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Incapsulated or Unincapsulated Crawlspace

ScottRod's picture

I"ve just received two completetly diferent suggestions for dealing with a crawl space. One is incapsulationwith a type of drain sytem the other is to let air move freely through vents to exterior. Vents are designed to open and close with temperature changes.  Both companies do basement wall and foundation repair work and where recommended by a structursal engineer.

Who is correct herea? Where is the  science for one or the other coming from?

The question is... (post #207383, reply #1 of 5)

What is a crawlspace?

In essence, its a really short basement.  How many people are told to put in vents or open windows in their basement? 

and what do they tell you to do with the vents?  Most are told to open them in the summer and close them in the winter.  Well in most of the US, the summer air is hot and Humid and the temps in the crawl are cool.  What happens to your glass of tea on you deck in the summer?  The hot humid air condenses on your cool glass.  In the winter, the air outside is cool but dry and the air inside your home is hot and humid.  So any movement of air from your home to your crawlspace won't get air circulation.


If you have a groundwater problem fix it.  Then seal the floor off so that water vapor from the ground can't migrate up and treat the walls like anyone else would in their basement. 

SR (post #207383, reply #2 of 5)

Where is this house and how is the ductwork going to be run in this crawl?  How are you dealing with the handling of water around the outside of the house?

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


Thank you for asking. We are (post #207383, reply #3 of 5)

Thank you for asking. We are located in South Central Indiana. There are flexible insulated ducts for A/C and a perimeter drain connected to rain gutters routed 20' from the house. This house is basement with crawl space additions with the kitchen and bath located above the additions. I say additions because there were two phases of additions over the years.  

Assuming that the sections (post #207383, reply #4 of 5)

Assuming that the sections are reasonably well connected to the basement, you should probably treat them as basement.  Plastic on the floor, seal obvious air leaks to the outside, make the space "communicate" with the basement, maybe add some insulation on the walls, and even on the floor. 

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

scott (post #207383, reply #5 of 5)

I'm in NW Oh.  I deal with most crawls as a conditioned space.  Cover the soil/gravel with 6 mil or thicker visqueen, seal all openings to the exterior including the vents. Insulate the foundation on the inside, make sure the outside is waterproofed and properly drained.  Use hard vent inside the crawl, flex is inefficient.  If there's a good quantity of venting in the crawl, run the trunk line in there (insulated) and then hard pipe off that.

The thought is - open vent in the summer-warm moist air contacts cool surfaces within the crawl-condensation.  In the winter, the outside air is much dryer, but I don't want the cold air in the crawl.

Look to the Building Science site for way further info.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.