Adjustable Unit Ties
Fig.3

Sheet Metals

Sheet metals used for flashing include stainless steel, copper, lead-coated copper and galvanized steel.  Aluminum should not be used since it can corrode in fresh mortar.  Stainless steel and copper materials are the most durable, but are also the most expensive.  Galvanized steel has also been used in limited applications.  These flashing materials have a greater life expectancy than composite or fabric flashing.  Sheet metal flashing is bent and formed on site and sealed by soldering or with adhesives and rivets.  This additional installation time can result in additional construction costs.  Stainless steel materials should conform the ASTM A 167 Specification for Stainless and Heat-Resisting Steel Plate, Sheet and Strip.  Copper flashing should comply with ASTM B 370 Specification for Copper Sheet and Strip for Building Construction.  Solder should conform to ASTM B 32 Specification for Solder Metal.

Composites

Composite or combination flashings are typically less expensive than sheet metal and are easier to install.  The most predominant type is a thin layer of metal sandwiched between one or two layers of another material.  The metal layer is usually of aluminum, copper or lead.  It is covered on one or both sides with various materials, such as asphalt coatings, kraft paper, fiberglass fabric or plastic films.  Product literature should be reviewed to determine whether these materials are appropriate for use in brick masonry cavity walls.  Consideration should be given to compatibility with adjacent sealants, delamination due to moisture penetration and movement of the wall system.

Plastic and Rubber Compounds

These flashing materials are usually the least expensive flashing suitable for brick masonry cavity walls.  They are flexible and can make complex shapes, except in the heavier thicknesses.  Polyvinyl chloride (PVC), Ethylene Propylene Diene Monomer (EPDM) and rubberized asphalt are the most common plastic flashings available.
PVC deteriorates and breaks down when exposed to ultraviolet (UV) light.  The material also becomes brittle and shrinks over time due to loss of plasticizers.  Some PVC flashing is not compatible with polystyrene insulation and can cause the insulation to degrade.  However, not all PVC flashings have experienced such problems.  Appropriate quality, density and thickness of PVC flashings are paramount to successful performance and should be obtained from well-recognized manufacturers. 
EPDM was originally developed as a roofing membrane.  However, this type of material has been gaining widespread use as through-wall flashing for masonry walls.  It has increased resistance to weathering and performs better in low temperature environments than PVC.  EPDM should be in a cured state.  Junctures and laps of plastic flashing are usually sealed with plastics or adhesives.  These materials may require a metal drip edge adhered to the flashing when exposed to exterior elements.  EPDM should be talc free or the talc should be removed where laps are formed.
Another type of fabric flashing is a self-adhering, rubberized asphalt.  This flashing material easily adheres to itself at junctures, laps and interior wall surfaces and can be self healing to some extent.  However, this material cannot be placed on damp, dirty or dusty surfaces.  The adhesion properties may be reduced during cold weather.  Rubberized asphalt can also degrade in the presence of UV light and therefore, requires the same type of drip edge as other plastic flashing materials.

WEEP HOLES

Weep holes channel moisture collected on the flashing to the exterior of the wall assembly. For best performance, weep holes should always be located directly on the flashing.  If weep holes are installed one to two masonry courses above the flashing, they will not perform their intended function.  Some types of weep holes may aid in drying out the wall system, although this is not their primary purpose.
Weep holes can be formed in a number of ways.  Some of the most common are: 1) omitting mortar in all or part of the head joint; 2) use of removable rods or ropes; 3) plastic or metal tubes; and 4) use of a wicking material.  There are also plastic and metal vents that cover weep holes used in lieu of mortar in vertical head joints.  Open head joints are recommended as weep holes; however, as long as weep holes remain open for drainage and positioned at the required flashing locations with the appropriate size and spacing, the specific type of weep hole selected is not critical.

