Moisture Sealing 101

Moisture is a home's enemy. It can cause mold damage, damage to carpet, damage to dry wall, and even lead to a flooded basement, and other big expenses. All of this also causes a boat load of stress and expenses. The remedy for the symptoms of moisture in one's home is prevention. Sealing windows appropriately is an easy and economic way to ensure that outside moisture stays out.

The Consequences of Not Sealing Windows Properly or At All

One of the signs a window is not sealed properly is a visible drip-area on the outside of a building, below a window. The surface of a window will likely acquire condensation and there can also be building envelope condensation. Excess moisture is sure to cause mold and mildew damage when not properly dealt with.

The insualtion of a home or building that does not have properly sealed windows will not work efficiently or effectively, and the air quality within the building will be poor. If given enough time, the building materials of a home or building will begin to rot, possibly causing structural damage.

Faulty Window Seal Options

One can tell a window seal has failed if condensation or fog is noticed between the two panes. The first option to fix the moisture problem is to install a new window. Others may choose to replace the glass or have the current glass re-glazed on-site if the seal is not too bad.

Replacing the seal is another good option, depending on the condition of the window and the building. This usually involves having to install a new valve, making sure there is no more moisture between the panes of glass, and making a new seal.

Fixing or Installing a New Moisture Seal

People who know their way around tools, are comfortable with carpentry, or find they know more about home repair more than the employees at the local hardware store will find installing a moisture seal on a window to be just another weekend project.

New, double-hung windows sold in stores will usually have a moisture seal built in to it. However, it is recommended that one use bronze, nail-on strips for wood windows by inserting the metal strips between the sashes and jambs. These are then attached to the top and bottom-face of the upper sash. Here are the steps:

1. Prep the window. Scrape any loose paint or old seals away from the window. Check to see that the sash lock is pulling the upper and lower sashes together so a tight seal is formed when it is closed. If there isn't a tight seal, reposition one or both parts of the lock.
2. Install vertical strips. For both of the sashes, measure the side channels and cut the bronze spring strips with special scissors called "tin snips". Place the strips between the sash and jamb and make sure the nailing flange is against the sash stop. Slide the strip in until it comes in contact with the pulley or window.
   If a pulley is present, cut the seal in two pieces so the bottom part is flush with the bottom of the pulley. Cut the top seal so it is shorter than the bottom seal and place it above the pulley. Use brads to attach the strips to the jambs.
3. Install 3 horizontal strips. These will need to be cut so that the length is the full width of the window. Attach one strip to the bottom of the lower sash so the nail flange is against the inside edge of the window. The second strip will go on top of the upper sash, and the third will attach to the bottom of the upper sash so a seal is created when the window is closed.
   If a window has pulleys, cover them with caps to prevent air leaks.

Moisture seals are made of many different types of materials. For wooden windows, nail-on strips are the best. Other seals have self-adhesives made of rubber, which are good choices for windows made of metal or vinyl. EPDM is the best of the self-sticking seals as it is flexible and provides good insulation for many years. Other self-adhesive material options include closed-cell foam and high-density foam. Vinyl tubular gaskets are used when large gaps are present, but this type of seal is not self-adhesive.

Moisture seals will cost a home or building owner in one way or another: in installation or repair costs, or in costs due to a major repair because of water damage. It is cheaper and easier to make sure seals are installed correctly than to have to reinstall a new wall, carpet, or ceiling.

~ Flora Richards-Gustafson, 2009

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