Slab and Slab Edge Insulation

In cold climates careful consideration should be placed on how the building foundation will be insulated to limit heat transfer to and from ambient temperatures. The majority of heat loss through a slab occurs at the perimeter, as this is the portion most exposed. By properly addressing the ‘thermal bridging’ between your slab and the ground, expensive heat loss can be avoided. For more detailed information referencing a variety of foundation and footer designs, see this PDF deck : How to Properly Insulate a Slab by Mike Turns, PHRC.

 

Stretch Code & 2018 IECC Required Slab Insulation

The MA Stretch Code requires that on-grade slabs are insulated at the edge. We recommend insulating completely under all slabs that are beneath conditioned space.


[2018 IECC COde excerpt here]

 

If the slab is independent of the foundation wall, follow these steps:

  1. Make sure the slab is insulated vertically at the edge and horizontally at the perimeter or under the entire slab.

  2. Install the rigid insulation to provide a bond break between the slab and foundation wall.

  3. Ensure the protective membrane is adhered to both the slab and top of foundation wall.

  4. Whenever insulation is used in contact with ground or near ground, appropriate insect control measures must be used (BSC 2009).

 

If the slab is monolithic, follow these steps:

  1. Install rigid insulation on the exterior that extends to the bottom of the grade beam.

  2. Secure a protection board over the above-grade portion of the rigid insulation.

  3. Make sure the protection board is of non-water-sensitive material and coated to control absorption of water.

  4. Install a protective membrane adhered to the slab and wrapped over the top of the insulation.

  5. Ensure that insulation material is non-moisture-sensitive and not subject to degradation with ground contact.

Examples of slab and edge insulation

From Building Science Corporation BSI-059 “Slab Happy”

 
Proper insulation placement when the slab is independent of foundation walls.

Proper insulation placement when the slab is independent of foundation walls.

 
monolithic slab insulation detail

Monolithic slab with rigid insulation on the exterior of the slab extending fully from the bottom to the top of the concrete.