DRAINAGE MATERIALS

For brick masonry cavity walls to retard moisture infiltration, the air space separating the masonry wythes must be kept clean of mortar droppings or mortar that may bridge the air space.  These obstructions can render flashing and weep holes ineffective.
While it is important to keep cavities clear, there are a number of approaches available to keep open a drainage path to the weep holes.  Drainage materials can be installed above flashing consisting of materials configured and installed to allow water to flow around any mortar droppings.  The use of these materials does not negate the importance of good workmanship and may not be required in all situations.  Use of drainage materials may result in the mortar bridging the air space at certain locations, possibly above the flashing level.  This may lead to isolated spots of dampness on the interior or exterior wythe.  At worst, it could lead to a path for water penetration.  In all cases, the cavity size should be maintained.
A layer of pea gravel with an approximate diameter of 3?8 in. (10 mm) can be placed on top of flashing installations within the wall system.  This layer should be approximately 2 to 3 in. (50 to 75 mm) deep.  This will help to keep mortar droppings from clogging weep holes.  The smallest gravel size should be larger than the weep hole opening so as not to interfere with drainage.  It is recommended that a bed of mortar, conforming to the curve of the flashing, be placed under the flashing for additional support of the pea gravel.  Care must be exercised when installing pea gravel at bolted shelf angle locations.  The weight of the gravel on the flashing may cause tearing or puncturing at the bolt head.  Pea gravel at loose lintels needs to be contained so it does not flow off the end.  Fig. 5 shows a typical detail for the use of pea gravel although it would apply to many of the drainage materials.
Mesh materials are gaining popularity.  These materials are usually manufactured from high density polyethylene or nylon strand and are available in 1 in. to 2 in. (25 mm to 50 mm) thicknesses.  They keep weep holes open and permanently suspend the mortar above the flashing level.  Many have unique patterns such as dovetail shapes which break up mortar droppings so moisture has open flow paths to flashing and weep holes.
Another mortar dropping control device consists of staggered shelves inserted in the cavity such that they overlap each other.  The individual pieces are fixed in place by tabs which are mortared into the outer wythe of masonry.  This may collect mortar droppings above the flashing level and create a bridge for moisture to cross the cavity.
Some manufacturers of rigid board insulation provide a grooved face with an adhered filter fabric that is positioned in the air space towards the exterior.  The aligned grooves act as a channel which allow moisture to drain down to the flashing and weep holes in the wall system.  The grooves are intended to provide drainage capabilities in the event of the air space being clogged during construction of the masonry wythes; however, the grooves must align vertically for proper drainage.  Other rigid insulation boards have an adhered mesh material which behaves in a similar manner.

Rigid Boards

There are many rigid board insulation materials that can be installed in the air space of brick masonry cavity walls.  Among the most common are: expanded and molded polystyrene, extruded polystyrene, expanded polyurethane, polyisocyanurate, mineral fibers and perlite board.
Composition.  Rigid board insulations are many and varied.  They include the various mineral fiber boards and cellular insulation including polystyrenes, polyurethanes and polyisocyanurates.  Air, or other gases, introduced into the material expands the material by as much as 40 times.  Cells are formed in various patterns—open (interconnected) or closed (unconnected).  Most rigid insulation is expanded with hydrogenated chlorfluorocarbons (HCFC), pentane or other hydrogenated gases used as blowing agents.  Gradual air leakage into the cells may replace some of the original gas and eventually reduce the thermal insulating quality.  Some types of insulation use foil facers.  These facers keep air leakage to a minimum and must not be punctured during construction.  Aged R-values should be used when comparing different types of insulation.
Fibrous insulation materials include wood, cane, or vegetable fibers bonded with plastic binders.  To make them moisture resistant, they are sometimes impregnated with asphalt.  Fibrous glass insulation consists of a core board of non-absorbent fibers held together by phenolic binders and a surface coating of asphalt-saturated organic material reinforced with glass-fiber.
Properties.  Water entrapped in insulation can destroy its thermal insulating value.  Water vapor can flow wherever air can flow—between fibers, through interconnected open cells, or where a closed cell structure breaks down.  Wherever water replaces air, the insulating value drops drastically since water's thermal conductivity exceeds that of air by 20 times.
Fibrous organic insulations are especially vulnerable to moisture damage.  Free water will eventually damage any fibrous organic material or organic binder.  Fiberboard exposed to moisture for long periods of time may warp or buckle and eventually decay.  The expansion and contraction that accompanies the changing moisture content may lead to problems.
Though less vulnerable to moisture, inorganic materials are not immune.  Water penetrating into fiberglass insulation not only impairs the insulating value, but may also dissolve the binder.  Some types of cellular insulation may also break down under repeated freeze/thaw cycles.
Rigid board insulation should conform to one of the following: ASTM C 208 Specification for Cellulosic Fiber Insulating Board, ASTM C 552 Specification for Cellular Glass Thermal Insulation, ASTM C 578 Specification for Rigid, Cellular Polystyrene Thermal Insulation, ASTM C 1224 Specification for Reflective Insulation for Building Applications, ASTM C 1289 Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board, ASTM D 3490 Specification for Flexible Cellular Materials - Bonded Urethane Foam and ASTM D 3770 Specification for Flexible Cellular Materials - High Resilience Polyurethane Foam.  There may be other products available for rigid foam products; therefore, manufacturer's literature should be reviewed before selection.

