{"id":203344,"date":"2023-02-03T09:02:34","date_gmt":"2023-02-03T14:02:34","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=203344"},"modified":"2023-05-17T15:43:36","modified_gmt":"2023-05-17T19:43:36","slug":"insulations-crucial-role-in-creating-habitable-basements","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/insulations-crucial-role-in-creating-habitable-basements\/","title":{"rendered":"Insulation’s crucial role in creating habitable basements"},"content":{"rendered":"

\"\"<\/a>By Mike Fischer<\/strong><\/p>\n

One of the first questions to be asked when designing a basement foundation is \u201cwhat is the desired functionality of the basement?\u201d On one end of the spectrum, a basement may provide comfortable, fully habitable spaces comparable to the above-grade portions of the building (Figure 1). In the middle of the spectrum, the basement may be less habitable than the main living areas. In other words, it will be cold in the winter and damp during much of the year. On the far end of the spectrum, the basement may serve as a structural foundation only and nothing more.<\/p>\n

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In their study, Swinton and Kesik list service criteria and limitations\/allowances for different classes of basements.1<\/sup> According to their classification system, Class A basements provide a below-grade living space comparable to the living space of the floors above. To ensure long-term performance, the design and construction of Class A basements must be virtually defect-free and provide critical, redundant moisture control measures.<\/p>\n

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Figure 1 The successful realization of a habitable basement requires careful attention to design details. <\/span> Photo \u00a9 Adobe Stock\/courtesy Extruded Polystyrene Foam Association (XPSA)<\/em><\/span><\/figcaption><\/figure>\n

They emphasize the construction of a comfortable and habitable basement (i.e.<\/em> a Class A basement), which requires much more attention to the components and the system design compared to the design of basements not intended to be used as living spaces. There may also be health and safety requirements, as well as HVAC requirements, which go beyond the scope of the 2005 report by Swinton and Kesik.<\/p>\n

Thermal control challenges<\/strong><\/p>\n

Aside from the structural challenges, the thermal challenges for basements include the following functions: (1) facilitating moisture drainage at the face of the exterior insulation down to the foundation drainage system, (2) keeping temperature extremes outside the basement wall, especially cold temperatures, and (3) preventing condensation of the basement air onto the interior of walls in the basement. Insulation strategically placed on the exterior side of the foundation plays an important role in each of these objectives (Figure 2).<\/p>\n

Facilitating movement of exterior moisture to the foundation drainage system in basements<\/em><\/p>\n

In an NRC Institute for Research in Construction (NRC-IRC) Technology Update,2<\/sup> Swinton et al., describe their approach to managing water exposure to basements is in terms of \u201ctwo lines of defense\u201d:<\/p>\n

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Figure 2 Exterior insulation and damp-proofing or waterproofing along with effective drainage helps prevent water intrusion into the basement. <\/span>Photo courtesy Kingspan <\/em><\/span><\/figcaption><\/figure>\n

The most effective strategy for managing water is to provide two lines of defense. When exterior basement insulation is used, the first line of defense is the exterior surface of the insulation, which supplies a continuous means of managing water from the ground surface down to the gravel and drainpipe at the footing. The second line of defense is the outer face of the foundation (cast-in-place concrete, concrete block, or wood sheathing in a permanent wood foundation), which can handle the incidental quantities of water that may get by the first line of defense.<\/p>\n

Since 1999, much research has been dedicated toward accumulating valid experimental data on how insulations perform when placed on the outside of a basement wall in contact with the earth, and when insulation is placed beneath floor slabs. The continuous monitoring of the thermal performance of 13 different basement insulation systems by the NRC-IRC throughout two heating seasons provided some answers.3<\/sup><\/p>\n

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The military \u201ctwo lines of defense\u201d analogy in the IRC Technology Update is apt. The outer lines of defense are expected to protect against liquid water penetration. This outer layer is sometimes referred to as \u201ceffective environmental separation.\u201d If the first line of defense allows liquid water to reach the second line of defense, then the second line must provide some protection against liquid water penetration. In this case, the basement certainly could not be considered a Class A basement.<\/p>\n

