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Question DetailsAsked on 8/18/2015

Why is there tar paper strewn in the attic?

The house was built in 1900, a bungalow, and laid in the attic floor loosely was old fashion tar paper. Why? What purpose does this serve?

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1 Answer


Prior to WWII and even into the 60's this was commonly done - usually stapled down or adhered to the floor joists with staples (after hammer staplers were invented) or before that with a swipe of tar which might have released over the years so the sheets are loose. The theory was to hold in the warm air so it could not migrate to the attic - it was felt tarpaper was both a good air migration barriear (fair at that but only if fully joint sealed) and as an insulator - or course, negligable at that. Also acted as a barrier to water dripping through the ceiling due to condensation of warm household air leakage into the attic and condensing (or frosting) on the underside of the roof. One other thing is supposedly did (actually did not) is stop mice and rats and bats and insects and such from getting under it into the insulation or down through ceiling penetrations into the house, which of course is better done with eave screening today because we now have solid roof sheathing and a water barrier layer under the shingles - back then the roofing was usually applied to strips of wood with significant gaps between so vermin commonly got into the attic between shingles.

Today that would not be done (hopefully) - partly because it is not a really good product for those uses, but also (especially when placed over insulation) it puts the vapor barrier on the wrong side for most climates - should generally be on the house side of the insulation to keep any moisture from the house out of the insulation and to stop airflow through the insulation.

Answered 5 years ago by LCD

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