Crawl Space Systems

2010-01-31T13:04:00.000-08:00

Insight
By Joseph Lstiburek, Ph.D., P.Eng., ASHRAE Fellow

Crawlspaces are real simple to understand and deal with. When you vent crawlspaces you bring in hot, humid air and cause moisture and mold problems. The ground surface is typically colder than the dew point temperature of the exterior air. The underside of crawlspace floor insulation is radiation coupled to the ground surface and is very close to the same temperature of the ground. Moisture droplets can be seen all over the top surface of typical polyethylene ground covers as well as hanging from the bottom surface of the crawlspace floor insulation. Gee, I wonder how all the water got through the poly ground cover? It must have leaked through the walls. Give me another break. Now, when the moisture is in the insulation where do you think it wants to go? Where is the air conditioning? Moisture moves to the cold surface. Venting crawlspaces made sense only when you had no air conditioning and no insulation and no crawlspace walls.

New Light in Crawlspaces by Joseph Lstiburek

2010-01-31T11:47:00.000-08:00

Insight
By Joseph Lstiburek, Ph.D., P.Eng., ASHRAE Fellow

Crawlspaces stink, they rot, and are just plain icky. Photograph 1 shows the modern crawlspace, which is a forest of water droplets on the underside of fiberglass batt insulation. The exposed wood floor joists are rotting. The house over this crawlspace is not shabby (Photograph 2). Did I mention that this is a vented crawlspace (Photograph 3)? Oh, by the way, there is a continuous plastic sheet ground cover and excellent drainage. Everything in this crawlspace was done “right.” It has code specified ventilation, a continuous impermeable ground cover, excellent drainage and still we have a mess. What caused this mess? The floor insulation. No way. Yup.

Photograph 1: Icky Crawlspace—Note the condensation on the underside of the fiberglass insulation and the rot at the exposed portions of the crawlspace floor joists.

Photograph 2: Nice House Over Icky Crawlspace—This house with the crawlspace problem is in Washington, DC

Photograph 3: Ventilation Opening—Crawlspace has plenty of cross ventilation and good drainage.

Think of the good old days—the Civil War, WWI, the Great Depression, WWII—crawlspaces were uninsulated. They were ventilated and they didn’t have ground covers—and they didn’t have problems. Why? The floor framing was pretty much always warmer than the ground (Figure 1). Everywhere, even in air-conditioned buildings. This was a pretty big deal as the temperature of the floor framing was above the dew point temperature of the exterior air that was used for “ventilation.” And the old floor finishes tended to breathe—they were relatively vapor open. No one had heard of vinyl flooring yet.

Figure 1: Old Crawlspaces—Old uninsulated and ventilated crawlspaces had warm floor assembly surfaces due to heat flow downward from occupied space above.

The ground in crawlspaces is cold,1 much colder than the outside air during the summer months. In an irony not appreciated except by building science geeks ventilation air in the summer months in most parts of North America brings moisture into crawlspaces and deposits this moisture on surfaces that are below the ventilation air dew point. In the good old days this was the ground—or the ground cover which of course is at the same temperature as the ground. It was not typically the floor framing. And who cared if the ground or the ground cover was wet as long as the wood framing was not.

We don’t get much ventilation air change in crawlspaces—the typical ventilation air change rate in a crawlspace is approximately 1 air change per hour (ach).2 In determining crawlspace surface temperatures we can pretty much ignore the ventilation air change.3 We can’t ignore the ventilation air in the moisture balance but we can in the energy balance. Crawlspace surface temperatures are dominated by radiation and conduction, not by convection (Figure 2). And, as pointed out, old crawlspace floor framing was not only warmer than the ground but also warmer than the ventilation air dew point.

Figure 2: Old Crawlspace Temperatures—Surface temperatures are dominated by radiation and conduction, not by convection. Old crawlspace floor framing was not only warmer than the ground but also warmer than the ventilation air dew point.

That all changes when we install insulation in crawlspace floor framing. The most common insulation installed in this location are fiberglass batts. When fiberglass batts are installed between floor joists the exposed bottom edges of the floor joists become much colder (Figure 3). The surface temperature of the underside of the fiberglass batt insulation is also much colder than the floor sheathing—within one or two degrees of the ground temperature. The energy picture within the crawlspace is radiation dominated—the floor assembly surfaces are in essence radiation coupled to the ground. The exposed surface of the fiberglass batt insulation is below the dewpoint temperature of the air in the crawlspace as is the exposed portion of the wood floor joists and condensation forms on both the surface of the insulation and the surface of the exposed wood (go to Photograph 1 again).

Figure 3: Insulated Crawlspace Temperatures—The surface temperature of the underside of the fiberglass batt insulation is colder than the floor sheathing—within one or two degrees of the ground temperature. The exposed surface of the fiberglass batt insulation is below the dewpoint temperature of the air in the crawlspace as is the exposed portion of the wood floor joists and condensation forms on both the surface of the insulation and the surface of the exposed wood.

Now let’s look at the wood floor joist moisture content. Wood is hygroscopic—it “sees” relative humidity not vapor pressure. So we are going to need a psychrometric chart and a sorption curve for wood. The temperature of the wood floor joist is 75 degrees F at the top (i.e. interior temperature). We have to figure out the crawlspace conditions. The air in the crawlspace comes from the outside—who knew? Let’s pretend that this particular crawlspace is in Washington, DC. The average dew point of the exterior air during the summer months in Washington, DC is 65 degrees. Let’s bring this air into the crawlspace—so therefore the dew point of the air in the crawlspace is 65 degrees. Recall that the top of the floor joist is 75 degrees. The floor joist sees the dew point of the air in the crawlspace (we can ignore the vapor permeance characteristics of the fiberglass batt insulation since it is so vapor open—just pretend that we have air rather than insulation here—but not just any air—air with a huge temperature drop— “insulating air”), but because the floor joist is 75 degrees at this location, the relative humidity at this location is 70 percent yielding a wood equilibrium moisture content of 13 percent. The floor joist is “dry” at the top and “wet” at the bottom. Why wet at the bottom? The surface of the wood is cold, below the dew point of the air in the crawlspace and therefore condensation forms on the wood. At fiber saturation the moisture content of wood is 28 percent (go to Figure 3 again).

