Black paper layer in attic...what is its function and how do I patch it?

Question

I just went up into my attic (house was built in 1939) and found that there is black paper on the 'walls'.
Part of the reason for going up is to find out the back of holes that my electrician made while mounting something to the outside of my house.

What is the function of this black paper?  What if there's a hole in this black paper? Basically I can see to the outside of the house.  The hole is about 1.5" in diameter. How do I patch it?

Here are two pictures. One is with the black paper flap down, the other is with it up. I feel like there is black paper, then some sort of plaster (with metal wires) and then stucco on the outside? I don’t see insulation. All around there is black paper…except for the roof. I see some sort of foil type of material.

ArchonOSX · Accepted Answer

To this day tar paper is used as a moisture barrier under masonry products and roofing on the outside of homes.

You correctly identified the layers from inside out, tar paper, metal lathe, stucco. To repair it you will need to remove the damaged product and replace the layers.

Check the Internet for videos on repairing damaged stucco.

Good luck!

AndyW · Answer

Older homes usually had a layer of "tar paper" on top of the roof sheathing (plywood or OSB) and underneath the roof shingles. This paper was intended to be a "water resistant barrier" so that water or ice that migrated under the shingles would not soak the sheathing. Water-soaked sheathing will mould or rot, and create a health or safety hazard.

But I don't know what a layer of tar paper inside the roof would be for. Could be someone thought it would be a good idea to create a vapour barrier, before the common application of roof venting to control moisture?

Ali Reza Sharifzadeh · Answer

In new constructions method we use anti vapour membrane to prevent humidity penetration into the attic from inside of the house. The old black paper usually pasted on the plywood had the same functionalities except since they are not continuously isolate the roof there is a risque of humidity and heat infiltration into the attic

Answered by Ali Reza Sharifzadeh on March 9, 2021

Black paper layer in attic...what is its function and how do I patch it?

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