Thread: Crawl Space Encapsulation

Inspected a house today on the WDO side (haven't taken my state exam yet) that was extremely wet. In my mind I went through the HI checklist as I was doing the CL 100 inspection.

My question to the professional HI's is, what are your thoughts on total crawl space encapsulation? This is becoming big business here in South Carolina.

Also had water in a common basement, but I will defer that question for a later date or was that already covered in a previous thread.

Thanks,

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Originally Posted by Dan Popoff

Inspected a house today on the WDO side (haven't taken my state exam yet) that was extremely wet. In my mind I went through the HI checklist as I was doing the CL 100 inspection.

My question to the professional HI's is, what are your thoughts on total crawl space encapsulation? This is becoming big business here in South Carolina.

Also had water in a common basement, but I will defer that question for a later date or was that already covered in a previous thread.

Thanks,

Dan there are two basic types of closed crawlspaces. Closed crawlspace with dehumidifier, and closed conditioned crawlspace. The closed crawlspace is relatively new to this area and code requirements are changing like the shifting sands of the Sahara.

I have enjoyed inspecting the few that I have done. Very clean and moisture has not been a problem. I am concerned about what happens when the dehumidifier stops and there is a leak that goes unnoticed for months on end. It may look like a large petri dish with a runaway high school science project if no alarm is installed. As far as I know there is no code requirement for an alarm. I hope this changes. Also with the foundation walls covered, except for a small gap at the sill, it will be very hard to do pest/termite inspections. But IMHO I think we should go back to using chlordane and not worry about termites for the next 100 or so years. Just put notices every 10' around the foundation, "Do Not Roll Your Children In the Crawlspace Dirt"

Encapsulation is pretty much useless until the moisture problem is corrected.

408.1 Ventilation.
The under-floor space between the bottom of the floor joists and the earth under any building (except space occupied by a basement or cellar) shall be provided with ventilation openings through foundation walls or exterior walls. The minimum net area of ventilation openings shall not be less than 1 square foot for each 150 square feet (0.67 m2for each 100 m2) of under-floor space area. One such ventilating opening shall be within 3 feet (914 mm) of each corner of said building.
408.2 Openings for under-floor ventilation.
The minimum net area of ventilation openings shall not be less than 1 square foot (0.0929 m2) for each 150 square feet (100 m2) of underfloor space area. One such ventilating opening shall be within 3 feet (914 mm) of each corner of the building. Ventilation openings shall be covered for their height and width with any of the following materials provided that the least dimension of the covering shall not exceed 1/4 inch (6.4 mm):
1. Perforated sheet metal plates not less than 0.070 inch (1.8 mm) thick.
2. Expanded sheet metal plates not less than 0.047 inch (1.2 mm) thick.
3. Cast iron grills or grating.
4. Extruded load-bearing brick vents.
5. Hardware cloth of 0.035 inch (0.89 mm) wire or heavier.
6. Corrosion-resistant wire mesh, with the least dimension being 1/8 inch (3.2 mm).
Exceptions:
1. Where warranted by climatic conditions, ventilation openings to the outdoors are not required if ventilation openings to the interior are provided.
2. The total area of ventilation openings may be reduced to 1/1500 of the under-floor area where the ground surface is treated with an approved vapor retarder material and the required openings are placed so as to provide cross-ventilation of the space. The installation of operable louvers shall not be prohibited.
3. Under-floor spaces used as supply plenums for distribution of heated and cooled air shall comply with the requirements of Section M1601.4
4. Ventilation openings are not required where continuously operated mechanical ventilation is provided at a rate of 1.0 cfm (10 m2) for each 50 square feet (1.02 L/s) of underfloor space floor area and ground surface is covered with an approved vapor retarder material.
5. Ventilation openings are not required when the ground surface is covered with an approved vapor retarder material, the space is supplied with conditioned air and the perimeter walls are insulated in accordance with Section N1102.1.7.

5. Ventilation openings are not required when the ground surface is covered with an approved vapor retarder material, the space is supplied with conditioned air and the perimeter walls are insulated in accordance with Section N1102.1.7.

Isn't this the whole concept to the encapsulation?

Also Eric, great point but, when the foundation walls are "sealed" does moisture still get in?

Very interesting science to say the least.

Try this site: Advanced Energy

If the walls are insulated with extruded polystyrene (preferably two layers with the seams offset and taped or sealed with mastic),

and if the crawlspace floor is covered with a durable waterproof membrane (such as EPDM roofing), and if the membrane is wrapped up over extruded polystyrene and sealed tightly,

then the moisture boundaries that stop liquid water and water vapor are aligned outside the crawl space,

the envelope can dry to the outside,

and the crawlspace stays dry and reasonably warm.

The sill plate and perimeter joist at the top of the foundation should be air sealed and insulated with high density spray foam.

Originally Posted by Ed Voytovich

If the walls are insulated with extruded polystyrene (preferably two layers with the seams offset and taped or sealed with mastic),

and if the crawlspace floor is covered with a durable waterproof membrane (such as EPDM roofing), and if the membrane is wrapped up over extruded polystyrene and sealed tightly,

then the moisture boundaries that stop liquid water and water vapor are aligned outside the crawl space,

the envelope can dry to the outside,

and the crawlspace stays dry and reasonably warm.

The sill plate and perimeter joist at the top of the foundation should be air sealed and insulated with high density spray foam.

Ed, there is a 3" termite inspection gap required at the top of the foundation wall. Batt insulation is recommended so inspection and treatment can be preformed.

Dan, Being that a basement, L.L. or crawl are built into the ground I don't think that one should ever think that conditions are completely impervious to moisture. The last thing I want is a client with expectations that are too high.

Ed, I agree with Vern - install insulation that leaves the sill plate and rim joist accessible - especially under doors which are notorious for leaking to begin with. As an inspector, I pull insulation out to peek into these areas where I often find problems hidden.

In theory and best practice, many good ideas can be successfully implemented. But that's by people who are knowledgeable and take the time to do the work correctly. I wouldn't say that that covers a majority of contractors. I have great faith in BillieBob to screw up the best laid plans. With that in mind, I think that you have to tone down your own expectations as to what the end result will turn out to be.

Very true Eric. Thanks.