# attic doesnt have vapor barrier, should i remove paperback batting and add spray foam



## Windows on Wash (Aug 30, 2011)

Where is the home located?

The paper is a vapor retarder level.

While the spray foam is not likely needed for vapor control, it will help with conditioned air loss. You can do 99% of the same positive benefit with proper spot sealing (i.e. air sealing) prior to adding insulation.


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## wantboost (Nov 1, 2011)

I'm in Ontario Canada. What u mean buy conditioned air loss? How do u do spot sealing?


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## Oso954 (Jun 23, 2012)

Conditioned air means air that you paid to heat or cool.

Spot sealing means crawling around the attic, moving the insulation, and spray foaming from a can (or other method of sealing) around every electrical box, pipe, vent, Holes in the top wall plates, etc, that would be a source of conditioned air escaping.


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## wantboost (Nov 1, 2011)

I think I wanna do the spray foam seems worth it? I won't crawl into attic and do the spot sealing


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## Chewbacka (Feb 27, 2014)

First the existing batt insulation unless recently installed is about useless to keep air from passing through, which is your current main objective. To achieve the ideal effect with closed cell spray foam a minimum of 2" is required. If applied correctly it will fill all penetrations from living space to attic unconditioned space. Local codes may require fire rated spray foam at all electrical penetrations to block gasses and flames from traveling through wall cavities between floors. Once all penetrations are sealed to code then you would apply the closed cell foam. On top of the foam you can blow in cellulose, or add Roxul roll insulation blanket, or a combination of each. Your contractor should be able to salvage and reuse most of your blown in insulation for reuse.Make sure you have adequate air flow above the insulation from the walls top plate area so air can flow from soffit vents without being hampered by insulation that would otherwise block air flow across the roof sheathing, preferably to a ridge vent where the moister air would escape via convection.
To accomplish this use rafter vents.
https://www.energystar.gov/index.cfm?c=diy.diy_rafter_vents
Make the attic access air tight too so losses of conditioned air are minimal.:thumbsup:


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## Windows on Wash (Aug 30, 2011)

So 2" of closed cell foam is require to form an air barrier?


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## Chewbacka (Feb 27, 2014)

No, 2" of foam is the minimum to stop the dew point from being able to pass through/penetrate at sill plate/ rim joist level of homes in the New England climate zone. Info from a Certified Energy Consultant/Auditor who my wife used to work for, and friend of our family. One could presumably use less in an attic in combination with other means of stopping air flow/penetration like Roxul/blown in cellulose, but 2" would provide an excellent vapor retardant, and a solid base on which to build the balance of an R50 in the attic envelope.


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## wantboost (Nov 1, 2011)

If I do r50 of cellulose should stop enough vapor?


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## Windows on Wash (Aug 30, 2011)

Chewbacka said:


> No, 2" of foam is the minimum to stop the dew point from being able to pass through/penetrate at sill plate/ rim joist level of homes in the New England climate zone. Info from a Certified Energy Consultant/Auditor who my wife used to work for, and friend of our family. One could presumably use less in an attic in combination with other means of stopping air flow/penetration like Roxul/blown in cellulose, but 2" would provide an excellent vapor retardant, and a solid base on which to build the balance of an R50 in the attic envelope.


I thought you were referring to the attic floor. 

2" on rims is good but entirely unnecessary on the attic floor where spot sealing will do the trick. 



wantboost said:


> If I do r50 of cellulose should stop enough vapor?


Is your attic vented? I am going to guess yes in this case. 

Vapor permeance across the attic floor is far less of a concern that is air tightness. Air movement carries 100X more moisture with it than diffusion if we are going to use round numbers.

Seal up all the gaps, cracks, penetrations, box out the lights, etc. and then blow cellulose over the top. You won't have any issues.


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## wantboost (Nov 1, 2011)

Ok I ll do that. Cause it's a difference of 6000$


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## Chewbacka (Feb 27, 2014)

Windows on Wash said:


> I thought you were referring to the attic floor.
> 
> 2" on rims is good but entirely unnecessary on the attic floor where spot sealing will do the trick.
> 
> ...


My reply is in blue text above....


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## Windows on Wash (Aug 30, 2011)

2" of CC spray foam is absolutely applicable on the rim joists. Your observations about the perm ratings are spot on with in regards to that location.

Bulk application of spray foam on an attic floor, in a vented attic design, is a poor allocation of resources in my opinion.

Once you seal up the bulk air leaks an envelope bypasses, the reality is that there is very little moisture make it into the attic via diffusion.


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## Chewbacka (Feb 27, 2014)

Windows on Wash said:


> 2" of CC spray foam is absolutely applicable on the rim joists. Your observations about the perm ratings are spot on with in regards to that location.
> 
> Bulk application of spray foam on an attic floor, in a vented attic design, is a poor allocation of resources in my opinion.
> 
> Once you seal up the bulk air leaks an envelope bypasses, the reality is that there is very little moisture make it into the attic via diffusion.


I wouldn't say 2" spray foam is a poor allocation of resources, unless what you refer to is $$ as the resource. I am not saying it is absolutely the only way to go, and there are ways to reduce the labor expense of installation, by buying the foam application materials and applying them oneself, depending on the skill level of the homeowner, etc.
I agree that one can achieve an R50 in the attic with other products like Roxul and borate treated cellulose, and the ultimate decision is the homeowner's to make.

Assuming the attic has proper ventilation, though I don't believe it has yet been confirmed, and proper remediation of existing air leaks into the attic from conditioned space, we are on the same page about needed R value at the attic floor.:thumbsup:


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## Windows on Wash (Aug 30, 2011)

Unless your funds are limitless, it is a poor allocation of funds. 

The ROI on 2" of CC foam over, for the sake of assumptions, 1,000 sq/ft is terrible as compared to spot sealing. 

All of the can light, flue, electrical, and other misc. sealing protocols are the same whether you are spraying bulk foam or spot sealing. 

Bulk application of 2" of CC SPF via froth packs or other homeowner applications is not recommended in my opinion either. Not only are they expensive and the yield is crappy, the quality is not nearly as good as it would be with a professional and rig set up. 

We are on the same page on the necessity of foam for air sealing, but in terms of R-Value in a traditional and vented attic, blown in insulation is the king when it comes to bang for the buck. 

$6,000 is a bunch to make up when you are looking at cost analysis. If the spot sealing will run him half of that, the additional $3,000 would go a long way towards other fuel savings measures. 

The poster has yet to confirm the ventilation equation but I hope his contractor would note that and make the necessary modifications.


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## wantboost (Nov 1, 2011)

I have a split level home one of the attics is 440sqft. Has 4 low vents and from what I can see 2 roof vents....?


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## Chewbacka (Feb 27, 2014)

Windows on Wash said:


> Unless your funds are limitless, it is a poor allocation of funds.
> 
> The ROI on 2" of CC foam over, for the sake of assumptions, 1,000 sq/ft is terrible as compared to spot sealing.
> 
> ...


Text in blue above is my reply.


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## Windows on Wash (Aug 30, 2011)

Good luck with the 600 board foot kits.

You have to get them good and warm for them to work well. I usually like them at about 100-110 degrees. You can warm them in a bath or bucket of warm water.

They are age sensitive so don't count on getting good yield if its more than a year old.


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## Chewbacka (Feb 27, 2014)

Yes, they don't improve with age.


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