8.3 Lintels, Control/Expansion Joints, and Flashing
Key Takeaways
- Lintels need minimum 4-inch bearing each end; add both ends to clear span to get total length (e.g., 72 + 4 + 4 = 80 in).
- Control joints serve CMU (shrinkage); expansion joints serve clay brick (expansion) — CMU = Control is the memory aid.
- CMU control-joint spacing is limited to the lesser of about 1.5x wall height or roughly 25 feet.
- Through-wall flashing must turn up at least 8 inches and pair with weep holes at 24-33 inch spacing; neither works without the other.
- Brick veneer ties allow a maximum of 1 tie per 2.67 sq ft, typically 32 in horizontal by 24 in vertical, with a 1-inch drainage air space.
Lintels, Movement Joints, and Flashing
Masonry must span openings, accommodate movement, and shed water. These three details — lintels, joints, and flashing — are where most field defects and most exam questions originate.
Lintels
A lintel carries masonry over an opening (door, window). Options:
- Steel angle (loose lintel): common for brick veneer; sized by span and load. A typical light residential opening uses a L 3-1/2 x 3-1/2 x 1/4 inch angle.
- Precast concrete lintel.
- Reinforced masonry lintel (bond-beam lintel): CMU lintel block grouted with rebar.
Bearing: lintels must bear a minimum of 4 inches on each end per common code/reference practice (some require the greater of 4 inches or span/12 for masonry lintels).
Lintel Worked Example
For a reinforced masonry lintel over a 6 ft (72 in) clear opening:
- Minimum bearing each end = 4 inches, so total lintel length = 72 + 4 + 4 = 80 inches.
- The lintel depth is built in 8-inch course increments; a single-course bond beam = 8 inches nominal.
- Reinforcement (e.g., 2 - #4 bars) sits in the bottom of the grouted lintel block with proper cover.
Always confirm bearing length first — under-bearing is a classic failure and a frequent exam distractor that gives only 2 or 3 inches of bearing.
Control Joints vs. Expansion Joints
These are opposites and the exam loves to swap them.
| Feature | Control Joint | Expansion Joint |
|---|---|---|
| Used in | Concrete masonry (CMU) | Clay brick |
| Movement type | Shrinkage (CMU shrinks as it cures/dries) | Expansion (clay brick grows with moisture/heat) |
| Purpose | Allow controlled cracking | Absorb expansion, prevent crushing |
| Material | Often left open with backer rod + sealant | Compressible filler + sealant |
Memory aid: CMU gets Control joints (shrinks); clay brick gets eXpansion joints (eXpands). Vertical control-joint spacing in CMU is commonly limited to the lesser of 1.5 x wall height or about 25 feet.
Flashing and Weeps
Through-wall flashing collects water that penetrates the outer wythe and directs it out. It is required at the base of cavity walls, over lintels, under sills, and at shelf angles.
- Flashing must turn up the backup wall at least 8 inches and extend through the face to form a drip.
- Weep holes sit immediately above flashing to drain collected water; spacing is typically 24 to 33 inches on center (open head joints or wicks).
- A clear cavity / drainage space of at least 1 inch (2 inches preferred) keeps mortar droppings off the flashing.
Exam trap: flashing without weep holes (or weeps without flashing) is useless — water gets trapped and causes efflorescence and freeze damage.
Anchorage and Veneer Ties
Brick veneer over wood/steel stud or CMU backup is held by corrugated metal ties or adjustable anchors:
- Maximum 1 tie per 2.67 sq ft of wall area (IBC veneer provisions), reduced in high-wind/seismic zones.
- Maximum tie spacing commonly 32 inches horizontal / 24 inches vertical.
- Air space behind veneer is nominally 1 inch for drainage.
Proper anchor spacing is a frequent quantity-takeoff and code-lookup question — note the area-per-tie limit, not just the spacing.
A contractor is building a CMU wall and must detail joints to manage the natural movement of the concrete block. Which joint type and movement applies?
A reinforced masonry lintel spans a 6-foot (72-inch) clear opening with the minimum 4-inch bearing at each end. What is the required lintel length?
Lintels and Bearing
A lintel spans an opening and carries the masonry above. Types: steel angle (loose lintel), precast concrete, or a grouted-reinforced masonry bond-beam lintel. Lintels need adequate end bearing — commonly a minimum of 4 in (often 6–8 in) on each side — and must be sized for the load triangle of masonry above plus any floor/roof loads. Under-bearing or undersized lintels crack the wall above the opening.
Control vs. Expansion Joints — Opposite Materials
The materials move in opposite directions, so the joints differ:
- Concrete/CMU shrinks → use control joints (vertical, allow the wall to shrink without random cracking), spaced commonly ≤ 25 ft or 1.5× wall height.
- Clay brick expands (moisture/thermal) → use expansion joints (compressible filler) to give it room.
Mixing these up — putting a shrink joint in brick or vice versa — is a guaranteed exam trap and a real-world cracking failure.
Flashing, Weeps, and Moisture Control
Masonry is not waterproof — it manages water. Through-wall flashing at the base, shelf angles, sills, and heads collects water that penetrates the outer wythe and directs it out through weep holes (spaced ~24–33 in o.c.) just above the flashing. A drainage cavity (air gap) behind the veneer with mortar droppings kept out lets water drain. Omitting weeps or flashing traps water and causes efflorescence, spalling, and interior leaks.
Common Exam Traps
- Trap: Brick needs control joints (it expands → needs expansion joints).
- Trap: Weep holes are optional in veneer. They are essential for drainage.
- Trap: A lintel needs minimal bearing. Provide ≥ 4 in (often more) each end.
- Trap: Masonry is waterproof. It is a drainage/screen system.
A clay brick veneer wall is being detailed for movement. Which joint type is correct, and why?
Parapets, Copings, and Movement Detailing
Parapets (the wall extending above the roof) are exposed on both faces and the top, so they move and weather more than the wall below — they need a coping (cap with a drip and slope) plus through-wall flashing and often a dedicated expansion joint. Where a long wall changes height, turns a corner, or meets a different material, concentrate movement at a joint so the inevitable expansion/contraction does not crack the field of the wall. The exam links parapet leaks and corner cracking back to missing coping flashing or movement joints.