Window Condensation
Ever wonder why condensation forms on your windows—and what you can do to prevent it? Below is a collection of questions and answers designed to provide you with a better understanding of condensation and how you can minimize it.
What causes exterior condensation?
Exterior condensation occurs when moist air comes into contact with cool surfaces, such as glass. This type of condensation appears when the dew point in the air is higher than the temperature of the glass. This occurs when a cool night follows a warmer day, most typically during the spring and fall seasons
How does low-emissivity (Low-E) glass affect exterior condensation?
Low-E glass reduces heat conducted through the glass from the warm interior of the home to the outside glass surface. Heat conduction can be reduced by as much as 50 percent with an efficient Low-E coated glass. This reflected heat energy reduces the outside glass temperature and can result in condensation on the glass. Exterior condensation is actually an indication that the insulating glass in the window is performing as it should.
What causes condensation on the inside glass of windows?
Whenever there is excess humidity in a home, it manifests itself in the form of condensation on the coldest area of a wall, which is normally the windows. The warmer the air, the more moisture it will retain, so when air in your home comes in contact with the colder glass surface, it is subsequently cooled and moisture is released in the form of condensation on the glass.
Do windows cause condensation?
No, condensation on windows is not the fault of the window. However, by replacing drafty windows and doors or installing a new roof or siding, you are reducing air flow in your home and making it tighter. Tighter homes actually retain more humidity.
Where on a window does condensation normally form and why?
Condensation often forms at the meeting rail and at the bottom of the lower sash on the interior of the glass. This is because when warm air cools, it falls down across the interior surface of the window at the same time the temperature of the air is falling. The air contacts the horizontal surface of the meeting rail, which acts like a dam, slowing the air’s rate of fall and creating the perfect opportunity for the trapped water vapor to escape and form on the meeting rail’s surface. The air then rolls over the edge of the meeting rail and again gains speed until it encounters the lower handle of the sash. At this point, the water vapor again makes its exit and lies at the b ottom of the sash.
Can I reduce the condensation on my windows?
Yes. In order to reduce condensation, humidity must be controlled and air movement must be generated. As the exterior temperature drops, the humidity level needs to decrease if condensation is to be controlled.
Where on a window does condensation normally form and why?
Condensation often forms at the meeting rail and at the bottom of the lower sash on the interior of the glass. This is because when warm air cools, it falls down across the interior surface of the window at the same time the temperature of the air is falling. The air contacts the horizontal surface of the meeting rail, which acts like a dam, slowing the air’s rate of fall and creating the perfect opportunity for the trapped water vapor to escape and form on the meeting rail’s surface. The air then rolls over the edge of the meeting rail and again gains speed until it encounters the lower handle of the sash. At this point, the water vapor again makes its exit and lies at the b ottom of the sash.
Can I reduce the condensation on my windows?
Yes. In order to reduce condensation, humidity must be controlled and air movement must be generated. As the exterior temperature drops, the humidity level needs to decrease if condensation is to be controlled.
What steps can I take to reduce humidity in my home?
The two main things you can do are to control sources of moisture and increase ventilation. To decrease or control excess humidity and condensation:
- Use exhaust fans in your kitchen, laundry and bathrooms.
- Vent gas burners, clothes dryers, etc. to the outdoors.
- Shut off furnace humidifiers and other humidifying devices in your home.
- Be sure that the ventilating louvers in your attic, basement or crawl spaces are open and amply sized.
- Open fireplace dampers to allow an escape route for moisture-laden air.
- Air out your house a few minutes each day.
What You Can Do, What You Can Use
Allow grass clippings to stay on the lawn, instead of bagging them. The cut grass will decompose and return to the
soil naturally.
WHAT YOU CAN DO, WHAT YOU CAN USE
Look for “Most Efficient”! When shopping for appliance or other products, look for the new Energy Star designation
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Check your UV index: http://www.epa.gov/sunwise/uvindex.html
Reduce mosquitos! Around your home you can drain pools of standing water where mosquitoes breed. Drain water
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UV Safety
Concrete Cracking
A common adage is that there are two guarantees with concrete. One, it will get hard and two, it will crack. Cracking is a frequent cause of complaints in the concrete industry. The Concrete Foundations Association has produced a new flyer to help contractors educate their customers about the causes of cracks and when they should be a concern. A more detailed explanation of cracking is presented in this article.
Cracking can be the result of one or a combination of factors such as drying shrinkage, thermal contraction, restraint (external or internal) to shortening, subgrade settlement, and applied loads. Cracking can not be prevented but it can be significantly reduced or controlled when the causes are taken into account and preventative steps are taken.
