Preservation Issues: Moisture Problems in Historic Structures
Water. Without argument, it's essential to us. But in terms of the places where we live or work, unwanted moisture means erosion, corrosion and rot! This mini-web class can help anyone who cares for, or about, a historic house to better understand and deal with the three most common sources of the "wet stuff."
Learn how they invade historic materials:
- From the outside "in"
- From the ground "up"
- From "within" the interior itself.
We'll show you what goes wrong when moisture is not adequately managed and how to turn the corner on present and future problems by providing some simple, common sense tips.
Moisture as home-wrecker.
Most moisture problems are the result of rain or snow, high humidity, or high water tables. But some of the most troublesome moisture damage in older houses can be caused inside the house by leaky plumbing, heaters and air conditioners, as well simply cooking and doing laundry. Taken as a whole, the wet invaders can control your house unless you manage them!
 It's good to understand the forces that move air and moisture through a building so you can better identify and correct a problem. The drawing shows how moisture can invade "inward" from the exterior; "upward" from the ground; and be generated from "within" the interior. All have damaging effects. |
A Little Science.
You probably already know moisture moves both as liquid and as vapor. This movement is directly related to differences in pressure.
For example, water as vapor--warm moist air--moves from a high pressure area to a lower pressure area where the air is cooler and drier. Liquid water moves as a result of differences in hydrostatic pressure or wind pressure.
How fast moisture moves depends on how permeable the building materials are and how quickly water is absorbed. More formal terminology may be used to describe moisture movement and how it invades a house: lateral penetration (from the outside of the house in), capillary action (wicking up from the ground), and vapor diffusion (condensation within the house's interior). The subject is infinitely complex and, thus, one of continuing scientific study.
Watch out for these disgusting signs.
Identifying the problem and discovering its source or sources (from the outside, the ground, or within) usually involves the human senses of sight, smell, hearing, touch, and taste! Here are some of the more common signs of visible--as well as hidden--moisture damage: * Presence of standing water, mold, fungus, or mildew
* Wet stains, eroding surfaces, or efflorescence (salt deposits) on interior and exterior surfaces
* Flaking paint and plaster, peeling wallpaper, or moisture blisters on finished surfaces
* Dank, musty smells in areas of high humidity or poorly ventilated spaces
* Rust and corrosion stains on metal elements, such as anchorage systems and protruding roof nails in the attic
* Cupped, warped, cracked, or rotted wood
* Spalled, cracked masonry or eroded mortar joints
* Faulty roofs and gutters including missing roofing slates, tiles, or shingles and poor condition of flashing or gutters
* Condensation on window and wall surfaces
* Ice dams in gutters, on roofs, or leaks in the attics
Moisture invasion from the outside "in" ...
Historic houses are notoriously "drafty." They can easily allow rain and damp airto enter through missing mortar in brick or stone and through cracks around windows and doors. In the winter, snow and ice can be particuarly damaging. Ice dams that form in roof gutters can lift up roofing tiles, allowing the ice to melt into attics and exterior walls. Often, deterioration caused by the weather will be evident on the interior before you ever see it on the exterior.
For example, whenever plaster is damaged around windows and you see damp wallpaper, the windows and roofing area above should be inspected. If you haven't found the source of moisture, don't repair!
Ongoing maintenance of the exterior is critical to deter the invaders. Repair deteriorated siding and damaged roofing materials, such as slate, tile, or wood shingles. Overall, keeping up with smaller projects is far preferable to replacing whole areas of historic material with new material. Not only will this be less expensive, your house will retain its authenticity for future generations to enjoy.
On another topic, if you let vines grow directly on brick or wood, they may look mellow, but, without a trellis to hold them away from the house, the roots erode mortar joints and foundations as they seek nourishing dampness within. Vines also hold moisture against exterior surfaces. Though almost everyone enjoys a bit of planned nature in the yard, when nature grows with abandon out of brick walls or cracks in the sidewalks, or on the roof, we should turn on it as the enemy!
Next, always keep gutters and downspouts in good repair. This is critical in order to convey moisture away from the house. Dry residue, such as pine needles from trees, can clog them, making rain water overflow onto the very historic materials you call "home."
What to do--or not do.
The best advice is to use common sense maintenance approaches to keep rain and moisture from entering your house. Here are suggestions to keep the invaders under control.
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Roofs, gutters & downspouts: Don't apply "tar goop" (asphaltic compounds) to try to make repairs because it doesn't work in the long run and can actually damage historic materials! Keep your roof weather-tight and functioning properly. Repair the flashing and cracked or broken downspouts. Inspect the roofing itself at least once a year, preferably in the spring.
Replace any missing or damaged roofing shingles, slates, or tiles.
Window and door openings: Eliminate any cracks or open joints.Caulk or repoint around openings or steps. Repair or re-set weatherstripping, then repaint, as necessary.
Walls: Don't ever apply a waterproof coating to an above-ground masonry wall--it can trap moisture underneath, causing further damage to the historic material. Repair damaged surface materials with care. Repoint masonry with appropriately formulated mortar. Prime and repaint wooden, metal, or masonry elements or surfaces.
Foliage: Keep all foliage and vines away from the house. Trim overhanging trees to keep the debris out of gutters and to prevent limbs from rubbing against building materials. Remove moisture-retaining elements, such as shrubbery, from foundations.
Moisture invasion from the ground "up."
Below-grade ground moisture can be a major problem. To do battle and win means you have to find an efficient way to handle surface rain run-off. The statistics would seem discouraging for those who care for a historic house. A heavy rain of 2" in an hour can produce 200 gallons of water from downspout discharge alone!
