Crawl Space Drying >> Put A Moisture Barrier In The Crawl Space Under A

To further separate the conditions in the crawl space from those of the outside, mechanical drying systems such as a stand-alone dehumidifier should be used (Dastur et al. 2005). All water discharge from appliances should be terminated to the outside or to a sealed sump. Put A Moisture Barrier In The Crawl Space Under A All kitchen and bathroom exhaust vents should terminate to the outside. 

If fuel-fired appliances are used and located in an unvented crawl space, ensure that their air intake and exhaust are both routed directly to the outside. Put A Moisture Barrier In The Crawl Space Under A Although a crawl space foundation is not as deep as a full basement, it is highly desirable to keep it dry. 

Good surface drainage is always recommended and, in many cases, subsurface drainage systems may be desirable. Put A Moisture Barrier In The Crawl Space Under A The goal of surface drainage is to keep water away from the foundation by sloping the ground surface and using gutters and downspouts for roof drainage. Figure 3-3, 3-4, and 3-5 describe three different drainage techniques for crawlspaces. 

Figure 3-3 applies when the crawlspace floor is flush with (or above) the surrounding grade. In most cases, this type of crawlspace will not require perimeter drainage. Put A Moisture Barrier In The Crawl Space Under A On especially wet sites, or on sloping sites where part of the crawlspace floor is below-grade, it may still be wise to install a perimeter drain system, described below. 

Figure 3-4 and 3-5 describe foundation drain systems, Put A Moisture Barrier In The Crawl Space Under A which are recommended for all crawlspaces where the floor is below the level of the surrounding grade. On especially dry sites, it may be possible to eliminate the drainage system and not experience moisture problems. Figure 3-5 describes the recommended best practice. 

It consists of two independent loops of perforated foundation drain, one inside the footing and one outside. These drain independently, either to daylight or to an internal sump. Figure 3-4 shows another option that is appropriate when site drainage conditions are good. Put A Moisture Barrier In The Crawl Space Under A There is no provision for drainage of the space inside the footings. 

Its single loop of foundation drain is on the outside of the footing, and drains to daylight or to an internal sump. Another important factor to consider when managing moisture in a crawl space is the way it is to be insulated. Put A Moisture Barrier In The Crawl Space Under A Crawlspaces can be insulated at the exterior walls, or vented and insulated at the crawlspace ceiling (Figure 3-6). 

Insulation not only plays a role in the thermal efficiency of a home but also in the way that moisture behaves. Put A Moisture Barrier In The Crawl Space Under A Cooler surfaces in a crawl space can cause moisture from the air to condense on the surfaces. For unvented crawl spaces, the best approach is to treat the crawlspace as a short basement, placing insulation on the exterior or interior surface of the crawlspace walls. 

Research has shown that closed crawl spaces with wall insulation perform better than wall-vented crawl spaces with ceiling insulation (Dastur et al. 2005). Put A Moisture Barrier In The Crawl Space Under A A key question in the design of an unvented crawl space is whether to place insulation inside or outside the wall. 

In terms of energy use, there is not a significant difference between the same amount of insulation applied to the exterior versus the interior of a concrete or masonry wall. Put A Moisture Barrier In The Crawl Space Under A However, the installation costs, ease of application, appearance, and various technical concerns can be quite different. 

Rigid insulation placed on the exterior surface of a concrete (Figure 3-6a) Put A Moisture Barrier In The Crawl Space Under A or masonry wall has some advantages over interior placement in that it can provide continuous insulation with no thermal bridges, protect structural walls at moderate temperatures, and minimize moisture condensation problems. 

If the exterior insulation value is high enough, the joists and sill plates can be left open to inspection from the interior for termites and decay. Put A Moisture Barrier In The Crawl Space Under A On the other hand, exterior insulation on the wall can be a path for termites and can prevent inspection of the wall from the exterior. 

