Vented Crawlspaces vs. Un-vented Crawlspaces
There has been much talk about lately about vented crawl spaces vs. un-vented crawl spaces. The popular opinion in the past has been that foundation crawlspace vents would allow for air movement inside the crawlspace that would help keep the crawlspace dry and help stop mold development.
In recent years view has changed and study have been conducted that have determined that un-vented crawlspaces are extra beneficial in preventing moisture buildup and mold growth then vented crawlspaces. The interior of the vented crawlspace is subjected to the outside environment and humidity. For example if it’s in the summer time and there is high moisture the hot moist air will enter the crawlspace and elevate moisture levels inside. In the colder months cold air enters the crawlspace and makes the heating system less efficient and can make for cold flooring. Not to mention possible plumbing leakage issues that can arise with freezing pipes.
In my view the un-vented crawlspace has a lot of merit and really makes sense in most climates. Where un-vented crawlspace may not make sense are in very cold climates and for areas that have a naturally happening high water table. For most areas un-vented crawlspaces are the way to go. Many new homes now have been built with un- vented crawl spaces and many more existing homes are in the process of being transformed.
To change the crawlspace from being vented to un-vented is a development, but one that can be very beneficial throughout the life of the home and contribute to the better health of the occupants. The first step is to install an adequate vapor barrier on the crawlspace floor particularly if the floor is a dirt floor. The setting up of a fixed vapor barrier that runs the entire area of the floor and 2 feet up the foundation walls is required. There must be not any holes, rips or tears, any areas that are compromised will negate the effect of having a vapor difficulty.
After that stop the existing crawlspace foundation vents. This should be done in a conduct that tightly seals the vents and does not let any air infiltration through. This is an extremely important step because it will prevent the outside environment and humidity from entering the space. Next the interior crawlspace walls should be properly insulated with a blanket style insulation that is tightly secured to the sill plate and secured at the base of the foundation wall. The blanket filling should extend inward two or three feet toward the center of the crawlspace. The blanket insulation can be secured at the base using 2 x 4 framing members.
In an un-vented crawlspace the ceiling or sub flooring is not insulated. The foundation walls in an un-vented crawlspace are insulated. The goal is to achieve a similar environment to the rest of the house. In effect we are building the crawlspace an extension of the home environment. The next step in converting a vented crawlspace to an un-vented space is to properly situation the crawlspace. This can be done easily if the heating equipment is located inside the space because the installation of a heating register is the only thing that will bring warm or conditioned air to the space. If the heating equipment is located on another floor ducts may have to be installed to bring heated and conditioned air into the crawlspace. This is not essential when the crawlspace is connected to a basement area that is properly conditioned. The conditioned underground room air will circulate into the crawlspace allowing for the same basement environment to exist in the space. If the home is equipped with a non-forced air heating system say for example hot water baseboard heat, the fitting of a venting system that brings the room air into the crawlspace may be a solution in order to help create a positive crawlspace environment.
Humidity control is also very important in any crawlspace. A dehumidifier capable of dehumidifier the entire crawlspace area is necessary. Humidity levels in the crawlspace should be no more than 40%. Managing humidity levels will help control mold growth and moisture.
Of course any of these actions to convert a vented to and un-vented crawlspace assume that there are no water infiltration issues in the space. If there is any water infiltration troubles they need to be corrected first before any of the measures are taken. The installation of crawlspace water controls such as a perimeter drain tied into a sump pump may be required if a high water table exists or if the home is prone to flooding. The interior of the crawlspace walls may also have to be sealed with hydraulic cement in order to help keep moisture to a minimum.
There are many benefits to having an un-vented crawlspace. Although converting a crawlspace from a vented to a conditioned crawlspace can be consummate by a DIY is often time-consuming and challenging to accomplish by oneself. You may want to contract with a sound basement or crawlspace professional in order to accomplish the renovation.
Ethen Hunt - About Author:
Author John writes here about benefits of Un-vented Crawlspaces over Vented Crawlspaces. He is one of the few independent Home Inspectors in New Jersey and Certified NJ Mold Inspector.
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