This article is about guidance in the construction of an exterior masonry wall of a single course, or wythe, over blocked or placed concrete wall.
DESIGN STANDARDS IN CONSTRUCTION OF AN EXTERIOR MASONRY WALL, OR WYTHE
Comment: To be clear from the outset, a faux or true masonry finish clad shall have a full-surface, continuous drainage plane behind it and to earth - notably of different sorts based on the cladding materials - or there'll come a day when it becomes exceedingly obvious in remediation that the clad installation was insufficient.
The following shall apply to a wythe of masonry or masonry substitute
Without regard to wall height and
Without regard to habitability of the attached structure
A masonry wythesystem shall comprise (from the exterior)
Masonry veneer
With weep holes at its base (as below)
With ties to structure (as below)
Air gap of
Not less than 1 linear inch
Preferably 2 linear inches
House wrap lapped over flashing (as below)
At top of a window frame
At top of a door frame
Over any other protrusion from structure through veneer
At base, or shelf, or ledge (as below)
Not less than 1 linear inch rigid insulation (as below)
Thence to exterior sheathing and wall frame
A single wytheshall be supported along the entirety of its footprint by foundation
As a masonry shelf or ledge which is in wall and footing not less in construct than the structure to which it is attached and
Which is contiguous with the foundation of the structure to which it is attached either
Monolithic placement
Retro placement durably fastened to existing
Concrete block or other masonry wall buildup durably fastened to existing
The footing of which shall extend not less than
Evenly revealed on the horizontal on both sides of the foundation walls
Which footing thickness shall be not less than foundation wall width
Which footing width shall be not less than twice footing thickness or twice foundation wall width
The shelf of which shall be reinforced
By not less than 2-#5 deformed rebar
Continuously on the horizontal
With 3/4 linear inch plus aggregate size cover
Whether as tie beamor bond beam
Which shelf shall be at the top of its face–
Not less than 6 linear inches above finish grade level
Not less than 1-2 linear inches below interior slab-on-grade top of face, or, less preferentially
Not less than 1-2 linear inches below concrete curb on which would rest a framing mudsill atop a slab-on-grade (the latter being potentially less resistant to moisture intrusion)
A single wythe
Shall be spaced open and unblocked not less than 1 linear inch and preferably 2 linear inches between wythe back of face and insulation front of face
Shall be protected from mortar debris blocks, or dams, from stopping moisture migration
Shall be fastened
To frame structure at
Not less than 16 linear inches on center, except 12 linear inches on center in basic wind speeds in excess of 90 mph with
2-piece adjustable masonry ties
Weep holes
Shall be placed
At not greater than 16 linear inches on center at bottom of natural masonry walls and
At 16 linear inches on center for brick walls and at window and door tops flat or arched
Shall each be fitted with WeepVent by Mortar Net USA, Ltd. (http://www.mortarnet.com/,1-800-664-6338) or equivalent
To block critters' intrusion to the air cavity and
To let moisture migration
Shall be sized
As head joint for WeepVent according to manufacturer or
According to manufacturer of equivalent and
In any case not less than 3/8 linear inch width x 1 linear inch height
Shall be continuously flashed along the masonry ledge
Shall be flashed
Front to back running from the exterior and
Across the air cavity and back to the wrapped or insulated wall structure and then
To the greater of not less than the greater of 12 linear inches upwards on the vertical or according to manufacturer specifications
Above a window, door frame, vent pipe, and any other protrusion from house structure through veneer and
Under the house wrap
Not less than ¾ linear inches exposure to the exterior, past the foundation wall
Shall cover flashing wherever sited in the air cavity continuously with MortarNet by Mortar Net USA, Ltd((http://www.mortarnet.com/,1-800-664-6338) or equivalent
Shall be in decreasing preference
Most preferably, open head joints with mesh insert as with MortarVent by Mortar Net USA, Ltd., http://www.mortarnet.com/,1-800-664-6338or equivalent or
Much less preferably, cotton rope wick
At not less than 16 linear inches on center and
At not less than 10 linear inches in length and
Attached to the back wall and
Shall not be PVC pipe or plastic or rubber tube and
Shall not be less than 6 linear inches above finished grade level
Comment:This custom home designer respectfully notes that this rendition of weep holes is not without its alternative.For example, some folks put open heads last for their seeming difficulty to be adequately blocked to critters, and still pass moisture.And some folks set cotton rope wicks last because either they've seen other than cotton used (to no good end) or because they know that of the three alternatives, this one weeps most slowly.
Flashing
Shall be more preferably high puncture resistant EPDM with metal drip edge or
Shall be less preferably shall be stainless steel, copper, copper laminate, and rubberized asphalt
Shall not be permitted PVC, vinyl, galvanized steel and polyethylene and
Shall be sealed to moisture when pierced by fasteners and
Shall be lapped upper over under, or higher over lower and
Shall be metal-edged if exposed to exterior
Air vents blocked to critters
May be placed at top of exterior wood sheathing
At not less than 2 linear inches diameter or equivalent surface area and
Spaced on center 1 per stud bay
A clear passage shall be assured from air cavity into attic (unobstructed by insulation) where applicable or otherwise to soffit or wall vents not less in surface area than the combined sheathing vent surface area times 1.5, evenly distributed
Foam sheathing insulation where applied shall be installed to form a drainage plane to direct condensation away from the interior wall structure facing the air cavity
Foam sheathing shall run on the vertical with the largest pieces of foam placed at the bottom of the wall
Vertical joints of foam sheathing shall not be taped
Horizontal joints of foam sheathing shall be taped
Foam sheathing shall have ¼ linear inches gap on the vertical between sheets
Loose materials of any kind shall not be left within walls
Double tar paper
Shall be used under masonry stucco walls, silicone-sealed at penetrations and laps
So that layers from the exterior are
Finish or skim coat
Brown coat
Scratch coat
Metal lath
2 layers of 30-pound felt paper
Sealed individually at penetrations and
Lapped on the horizontal by upper over lower and
Lapped on the vertical by not less than 18 linear inches, house wrap, and, finally, house structure
Comment: Masonry stucco needs to drain moisture on its interior.Double (i.e., not single) tar paper layers allow a bond break between stucco and structure.
Stucco weep screed
Shall terminate to light not less than 8 linear inches above finished grade level
Shall let moisture from a masonry shelfstepped down at a slab-on-grade or foundation perimeter
Comment: Among descriptions of masonry wythe flashing and drainage, please consider Continental Cast Stone, Inc., Flashingand Weep Holes, Design Tips - Technical Bulletin #47, http://www.caststone.net/csi/47.html
Comment:It's not just that stucco weep screed can end up below grade level in an aggressive backfill or a genuinely mistaken grade line on stucco installation; worse yet is the stucco weep screed closed off by the placement for a walkway, slab-on-grade, patio, etc.
A masonry reveal–
Shall be of solid brick at the ledge
Shall be of chamfered edge at its base
Shall have no sealant applied if low maintenance is a use objective
Shall not be mortar washed
Contractor shall assure continuous bond break between wythe bottom of face and masonry ledge top of face
Any penetration of a masonry wall shall be flashed from structure outwards, including but not limited to
Hose bibb
Clothes dryervent
Bath exhaust
Window
Transom
Clerestory
Door
Engineering latitude shall prevail when
Unbalanced fill exceeds 4 linear feet of wall
Wall height exceeds 8 linear feet, including depth of footing
The site is in Seismic Zone 3 or greater
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