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Lantern Junkie
Hi everyone ..
So I know there is a wealth of knowledge here on this forum and I'm looking to have some insulation done in my attic . I have a company coming to spray foam in-between the roof joist . My question would be should I run the ventilation batting from the eve to the peak or do I not have to worry about it with the spray foam . 
The company I have doing it said it's not needed because there won't be any change in temp between the outside and inside to cause mold or mildew . Ive done some research online and found it done both ways . 
I'm just curious if anyone has ever done similar and has a preference .
Thanks very much...Ernie 
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Taco912
I have found that insulation preferences, types, method of installation and opinions, are very regional in the USA.  North, South, East, West and the heartland will vary with weather conditions, construction methods and local opinion.  In some regions there has been a push to treat attic space as "conditioned" space.  It is easy to get information overload when searching the internet.  I know, I didn't answer your question.  

On a practical level, doing repairs of any sub-system when buried in spray foam insulation adds a level of difficulty and cost way beyond.  Just an opinion.  
Coleman 243 Blues  #812
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Chucker
Growing up and living in the U.S. Midwest I've been told if you have ventilation in the attic (soffit vents, gable end vents, ridge vent, etc.), insulating the 'floor' of it is all you need to do. Here 12"-14" of blown in or fiberglass batting is good. 

If you want to 'condition' the temp/air in the attic, you've got a bigger job ahead, IMO.
Chuck
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Ridge Runner
It sounds like you currently have an insulated ceiling above a conditioned living space, with an open unconditioned attic space which includes soffit vent and ridge or gable vent?

If so, they shouldn’t block the existing attic venting system.

It would also be more beneficial to increase or correct your existing attic insulation level as opposed to adding a separate layer on the underside of the roof sheathing.

I don’t know what the code requirements are in your region but when we built in 2009 here in western Massachusetts it was R38 for flat ceilings and R30 for sloped ceilings. We installed two different layers of fiberglass batting criss-crossed to achieve R49 on the flats.

— L.J.
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Lantern Junkie
Thanks everyone for the replies ..
If this helps..my house is a single level with the attic space being just for storage . I did insulate the floor between the lower level and attic space with loose insulation and a vapor barrier . The roof in the attic space is just open spaces between the trusses . I may in the future turn the attic space into a bedroom or office space down the road . 
My house was built in the 30's so the walls have very minimal insulation and I was told it's more beneficial to insulate the attic space rather then the walls because 75 percent of heat loose is through the roof rather then the walls . Im thinking thats true in my case because the snow melts off the roof in the winter . 
I'm just concerned with the ventilation with the spray foam between the roof trusses directly against the roof sheeting . 
Thanks very much...Ernie 
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RobSchroff
"Joists" run horizontally - it sounds like you've already insulated the main floor ceiling/attic floor.  

Your house, if built in the 30's, likely has "rafters" rather than "trusses" 

If you intend to condition the attic (heat or cool it) at some point, then it makes sense to insulate the space between the rafters (the underside of the roof sheathing) 

If you're not planning to condition that space, your time, energy, effort, and money will be better spent insulating the conditioned building envelope, including the exterior walls and the horizontal space between the main floor and attic.  
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Gunhippie
Thanks everyone for the replies ..
If this helps..my house is a single level with the attic space being just for storage . I did insulate the floor between the lower level and attic space with loose insulation and a vapor barrier . The roof in the attic space is just open spaces between the trusses . I may in the future turn the attic space into a bedroom or office space down the road . 
My house was built in the 30's so the walls have very minimal insulation and I was told it's more beneficial to insulate the attic space rather then the walls because 75 percent of heat loose is through the roof rather then the walls . Im thinking thats true in my case because the snow melts off the roof in the winter . 
I'm just concerned with the ventilation with the spray foam between the roof trusses directly against the roof sheeting . 
Thanks very much...Ernie 


Please, please tell me you put the vapor barrier against the ceiling and NOT over the insulation!

I've replaced three drywall ceilings due to homeowner putting vapor barrier over the insulation. This traps all inside moisture inside the insulation and results in collapsed ceilings!

You're much better off with no vapor barrier than with one on the wrong side of the insulation!
It's priceless until someone puts a price on it.
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Phat_Daddy35
I'm an insulation contractor in New England. If we were spraying this job we would not necessarily install ventilation. Ventilation is used to get the moisture out before it condenses on the underside of the roof. As long as your contractor is using closed-cell spray foam there is no need for ventilation because moisture and vapor cannot get through the foam. If they are using open-cell foam you might consider using ventilation since it can allow moisture and vapor to move through it. Although even with OC ventilation may not be necessary, your contractor will know your situation better than I would.
Just a word of caution make sure your contractor is reputable. Spray foam is great if there are no issues with the application. Off ratio foam doesn't happen very often but if it does it's a nightmare.
Chad
As my good friend Tom says " I'll leave the light on for you" (242 in my case)
Coleman 275 Appreciation Syndicate member #3535
MilSpec Ops #0350
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Lantern Junkie
Chad..
Thank you very much for the advice ! 
My contractor is using closed cell foam and they are very reputable in my area . They are spraying 3.5 inches from the eves to the peak . They also recommend I don't put the ventilation bats in for the same reason you stated . 
Thanks very much again....Ernie 
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