Hello!

I was wondering if anyone could give me a few pointers on how to resolve a noise issue we are having.

Background

We bought a house with an attached ADU (converted garage, now a studio apartment) in Joshua Tree, CA and are in the process of flipping them to use as 2 vacation rentals. We recently started renting out the studio/converted garage side. It's going well so far!

Issue

When people are talking in the studio, that can be heard in the main house.  This will be a problem once we are done renovating the main house and start renting both units (the main house and the studio) separately to 2 groups...

Layout

The studio/converted garage is connected to the main house via 2 doors.  There is a tiny space in between, which has a water heater.  So, it look like this.

STUDIO | WATER HEATER | MAIN HOUSE (Dining Room)

Question

Is there anything we can do to resolve this sound/noise problem?  

Can we have sound proof materials installed in the tiny space between the studio and main house to reduce the noise level?

What type of materials should we use?

If there's no good solution, we are thinking we might need to treat them as one unit and rent out the entire space, but if possible, we would like to avoid it.

If you know of a good solution, can you please share?  Thank you so much!