Gaps, voids, and compressions that cause the insulation to lose contact with the surface it is intended to insulate can cause cold spots in walls, ceilings, and floors. These cold spots may encourage the formation of condensation in the wall cavity, floors, or ceilings. 

The Residential Energy Services Network (RESNET) grades insulation installation quality in its Home Energy Rating System Standards, with Grade 1 being the best installation (RESNET 2013).

Grade 1 Installation requires that insulation material should uniformly fill wall cavities, filling each cavity from side to side and top to bottom, without substantial gaps or voids around obstructions. Batt insulation should be cut to fit around any wiring or piping installed in the wall cavities.

Blown insulation, such as loose fiberglass, cellulose, or mineral wool fibers, flows easily around obstructions, such as wiring and piping, to provide complete coverage in the cavities. To install blown insulation, the open cavities are first covered with a netting that is stapled to the stud faces. A slit is cut in the netting in each cavity and the insulation is installed with a hose inserted through the slit. The installer can easily see where the insulation is going to ensure that each cavity is completely filled without voids.

Spray foam is another option that readily fills areas around obstructions in wall cavities, and it has the advantage of providing both air sealing and insulation. The foam completely fills the open wall cavities and is trimmed flush with the stud faces before installing dry wall. Spray foam insulation is made of petroleum, soy, or castor oil-based polyurethane and is available in open-cell, low-density products or closed-cell, high-density products. Both insulate and air seal; high-density products can also provide a vapor barrier. Another option is sprayed-on cellulose or mineral wool that is mixed with adhesive and water then sprayed into the open cavities and allowed to dry before drywalling.

Additional information about insulation, including descriptions of the many types of insulation available, their R-values, applications and advantages and disadvantages of each kind, and installation guidance can be found in the Building America Best Practices Series Volume 17: Insulation, A Guide for Contractors to Share with Homeowners.  

How to Install Insulation to RESNET-Defined Grade I 

1. Install insulation without misalignments, compressions, gaps, or voids in all wall cavities along the thermal barrier of the house. Figure 1 shows proper installation of batt insulation without gaps or voids. Figure 2 shows incorrect installation; the insulation was not cut to fit around wiring so the insulation will not be in full contact with the drywall along the length of the wall cavities.

   

   

2. Install wall insulation so that it is enclosed on all six sides in each wall cavity. It should completely fill the wall cavities as shown with the blown fiberglass insulation in Figure 3, the blown cellulose in Figure 4, and the spray foam in Figure 5. It should be in substantial contact with the sheathing material on at least one side (interior or exterior) of the cavity.

   

    

   

    

   

3. Faced batt insulation should be stapled to the surface of framing (Figure 6). Side-stapling is permitted, provided the tabs are stapled neatly (no buckling), the batt is only compressed at the edges of each cavity to the depth of the tab itself, and the batt meets the other requirements of Grade I.

   

4. Install slab edge insulation for slab-on-grade floors if the floor surface is less than 12 inches below grade and if required by code in your climate zone. Slab insulation should extend to the top of the slab to provide a complete thermal break (Figure 7). If the insulation is installed between the exterior wall and the edge of the interior slab, the insulation may be cut at a 45-degree angle away from the exterior wall, allowing the poured slab concrete to cover and protect the top edge of the insulation.
   Insulating the slab edge will keep the floor warmer and reduce the potential for condensation and elevated relative humidity by allowing the inside surface temperature of the slab perimeter to more closely track the home’s interior temperature. If the slab is monolithic with a grade beam (Figure 7), the insulation is installed on the exterior of the slab edge/grade beam and continues vertically to the bottom of the grade beam. Use insulation material that is appropriate for ground contact such as XPS, rigid fiberglass, or rigid rock wool and use insect controls appropriate for the region. The above-ground portion of the rigid foam should be protected from UV and impact damage with coated fiber cement board.

   

   
   
   When the slab is independent from the perimeter foundation wall, insulation may be installed either on the exterior of the foundation wall or between the foundation wall and the slab (Figure 8), which provides more protection for the insulation from the elements. When the insulation is between the foundation wall and the slab, it forms a bond break and it should also extend horizontally under the slab either at the perimeter or under the entire slab.

   

5. Where an insulated wall separates a garage, patio, porch, or other unconditioned space from the conditioned space of the house, install slab insulation to provide a thermal break between the conditioned and unconditioned slab. Where specific details cannot meet this ENERGY STAR Ver. 3, Rev 11. requirement, provide the detail to EPA to request an exemption prior to the home’s qualification.