# Ceiling Insulation Question



## drewdin (Nov 25, 2012)

I am insulating the ceiling in my sunroom. The rafters are 2x6 so I only have 5.5" of space for insulation, I planned on getting an R23 for the 2x6 and I also planned on putting a 1" Rigid foam under that to try and get to an R value of 30.

My question is with the many different types of foam insulation, which one should I choose? I found one at Lowes and one at Home Depot but i am not sure which is better, both have an R value of 6.5 but i am not sure which is better for an interior ceiling?

Any help or suggestions would be greatly appreciated, thanks!

Home Depot Insulation

Lowes Insulation


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## nealtw (Nov 26, 2012)

You need to leave a gap above the insulation so air can travel from the soffet to the house roof for proper venting of the house roof.


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## AndyGump (Nov 27, 2012)

Well the foam should go directly under the roof deck sheathing, tight up against it too.
Then fill the rest of the bay with the fiberglass insulation.
This is just a very general description of how the code requires insulation in an un-vented attic space. I do not know your location and your local jurisdiction may require more insulation than what you have described here.

Andy.


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## drewdin (Nov 27, 2012)

Thanks for the info, the ceiling im trying to insulate is a porch that was turned into a sunroom. There are no soffits or attic, its more of a slanted roof off the back of my house.

@andyGump, I though the foam insulation acted like a vapor barrier and it should be under the insulation between the warm and cold zone?

Although its not the best picture, this is what I am in the process of insulating. My plans were to add insulation and then the foam. Do you recommend that I put the foam first and then the insulation? I live in Boston and its 20 degrees and snowing today, im trying to seal this up quick, thanks!


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## nealtw (Nov 27, 2012)

drewdin; Are we not looking at the bottom of the house roof at the top of this roof?


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## drewdin (Nov 27, 2012)

@nealtw, no the house roof is above and off to the side of this roof. Here is an outside side picture of the sunroom.


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## nealtw (Nov 27, 2012)

So we are looking at the original soffet inside. That is what I was talking about. If you close this up, you will have no soffet vents for that part of the main roof. The common way to deal with that is to allow air to travel from the outside of the shed above the insulation and into the attic of the main roof. Have I missed something?


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## drewdin (Nov 27, 2012)

Hi Neal, this roof buts up against the side of my house, the air would have no where to travel if I had soffits and a path for the incoming air from the soffit to go other than the inside of the house.

maybe this picture is better. my soffits, ridge-vent and everything else are on the top roof, not the sunroom roof. Since the house is a colonial gambrel, those side panels you see are parts of the interior of the house.


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## nealtw (Nov 27, 2012)

Now I understand that two don't meet. I would still look at venting this roof. This low slope and snow will sit here and the outside wall will still be a place to have the most heat loss. That heat loss is what causes ice dams and free flowing cool air above the insulation is your only defence. And yes you can vent the roof where it meets the wall.


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## drewdin (Nov 29, 2012)

the ceiling joists are only a 2x6, i dont have much space. I planned on putting Roxul R23 which is 5.5" thick for insulation there. My thoughts are that the insulation would help keep the heat in vs losing valuable space to try and vent the ceiling. What are your thoughts


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## nealtw (Nov 29, 2012)

This article talks about it.
http://www.inspectapedia.com/Energy/Roof_Venting_Need.htm


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## GBR (Nov 29, 2012)

If you don't want to vent the rafters, (as Andy Gump said), you need rigid or SPF (R-20) tight against the sheathing, then cavity insulation to meet your location's total R-value (R-38), see the chart map; http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting
The rigid foamboard requires canned foam at all edges for an air-tight seal. ADA the drywall to prevent air infiltration through any fiberglass/Roxul cavity insulation; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/

Gary


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## nealtw (Nov 29, 2012)

GBR: If you look at the whole room. Massive amount of windows will be hard to heat the room. As cool as the windows make the room feel the area above the windows will be the warmest and adding more heat for comfort will make the ceiling warmer than normal. So with that in mind insulating with out a gap will require more insulation than can fit in the space. Evan if Drewdin puts foam board below the rafter as mentioned he will still have less over the wall above the windows which will have no insulation at all.
I beleive that "could" cause ice damming which would be bad enough for roof leaks and redo situation but with no headers over the windows the weight of an ice dam could also cause structural damage.
A little heat lose thru the ceiling may be good insurance when you think about one bad ice dam bringing down a structure.


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## drewdin (Nov 30, 2012)

@GBR, would you recommend putting the rigid foam against the sheathing and then the roxul insulation? I planned on doing it the opposite way, roxul against the sheathing and then foam board. I have not mentioned it prior but the roof is a rubber in case that factors into anything. There is a 1" foam board and then its one giant sheet of rubber. 

I don't plan on venting the rafters, it will take to much time and money that I don't have right now. I do plan on the Roxul R23 and a rigid foam board as I stated earlier. I will tape the foam board seams but its going to be hard to seal around the recessed lights.

I looked into spray foam and it would cost ~1500 to coat the area with 1", the foam board and roxul will cost $500. Its a no brainer...

I might get the DOW spray foam and seal under the recessed light and then add the roxul/rigid foam but thats only an R4.


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## drewdin (Nov 30, 2012)

I also just realized that the electrician installed non-IC rated recessed lights in this area. Is this something i should have replaced? It would kill me to have 3" around each light that could not be insulated.


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## nealtw (Nov 30, 2012)

I would want IC but I don't think you have room for them. Recessed lights are not a good idea here.


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## drewdin (Nov 30, 2012)

Thanks neal, i hope i can make them work somehow.


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## nealtw (Nov 30, 2012)

If nothing else you could flatten half of the ceiling, you would have room for the lights closer to the house wall.


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## drewdin (Dec 3, 2012)

Hi neal, i got the electrician to replace the light fixtures with IC rated ones, on a side note. What do you mean when you say flatten half the roof? Thanks


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## nealtw (Dec 3, 2012)

2x4s level from the house wall to about half way on the ceiling.


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## drewdin (Dec 3, 2012)

ahhh, i see what your saying. so it would remove the jog in the ceiling and add insulation.

would you recommend using the foam board against the roof and then the insulation or have the insulation first and then the foam board? Thanks


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## nealtw (Dec 3, 2012)

I would put foam below the insulation so you don't get into a two vapour barrier situation.


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## drewdin (Dec 3, 2012)

Thanks again


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