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Seal or Vent Your Crawl Space – What’s the Best Option?

Friday, February 28th, 2020


For many years, home ventilation was an essential way of keeping attics dry and the house cool during sultry weather. So successful that many building codes in the 1950s adopted it as a requirement for crawl spaces to have vents. The reasoning behind this was that vents would ensure better air circulation and keep moisture levels down within the crawl space environment.

 In recent years, vented crawl spaces have proven to be retrogressive. Instead of aiding air circulation and regulating moisture levels, it encourages them. Because of its ineffectiveness, it’s slowly being phased out of many local building codes. Contractors are also encouraging homeowners to install crawl space vapor barriers below their homes.

Cons of Vented Crawl Space

Though it’s possible to seal the crawl space during cold winter months, there are seasons that ventilation makes no sense. A good example is venting the space during rainy weather. It’s not going to remain dry. Plus, what happens during damp or humid weather?

On a hot, humid day when condensation is high, the crawl space will be damp. Wood, fiberglass insulation and other materials will get soaked with moisture. If the conditions remain the same for 48 hours, mold will grow on wood and other organic surfaces in the crawl space, eventually causing severe damage, including structural problems.

Another downside to a vented crawl space is that it will damage your fiberglass insulation in two ways. First, fiberglass has resins and dyes that do encourage mold growth. The same goes for installations as they usually have paper backing that can support mold growth in the crawl space. Secondly, fiberglass is absorbent just like a sponge, so moisture can build up with its material and weigh down. Eventually, it will sag and drop to the floor.

Let’s not forget that a vented crawl space lets in termites. A mouse only needs a space that’s ¼ of an inch wide to squeeze its way into the crawl space. In hot and dry weather, all small pests will come in to escape the harsh outdoor weather. When they find their way to the crawl space, they will chew your beams and leave droppings that will make the whole space smell.

As well as letting in toxic air to your home, vented crawl spaces are known to increase the energy costs by as much as 20%. Vents let in cold air, which has a stack effect on the home. This means you will have to run your HVAC for a long time to attain the desired internal conditions.

Air is constantly moving and going upwards in your home, exiting from the roof or attic. When this air goes out, a vacuum is created in the lower sections of the home. External air comes in to replace it. If the crawl space air is dusty or filled with allergens, you can be sure it will enter the living space and cause respiratory problems.

Is Venting Really Worth It?

It’s apparent that vents are a bad idea. Your crawl space will get more damp, musty, pest-ridden, and toxic than when it’s sealed, so the sooner you seal the crawl space, the better.

If your crawl space has moisture issues, sealing or encapsulation is the way to go. The process involves covering the walls and floor of the crawl space with a thick plastic vapor barrier. In effect, this isolates the under-house area from external temperature and humidity. Plus, it locks out crawling insects and toxic air.

Have a vented crawl space that’s causing moisture problems or letting in pests? We can help you seal the crawl space and create a dry, healthy, and energy-efficient space. Schedule an inspection and get a free crawl space repair quote in writing. We’re happy to answer your pressing questions and make solid recommendations to transform your crawl space.