I recently bought a house and want to add insulation to the attic, the existing insulation has the vapor barrier facing down to the sheetrock and there is a section where it appears that there is a silver aluminum vapor facing up. My question is If I want to add at least 3" of insulation what type do I get, The insulation with no vapor barrier? or with a barrier? I intend to put 3/4" plywood down on top of the rafters so I can have a storage space. Thanks mike

Quote:

---

Originally Posted by M21519

I recently bought a house and want to add insulation to the attic, the existing insulation has the vapor barrier facing down to the sheetrock and there is a section where it appears that there is a silver aluminum vapor facing up. My question is If I want to add at least 3" of insulation what type do I get, The insulation with no vapor barrier? or with a barrier? I intend to put 3/4" plywood down on top of the rafters so I can have a storage space. thanks mike

---

Ok Mike, I see what you are doing, I think. Building up a single blanket of batts between ceiling joists with another one on top is no problem. Minimize compressing the fluffed up batts when putting on the new ply sub-floor. Compressing insulation reduces the air pockets to a lower R value of the original design. Insulation batts come in 3 1/2 and 5 1/2 inch thickness and 16" or 24" widths of standard framing widths.
When rolled out they must be expanded (fluffed) to their thickness for optimum value. Moisture barrier craft or foil is always faced inward toward living areas.

If I am adding 3" on top of the old insulation do I get the insulation without the vapor barrier. The old insulation has its barrier against the sheetrock. In addition i have section of the attic that has old insulation with a black vapor barrier against the sheetrock and another foil barrier facing up. Can I put an additional 3" on top of the foil?

Conventional wisdom says a vapor barrier on the outside of insulation can lead to condensation and R value killing dampness and rot. So what you want is the one vapor barrier you already have next to sheet rock. It might be interesting to check the section with the foil on the top. It should be trapping moisture under it. Some moisture will always pass through any vapor barrier. You want it to be free togo out the roof vents.

I wouldn't take any chances. If there isn't any vapor barrier next to the sheet rock, I would turn it with the foil down. Then I would add batts without a vapor barrier or loose fill to the top of the joists. Be sure and leave room for air to circulate from the fascia vents up through between the plate and roof sheathing. Good air circulation is the key to avoiding condensation and ice dams.

Quote:

---

Originally Posted by M21519

if i am adding 3" on top of the old insulation do I get the insulation without the vapor barrier. The old insulation has its barrier against the sheetrock. In addition i have section of the attic that has old insulation with a black vapor barrier against the sheetrock and another foil barrier facing up. Can I put an additional 3" on top of the foil?

---

Sure, barrier is in, you can even blow your insulation in if there is a material house that loans the equipment, providing there is a minimum purchase. Putting another layer over the foil doesn't compromise anything either. Nm

Id Get Some R 13 With No Backing , The Barrier Sounds Like Its Already There, Hope This Helps , Nichols Trim And Carpentry