The concept is excellent: a three-in-one energy-efficient and labor-saving product able to provide 1) packed insulation for exterior walls, 2) moisture protection and 3) structural strength.
The product is called EIFS (Exterior Insulation and Finish System) or Synthetic Stucco... But is it as good and as energy efficient as it seems?
Let's begin by looking at its three components, before weighing its pros and cons:
- the energy-efficient insulation board is made from polyisocyanurate foam or from polystyrene; this board is attached to the wall surface using mechanical attachment or proprietary adhesives.
- the water-resistant base coat is applied on the top of the insulation board; this coat is typically reinforced with fiberglass mesh to provide strength to product.
- an acrylic co-polymer finish coat (available in multiple possible colors, textures and designs);
For more details on what EIFS stucco is, see this EIMA pdf.
EIFS manufacturers and installation rules
- Manufacturers: Dryvit, Senergy and Sto and BASF;
- Design and installation are extremely important for effectiveness.
- Installation requires trained contractors.
- The NAHB Quality Control Plan should be followed.
- For project and installation checklists, use the NAHB Research Center guides. See also: EIFS Industry Manufacturers Association (EIMA)
Most EIFS products use insulation board with an R-value that ranges between R-4 to R-5.6 per inch. And since the typical thickness of EIFS amounts to 3/4 to 4/4 inches, EIFS boards will increase the insulation value of walls by about R-4 to R-5.6 (thicker pieces of EIFS, called foam shapes, are rarely used).
And the meaning of all this is obvious: EIFS provide reasonable or good insulated sheathing; EIFS can minimize thermal bridging and boost the overall insulation performance of the wall (obviously, it doesn't replace stud/cavity insulation).
Alone, EIFS boards do not provide the insulation-value required by energy-efficiency standards. Highly energy-efficient walls require an R-value around 10-20 (hot and moderate climates), 40 (cold-climates) or 50 (super-insulated homes), and EIFS boards fall short of it...
EIFS can be excellent
to improve the energy-performance of exterior walls.
Expect prices between $8 to $16 per square foot.
EIFS are difficult to install.
There are serious doubts about their performance in cold climates.
EIFS do not replace cavity insulation.
EIFS can be an effective product, able to minimize thermal bridging through studs or ducts or other elements of the walls.
The advantages of EIFS stucco are significant; the labor-savings and their flexibility are unquestionable.
Besides, manufacturers are now offering drainable EIFS, to tackle moisture problems. Older EIFS systems (often called simple EIFS systems) were very resistant to water penetration through their outer surface but did not respond properly to infiltrated water.
Anyway, there are concerns that remain unresolved, and that you should take into consideration. Empirical evidence shows some weak points that should not be underestimated (the product is being installed since the 1950s in Europe and the 1980s in North America).
EIFS cons: Moisture problems
So, let’s look more closely and see what experts are saying about EIFS. Are EIFS environmentally-friendly?
EIFS are often considered an eco-friendly product; their acrylic polymers are made from natural materials, and the manufacturing process yields a relatively small environmental impact.
First of all, EIFS are difficult to install. The ambient temperatures in the moment of construction matter (see this document from BASF) and the product should not be installed by untrained contractors. Manufacturers require EIFS to be installed only by experienced applicators, with a complete EIFS training program.
But, most of all, their effectiveness and water-resistance in cold climates is often questioned. Manufacturers and associations claim that problems in these areas are due to poor installation; on the other hand, experts agree that EIFS are a reliable product in dry climates - though not necessarily in cold-rainy climates, in buildings very exposed to harsh conditions.
Prices - expect prices between $8 to $16 per square foot - and doubts about the performance of EIFSs in cold climates make them a disputable choice.