Drainage does more than just helping in preventing leaks through the basement wall. It helps to address potentially significant reductions in R-values of insulation (up to 50 percent) due to water absorption and retention; refer to the section \u201cGetting practical\u201d later in this article. However, water drainage does not address the negative effects of water absorption on R-value entirely.
\nIf liquid water and water vapor are not properly managed, the insulation R-value is reduced.<\/p>\n

To summarize, the defense against liquid water for the structural foundation is an applied layer of damp-proofing or waterproofing. The defense against liquid water for exterior insulation is to assume a reduced R-value and increase the thickness of the insulation accordingly and provide proper drainage of water. Highly water absorbent insulation materials are impractical for this application because of the dramatic drop in R-value (due to the presence of water) and reduced longevity after repeated freeze-thaw cycles over the life of the building. Lower absorption insulations, such as polystyrene foam are favored exterior insulation materials, and polystyrene foam (i.e.<\/em> extruded polystyrene [XPS] or expanded polystyrene [EPS]) should have their thickness increased based on reliable data from long-term, in-service studies. Facers could be used to mitigate water absorption in the insulation, but the facers may eventually be compromised over the life of the building, and the insulation thickness adjustment, nonetheless should be applied.<\/p>\n

Keeping temperature extremes outside, especially cold temperatures<\/em><\/p>\n

Structural materials typically perform rather poorly in keeping heat and cold outside. On the contrary, insulation plays a significant role in decreasing heat transfer through basement walls and floors. Heat from the interior of the basement can quickly transfer through basement walls in contact with the surrounding soil if the basement is not sufficiently insulated on the walls below grade.<\/p>\n

Insulation of basement walls above-grade and insulation beneath the floor slab are also important in managing basement temperatures, especially when the intention is to create a habitable space. Basement insulation moderates the surface temperatures of basement walls and floors. As for sustainability objectives, insulation reduces the environmental footprint and energy costs by decreasing the heat transfer which occurs in the heating and cooling of basements.<\/p>\n

The placement of the insulation on either the interior or exterior of the wall (or both) makes a difference in human comfort. When the interior surface of the basement wall is warm, it feels much more comfortable to the occupant. Placing the insulation on the exterior side of the basement wall keeps its wall surface temperature closer to the overall interior temperature of the room.<\/p>\n

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\"\"<\/a>XPS and EPS do not have the same thermal resistance and are impacted differently by the presence of moisture. R-values for XPS and EPS insulation are listed in Table 1. The \u201cdry\u201d EPS and XPS insulation values are what is shown on the insulation label and literature. The \u201cwet\u201d insulation values for EPS and XPS are building code approved reduced R-values that assume long-term water absorption over the life of the building. The \u201cwet\u201d insulation values for XPS includes the effects of both moisture and aging.<\/p>\n

Preventing condensation of interior moisture in the basement<\/em><\/p>\n

Once the basement wall is protected from liquid water penetration, it is also necessary to protect the basement wall from the condensation of water vapor in the air space. Figure 3 shows various basement wall materials. If the basement wall has already been compromised by a failure to provide protection from bulk water, then such additional measures will not be very effective (Figure 4). In this sense, the basement wall assembly is a system of components, and each component must be free from defects. No one element is independent of the others.<\/p>\n

Basements may be prone to high humidity; interior moisture often is removed using dehumidifiers but it is not a complete solution. If thermal conduction between the masonry or concrete walls and floors to the surrounding soil is excessive, then the masonry or concrete may become cold enough for moisture condensation even at moderate humidity levels.<\/p>\n

When moisture condenses on or is absorbed into concrete walls and concrete floor slabs, basements can become cold, dank, and musty (Figure 5). The most reliable long-term solution to prevent condensation is to maintain concrete wall and floor temperatures well above the dew point of the ambient air in the basement space. In this manner, condensation on the concrete wall and floor slab can be avoided.<\/p>\n

Depending on the types of insulation and the quantity and locations of it on the basement walls and floor, insulation can have a positive effect on managing the condensation of interior moisture.<\/p>\n

Exterior or interior insulation?<\/strong><\/p>\n

Considering all the above thermal challenges, a good question to ask is, \u201cwhere should the insulation be placed relative to the basement walls and floors?\u201d<\/p>\n