How do I seal off an open attic shared with the townhouse next door?

Building codes usally require at least a one-hour fire-rated assembly between townhomes, so finding just a layer of plastic is a massive safety violation that should have been caught during the original inspection. Since the unit next door is currently empty, you have the perfect window to fix this without anyone complaining about the noise, but you need to prioritize fire-rated materials over just standard insulation or rigid foam board. The biggest challenge you’re facing is that HVAC blower and the ductwork cluster. In those tight spots where you can't realistically maneuver a full sheet of drywall, **mineral wool** (like Rockwool) is your best friend. It’s fireproof, doesn't itch like fiberglass, and it’s rigid enugh that you can cut it into "plugs" and jam them behind the ducts. You want to pack it tight enough that it stays put by friction alone, then use fire-rated "orange" spray foam to seal the perimeter gaps.

For the larger open areas where you can reach, you relly should try to get some 5/8-inch **Type X drywall** up there. Even if you have to cut the sheets into smaller, more manageable 2x4 foot sections to fit them thru the attic hatch and around the machinery, it’s worth the effort. Screw them into the framing if there’s any available, or use fire-rated construction adhesive to bond the pieces togather. You're basically building a patchwork quilt of fire-blocking. While you're at it, check the seal on your own attic access panel. If it's just a loose piece of plywood, you're losing a ton of AC through that door every day. I usually add some heavy-duty weatherstripping and a couple of latches to pull it tight against the frame. It's tedious work crawling around those blowers and ducts, but getting that barrier solid before a new neighbor moves in is the only way you're going to get any real privacy or peace of mind regarding fire safety.

That part about the attic hatch got me thinking. If the wall is supposed to be fire-rated, does the actual door to the attic need to be special too? Mine is just a thin piece of wood that rattles when the wind blows. I saw these insulated 'attic tents' online that zip up—woud those actualy help with the fire safety part or are they just for the heat? I'm worried if I fix the wall but leave a cheap door, I'm still in trouble if somthing happens next door.

Those zip-up tents are strictly for thermal gain and won't do a thing for fire safety. If you’re trying to meet code, the hatch needs to match the fire rating of the ceiling. Most people just glue a piece of 5/8-inch Type X drywall to the top of thier plywood hatch. For the door itself, look into intumescent gaskets. They're peel-and-stick strips that look like regular weatherstripping but swell up to seal the opening if they get hot. It’s a cheap way to upgrade a standard wood panel without having to install a heavy steel fire door in a ceiling.

Just a heads up if you go the drywall route on the hatch—that door is going to get heavy fast. I added Type X to mine and the original trim couldn't hold the weight, so the whole panel started bowing. I had to beef up the framing around the opening with some 2x4s just so the door had a solid ledge to sit on. If your hatch is the drop-in kind, definitly swap those flimsy plastic tabs for some solid metal barrel bolts to keep it flush and airtight.