crawl space

RUGMAN · 08-22-2016, 09:55 AM

recently renovated our cottage , created a crawl space with foam insulation in floor. , now we have created a very damp space, does anyone have recommendation for solutions. I could put dehumidifier down there , guess is it would be a killer on my electric bill. Friend mentioned a Wave air system.

DickR · 08-22-2016, 11:10 AM

The source of moisture down there would be the ground, perpetually wet, but the surface of which is kept at least looking dry by a lot of air passing over it. When you enclose the space over that piece of ground, creating the crawl, you eliminate the drying.

First, you need to retard the unimpeded diffusion of ground moisture into the air above it in the crawl space. Assuming the "floor" of the crawl is dirt, then remove the junk over the ground (stored stuff), and cover the entire floor with a tough vapor barrier, like 10-mil polyethylene or StegoWrap, and run it up the sides of the material walling off the crawl. Tape all the joints, and tape the upper edge to the crawl walls.

You can't totally eliminate diffusion of water vapor into the crawl space, although you can slow it down dramatically. You can add vents to the walls of the crawl and run a low-flow blower to exhaust one end while drawing in from another. The problem with ventilation using outside air is that summer air tends to be humid regularly, with the dew point above that of ground surface. This results in condensation. This happens in particular on cold water piping exposed in the crawl, with the drips pooling on the plastic.

The Wave air system works by ejecting air from the crawl space, replacing it with conditioned air from the space above it. But that air in turn must be replaced by outside air, via open windows or leaks in the building shell. In summer, that just heats up the house more during the day.

A better ultimate solution is to turn the crawl space into unvented, conditioned space. A good read on that can be found here:
http://www.greenbuildingadvisor.com/...ed-crawl-space

winterh · 08-22-2016, 12:02 PM

I recently had my crawl space "encapsulated" or turned into unvented conditioned space. It was a dirt floor with batt insulation in joists above. Batts were hanging in places which is a sign of dampness. There was plastic over floor but walls were not insulated and space was vented. The company laid down very thick plastic on floor and up walls. Then spray foam insulation up the walls and in rim joists. I do have a humidifier but its not on much as space is nowhere near as damp as it used to be. I am very happy with it.

08-22-2016, 09:55 AM	#1
RUGMAN Senior Member Join Date: Jul 2015 Location: weirs beach, Posts: 281 Thanks: 37 Thanked 39 Times in 32 Posts	crawl space recently renovated our cottage , created a crawl space with foam insulation in floor. , now we have created a very damp space, does anyone have recommendation for solutions. I could put dehumidifier down there , guess is it would be a killer on my electric bill. Friend mentioned a Wave air system.

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08-22-2016, 11:10 AM	#2
DickR Senior Member Join Date: Apr 2008 Location: Moultonborough Posts: 735 Thanks: 4 Thanked 254 Times in 166 Posts	The source of moisture down there would be the ground, perpetually wet, but the surface of which is kept at least looking dry by a lot of air passing over it. When you enclose the space over that piece of ground, creating the crawl, you eliminate the drying. First, you need to retard the unimpeded diffusion of ground moisture into the air above it in the crawl space. Assuming the "floor" of the crawl is dirt, then remove the junk over the ground (stored stuff), and cover the entire floor with a tough vapor barrier, like 10-mil polyethylene or StegoWrap, and run it up the sides of the material walling off the crawl. Tape all the joints, and tape the upper edge to the crawl walls. You can't totally eliminate diffusion of water vapor into the crawl space, although you can slow it down dramatically. You can add vents to the walls of the crawl and run a low-flow blower to exhaust one end while drawing in from another. The problem with ventilation using outside air is that summer air tends to be humid regularly, with the dew point above that of ground surface. This results in condensation. This happens in particular on cold water piping exposed in the crawl, with the drips pooling on the plastic. The Wave air system works by ejecting air from the crawl space, replacing it with conditioned air from the space above it. But that air in turn must be replaced by outside air, via open windows or leaks in the building shell. In summer, that just heats up the house more during the day. A better ultimate solution is to turn the crawl space into unvented, conditioned space. A good read on that can be found here: http://www.greenbuildingadvisor.com/...ed-crawl-space

08-22-2016, 12:02 PM	#3
winterh Senior Member Join Date: Jun 2009 Posts: 230 Thanks: 21 Thanked 119 Times in 54 Posts	I recently had my crawl space "encapsulated" or turned into unvented conditioned space. It was a dirt floor with batt insulation in joists above. Batts were hanging in places which is a sign of dampness. There was plastic over floor but walls were not insulated and space was vented. The company laid down very thick plastic on floor and up walls. Then spray foam insulation up the walls and in rim joists. I do have a humidifier but its not on much as space is nowhere near as damp as it used to be. I am very happy with it.