What's the Best Way to Add Attic Insulation to a Floored Attic?

curiousburke asks,

Hi Money Pit! I have a pine board floor in my attic. The attic has a walk-up staircase and 2×10 joists, so it’s meant to store lots of stuff. The old attic insulation is minimal, probably wool, but in fair condition. I would like to add more insulation, either batts or blown-in. I’m considering removing the flooring and adding 2x4s across, but I think that would mean I have to do blown-in insulation. I prefer batts because it would allow me to do the attic in stages without having to rent a machine several times. The flooring will of course be put back after. What do you recommend?

Our Answer

You’re wise to tackle this home improvement project. Attics offer the greatest potential for home energy savings, and also happen to be the easiest area to improve.

Whichever insulation material you choose for this space, make sure to maintain proper attic ventilation. It’ll protect insulation from the dampness of wintertime condensation, which can cut insulating power by one third and introduce a host of structure-threatening moisture problems.

Now, in terms of your specific project insulating an attic that has a floor, you have the right idea: You have to resist the urge to overstuff those 2×10 bays with insulation. Insulation works on the principle of trapped air, so if a space is too compressed or overstuffed, the insulation benefits are reduced or even eliminated. You asked about batts versus blown-in insulation, but I recommend a third option: spray foam insulation.

I insulated my own (older) home with spray-foam insulation recently, and it drastically decreased my monthly utility costs. Specifically, I used Icynene Spray Foam Insulation, which you can install in one step. Icynene is formed through mixture of two components—ISO and resin—which react and expand to create tiny bubbles in the plastic matrix that fill and insulate the space. Check out our Money Pit Guide to Insulation for my complete Icynene story. Good luck, and let us know how it goes!