Water Protection and Exterior Basement Insulation

Basement are increasingly used as living space. Yet the way most builders build basements has not changed from the days they were nothing more then foundations and cold cellars.
Basements insulated on the exterior not only create warm interior space, but also solve many basement moisture problems. Exterior basement insulation provides thermal resistance between the soil and the interior, keeping the foundation wall warmer, and protects the structure from moisture in the wet soils, and from heaving and adhering soils due to the frost action.  Exterior basement insulation also provides a means of water management at the surface between the soil and the insulation and helps the structure to dry out. 
Rigid foam and rigid fiberglass insulation are the most commonly used exterior basement insulation. It is also possible to use spray - in - place foam insulation applied to the outside of the basement walls. 
Spray - in - place foam insulation on the exterior of the basement walls may seem an unusual application of the product but it can be used successfully for moisture management of foundations. The Canadian Urethane Foam Contractors Association did a two year research project to test the performance of exterior basement insulation products in contact with the ground.
The weather during the test period went to several extremes, included record rains and winter thaws. To create a worst case saturation, the soil at grade was sloped 5% toward the wall to simulate a settled condition.
As expected, water was observed at the outer surface of the foam insulation during the periods of heavy rain and major thaws throughout the two year period. Over the same period, the outside face of the concrete (inside the insulation) showed no evidence of water penetration through the insulation layer. 
After 31 months of exposer in the soil, samples of the foam insulation were analyzed. Its performance did not change, and the measured values of the water permeability matched published values. The insulation was not affected by water movement over the exterior face. 
However, the foam must be protected at grade and above. Once the insulation was in place, cementations boards were fastened to z-bars and a wood spacer. No other fasteners were used, so the cementations board was effectively “cantilevered” over the insulation specimens.
Damp-proofing, which is not water-proofing as many think, should not be needed with a spray - in - place foam insulation strategy. Damp - proofing is applied to create a capillary break in the concrete surface, but with a spray foam insulation it is the insulation that provides the moisture protection as well.
The tests confirmed the moisture management capabilities of unprotected spray polyurethane foam insulation. The thermal performance does not change and the material does not absorb water

SOLPLAN REVIEW 
September 2001