Insulation and Vapor Barrier

We have an old house. We are redoing the old original half of the house. Wood Frame. Blown in insulation into the walls. Lath and plaster on the walls. Before I bought the house. The owner started to add insulation to the walls and screw sheetrock to all the walls. It is just held on by sheetrock screws. Now that part of the house does not heat well.
I watched an insulation video. It said put a vapor barrier on the heated side of the house. This keeps water vapor from being trapped in the walls.
My question is.... Since I am already insulated and have lath and plaster on the walls and then sheetrock .... Would there be a benefit to take down the Sheetrock. Put plastic on the plaster of the wall and then reinstall the sheetrock? or would it be to my advantage to put up Styrofoam sheets maybe a quarter inch thick to plaster and then install the sheetrock. What about vapor barrier?
Any input with experience doing this would be appreciated.
Thanks

Sorry trouble with posting - took too long to think.

Is there styrofoam then drywall tacked up over the old plaster and lathe walls? My best guess is that that was meant to provide a better surface for paint.
I would have resurfaced teh plaster, or ripped it out.
Not much real world gain in adding the styrofoam, unless there was NO insulation in the walls.

Unclear on the insulation - is this loose fill blown in? Did previous owner top up the stud cavities and the attic? That's the way to go if you don't plan to tear out plaster.
Focus on kitchen and bath spaces - anywhere with water vapor sources.
They need ventilation to outside, with condensate lines if possible (sometimes this is required by code).
The vapor barrier should be built around these areas for sure if you plan to go and add it in. And new insulation there while the walls are open.

Just suggestions.

Also see if your utility company, extension service or whatever can put you onto a good place to do a infrared chekc of where the heat is leaking out of your house. Pays off in the long run when you are buying heat!


good luck

Ok, Part of the old section of the house had the plaster and lather removed. But with all the insulation that was blown into the walls. That was a real mess. In other areas of the house. The walls still have the lath and plaster on the walls. Behind the lath there is blown in insulation in the walls. Then.......... He just screwed on sheetrock onto the walls. It is very strong. But it seems to me that that part of the house does not heat very easily. It could be my imagination. My Idea was that it needed vapor barrier. So I was asking if anyone thinks that it would be better to remove the sheetrock. (only screwed on). Then put plastic on the walls before re attaching the sheetrock or would I put on thin Styrofoam insulation on the walls, Actually right between the old plaster and the sheetrock sheets? I still have bags of blown in insulation that was saved by old owner, I plan on using this to fill in any gaps I see. There are very few gaps though.
Thanks

Hi Jeremiah,

As a historic home restoration professional, I get this asked a lot. I always recommend no vapor barrier as these do not allow the building to dry to the inside. This may seem like no big deal, but if you didn't detail your windows or roof properly, then it will soon become your worst nightmare.

What you are really after is a way to stop the air from exiting the home into the wall, as this air typically has a higher moisture content than outside air and if temps are lower than the dewpoint, that airborne moisture will condense inside of the wall. If it were me, I would remove all the drywall that is practical, tidy up the insulation and then either add an air barrier/vapor retarder or go with what's called the air tight drywall approach, since drywall with plaster/paint is a vapor retarder/air barrier.

Air tight drywall is easily achieved with a latex-modified gypsum plaster. This sounds expensive, but is the very cheapest finish for the DIY type. For each 5-gal bucket of all purpose joint compound add 1 gal of latex paint. Make sure to buy the non-toxic varieties of both; I use Proform joint compound which is Greenguard certified and a zero VOC latex paint like Benjamin Moore's. Mix the 2 well and then apply with a 9" roller, troweling smooth before it dries with a Marshalltown plasterer's trowel or similar.

Sand between coats to get that really flat pro look. If you are happy with that cool, but I usually will paint on a lime wash and trowel that wet as well. This gives the wall that old world look that is finally becoming popular. Lime is extremely hygrophilic, so this final layer will actually pull moisture out of the wall assembly and move it to the interior where it can be dissipated.

I've attached a photo of the job we are currently working on that sounds similar to yours. I am using a paper smart retarder that is a little like goretex; cool but expensive. webpagewebpage

Sorry about the photo, it shows the original exterior doors mounted to a new frame in a wall built inside of the old blown in insulation with lath and plaster wall, insulated with rockwool and sealed with DB+. Hard to tell, I know.

Excellent advice from Bill. If you are noticing discomfort, try to track down air leakage and seal it up. The ceiling penetrations, basement/crawl/mudplate, and window jamb to rough framing are usually the biggest culprits to pay attention to.