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insulate finished attic

How to Insulate Finished Attic

I have a large attic with a ridge vent, but no soffit vents or other vents for air intake. As such, the attic gets very moist and cold/hot. I would like to finish the attic for additional living space. As such, would blow-in insulation be suitable to insulate and seal the attic prior to finishing? As I live in the Northeast, would I need to extend the rafters to get adequate insulation? Also, would I remove the ridge vent and leave in the floor insulation?

Our Answer

Insulating in small spaces is often tough. When your rafter is only 8" deep, you can use only 6" of fiberglass insulation as the rest needs to be saved to allow for ventilation, which is hardly enough. Additionally, it is very difficult to get insulation into such a tight space.

However, spray foam insulation can fill in the entire cavity. It has a higher R-value and doesn't need to be ventilated, and in my view, the best way to insulate a finished attic or cathedral ceiling. The Money Pit Guide to Insulation might be a useful resource. Good luck with the project.

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Best Insulation for Small Attic

Hi guys! Love the podcast! My husband and I are under contract on a house. During inspection, mold was found in the attic on sheathing and in the insulation. We are getting the mold on the sheathing remediated, insulation replaced and improving the ventilation by rerouting bathroom exhaust duct, adding a new ridge vent and air sealing penetrations like the recessed lighting.

The attic is not an occupied space and really too small and too cumbersome to get into (small scuttle in the linen closet). The quote we got was for cellulose insulation. However, we were wondering if it makes sense to pay more for spray foam or a polyiso insulation?  Thanks for any input!

Our Answer

Great job identifying the source of the mold issues in the attic!  Improving ventilation (the most important of which is getting that bath fan exhaust duct  extended), was absolutely the right thing to do.  As for insulation types, cellulose and spray foam are quite different. If you went with cellulose, for one, you'd need all that ventilation. Like fiberglass, cellulose is designed to work in an "unconditioned" space.  Heat is held to the ceiling level, and everything above that is at ambient temperature (hot or cold).

Spray foam, on the other hand, is designed to convert that to "conditioned" space, meaning ventilation is no longer an issue.  We used this on our 1886 home and it's never been warmer in the winter or cooler in the summer.

When it's very difficult to get insulation in a tight space in either case, spray foam insulation might be your best bet. It can fill in tough-to-get-to cavities, has a higher R-value and does not need to be ventilated. A good resource is The Money Pit Guide to Insulation, which discusses pros and cons of spray foam insulation and its types. Best of luck with the project!

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attic insulation, floor

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

Hi Money Pit!  I have a pine board floor in my attic.  The attic has a walk-up staircase and 2x10 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, you have the right idea: You have to resist the urge to overstuff those 2x10 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!

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Attic Insulation Question

I have a bungelow house with a metal roof. IN the attic space I am planning to convert it into living space and would like to insulate and drywall is off. When I look at the underside of the roof I see there is boards running length-wise and a space of a few inches in between them. In the spaces in between I see the underside of the metal roof. How would I go about insulating that? Would a spray insulation be best or batts? I am worried about condensation and making sure i do the job right. if spray, what happens in 10 years when i need a roof? Thanks for any help.

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Attic Floor Insulation: Adding New Attic Insulation and Floors

We want to add wood flooring up in our attic.  Before doing so, we were going to replace the existing installation.  Are we going to encounter any moisture problems with the new attic installation if we cover it with a wooden floor?  Are there any special precautions we should take?

Our Answer

When flooring an insulated attic, the most common mistake people make is squishing the insulation. Attic insulation works because it traps air.  Compress that insulation under a floor and the air gets pressed out, robbing the insulation of it's efficiency.
In a perfect world, you'd buy insulation just thick enough to fit inside ceiling joists, floor over and be done.  But, here is the kicker.  Most ceiling joists are simply not deep enough to hold the 15 to 20 inches of insulation required by today's energy standards.
I suggest you only floor the portion of the attic you absolutely need for storage.  For the rest, install 15 to 20 inches of insulation and let it rise above the thickness of the joists.  Also, be sure to use unfaced fiberglass batts, and make sure you have enough attic ventilation to avoid moisture build-up in your newly insulated attic floor.