If the shiplap has gaps between boards, as is typical, it will not result in much soundproofing. Even perfectly tight and sealed shiplap won't do much unless you also engineer it for sound deadening. No ordinary wall material can compare acoustically to pre-engineered soundproofing drywall. https://modernize.com/home-ideas/17760/soundproof-drywall-creating-a-sound-barrier-comparable-to-8-layers I'd recommend using the soundproofing drywall along with a surface treatment to get the look: https://lelandswallpaper.com/product/joanna-gaines-shiplap-wallpaper/

Hello Lizzie, I live in a condominium and was tired of all the sounds coming from my upstairs neighbor. When I renovated the hall bath and used durock in the entire room (even the ceiling). My contractor also insulated the walls prior to installing the cement board.

Thanks for the quick reply. I will look at durock as an option. Using cement board I'm assuming you have a shower/tub in this room? My room is commode and sink only.

Solid boards (reg. drywall, plywood, ship lap, etc) have low acoustic ratings. About 3-5 dB worth for every 5/8" (thick) material. Unless your ship-lap is 3-5 inches thick, it won't do very much other than look different.

A regular layer of drywall (5/8") is roughly 5 dB. A solid 3/4" hardwood floor is roughly 0-5 dB. Ship lap won't be any different.

Acoustic 5/8" drywall = 18 dB. Hmmmm. That is SIGNIFICANT! It is also 3-4 times more expensive than regular drywall. But then again you get 3-4 times MORE acoustic insulation. You get what you pay for.

Personally, I would look at using Green Glue (not a glue...you still need fasteners) underneath the next layer of "finish" (whether that is regular drywall or ship lap). Green Glue (properly used) sandwiched between 2 layers of "rigid" boards (drywall, etc) can offer 18 dB worth of acoustic insulation. It is roughly $1/sf for the glue + the cost of the rigid material you are about to install. This is SIGNIFICANTLY cheaper than acoustic drywall - but requires more work/knowledge of how to use it.

And just to be clear - green glue is a liquid material that must CURE to become 100% effective. The cure-rate = 30 days. That means it gets BETTER as it ages. Don't expect 100% INSULATION on day 1. It will take one month to realize the FULL benefits of green glue.

Acoustic retrofits are one of the most expensive (most frustrating) renovation events we have. The average cost is $10/sf. If it can be done for LESS THAN $5/sf, then you are LAUGHING (but many people still cry at that price tag). Green glue + ship lap will get you a MUCH better situation than you have right now...but you must find the way to attach the ship lap to the wall. Green Glue is NOT glue.