ASK THE CONTRACTOR: Is your crawl space sealed or vented?

With so many homes built into the hillsides here in Prescott and having a walk space under the house, we have an unfinished area, just dirt with plastic covering the dirt. Could you please tell me about the humidity levels? Are they safe or good or bad? Should any actions be taken to control the air? Our home is 2 years old with the foam insulation and humidity right now is about 55 percent and it has been higher. Please let me know your expertise on this. Thank you in advance. — Rita, Prescott.

Rita, your question was way beyond my degree of knowledge and comfort to even begin to answer, so I called for a “life line” and asked Ed Stahl, certified green professional and owner of R.E.S. Contracting to answer your question. R.E.S. Contracting has more than 25 years of experience building custom homes in the Prescott area. Ed and Connie Stahl and their partner, Matt Bohannon, have a commitment to use the latest building science technology to help their clients save money on utility bills and most importantly, provide a healthier and more comfortable living environment.

Rita, many modern homes built today have plastic covering the dirt in the crawl space. (I’ll use the conventional term “crawl space” even though with the homes being built today, that area can be much taller when being built on a hillside). Without knowing all of the details of your particular space, here are some assumptions: If the space has foam insulation on the walls it may be a sealed crawl space without vents to the outside. Sealed crawl spaces can provide many advantages over traditional vented crawl spaces. The crawl space is within the thermal envelope and furnaces, ducts and other equipment within the crawl space aren’t subject to the wind and cold. Regardless of the type of crawl space, high humidity levels can be a problem. Moisture can condense on cold surfaces and create an environment for mold growth.

You could check the crawl space for any damp areas that may be the source of moisture. The plastic ground cover should be sealed to the walls and the seams should be taped for air tightness. The purpose of the plastic is to isolate damp soil from the crawl space, so it needs to be nearly air tight. Check for any other sources of moisture and especially look for mold. If you find mold call a professional for remediation.

Check outside the house on the uphill side and make sure you do not have a drainage problem. Rain water coming from the roof and gutters should drain away from the foundation of the home.

Inspect your drip irrigation system for leaks or plantings that get too much water and maintain wet soil against the house. Especially in Prescott, many hillside building sites have underground moisture. We have seen homes that have percolated moisture issues created by underground springs flowing from excavated areas several lots away or from hillsides where excavation has cut into the granite shelf and has caused the water to travel a different path. Not every moisture issue is from the surface surrounding the home and some conditions only reveal themselves during rainy seasons with high water tables.

Waterproofing may have to be added to underground retaining walls to prevent moisture from wicking through the walls. It’s always more effective and less expensive to deal with subterranean water conditions during the construction of the home.

With your stated humidity level of 55 percent, how did you check that level? Inexpensive hygrometers are notoriously inaccurate. A sealed crawl space can also be ventilated with a small exhaust fan to help reduce humidity levels. Always correct the source of the moisture first.

If you do have a sealed crawl space and nothing else remediates the moisture, you could install exterior vents. However, you would lose the thermal advantages of the sealed system. It is always important to check with a professional before making and change to the thermal envelope of the home. If you switch to a conventionally ventilated crawl space, make sure the subfloor above is insulated.

If you find problems and need help we have another “life line” that we call on and that is Advantage Home Performance in Prescott.

Thanks Ed Stahl, Connie and Matt for being my “life line” to Rita. R.E.S. is truly a well-respected local company and it is YCCA’s privilege and honor to know you. Thanks for your stellar building practices and love of the industry.

Remember to tune in to YCCA’s “Hammer Time” every Saturday or Sunday morning 7:00 am on KQNA 1130AM, 99.9FM, 95.5FM or the web kqna.com. Listen to Sandy to Mike talk about the construction industry meet your local community partners and so much more. You will be entertained.