Veneer Wall: Concrete Block Veneer/Reinforced Concrete Block

• Schools, commercial and institutional buildings
• Buildings requiring a high fire rating
• Noisy environments
• Areas with frequent rainfall

• Most economical of all masonry cavity wall systems
• Tough, beautiful concrete block exterior over a structural backup system
• Extremely durable, long-lasting wall system
• Minimal long-term maintenance
• Great design flexibility with many colors, textures and bond patterns available
• Concrete block backup acts as the structure, with vertical and horizontal reinforcement grouted into place
• Less flexible, less prone to rot and rust than a wood-stud or steel-stud backup wall 
• Cavity system inherently weatherproof – great for moist environments
• Excellent insulating value and heat capacity
• Inherently fireproof with fire ratings up to 4 hours
• Great for noisy environments – naturally absorbs sound
• One trade erects both the structural and skin layers of the wall

• Lower life cycle costs offset a somewhat higher initial investment
• This substantial wall system may require larger foundation

• Backup: Lightweight plain gray concrete block (CMU), 8” x 8” x 16” (nominal)
• Vertical Reinforcement: #6 vertical reinforcement @ 32” on center
• Horizontal Reinforcement: 9-gauge joint reinforcement @ 16” on center (Reference: Colorado Masonry Systems Design Guide, Chapter 6, Table 6-4)
• Veneer: Decorative concrete block veneer, (nominal 4” x 8” x 16”)
• Cavity: 4-inch air space (2” filled with insulation, 2” open)
• Insulation: 2-inch rigid extruded polystyrene in the drainage cavity (Reference: Colorado Masonry Systems Design Guide, Chapter 8, Table 8-3)
• Flashing: Self-adhered bitumen flashing paired with a termination bar at the top edge and a metal drip edge at the face of the wall (Reference: Colorado Masonry Systems Design Guide, Chapter 6, Shelf Angle Flashing Options, Fig.6-3 (Option 2))
• Masonry Ties: Eye and pintle joint reinforcement @ 16” on center, vertically
• Mortar: Type N, Portland cement/lime, plain gray
• Joints: Concave tooled

• In areas with high seismic risk, masonry ties and anchors might have special requirements. Check your local building codes.
• In high seismic zones, the CMU back-up wall is required to have additional horizontal bond beams to resist earthquake loads. Check with your structural engineer to verify requirements in your area. These bond beams can take the place of horizonal reinforcement in the structural back-up. Horizontal reinforcement is still required in the veneer to resist shrinkage.

• Fire Rating of a multi-layered cavity wall = (Rating₁ ^0.59 + Rating₂ ^0.59 + 0.3)^1.7
• CMU grouted @ 32” on center: 4 hours
• CMU fully grouted: 4 hours

Reference: NCMA TEK Manual 07-01D

• CMU veneer + CMU Grouted @ 32″ on center:  59 pounds per square foot
• CMU veneer + fully grouted CMU:  94 pounds per square foot

• STC = (weight of wall)^0.233 x 21.5
• CMU grouted @ 32” on center: STC = 55.60 dB
• CMU fully grouted: STC = 61.97 dB

• R-value: 17.68
• Calculations
  • Outside air film                                          0.17
  • Lightweight CMU veneer                          3.86
  • Air gap                                                         0.97
  • 2” EPX board                                            10.00
  • 8” CMU, grouted at 32” on center           1.45
  • Interior air film                                           0.68
  • TOTAL                                                        17.68

Thermal mass benefit:  “Thermal Advantages of Masonry Walls” by David Woodham, PE
Reference: NCMA TEK Note 06-01C

• Place rigid-board insulation in the drainage cavity to maximize interior usable space and take advantage of the huge thermal mass provided by the masonry backup system.
• Consider using water repellent coating on the CMU veneer. You can either use block with an integral water repellent in the mix or you can finish off the wall with a penetrating, breathable coating of spray-applied water repellent. The CMU structural wall does not need water repellent because it is not exposed to weather.
• All concrete products shrink over time. Do not forget to design and install control joints in both the veneer and the back-up wall to minimize shrinkage cracks.
• Concrete block is porous and absorbent. Make sure the cavity is properly detailed to keep moisture from getting into the building.
• Untreated concrete block is too porous to be used as a coping or a sill. Call for precast concrete, cast stone, or metal units at these vulnerable locations.
• Shelf angles may not be required for veneer support at every floor line. Cut down on the number of shelf angles to save money and simplify construction. If your CMU veneer is less than 30’ above the top of the foundation, it might not need relieving angles at all.

• Always use joint reinforcement in concrete block walls, even in the veneer. The horizontal reinforcement is needed to control shrinkage cracks.
• Simplify construction by requesting to use the same mortar type on the veneer as the backup. Type N is usually fine for both, except in high seismic zones where Type S is required.
• Back bevel the mortar bed to keep mortar blobs from filling the cavity space. The cavity needs to be open enough to permit water to drain down onto flashing below.
• If you are doing high-lift grouting, a rebar positioning device can help you keep the rebar in place where it will give maximum structural effect. See example.
• Use 16” wide rigid insulation that will fit neatly between the eyes of the horizontal reinforcing.  Use the legs of the pintles to hold the insulation board securely against the CMU back-up, leaving the cavity open for drainage.
• If the design calls for insulation in the cavity, you might consider using full sheets of insulation paired with standard two-piece adjustable anchors screwed to the face shells of the CMU instead of using pintle/eye horizontal reinforcing to tie the two wythes of the wall together.  This system allows you to use large sheets of rigid insulation and minimizes the amount of time spent taping seams between pieces of insulation.  Reference: Colorado Masonry Systems Design Guide, Chapter 6, Table 6-4

Flashing

Self-Adhered Flexible Flashing: This tough, flexible flashing strip comes with a removable release liner for easier installation. The liner MUST be removed to allow the sticky layer of the flashing to self-heal around any punctures from nails or screws. If the sticky layer of the flashing is bitumen, hold this flashing at least ½” from the edge of the masonry so that the tar layer does not melt and form ugly black drips on the face of the wall. Bitumen-based flashing is often paired with a metal drip edge which can be exposed to sunlight. This flashing will stick to masonry, concrete, gypsum, wood, or steel.

Base of Wall —Flash Vent Self-Adhering SS Flashing with Drip Edge 

Roof to Wall Parapet Detail —York 304 SA Self-Adhering Stainless Steel Flashing (view from face of wall)

Roof to Wall Parapet Detail —York 304 SA Self-Adhering Stainless Steel Flashing (view from roof)

Joint Reinforcement

Ladder-Eye Horizontal Reinforcing: Attaches the veneer to the horizontal reinforcing in the back-up CMU wall. The hooks of the pintles allow some vertical adjustability if the bed joints in the veneer do not exactly align with the bed joints in the CMU behind it. The horizontal legs of the pintles have been tested to transmit a lateral force of over 200 pounds per lineal foot from the veneer to the structural CMU wall behind it. This system allows the builder to fit 16″ tall rigid insulation between the projecting eyes of the horizontal reinforcing.

H-B 270 Ladder Eye-Wire

Masonry Anchors & Ties

Barrel Veneer Ties: Designed to minimize thermal transfer. The thickness of the barrel resists bending, and the single screw allows the anchors to be installed quickly. These ties can be screwed into concrete, CMU or wood studs. The factory-installed EPDM washers seal the penetration the screw makes in the air/vapor barrier. Using this style of masonry anchor will minimize the amount of tape used to seal joints in the rigid insulation.

H-B 2-Seal™ Thermal Concrete Wing Nut Anchor