# can you overinsulate?



## amakarevic (Apr 12, 2007)

Can you overinsulate if you have extra space? I mean, can extra (beyond of what's recommended for the application) insulation, let's say in an attic be bad in any way?


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## joecaption (Nov 30, 2011)

Only if it blocks the venting. At some point your just wasting money by adding more.
Where are you, and what do you consider over insulating?
Air sealing before insulating and having proper venting is just as important as how much insulation you have.


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## amakarevic (Apr 12, 2007)

Area around AC ductwork in the attic. The ducts have duct wrap insulation but the ceiling insulation is under it so I was going to put some 6" sheets without paper backing for extra protection. There is a condensation problem in this short stretch that is between the drywall and the insulated duct above. I will wrap some around there but was thinking about regular sheets above for extra insulation


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## amakarevic (Apr 12, 2007)




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## Windows on Wash (Aug 30, 2011)

+1

Can't really over insulate but there is a diminishing law of returns.


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## Fix'n it (Mar 12, 2012)

plus the weight. too much on the ceiling will cause problems.


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## grossjurry (Jul 16, 2014)

The only drawback I can think of would result from blocking air flow inside an insulated space. That would result in condensation. leading to mold.


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## noquacks (Jun 5, 2010)

Overinsulating by defacto, means you put on too much insulation . yes, you can!! 

How? after the optimum amount (determined by your local utility Co) you are wasting your $$ cuz it wont do anymore good in preventing loss of heated/cooled air. Thats all- waste resources/time, $$. In an attic, I believe its about 12" in FL/south. , more than that is a waste.


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## Windows on Wash (Aug 30, 2011)

grossjurry said:


> The only drawback I can think of would result from blocking air flow inside an insulated space. That would result in condensation. leading to mold.


What are you referring to specifically?


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## yuri (Nov 29, 2008)

It is not bad but you have to determine what your payback time per inch of insulation is. Depends on where you live ( temp diff between inside and out ). If you put too much insulation in and block the venting on the soffits then your attic won't breathe and problems will occur. They use a treated cardboard blocker where I am and mark the depth of blown in insulation on a rafter riser so they don't overspray. I have heard of houses having R60 where I am and if you stay in the house long enough it is worthwhile. Also will make the house more comfortable. However the best bang for your $$ is triple pane low e argon windows and sealing all air leaks before adding more insulation ( above R40 where I am ).

I doubt the weight has any issue as it is light. Maybe if you use fibreglass batts but even then I doubt it.


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## Energyrater (Dec 11, 2009)

Air sealing in an older home will pay off.

Insulating where there is little to none already will pay off, not so much when adding insulation where there already is plenty (see law of diminishing returns as mentioned above)

Replacement windows won't pay off (especially triple pane) unless your current windows are single pane wooden windows with the panes broken. :laughing:

Done plenty of energy modeling to show that replacement windows will not payoff no matter what the manufacturers or salespeople try to say.


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## Windows on Wash (Aug 30, 2011)

Energyrater said:


> Air sealing in an older home will pay off.
> 
> Insulating where there is little to none already will pay off, not so much when adding insulation where there already is plenty (see law of diminishing returns as mentioned above)
> 
> ...


That is a bit of a broad based statement when it comes to the windows. 

I agree with you that window companies gratuitously overstate the savings claims and hence the AG in various states have hammered them. 

If you are modeling solely on the thermal improvements of the windows, the payback ROI is much longer. 

I have done test in and test out on several homes after a window replacement project and the blower door number improvements were significant and absolutely will translate into savings over time and a tangible payback schedule. As fast as air sealing and insulation...not a chance. 

That being said, most folks are not buying windows based solely on energy savings. Most window purchases are facilitated by lack of operability and rot. Tell a person that has some single pane window with storms that sweat regularly in the coldest part of the winter (and have reasonable RH levels) that they just need air sealing and insulation and see what happens.


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## Energyrater (Dec 11, 2009)

> That is a bit of a broad based statement when it comes to the windows.
> 
> I agree with you that window companies gratuitously overstate the savings claims and hence the AG in various states have hammered them.
> 
> ...


It sound like we generally agree in that there needs to be an air leakage component (flaw) in the window for them to pay off. But triple pane windows are so expensive that if a homeowner replaces a double pane window with tiny leaks at the corners with a triple pane, they will never pay off.

Now if I was building my own house, because of my experience in this specific field, I would be willing to pay some of the first costs of some of the higher efficiency components for the comfort and lower utilities but only if they are financially viable.


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## Windows on Wash (Aug 30, 2011)

I think we are probably in agreement here.

As stated previously, most homeowners are replacing the windows because they are just worn out and not working. In that equation, upgrading and paying the slight premium for the triple pane over double, assuming the replacement cost is a fixed number to begin with, is a sound investment. 

I would always prefer to have the more efficient window and the total impact on wall R-Value when you compare a barely Energy Star window at U-Factor 0.30 vs. a nice triple pane unit of U-Factor of 0.18, can be noticeable. 

If you were building new, then we really have to get into the specific glazing packages for the different elevations and what makes best sense.


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## Energyrater (Dec 11, 2009)

> I would always prefer to have the more efficient window and the total impact on wall R-Value when you compare a barely Energy Star window at U-Factor 0.30 vs. a nice triple pane unit of U-Factor of 0.18, can be noticeable.


You know that thermally we're talking about an area weighted R-value of 3.33 as opposed to the the 5.55.

But you're right on, it's all about the air leakage and operation.


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## Windows on Wash (Aug 30, 2011)

Energyrater said:


> You know that thermally we're talking about an area weighted R-value of 3.33 as opposed to the the 5.55.
> 
> But you're right on, it's all about the air leakage and operation.


Yes.

The impact on total wall R-Value can be significant as the relationship is not linear. 

If you view a 2x6 wall as an R-12 wall (R-19 but figuring on all the thermal bridging of the framing), the total wall to window ratio to be 70 - 30 (not uncommon to see more window than that in these houses that are full of windows), the data shakes out like such:

U-Factor 0.30 window yields a net total wall R-Value of 6.74

U-Factor 0.18 window yields a net total wall R-Value of 8.90

That is a 32% increase in average wall R-Value across the total. That is nothing to shake a stick at. 

:thumbsup:


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## MaineLL (Jun 23, 2013)

Energyrater said:


> Air sealing in an older home will pay off. Insulating where there is little to none already will pay off, not so much when adding insulation where there already is plenty (see law of diminishing returns as mentioned above) Replacement windows won't pay off (especially triple pane) unless your current windows are single pane wooden windows with the panes broken. :laughing: Done plenty of energy modeling to show that replacement windows will not payoff no matter what the manufacturers or salespeople try to say.


For me (especially as a landlord) the removal of lead encrusted windows may be of greater value in replacing the old wood windows with lead weights than the significant improvement in appearance, function, thermal performance, and eliminated maintenance. It is impossible to keep up on the maintenance of 50 peeling lead painted and dried out glazing compound windows!


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## Energyrater (Dec 11, 2009)

MaineLL, been there done that with the landlording thing.

I'll tell you what's hard to keep up with..... The repeated repair and destruction of your property by lowlifes. :furious:

Sorry for the hijack :laughing:


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