Drafts, pissed off landlord, permit violations, asbestos issues. Sheet rock or lathe and plaster? Exposed beams, pumbing, conduit, etc. Critters!

Dust. Shitloads of dust.

And noise

Possible lead exposure, due to paint dust.

The thermal conductivity of brick is relatively high when compared to wood. 6 to 10 times higher. It is 30 times higher than insulation.
As a good rule of thumb you can estimate brick’s thermal conductivity at 1 Watt / DegC m^2/m meaning if you have one square meter of wall, 1 meter thick you will lose 1 Watt of heat if the temperature difference is 1 deg C. If the wall is half a meter thick you will lose 2 watts. if the wall is 10 square meters you will lose 20 watts. Get the idea? And that is assuming there are no leaks! .

@LuckyGuy I can’t figure out what thermal conductivity means because of a runaway definition crisis, and I can’t imagine that my wall is a meter thick! I’ll figue that you mean to convey the idea that it’d be a significant amount of heat loss.

But it looks so nice! Plan B: Maybe I’ll just whip up some mortar and build a brick wall on top of the insulated wall!

Here’s another idea. You might need to hunt around a bit, but there are various kinds of faux brick looking wallpapers, contact paper and even flooring (think vinyl sheets) since it’s the look you’re after.

You could also do a faux wall treatment yourself by skillful use of cut up sponges (for painting bricks) and a yardstick for ruling straight horizontal lines.

First paint the entire wall whatever color of gray or white you want the “mortar” to be.

Then choose several shades of maroon/orange/gray/red to give a mottled effect to the bricks and have at it.

I’m sure there’s a step by step online tutorial somewhere. There are lots of sites devoted to painting faux wall finishes so not that hard to find.

Years ago I did one small wall area in an apt of mine to look like faux burgundy leather with basically saran wrap and the right shades of paint. Then accented the edges with antique gold studs using a pencil eraser and gold and black paint. It came out pretty good if I do say so myself and all my friends loved it.

Doing faux wall treatments is tons of fun and very rewarding.

Here are a few options (both to purchase or DIY)
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https://www.simpleshapes.com/catalog/product/view/id/340/s/brick-wallpaper-peel-and-stick/?gclid=CLzNk9LO6coCFVc1aQodmOUPBQ
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https://www.etsy.com/listing/184577091/vintage-brick-vinyl-self-adhesive-peel?utm_source=google&utm_medium=cpc&utm_campaign=shopping_us_supplies-commercial-low-other&utm_custom1=7f5f1e61-73da-4bbc-8e53-19445076496d&gclid=CN2axLjP6coCFYg-aQodwtkAzg#
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https://youtu.be/qi3_xc8RrXg
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http://homeguides.sfgate.com/make-sponge-bricks-walls-46633.html

Ranking the answers you already received (IMO):

Winner!: @cazzie Dust. Shitloads of dust.
Runner up!: @stanleybmanly. Pissed off landlord & noise.
Honorable mention: @Seek. Possible lead exposure.

Unaddressed: Mess, time and money

@Buttonstc Thanks for the ideas. I like the wallpaper one. I’m trying to see if those wallpapers are 2D or 3D. The problem is the walls are currently blue. I suck at painting so I probably won’t get the look with sponge painting, and I can’t see how I’ll get the natural look that way, either. Those people in the video make it look so easy.
@ibstubro I definitely wouldn’t do it without asking the landlord. I’m not that much of a jerk.

@dxs
There is such a thing as 3D wallpaper?

The links I put there are only two among many. I’m pretty sure you can find something that would fit what you’re looking for. I was pretty surprised by how realistic looking were the 2 that I linked to.

I know that the floor options (which are basically vinyl sheeting) do have bricks that are somewhat raised with the mortar sections indented somewhat if that’s what you mean by 3D.

I used something like that about 20 yrs ago for a really small kitchenette area. But it was obviously not going to be confused for actual brick. But it just made for a nice looking floor. Plus, it was easy to mop clean since it was a single sheet of vinyl.

I don’t know how large an area you’re dealing with but it could get expensive using a flooring option for a wall treatment.

How long are you going to be there, @dxs?
Have you found a place?

Hopefully indefinitely, year lease.
Have I found a place? Not until I find someone else to rent it. Until then, I’ll be looking at pull-ins.

Good luck with finding a decent roommate, @dxs. At least you have the upper hand for now.
Is it just the one room?