11. MASONRY LOADBEARING WALL CONSTRUCTION

Chapter 10Masonry Loadbearing Wall Construction

11.1 MASONRY LOADBEARING WALL CONSTRUCTION - OVERVIEW

11.2 THREE TYPES OF WALL CONSTRUCTION

11.3 DETAILING OF MASONRY WALLS

11.4 TYPES OF THERMAL INSULATION FOR MASONRY WALLS

11.5 MOVEMENT JOINTS IN BUILDINGS

11.6 OTHER SPECIAL PROBLEMS

11.2 THREE TYPES OF WALL CONSTRUCTION

11.2.1 Reinforced or Non-reinforced wall - Non-reinforced walls cannot carry high stresses and are generally used as parapet walls; sometimes buildings, of 16 story heights, have been built with non-reinforced masonry - Reinforced walls are reinforced with vertical and horizontal steel reinforcements and are less thick

11.2.2 Composite masonry walls: Usually constructed with an outer wythe of stone or facing brick and a back up of hollow concrete block masonry - The two wythes are bonded together by steel horizontal joint reinforcements or by headers from the outer wythe that penetrate the back up wythe

11.2.3 Cavity walls: Since exterior walls must resist water penetration and heat transfer, these walls are built with internal cavities - Masonry cavity walls consist of an inner, structural wythe and an outer wythe of masonry facing - These two are separated by a continuous airspace that is spanned only by corrosion-resistant metal ties that hold the wythes together - Cavity walls prevent water from reaching the interior by interposing the cavity between outside and inside wythes of the wall - When penetrating moisture reaches the cavity, it goes down and is caught by a thin, impervious membrane called flashing and drained through weep holes to the exterior

Masonry Wall Types

Reinforced or Un-reinforcedReinforcing Increases Load Carrying CapacityUses: Low Rise Construction, Foundations

One Type or Composite Masonry WallsComposite; Two Wythes of Different MaterialTyp. - CMU & Brick

Solid or Cavity Walls

Reinforced Masonry Walls

Cell Reinforcing

11.3 DETAILS OF MASONRY WALLS

11.3.1 Flashing and weep holes: A flashing is a continuos sheet of impervious material that is used as a barrier against the passage of water, into the building - Weep holes drain water from the cavity to the exterior

11.3.2 External flashings: Used to prevent moisture from penetrating the roof edge to wet the masonry wall, at the intersection of roof and the parapet wall - Uses a base flashing and counter flashing to achieve the purpose - Roof membrane becomes the base flashing; counter flashing comes from the outer wall to cover the base flashing - Should be turned in 8” into the wall to prevent water penetration

Internal flashings: Used to catch the water that has penetrated the outer wall and to drain it through weep holes to the exterior - Internal flashings should be placed at the bottom of the wall cavity and at every location where the cavity is interrupted; at heads of windows and doors, at window sills, at shelf angles, and over exposed spandrel beams - Should be accompanied by a weep hole - Should be turned up 6” to 8” at the interior face of the wall and penetrate at least 2” into the back up wythe - Outside the wall, flashing should be carried at least 3/4” beyond the outside face and turned down at 45o angle

11.3 DETAILING MASONRY WALLS (Cont’d)

Weep holes should be placed at every 24” c/c horizontally - Min. diameter for a weep hole is 1/4” - Made by inserting a short of rope laid in the mortar joint and later pulled out - Plastic tube and metal accessories should be provided to prevent insects from entering the cavity

Material for flashing: Made of sheet metal, UV resistant plastics, elastomeric compounds, or composite materials - Galvanized steel is unsuitable but stainless steel and copper are suitable; aluminum and lead are unsuitable

Cavity Walls

Common Construction for Exterior WallsInsulating ValueReduced WeightDrainage

Cavity Wall Construction

Inner Wythe or support wallAir Space (Insulation & Drainage)Outer Wythe of MasonryMasonry Ties to hold the Wythes together

11.4 TYPES OF THERMAL INSULATION FOR

MASONRY WALLS

11.4.1 Thermal Insulation of Masonry Walls: A solid masonry wall is a poor insulator - Solid masonry wall is massive and as such absorbs and stores heat during day and gives up during night; but in regions of sustained cold weather measures must be taken to improve the insulating qualities of masonry walls

11.4.2 Three different modes of insulation used - (i) Insulation on

the outside face with EIFS (exterior insulation and finish system), which consists of panels of plastic foam that are attached to the masonry and covered with a thin, continuous layer of polymeric stucco reinforced glass fiber mesh - Masonry is completely covered with stucco - Disadvantage is that this stucco is easily dented and EIFS is combustible