Now--if a downspout is clogged or broken, it can't carry water away from the house, which is its function. As a result, the ground around the foundation quickly becomes oversaturated. Moisture is absorbed by the foundation walls, making for a damp basement, and may cause the masonry and adjacent wooden structural elements of the house to deteriorate.
Another, more sinister, kind of invader is called "rising damp." Generally the result of high water tables or a constant source of dampness under the footings, you have probably seen a stain on masonry houses, often reaching 2 or 3 feet above the foundation. It really looks ugly. But don't try to apply some kind of waterproof coating to the wall. It only makes things worse! Improve the drainage, or, if that doesn't work, have a physical barrier, such as a slate course or plastic sheeting, professionally installed.
Sometimes further investigation is needed to get a dryer foundation. There may be underground wells, cisterns, abandoned pipes or other "hidden holders" of moisture. Tidal areas may have a history of chronic ground moisture, and there are seasonally high water tables to deal with as well. If regular maintenance procedures don't rid your house and yard of moisture problems, then more extensive remedial work will need to be done.
What to do--or not do. The best advice is to use common sense maintenance procedures to eliminate standing water and increase ventilation of the basement, or to correct existing high moisture levels, if necessary. Here are suggestions to keep the invaders under control.
Foundation and Yard: Eliminate low spots around building foundations. Clean out existing downspout boots twice a year or add an extension to leaders to carry moisture away from foundation. Do a hose test to verify that surface drains are functioning.
Reduce moisture used to clean steps and walks. Eliminate the use of chlorides to melt ice, which can cause damage to masonry. Check the operation of irrigation systems, hose bib leaks,and clearance of air conditioning "drip" drain outlets.
Consider installing a "French drain" to reduce splash-back onto foundation walls.
Or, a more expansive drainage system may be installed to direct water away from the house and into the yard.
Crawl space: Check the foundation grilles to be sure they provide enough ventilation; vents may need to be added if there are none.
Close grilles seasonally in winter, if they are not needed, or in summer, if hot humid air is getting into air conditioned spaces.
Basement: To reduce the amount of moisture,add a de-humidifier. If there are vents, increase air flow by installing a vent fan. To remedy a chronic moisture problem in the basement, such as a visibly wet floor or periodic ponding, install an electric sump pump (right). Then, once any mechanical device is in place, be sure to take care of it provide by providing routine maintenance.
Piping/ductwork: Check for condensation on pipes and insulate the pipes or seal the joints. Replace older pipes subject to leaking or overflowing.
Moisture Invasion from "within."
The most obvious problem you may encounter is from leaky plumbing pipes and mechanical equipment. Even new plumbing can leak, but older water and sewer pipes are particularly vulnerable.
As a result, slow leaks at plumbing joints hidden within walls and ceilings can stain ceiling plaster or wallpaper, ultimately rot floor boards, and even lead to decay of structural members! Maintaining and repairing, or, if necessary, replacing older plumbing and mechanical equipment are the most common solutions.
Next, condensation produced inside the house can create some real headaches! It's caused when moist warm vapor in the air cools on interior surfaces and changes into liquid. Usually settling on paint, the moist film can result in an unhealthy interior, heavy with mold and mildew spores.
What makes it worse is that the condensation invader is primarily occupant produced! Did you know that a house with four people in it can generate between 10 and 16 pounds of water a day (approximately 1 ½- 2 gallons) from normal, every day activities, such as showering, cooking, and doing laundry? Unvented gas stoves and kerosene heaters also give off a large amount of unwanted moisture. Bathrooms, kitchens, and laundry areas should all have vent fans that are turned on when the rooms are in active use.
When moisture appears as a film on interior window surfaces, it's a sign that you need to take defensive action. In cold climates, install storm windows. This reduces condensation and its damaging effects to historic materials, as well as your health.
In summary, reducing condensation through additional ventilation or installing storm windows can really help preserve your historic house!
What to do--or not do.
The best advice is to use common sense maintenance procedures to reduce damage from interior moisture. Here are suggestions to keep the invaders under control with a focus on keeping equipment functioning; replacing broken components; and even installing additional equipment where moisture problems are evident.
Plumbing pipes: Consider use of a floor water sensor in the basement to let you know if you have a problem! Add insulation to plumbing or radiator pipes located in areas subject to condensation or freezing, such as along outside walls, in attics, or in unheated basements.
Replace older pipes that are subject to leaking or overflowing!
Mechanical equipment: Check condensation pans and drain lines to keep them clear at all times. Insulate and seal joints in exposed metal ductwork to avoid drawing in moist air.
Cleaning: Routinely dust and clean surfaces. Caulk around tile floor and wall connections and keep floor grout in good condition.
Ventilation: Reduce household-produced moisture, if it's a problem, by increasing ventilation, especially in the basement.
Vent clothes dryers to the outside. Install and always useexhaust fans in bathrooms,
showers, and kitchens. Control mold and mildew by adding a whole house fan for increased air flow throughout the house.
Interior climate control: Adjust the temperature and relative humidity to manage interior condensation.
Correct areas of improperly balanced pressure for HVAC systems that may be causing a moisture problem.
THE NEXT STEPS
The moisture problems discussed in this article are common for historic homeowners and the stewards of historic buildings. We provide qualified consultation and contracting services for adaptive re-use projects as green building practices are applied to repurposed structures for improved sustainability. Contact Olde Mohawk to discuss options and solutions that will preserve the historic fabric of your structure and improve the quality of life for the occupants.
Content source: National Park Service publication All Wet & How to Prevent It...Managing Moisture in Your Historic House, created by Kay Weeks with Sharon C. Park, FAIA, and Anne E. Grimmer in January 2000, using established treatment methodology from Preservation Briefs 39, but presenting an entirely new product for a web audience in a long distance learning format.