How to Insulate 1920’s House Balloon Framing
Ruth Hendrickson, who lives in Lincoln, MA wrote to me with a very fascinating question:
"My wood frame house built in 1927 has wood shingles outside and plaster over rock lath inside. No wall insulation. Probably balloon construction. Is it safe to put insulation in the walls, or will I get water vapor condensing in the insulation causing mold and rot problems. I did search but didn't find anything on this topic."
Here's the answer Ruth.
Because of where you live in the cold Northeast - I'm just above you in NH - it would be a GRAVE mistake to add insulation in the wall cavity.
The reason your house is still standing with no wood rot is simple. The balloon framing used in houses of that period - I lived in one back in Cincinnati, OH in the 1970's and 80's - allows water vapor that passes through the plaster and lath to be vented up into the attic of your home.
Once up there, it usually was able to dissipate out gable vents or through the roofing. Many older homes had roofing material and roof sheathing that would allow lots of air to pass through them, but not rain water back into the attic.
Balloon construction was probably invented to do this job as houses built without this open passageway probably developed rot in short time as the water vapor in the winter time would condense in the cavity and be unable to EVAPORATE quickly.
Read this column I just posted about Vapor Barriers vs House Wraps to give you more background.
If there was a way for you to install a vapor barrier to STOP the water vapor from getting into the wall cavity, then I'd say move ahead with the insulation. But I don't know of any TRUE paint-on or spray on vapor barrier that would provide enough of a seal.