Roof rafters against Styrofoam ceiling

[BearOrleen]

I have a split-level house where the entire lower floor has a ceiling made of polystyrene glued directly to the concrete. Now we're planning to build two bedrooms in the recreation room, and I'm wondering how best to attach the studs to the ceiling: should I remove the polystyrene or cut "channels" for the studs so they fit snugly against the concrete ceiling, or can I place the studs directly against the polystyrene and secure them with expansion nails?

I've asked both various building suppliers and my brother-in-law who has a construction company, and everyone gives different answers. Some say to remove/score the polystyrene, while others say I can keep it and secure through the polystyrene.

What are the pros and cons of the different options?

We will put up another ceiling sometime, but that is far off in the future.

 

[Duttarmajster]

I would remove the polystyrene to increase ceiling height and reduce fire risk. I assume the polystyrene was installed when the basement wasn't used as living space, to save a bit on heating. Alternatively, it might have been used for a rehearsal space in the basement. Now you want the insulation against the floor, not the ceiling. Concrete slabs should provide enough sound insulation between floors.

 

[BearOrleen]

I would remove the styrofoam to get higher ceiling height and reduce the fire risk. I assume the styrofoam was put up when the basement wasn't used as living space to save a bit on heating. Alternatively, there was a rehearsal room in the basement. Now you want the insulation on the floor, not the ceiling. Concrete joists should soundproof sufficiently between floors.

The ceiling height isn't affected much since the styrofoam is only about 15mm.

The styrofoam was put up when the house was built in the mid-60s and all 4 bedrooms, bathroom, laundry room, storage room, and recreation room are on the lower floor. There's only the kitchen, living room, family room, and a small panic toilet and walk-in closet on the upper floor. So the styrofoam ceiling wasn't put up afterward, and it's in all the rooms, including the bathroom.

 

[Duttarmajster]

Okay, I would remove the styrofoam anyway to make it easier to attach the battens and again, if it starts to burn you don't want styrofoam in the ceiling.

 

[Matti_75]

Just attach the studs through the insulation.