilation
 Roof Coupola

Now that we are getting cooler days and closing up the windows and are no longer using air conditioners we are starting to notice the musty smells more. It is cold enough to close the windows, but not quite cold enough to turn on the heat, which will help dry things out. Plus over 2 inches of rain this week hasn’t helped any!  As I write this I am sitting in our small cottage and I have tracked one source of musty odors, which was the  pressboard back of our dresser and the wall behind it. I washed the wall and threw the pressboard away and will replace it with solid wood.

The majority of the issues I address in my preservation contracting business have their root causes in moisture. Finding solutions to moisture problems, be they condensation or water problems, is often difficult, time-consuming and can be an expensive undertaking. There are some simple things that can be done, in a note to a potential client I recently referred to  these measures  as “low hanging fruit“.

The first step in any situation is to identify the source of the problem. This may not be easy because two and often more things may be working together to create the problem. This issue is complex so I will break my thoughts into more than one article. First I would like to talk about the causes, particularly in historic homes, but much will be applicable to newer homes as well. In the next installments I will go over solutions.

The original design and construction of the historic home and the heating systems used prevented most of these moisture issues. The very things that made old houses drafty and hard to heat also prevented most moisture issues. What we have done to make our houses more comfortable and “modern” are often the root causes of moisture issues. Historic homes are usually timber frame or stick constructed with little or no insulation and single pane, wood sash windows. The sheathing on the outside of the house and the roof were made up of individual boards that had gaps between them and were covered with wood shingles or clapboard siding and wood shingles on the roof. They were heated from many fireplaces that burned wood, or later coal. There was a central chimney or chimneys. Cooking was done over or in the kitchen hearth. There was a fire in the kitchen hearth year around and in the winter there was a fire in every fireplace. There was no indoor plumbing. Water would be brought in from an outside source and any of the moisture generated by cooking or heating water went right up the chimney.

So you had a central thermal mass (the chimney) which generated dry heat year around and a structure that “breathed”, ie. was drafty. The air in the house was exchanged up to 1 or 4 times per day. In the winter dry outside air was drawn into the house to make up the air that was going up the chimney and the heat generated by the fires was escaping through the walls, windows and ceiling, taking any moisture generated by the human residents and any other source with it . In the summer there was passive air circulation, ie open windows and screen doors, cupolas and attic vents. The dry heat from cook fires helped to dry out the building materials from the humid outside air.

A relatively recent phenomenon is that homeowners have added insulation to cut heat loss and heat gain, while others have caulked and weather- stripped around windows and doors to reduce the infiltration of cold air into their home. The same practices that trap heat in the home also trap high levels of moisture. For example, without some kind of moisture barrier in the walls the water vapor that used to pass right through the walls can be absorbed by the insulation, causing dampness both inside and outside the house. We now have indoor plumbing which can leak inside the walls or cause condensation on cold water pipes and toilet tanks in summer and we bathe or shower inside and much more frequently than in past centuries. Much of the housing stock on this island is seasonal and the plumbing is drained in the winter and the houses stand unheated during the coldest dampest season. Winter winds can drive rain and snow into places that you would never even imagine.

Well, now that I have bummed you out, there really are solutions and I will go over them in the following articles.  Be of good cheer, there are low cost, simple measures and lifestyle changes that can be made by a homeowner. In the next article I will start with those and work up to more complicated and expensive solutions that are best implemented by a professional.

As always you can contact me with specific issues you would like to see addressed by posting a comment or emailing me at [email protected]

Here are some articles and websites that I used as inspiration beyond the knowledge that I have gleaned from over thirty years in the building trades.