The wood floor joist moisture content increases in the downward direction as the wood becomes progressively colder (Figure 4). Another way of saying this—the warmer the wood, the drier the wood. Duh. If we were to wrap the floor joists completely with insulation we would warm up the wood thereby lowering the relative humidity the wood “sees” thereby lowering the moisture content. This is a pretty neat strategy that I will refer to later. So how low do we need to lower the moisture content of the wood? Below 19 percent to never see rot. Below 16 percent to never see mold. We could do this a couple of ways. One way is with spray foam insulation (Figure 5).

Figure 4: Moisture Dynamics—The wood moisture content increases as we move down the floor joist. At the same time the vapor drive is upward. The entire shaded area “sees” the same vapor pressure (dewpoint) due to the vapor openness of the fiberglass insulation. The entire vapor resistance is at the floor sheathing and flooring. If only the floor could breathe…it used to in the old days when we had wood floors and not vinyl…

Storm and/or Flooding Damage? Insurance Claim?

2010-01-01T15:05:00.000-08:00

Did you experience flood or storm damage?

We are trained infrared camera inspectors that can pinpoint water intrusion, find moisture beneath the surface, and document dryness with accuracy and confidence.

Our trained IR Inspections will find moisture that
your insurance adjuster won't.

Mold growth in buildings can lead to a variety of health issues.
http://www.epa.gov/mold/moldguide.html

Our IR Inspections will maximize your insurance claim.

Protect your home and your health.

IR Camera Inspections; Air Infiltration, Roof Leaks, Moisture Problems

2009-12-27T11:08:00.000-08:00

Infrared Camera Inspections

Our Services Include the Following:

Building and Roofing Moisture and Missing Insulation Issues

Leak Detection on Commercial Roofs

Find Missing Insulation

Advanced Energy

2009-12-26T16:00:00.000-08:00

Crawl Spaces

Many homes built on crawl space foundations in the Southeastern United States suffer from poor moisture management. Some of the common symptoms of a crawl space moisture problem are:

Mold or moisture damage in the crawl space or living area
Musty odors in the living area
Condensation ("sweating") on air conditioning ductwork or equipment
Condensation on insulation, water pipes or truss plates in the crawl space
Buckled hardwood floors
High humidity in the living area
Insect infestations
Rot in wooden framing members

These symptoms are most often noticed in the humid spring and summer seasons but can occur at any time of the year. Often, the heating and air conditioning contractor is the first person the residents call to deal with the problem. Typically though, the problem is not due to a failure of the air conditioning system; it results from poor moisture control in the crawl space.

For many decades, building codes and conventional wisdom have prescribed ventilation with outside air as the primary method of moisture control in crawl spaces. In the humid Southeast, however, ventilation with outside air only makes moisture problems worse. Recent research by Advanced Energy and others indicates that a new type of crawl space system, with NO vents to the outside, can provide greatly improved moisture control and significant energy savings when properly installed.

We hope this information can help you to improve your existing crawl space or to design and install a properly-closed new crawl space.

PierTech Systems Hercules Pile Video

2009-12-26T15:33:00.000-08:00

PierTech Systems launches its groundbreaking Hercules Pile, the first piering product of its kind suitable for heavy duty applications. The patented high-strength, high-capacity pile is available in both round and square shaft.

PierTech Systems Video

2009-12-26T14:44:00.000-08:00

Find out how PierTech’s unique foundation solutions are used in residential, commercial and industrial applications. The huge range of piering products and concrete repair systems designed and manufactured by PierTech have played a crucial role in some of the most demanding construction problems you’ll ever face.

Foundation Solutions; Residential, Commercial and Industrial

2009-12-26T14:27:00.000-08:00

We are now a dealer for Pier Tech Systems

PierTech Systems is your permanent foundation specialist. From helical piers and helical anchors to complete tilt-up construction applications, we provide the construction industry with the highest quality, most versatile and economical permanent foundation and soil stabilization products.

Our helical piers and helical anchors are suitable for both residential and commercial applications. So from the smallest cracked wall to industrial grade towers, dry and wetland boardwalks, deep foundation piers for new construction and underpinning for commercial and residential buildings, PierTech Systems is the manufacturer of choice for thousands of engineers throughout the World.

Using ground-breaking, patented technology, PierTech Systems produces its own line of purposefully designed cross-bolt technology, helical anchors, and helical piering systems in both round and square shafts. Tie downs, tie backs and tilt up products are made from the strongest steel, quality controlled, and backed by the Pier Tech Systems commitment to performance and reliability.

With a product line that consists of galvanized round shaft Helical Piers, 2 7/8” - 12 3/4”, and square shaft Helical Anchors, 1 1/4” - 2”, no job is either too BIG or too SMALL. PierTech Systems carefully selects and trains each distributor and dealer in our organization.

We take pride in the fact that our network of people are highly experienced, and strive to serve the customer with integrity.

PierTech Systems is your permanent foundation solution.

Before and After

2009-11-13T11:55:00.000-08:00

New Website Online

2009-11-13T11:46:00.000-08:00

www.crawlspacesystems.net

Closed Crawl Space by Crawl Space Systems

2009-09-28T07:52:00.000-07:00

We are a Certified Green Professional

2009-06-21T07:04:00.000-07:00