Granular Fills

Granular fills are typically used in the hollow cells of concrete block backing.  However, they can be used in the cavity.  One advantage of granular fills is that they can be installed after wall sections have been completed.  This permits the mason to work uninterrupted thus shortening construction time and lowering costs.  However, the water resistance of the fill is of utmost importance.  Settling of the fill material could lead to thermal bridging in the wall system.
Two types of granular fill insulation have been found to meet the objectives of cavity wall insulation.  These are water-repellent vermiculite and silicone-treated perlite insulation.
Vermiculite is an inert, lightweight, granular insulating material manufactured by expanding an aluminum magnesium silicate mineral, which is a form of mica.  The raw material is made up of approximately one million separate layers per inch, with a minute amount of water between each layer.  When particles of the mineral are suddenly exposed to temperatures in the range of 1800?F to 2000?F (982?C to 1093?C), the water changes to steam, causing the vermiculite to expand into cellular granules of vermiculite insulation about 15 times their original size.
Perlite is a white, inert, lightweight, granular insulation material made from volcanic siliceous rock.  When the crushed stone is heated to approximately 1800?F (982?C), it expands or pops much like popcorn as the combined water vaporizes and creates countless, tiny bubbles in the heat-softened, glassy particles.  Perlite can be expanded up to 20 times its original volume.
Water-repellent vermiculite and silicone-treated perlite should conform to ASTM C 516 Specification for Vermiculite Loose Fill Thermal Insulation and C 549 Specification for Perlite Loose Fill Insulation, respectively.  Each of these specifications contains limits on density, grading, thermal conductivity and water repellency.  Some properties of these materials is given in Table 3.

Foamed-in-place Insulation

Foamed-in-place insulations have traditionally been used to fill the cells of hollow masonry units.  However, new technology has now produced foamed-in-place insulations that can completely fill the air space between the two wythes of a brick masonry cavity wall.  One advantage of these foamed-in-place insulations is that they can be installed after wall sections have been completed.  However, the water resistance of brick cavity walls with these types of insulation materials are unproven in the field.  Shrinkage of the foam material could lead to moisture drainage paths through the wall system.  In addition, mortar bridging in the cavity may not allow the foam to flow around it properly.  These materials used in the cavity contradict the drainage system and should be considered a barrier wall system.
Most foams are a two component system.  They are formed by a chemical reaction of two liquids.  They are placed under pressure, so newly constructed walls must be cured long enough to resist the pressures.  Typical compositions of these foams are urethane, polyicynene, magnesium oxychloride cement and ceramic talc and amino-plast resin.  Since most of these products are proprietary, there are no ASTM standards at this time to verify quality.  Therefore, manufacturers literature should be consulted for technical information on applications and usage.

AIR AND VAPOR RETARDERS

Sheets or layers of materials which effectively retard or reduce the flow of air and water vapor are called air retarders and vapor retarders, respectively.  In recent years, there has been much confusion pertaining to the functions of each within a masonry wall system.  Air retarders limit the amount of air flow through the wall system.  Vapor retarders are intended to control transmission of water vapor through building assemblies.  A vapor retarder can also serve as an air retarder.  An air retarder may or may not serve as a vapor retarder.  It is sometimes difficult to ensure that either retarder performs only one function.  For example, polyethylene films will function as a vapor retarder, but it will also resist the passage of air.
To provide effective air and vapor retarders, it is necessary to seal joints in these materials so that continuity is provided.  It is also necessary to seal around the edges of wall openings such as windows, doors and access for utility services.  Adhering or taping of the joints should be specified.  The adhesive or tape used must be compatible with the material composition of the retarder in addition to performing adequately when exposed to moisture.

