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How To Install A Plywood Attic Floor Over Insulation






Don M. from Enid, OK wrote:

I have rock wool �tween 6� X 24� joists in the attic. Can I install �� plywood on the floor, then lay batts to my R value? I�m trying to make sure that future electrical needs can be done without disturbing a whole attic full of fluff and make it easier to move around in a low attic.


Good question Don.

Many people lay plywood over insulation on an attic floor for a variety of reasons - maybe they want additional storage space or maybe just to make it easier to move through the attic. Whatever the reasons, I'll give you some basic guidelines.

Before you consider covering an insulated attic floor with plywood you need to determine if the attic floor will support it. As an example if you had 2 X 4 trusses it would be rated at about 10lbs per square foot which is about enough for the drywall underneath it and the insulation. So, if that was the case it probably wouldn't be a good idea to lay plywood over the attic floor. In your case you have 6" joists so you should be good to go.

Before laying plywood over an insulated attic floor take a look at the existing insulation. If it is batts, make sure the paper side is down. Also make sure the existing insulation isn't extending over the top of the joists. If so you may need to spread it around as compressing it will cause it to lose it's R-Value.

Take a look around the attic. Do you have any heated fixtures such as lights. If so don't cover them with plywood as it will create a fire hazard.

When nailing plywood sheets over an insulated attic floor you need to make sure there is adequate ventilation. If not you could encounter moisture problems particularly in the winter months which could cause the insulation to become wet and could eventually lead to dry rot of the structural members. It's important to lay the plywood perpendicular to the joists leaving at least half inch gap between the edges of each of the sheets of plywood. It would also be a good idea to drill small holes in each sheet of plywood to ensure adequate ventilation.

Finally, in your case you asked if you could add batts over the plywood attic floor. The answer is yes - just make sure you have followed my guidelines above first.

Related Tips and Advice:

How To Insulate Garage Walls
How To Install Blown In Insulation In Your Attic
How To Insulate A Concrete Wall
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