Masonry Veneer Anchors

Masonry Flashing

External Flashing

Prevents Moisture Penetration

Types

Material

Internal Flashing

Through Wall (Concealed) FlashingCollects waterDrainage Through WeepsPlacement

Shelf Angle

Dampproofing & Flashing

Flashings over Wall Openings

11.4 TYPES OF THERMAL INSULATION FOR

MASONRY WALLS

11.4.1 Thermal Insulation of Masonry Walls: A solid masonry wall is a poor insulator - Solid masonry wall is massive and as such absorbs and stores heat during day and gives up during night; but in regions of sustained cold weather measures must be taken to improve the insulating qualities of masonry walls

11.4.2 Three different modes of insulation used - (i) Insulation on

the outside face with EIFS (exterior insulation and finish system), which consists of panels of plastic foam that are attached to the masonry and covered with a thin, continuous layer of polymeric stucco reinforced glass fiber mesh - Masonry is completely covered with stucco - Disadvantage is that this stucco is easily dented and EIFS is combustible

11.4.3 Insulation within the wall: If the cavity in a wall is made sufficiently wide, the masons can insert slabs of foam insulation against the inside wythe as it is built; the overall width of cavity must be adjusted so that the net width of air space is at least 2” - the hollow cores of the cavity wall can be filled with loose granular insulation

11.4.4 The inside surface of the masonry wall is insulated, by attaching plastic foam to the wall and applying plaster directly to the foam, or attaching wood/metal furring strips to the inside of the masonry wall with masonry nails - Presence of furring strips creates a space in the wall in which the electrical wiring and plumbing can easily be concealed

11.4 TYPES OF THERMAL INSULATION FOR MASONRY WALLS (Cont’d)

Thermal Insulation

Outside Face (typically EIFS)

Within the Wall

In the Cavity or

In the Hollow Cores

On the Inside Face

Insulation in CMU cells Insulation in Cavity

Insulation in CavityExternal Insulation

Insulation being installed in the cavity

Masonry Construction

Masonry and Wood

Masonry and Steel

Masonry and Concrete

CMU Masonry with Joist & Metal Decking

CMU with Precast Concrete Decking

MPE Rough-In

Rough-in•Electrical•Plumbing•HVAC

Fire Damper

Electrical Rough-in

Electrical Roughin

Building materials and building experience small displacements continuously - Many of these motions are cyclical and never-ending - All materials shrink as they grow colder and expand as they grow warmer, each material doing it at its own characteristic rate - All these motions or displacements are small in magnitude, but they occur in every building - If they are ignored in design, they can tear the building apart, causing cracking of brittle materials

These small motions are accommodated by:

- Strengthening of structures so as to resist the expansion stresses

- Providing of movement joints

- Construction joints

- Structure/Enclosure joints - Sealant joints at the top of an interior partition

- Surface divider joints

- Control joints

- Expansion joints

11.5 MOVEMENT JOINTS BUILDING

Expansion & Contraction

Structure Movement, Masonry Changes

Expansion JointsWithin Masonry WallTwo-way Movement@ Change in Thickness, Height, or Openings

Isolation Joints

Expansion Joint

Weep Holes

Expansion Joint Material

11.6 OTHER SPECIAL PROBLEMS

11.6.1 Expansion and contraction: Due to temperature and moisture content - Should be accounted for in the design

11.6.1 Efflorescence: A fluffy white powder, that sometimes appears on the surface of a brick, stone, or concrete block wall - Consists of one or more water soluble salts that migrate to the surface - Can be prevented by proper choice of masonry units

11.6.2 Mortar joint deterioration: Water running down a masonry wall tends to accumulate at mortar joints - Due to freeze and thaw cycles the mortar in the joints expands and contracts alternatively and deteriorates - Weather-resistant mortar must be used to prevent deterioration

11.6.4 Moisture resistance of masonry: Moisture resistance of masonry units must be specified to minimize water absorption - Flashing and weep holes must be provided - Exterior wall must be coated with stucco or paint - Below grade masonry should be parged with two coats of type M mortar, 1/2” thick - The exterior wall must be coated with damp-proofing compound

11.6.5 Cold and hot weather construction: Special precautions are necessary to prevent mortar freezing before curing is complete - Keep masonry units dry - Protect them from freezing before use - Use type 30 cement (high early strength) and warm water to produce mortar at a optimum temperature - Mix mortar in small quantities - Protect the wall from wind, as the mason builds it - Protect against freezing for at least three days - Try to avoid chemical accelerators and “anti-freeze” admixtures since they are harmful to mortar and reinforcing steel - In hot weather, dampen the masonry units before laying them in place - Also keep the masonry units and mortar ingredients in shade before use

11.6 OTHER SPECIAL PROBLEMS (Cont’d)

Other Special Problems

Efflorescence

Joint Deterioration

Moisture Penetration

Hot & Cold Weather Construction

Efflorescence

Efflorescence

Masonry and the Codes

Masonry often used as a fire separation wall

Used with Steel and Concrete Decks - Type 1&2