# 7 inches of R-38 really necessary?



## MT Stringer (Oct 19, 2008)

I just insulated the ceiling above our garage with R38. It was not previously insulated, but I installed a slit system AC unit so I can be comfortable in my woodshop!  While at it, we also increased the insulation over one bedroom and bathroom on the same end of the house as the garage.

The insulation company said in our area R38 has become the standard. No argument from me.
Amazingly, it has helped reduce sound coming in from outside of the house.


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## Windows on Wash (Aug 30, 2011)

R-30 to R-40 is not going to be that big a deal.

Going from R-10 to R-38 is a big deal.

Keep in mind though, if you have blow in fiberglass, it is only working at about 50% of its intended R-Value.


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## joecaption (Nov 30, 2011)

For a better ansewer go back and add where it is you live in your profile.
http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table

You also need to concider what type venting you have, if the attic has been air sealed (filling any holes where wiring and plumbing were run through the top plates, light fixture and ceiling fan boxes)
Really need to make sure the soffit vents are not covered with insulation and in most cases a vidge vent works best.


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## LuckyFoot15 (Jan 3, 2012)

May be trying to get the extra work. The highly rated company in IL that came out to quote me wanted to install a few hundred dollar attic fan, but had zero experience or knowledge of air sealing or ventilating the attic. They just blow the insulation in for $2k. Yikes! 

Get a few more quotes and see how they compare. Another tip is: look up a few home inspectors and see what they recommend. A good inspector will know the minimum values and methods recommended for your area.


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## AllanJ (Nov 24, 2007)

If you already have R-30 in insulating value, it's certainly more than one inch. (It could be one inch of fiber glass fluff plus several inches of somethine else underneath.)

If it is really just one inch of insulation over the ceiling panels or plaster then the R-value is certainly much less than R-30.

Fiber glass batts intended to provide R-40 of insulating value will actually provide much less if squashed to less than the intended thickness.

It is okay for insulation in the ceiling to extend above the tops of the joists. If you wanted to add an attic floor at a later date, you would need to shim the tops of the joists so the floor boards or panels don't squash down the insulation.


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