Air Retarders

Masonry cavity walls can appear to be relatively air tight, but may experience high air leakage rates.  Parging the exterior or interior face of the interior masonry wythe with mortar is one method to reduce air leakage, but it will crack if the wythe cracks.  Membranes or liquid-applied materials usually provide superior performance.  Special attention must be given to adjacent materials or structural members intersecting the interior wythe and the membrane.   Permanent fixtures in the interior wythe and movement joints at the top and sides of the wythe must provide a continuous air seal to perform successfully.
For improved air retarder performance, the air and vapor retarders can be included in combination with mortar parging.  The parging provides a base for the application of the vapor retarder.  The vapor retarder must be able to span possible movement cracks in the interior wythe.
Interior or exterior insulation boards applied to the interior wythe can also form part of the air retarder system.  For insulation to work effectively as a retarder, proper adhesion to the interior wythe by the use of full grid of adhesive will eliminate air spaces between the insulation and the interior wythe.  Mechanical anchorage may provide a tight fit of the insulation to the interior wythe.  Joints between insulation boards must be sealed with a moisture resistant tape or sealant.
Interior gypsum board finish materials can be used as air retarders when joints are properly sealed.  Even when the interior wall covering is not intended to serve as the main air retarder, it is suggested that steps be taken to provide good air tightness in order to reduce possible air circulation in air spaces in the interior wythe.

Vapor Retarders

There are many materials that can be used to effectively provide vapor transmission resistance.  However, the installation methods vary just as much as the materials themselves.   Selection should consider the material and ease of application for the best results.
The vapor retarder selection depends on the type and location of insulation in the brick masonry cavity wall and the interior and exterior climate.  While some materials and methods of application may be successful in the cavity or on the interior side of the interior wythe, there are certain vapor retarders which perform better on one side that the other.
Suitable vapor retarders consist of two coats of oil-based or alkyd emulsion paint on the interior side of the wall finish; a 15-mil thick polyethylene sheet over the insulation; or the insulation itself if it is highly impermeable to water vapor transmission and has taped or sealed joints.  Foil-faced insulation and extruded polystyrene insulation boards meet these criteria.
When the vapor retarder is installed within the cavity space, other material options are available.  Paints or suitable coatings can be applied to the outside face of the interior wythe, but must have the ability to span or bridge small cracks.  The vapor retarder can also consist of torched-on or spray-applied bituminous coatings, self-adhesive plastic sheets or plastic materials.
The material must be continuous and be able to accommodate possible movement cracks that may form in the masonry.  For long term performance, vapor retarder materials must remain firmly affixed as vapor pressure differentials occur.  These materials must be chemically compatible with any insulation placed in the cavity.
If the insulation is used as the vapor retarder, it must be held firmly in place by adhesives or mechanical anchorage.  In addition, the joints between the insulation boards must be fully sealed with moisture resistant sealant or tape.

SUMMARY

This Technical Notes is the second in a series dealing with brick masonry cavity walls. It is concerned primarily with recommended properties and selection of materials.  Other Technical Notes in this series discuss cavity walls in general, design, detailing and construction. 
The information and suggestions contained in this Technical Notes are based on the available data and the experience of the engineering staff of the Brick Industry Association.  The information contained herein must be used in conjunction with good technical judgment and a basic understanding of the properties of brick masonry.  Final decisions on the use of the information contained in this Technical Notes are not within the purview of the Brick Industry Association and must rest with the project architect, engineer and owner.

REFERENCES

1."Brick Masonry Cavity Walls," Technical Notes 21 Revised, Brick Industry Association, Reston, VA, August 1998.
2.Handbook of Fundamentals, American Society of Heating, Refrigeration and Air Conditioning Engineers, Inc., Atlanta, GA, 1997 Edition.
3."Thermal Insulation, Environmental Acoustics," Volume 04.06, Annual Book of ASTM Standards, American Society for Testing and Materials, West Conshohocken, PA, November 1998.
4."Through-Wall Flashing," Engineering and Research Digest, Brick Industry Association, Reston, VA, 1996.
5."Wall Ties for Brick Masonry," Technical Notes 44B, Brick Industry Association, Reissued Sept. 1988.
6."Water Resistance of Brick Masonry, Design and Detailing - Part I of III," Technical Notes 7 Revised, Brick Industry Association, Reston, VA, Reissued Feb. 1998.
7."Water Resistance of Brick Masonry, Materials - Part II of III," Technical Notes 7A Revised, Brick Industry Association, Reston, VA, Reissued Dec. 1995.