I have a 3-story 1979 built multi-home apartment that I’m replacing a rotted-out subfloor. The subfloors throughout the apartment have a 2” concrete screed placed on top of it. My thought is that the screed is to either to maintain fire protection or a sound barrier between the floors. When replacing the floor my thought was to simply install a concrete board on top of a new subfloor. Would a concrete board be sufficient to replace the existing 2” screed? Any other ideas that I could use besides placing another 2″ screed?
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Your attached images are of an unknown format and require downloading. I will not download ANY files for fear of what they may contain. You should consider posting them in .JPG or .JPEG format.
As far as the concrete "screed" goes, your terminology is off. I presume you mean that there is a 2" thick concrete TOPPING over the subfloor. It may very well be a gypsum material (aka gypcrete) rather than concrete. There is a density (weight) difference - gypcrete is about 70-75% of the weight of an equal thickness of concrete (about 18 PSF vs 25 PSF).
I also assume that you are removing that cementitious material in order to get to the subfloor, so it would have to be replaced in order to maintain the original floor elevation.
I'm not sure about the building code implications of NOT replacing the 2" of cementitious material - perhaps a conversation with the local building official is in order before you go too far.
Wow, that makes a lot more sense. Thanks for the insight.
Consider using a self-leveling compound to replace the concrete screed for your subfloor. It offers a smoother finish and easier application, ensuring a level surface for your flooring installation.
My guess would be that the cementitious layer is for sound deadening. Fire resistance is usually obtained with drywall on the ceiling. Fire burns up, not down so a layer of cement that probably doesn't have the strength to be self-supporting without the wood framing wouldn't offer any protection if the framing and subfloor catch fire from below.
In an apartment building 50 years older than yours, there was a similar material, about 1 inch thick only in the bathrooms. It had cracks and some damaged subfloor so I have removed 3 of the four bathrooms, glued and screwed cement board and then installed ceramic tile. I am in the process of the fourth. In my case, one layer of cement board and the ceramic tile provided the correct thickness to blend in with the wood flooring elsewhere. It has always been my guess that the original plan would have been for ceramic tile but as the building was divided into a fourplex in 1929 and things were generally well done that whoever was having the work done, as the project was getting near completion, looked at his stock portfolio and in a panic asked his contractor to save money anyway he could. This, of course could just be my fantasy.
Back to your floor, you will need to do something to level the floor. An inch and a half or two inch height difference is a recipe for falling flat on your face. I would do it in multiple layers of plywood subfloor or cement back board to make your finished floor the same height as the floor on the other side of the door. If you are good at concrete finishing, replacing it with concrete of gypcrete would most likely be cheaper and possibly faster. I know that no matter how many YouTube videos I watch, my concrete work still will not be smooth or level so I would not try concrete unless there was no other option.
I would second the first poster's advice that if code officials may ever be looking at this, get their opinion, not ours before you commit to a solution.
Replacing the existing 2" concrete screed in your multi-home apartment presents a significant structural challenge, especially considering its potential role in fire protection and soundproofing between floors. While concrete boards can provide durability and support for new flooring, they may not offer the same level of fire protection or soundproofing as the original screed.
Instead of replacing the screed entirely with concrete boards, you might consider a hybrid approach. One option could be to remove the rotted subfloor, repair any damaged sections of the existing screed, and then install a thinner layer of concrete or self-leveling compound over the repaired screed. This would help maintain the fire protection and soundproofing properties of the original construction while providing a smooth surface for new flooring.
Alternatively, you could explore modern soundproofing materials and techniques to supplement the concrete board installation. This might involve adding layers of acoustic underlayment or soundproofing membranes between the new subfloor and concrete board to enhance sound insulation between floors.
Before proceeding with any renovations, it's essential to consult with a structural engineer or building contractor familiar with local building codes and regulations. They can assess the existing structure, provide recommendations for replacement materials, and ensure that any modifications meet safety standards and building requirements for multi-home apartments.