Old historic attic, need insulation recommendations

Old 05-05-14, 12:33 PM
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Old historic attic, need insulation recommendations

I have a farmhouse built in 1816, unevenly spaced hand shaped 4" x 4" roof trusses supporting a slate roof, the slate is exposed on the attic side. The floor is open but needed for storage, so the only place for insulation is against the slate roof.

I was going to use fiberglass R30, lay it in and join pieces as needed to fill the uneven width. I was going to staple the 11 1/2 " batt down at the joists. Then I was going to use clear plastic or Tyvek wrap to cover all the joists giving it a little more strength to hold the batts into place.

I know you do not want to compress the batts but I do not know of any way to get R30 or more into the space without scabbing on extra wood to the joists and I hesitate to do this on a historic house.

I need help on ideas, I plan on buying material in 48 hours in PA. Also, can the insulation go up directly against the slate rooF?
Old 05-05-14, 02:31 PM
Join Date: Oct 2008
Location: New England
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Since you are on a tight time frame I'll get you started, but forgive me for being blunt.
No! No! and No!

Is this barn in CA or PA? If in CA, snow country or all warm.

I've been in several old buildings with the slate exposed to the inside and all were "see through". Last I talked to the building manager said it was common to get dripping during a rain storm.

R-30 can be compressed a bit, but its final depth determines the final r-value.

Insulating the rafters without ventilation is what we call a hot roof. If this is really a historic house a hot roof option is not the best choice. Those old boards and beams have lasted two centuries by being able to dry out naturally. Very difficult to predict what will happe if you enclose them.

Filled with fiberglass but exposed to the weather through the slate will fill the cavities with humidity which will condense at night with radiant cooling.

Clarify where this barn is located before I go into other options.


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