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Discussion Starter · #1 ·
I am planning an attic remodel for a client and have some questions about the insulation. I am going to get a rescheck done on the property to cover myself for inspection and to keep the insulation company honest. I know spray insulation is a great way to go but the rafters are 2x6's. I was told by the spray foam insulation company that I may have to fur them out because they are only 5 1/2" and more foam would possibly need to be added. There is currently a foil-coated foam in the bays. If we spray foam, that will obviously need to come down. Would bat insulation be a better way to go on this? Also, the homeowner wants to use the space behind the knee wall as storage so I will need to line the bays with plastic to keep the insulation contained. The access door will need to be well insulated. I looked online at some insulated knee wall access doors, but does anyone have a better suggestion? There will be a 5 ft knee wall added along the longest dimension of the attic. Help me out if you have some feedback, thanks.
 

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Discussion Starter · #8 ·
Why do you have to take the foam board out?

It probably has the same insulating value as the spray in foam.

The radiant barrier will no longer be any good but so what.

Andy.
i assumed that the board would have to come out so the spray foam would adhere to the bay. The slick coating wouldn’t be a solid bond, but perhaps the sides of the 2x6’s would be a good enough bond?
 

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Sean
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Clean & Primer on the radiant - check with foam manufacturer but that should be adequate & yes they will tell you which primer to use. Sure that is foam? Looks like radiant sheathing to me. If it is foam you have it made as you should easily hit the R38 with that foam / CC filling cavity & then plywood. Of course doing a hot roof means that rafters should be fully encapsulated by 2" Air Sealing: The Hot-Roof Option (thehtrc.com)
 

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Closed cell spray foam. Over spray the areas that will be hidden behind knee walls and above ceiling joists so the average insulation of the whole system gets above R-38.

You will have to provide the calculations that show the wall system as a whole meets code. Also, get a verification letter from the insulation company.
 

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Discussion Starter · #11 ·
Clean & Primer on the radiant - check with foam manufacturer but that should be adequate & yes they will tell you which primer to use. Sure that is foam? Looks like radiant sheathing to me. If it is foam you have it made as you should easily hit the R38 with that foam / CC filling cavity & then plywood. Of course doing a hot roof means that rafters should be fully encapsulated by 2" Air Sealing: The Hot-Roof Option (thehtrc.com)
I read the article, that was helpful. The attic is a little "cut-up" so CC foam is going to be the way to go. Also, since the client wants to be able to access the storage area behind the existing knee wall "pictured", it would be better to insulate from the ridge to eave. In the article, it says there are two ways to create a hot roof, either foam sprayed in place or foam board. What will be best to do with the current situation of the attic since it has the radiant barrier panel through the bays? I don't fully understand your post.
 

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Discussion Starter · #12 ·
Closed cell spray foam. Over spray the areas that will be hidden behind knee walls and above ceiling joists so the average insulation of the whole system gets above R-38.

You will have to provide the calculations that show the wall system as a whole meets code. Also, get a verification letter from the insulation company.
This is the first attic remodel I have done so I am trying to cover all my bases with a rescheck. This report should outline all of the required thicknesses of spray foam correct? Then you're saying overspray the areas behind the knee walls and above the ceiling joists just to cover myself for inspection. Thank you for the suggestion of getting a verification letter from the insulation company, I will definitely do that.
 

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Discussion Starter · #13 ·
I also heard that if you spray the radiant barrier sheathing with closed cell then you lose all the value of the radiant barrier.
 

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Sean
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Radiant barrier - yes it loses its effectiveness as mentioned above as it requires an air gap - BS4D: Radiant Barriers (thehtrc.com)
ResCheck = garbage in garbage out, remember it is just a simple calculating tool. In order to enter information in correctly you have to know the specs & more importantly it has to be installed properly to achieve those specs. i.e. full fill & what is the R-Value per inch?
Glad you did check out the article - sprayed in foam is for the interior while foam board is if you apply it above the roof sheathing. So if you are redoing the roof, you could add 2 layers, offset & taped seams to insulate then sheathe over it & roof like normal. In your situation - are you adding drywall - you can spray the cavity full & then as mentioned above the rafter has to be encapsulated BUT you could add a layer of foam board under it to break up the thermal barrier & then attach drywall over that which would give you a nice flat surface
 
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