I've got a 70-foot-long hallway ceiling with no breaks in it.

Yes, you need control joints. For a 70-foot ceiling, install control joints every 30 feet maximum per ASTM C840 and GA-216.

Placement:

• At 30 feet from each end (so joints at 30' and 60' from one end)
• Or center the joints: place one at 35' and another at 70' (end)

Installation details:

• Use proper drywall control beads or expansion joints
• Leave 3/8" gap between drywall panels at joints
• Install backing (wood or metal) at joint locations
• Use flexible sealant or joint compound designed for movement

Additional considerations:

• If ceiling is perpendicular to joists, joints should align with joist direction
• For gypsum board ceilings, ensure joints don't coincide with structural framing changes
• Consider HVAC diffuser locations - avoid placing joints within 6" of fixtures

This prevents cracking from thermal expansion/contraction and structural movement. Without control joints, you'll likely get random cracking along the 70-foot span.

Yes, you need control joints. Per ASTM C840 Section 7.3 and Gypsum Association GA-216, control joints are required where:

1. Ceiling runs exceed 30 ft in any direction (you have 70 ft).
2. A control joint occurs in the structure above.
3. Ceiling construction changes (e.g., drywall to plaster).

Placement for your 70-ft hall: Install two control joints to break the run into three ~23-ft sections (well under the 30-ft max).

• Location 1: ~23 ft from one end.
• Location 2: ~46 ft from that same end (23 ft from the other end).

Critical Installation Details:

• Framing: You must double the joists/trusses at each joint location to create a 3-in. gap in the framing. The drywall cannot bridge the structural members continuously.
• Product: Use a manufactured vinyl "V" or "Z" control joint bead (e.g., Trim-Tex 093V or USG 093). Do not use tape or caulk alone.
• Alignment: Run the joint perpendicular to the joists (across the hallway width). Keep it straight.
• Fire Rating: If this is a fire-rated corridor (1-hr typical), you must use a fire-rated control joint system (UL 2079 tested) with intumescent backing or mineral wool packing behind the bead. Standard vinyl beads melt and fail in a fire.

Pro Tip: Snap a chalk line, cut the board back 1/4 in. from the line on each side, fasten boards to the double framing only (not across the gap), install bead, then tape/finish.