If needed a termite barrier should be installed through the insulation where the sill plate rests on the foundation wall. Put A Moisture Barrier In The Crawl Space Under A This option is shown in all drawings that depict exterior crawlspace foundation insulation. Vertical exterior insulation on a crawl space wall can extend as deep as the top of the footing.

If desired, be supplemented by extending the insulation horizontally from the face of the foundation wall. Insulation that is exposed above grade must be protected with a coating to prevent physical damage and degradation. Put A Moisture Barrier In The Crawl Space Under A Such coatings include fiber cement board, parging (stucco type material), treated plywood, or membrane material (Baechler et al. 2005). 

Exterior wall insulation must be approved for below-grade use. Typically, three products are used below grade: extruded polystyrene, expanded polystyrene, and rigid mineral fiber panels. Put A Moisture Barrier In The Crawl Space Under A (Baechler et al. 2005). Extruded polystyrene (nominal R-5 per inch) is a common choice. 

Expanded polystyrene (nominal R-4 per inch) is less expensive, but it has a lower insulating value. Below-grade foams can be at risk for moisture accumulation under certain conditions. Put A Moisture Barrier In The Crawl Space Under A Experimental data indicate that this moisture accumulation may reduce the effective R-value as much as 35%-44%. 

Research conducted at Oak Ridge National Laboratories studied the moisture content and thermal resistance of foam insulation exposed below grade for fifteen years; Put A Moisture Barrier In The Crawl Space Under A moisture may continue to accumulate and degrade thermal performance beyond the fifteen-year time frame of the study. 

This potential reduction should be accounted for when selecting the amount and type of insulation to be used (Kehrer, et al., 2012, Crandell 2010). Put A Moisture Barrier In The Crawl Space Under A Rigid fiberglass and rigid mineral wool panels (R-4 per inch) do not insulate as well as extruded polystyrene, but are the only insulations that can provide a drainage space for foundation walls because of their porous structure. 

Insulation that is exposed above grade must be protected with a coating to prevent physical damage and degradation. Put A Moisture Barrier In The Crawl Space Under A Such coatings include fiber cement board, parging (stucco type material), treated plywood, or membrane material (Baechler et al. 2005). 

Interior crawl space wall insulation (Figure 3-6b) is more common than exterior, primarily because it is less expensive since no protective covering is required. Put A Moisture Barrier In The Crawl Space Under A On the other hand, interior wall insulation may be considered less desirable than exterior insulation because it (1) increases the exposure of the wall to thermal stress.

Freezing may increase the likelihood of condensation on sill plates, band joists, and joist ends, (3) often results in some thermal bridges through framing members, and Put A Moisture Barrier In The Crawl Space Under A may require installation of a flame spread resistant cover. 

Interior insulation is not recommended on non-core filled masonry block walls, due to an increased risk of moisture accumulation within the assembly. Materials that are resistant to moisture damage are recommended for use in contact with concrete foundation components. Put A Moisture Barrier In The Crawl Space Under A Rigid foam plastic is typically used to insulate the walls of unvented crawlspaces (Figures 3-7 and 3-8). 

In areas not prone to termite infestation, rigid foam should be installed and sealed at the rim joist to prevent entry of moist air into the wood structural components. Put A Moisture Barrier In The Crawl Space Under A This air barrier is especially critical in cold climates, and when exterior insulation is not installed. 

Batt insulation should only be used at the rim joist where access is required for termite inspections. Put A Moisture Barrier In The Crawl Space Under A Expanded or extruded polystyrene rigid foam insulation should be used to cover the walls and attached with mechanical fasteners. 

A three inch wicking gap should be left between the wall insulation and the ground, and a three inch termite inspection gap or continuous termite shield should be present at the top of the wall and the sill plate (Marshall 2008). Put A Moisture Barrier In The Crawl Space Under A An ignition barrier or fire barrier may be required, based on code jurisdiction and occupancy.

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