Another problem associated with cracking is public perception. Cracks can be unsightly but many consumers feel that if a crack develops in their wall or floor that the product has failed. In the case of a wall, if a crack is not structural, is not too wide (the acceptable crack of a crack depends on who you ask and ranges from 1/16” to 1/4”) and is not leaking water, it should be considered acceptable. It is in the best interest of you, the wall contractor, to educate your customers that the wall will crack and when it should be a concern to them.
Cracks that occur before hardening usually are the result of settlement within the concrete mass, or shrinkage of the surface (plastic-shrinkage cracks) caused by loss of water while the concrete is still plastic.
Settlement cracks may develop over embedded items, such as reinforcing steel, or adjacent to forms or hardened concrete as the concrete settles or subsides. Settlement cracking results from insufficient consolidation (vibration), high slumps (overly wet concrete), or a lack of adequate cover over embedded items.
Plastic-shrinkage cracks are most common in slabs and are relatively short cracks that may occur before final finishing on days when wind, a low humidity, and a high temperature occur. Surface moisture evaporates faster than it can be replaced by rising bleed water, causing the surface to shrink more than the interior concrete. As the interior concrete restrains shrinkage of the surface concrete, stresses can develop that exceed the concrete’s tensile strength, resulting in surface cracks. Plastic-shrinkage cracks are of varying lengths spaced from a few centimeters (inches) up to 3 m (10 ft) apart and often penetrate to mid-depth of a slab.
Cracks that occur after hardening usually are the result of drying shrinkage, thermal contraction, or subgrade settlement. While drying, hardened concrete will shrink about 1/16 in. in 10 ft of length. One method to accommodate this shrinkage and control the location of cracks is to place construction joints at regular intervals. For example, joints can be constructed to force cracks to occur in places where they are inconspicuous or predictable. Horizontal reinforcement steel can be installed to reduce the number of cracks or prevent those that do occur from opening too wide.
The major factor influencing the drying shrinkage properties of concrete is the total water content of the concrete. As the water content increases, the amount of shrinkage increases proportionally. Large increases in the sand content and significant reductions in the size of the coarse aggregate increase shrinkage because total water is increased and because smaller size coarse aggregates provide less internal restraint to shrinkage. Use of high-shrinkage aggregates and calcium chloride admixtures also increases shrinkage. Within the range of practical concrete mixes – 470 to 750 lb/yd3 (5- to 8-bag mixes) cement content – increases in cement content have little to no effect on shrinkage as long as the water content is not increased significantly.
Concrete has a coefficient of thermal expansion and contraction of about 5.5 x 10-6 per °F. Concrete placed during hot midday temperatures will contract as it cools during the night. A 40°F drop in temperature between day and night-not uncommon in some areas-would cause about 0.03 in. of contraction in a 10-ft length of concrete, sufficient to cause cracking if the concrete is restrained. Thermal expansion can also cause cracking.
Structural cracks in residential foundations usually result from settlement or horizontal loading. Most (but not all) structural cracks resulting from applied loads are nearly horizontal (parallel to the floor) and occur 16” to 48” from the top of the wall. They are much more prevalent concrete block construction. They can be brought about by hydrostatic pressure or heavy equipment next to the foundation.
Diagonal cracks that extend nearly the full height of the wall are often an indication of settlement. In either of the above conditions, an engineer should be consulted. Diagonal cracks emanating from the corner of windows and other openings are called reentrant cracks and are usually the result of stress build-up at the corner. Diagonal reinforcement at the corner of openings can reduce the instance of crack formation and will keep the cracks narrow.
Other procedures which can reduce cracking in concrete include the following practices.
- Minimize the mix water content by maximizing the size and amount of coarse aggregate and by using low-shrinkage aggregate.
- Use the lowest amount of mix water required for workability and placement; do not permit overly wet consistencies.
- Use calcium chloride admixtures only when necessary.
- Prevent rapid loss of surface moisture while the concrete is still plastic through use of spray-applied finishing aids or plastic sheets to avoid plastic-shrinkage cracks (more important in slabs)
- Provide contraction joints at reasonable intervals, 30 times the wall thickness is a good “rule-of-thumb”.
- Prevent extreme changes in temperature after placement and initial cure.
- Properly place and consolidate the concrete.
Cracks can also be caused by freezing and thawing of saturated concrete, alkali- aggregate reactivity, sulfate attack, or corrosion of reinforcing steel. However, cracks from these sources may not appear for years. Proper mix design and selection of suitable concrete materials can significantly reduce or eliminate the formation of cracks and deterioration related to freezing and thawing, alkali-aggregate reactivity, sulfate attack, or steel corrosion.
For more information, refer to Design and Control of Concrete Mixtures, EB001, and Diagnosis and Control of Alkali-Aggregate Reactions in Concrete, IS413.