No one stood there with an instrument to check this out. There were no such instruments. However, with the construction techniques of the time, it was likely that no seal against the outside air or sealing the inside air in would have been possible anyway.
The advent of vinyl and aluminum siding sealed many a house up and promoted wet insulation and mold growth. damp air passed through the walls into the cavities and was stopped by the siding. Venting the siding helped but did not stop this problem.
There were no vapor barriers. There were few sheet goods. Plastic was new to the markets and unused when it was.
In the center of the photo you will see a trial spot where chemicals were tried out to remove the mold. Here is a building that I worked on. It was clad in Aluminum, then later capped with a metal roof. It was sealed up tight as a tuna fish can. Then the mold started as the basement was damp.
Also, I think we were much healthier when there was this exchange of air even up to my high school days, when plywood and heavy insulation with vapor barriers appeared in houses.
With a space heater heating a small space, a gas heater, small wood stove, a gas range, etc., it is necessary to let air into the house. First they need air inside to combust the fuel, and second, the inhabitants need air to replace what air the burning fuel consumes. Carbon monoxide and carbon dioxide are not the only people and pet killers in a confined heated space. Once a flame dies from oxygen deprivation and the fuel does not stop, there is the plain gas still coming in.
Of course we use gas and smoke detectors to warn us of these killers, but still, there is enough of these gasses in a small space to be uncomfortable, to be constantly smelling the air up and to make a very unhealthy environment, especially since we, too, exhale CO2 and consume oxygen. Our plants may love it, and provide a bit of oxygen, but it truly is not enough.
So you can choose to build lots of air leaks into your envelope, fill your house...literally... with house plants, smother in one of may ways in your small space or be constantly awakened by buzzers in the night.
I do not really have an easy solution to this impossible choice. Bring outside air in with an air vent and use outside air to combust your fuel....but is this really enough to be healthy in a small space?
All of this became critical when Jimmy Carter was in office, and fuel shortages became the norm. We buttoned up the houses at that time, and air simply does not easily come into your house anymore.
Another unexpected byproduct of this tightening, is MOLD! Some molds will not exactly kill you, but they can be awfully unpleasant, especially if you are sensitive to them. Spores go everywhere, and soon your walls and possessions are covered and often stained by the mold beyond recovery. Those few deadly forms must be promptly treated professionally, and can often put you in the position of having to find alternate places to go and burning or scrapping the materials infected and indeed, possibly the entire house.
Dehumidifiers will help. If you have no electricity, you can get the dryers that are available in grocery stores and hardware stores that attract moisture to a chemical. Some drop the moisture into a reservoir and last much longer especially with refill crystals.
Wash mold with chlorine or chlorine based products immediately, and always be on the lookout for it in corners, and in blind spaces like cabinets and closets...We are so fond of these in tiny houses!
Drill decorative holes in doors...clover patterns are easy with a bit and brace or electric drill, hearts are traditional, as are flowers and their stems and leaves along the seams between boards, using the seams as the stem of the flower. This will help air to circulate a bit. Leaving doors ajar will help as well.
Tiny computer fans that consume very small amounts of energy will help to circulate drier air into these spaces.
It is hard to pack these spaces with our possessions and still get air circulating to all the surfaces. The Damp-Rid crystals will help. but may not be enough.
If you get a leak from outside, or have a corner where there is no air circulation, you are almost certain to get mold or mildew.
Another issue is absorbent materials. Carpets in storage spaces are a real no no.
Clothing harbors mold, unpainted wood or plywood absorb moisture...Paint them.
If you do get mold and clean it off unpainted wood, paint it to seal it up. Cardboard boxes will absorb moisture and promote mold growth, but plastic will seal moisture in to a box and promote mold inside, even if it WILL keep mold from growing on the outside in a storage place. Let in all the air you can, but stop the water from coming in....now how do you do that????
You cannot make your house clean enough to stop mold!
Using those vacuum storage bags for all soft and absorbent articles will help immeasurably, but make certain that anything put inside is BONE DRY!
Do not cram your spaces full. Allow air to circulate in all spaces.
Remember, that mold spores are everywhere...you cannot eliminate them in the air, the soil, on pets and on you! You must be vigilant and watch for signs of mold and for places it may be starting, unseen. Be aware of smells and coughing or stuffy noses in your house.
Gas heat is notorious for putting moisture into the air, as there is lots of moisture in the gas. If you have it, or NOT TOO DRY WOOD heat, you must be doubly vigilant and should start the heating and cooking(steam trapped in the house from your tea water and the moisture from a composting toilet is pretty bad too.) season in your sealed up house is the time to start the drying inside the house.
Summer, as the mold grows above 45 degrees, can be awful, as the mold loves the warm and humid summer air.
If you live by the sea or a lake, make checking for mold a daily activity!
Mold is much like the barbarians on the borders of Rome....you may keep them at bay, but they will never be defeated. The only remedy is constant vigilance.