ALL ABOUT HOUSE
FOUNDATION PROBLEMS and YOUR HOME DESIGN FOUNDATION PLAN FOR AN EXTERIOR MASONRY
WYTHE
By Before The Architect Copyright 2009
YOU MAY FREELY QUOTE THE AG WITH PROPER ATTRIBUTION
Take courageous, considered risks; do not take brave,
foolish risks. You will be known for your successes and your failures. Failing
at courageous, considered risks is OK. Failing at brave, foolish risks is not
OK. Before The
Architect
QUESTION: WHASSUP WITH HOUSE FOUNDATION
PROBLEMS?
ANSWER: PRETTY NEAR NOTHING WITH A GOOD
HOME FOUNDATION PLAN.
EXTERIOR MASONRY WYTHE HOME FOUNDATION PLAN GUIDE
INTRODUCTION
This article is
about guidance in the home building of an exterior masonry wall of a single
course, or wythe, over blocked or placed concrete wall.
DESIGN STANDARDS IN
HOME BUILDING 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, or single course wall, of masonry or masonry substitute
Without regard
to wall height and
Without regard
to habitability of the attached structure
A masonry wythe
system 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 wythe
shall 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 beam or 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/,
1-800-664-6338 or 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 shelf stepped down at a slab-on-grade or
foundation perimeter
Comment: Among
descriptions of masonry wythe flashing and drainage, please consider Continental
Cast Stone, Inc., Flashing and 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 dryer
vent
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
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