Enclosed Porch Insulation


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Old 02-26-10, 02:15 PM
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Enclosed Porch Insulation

I am in the process of completing a 200sq ft enclosed porch. The porch will consist of approximately 90% low-e glass and is above ground with no foundation. The problem that I am encountering is that I have been informed by my County that I am required to have R-19 for the flooring and R-38 for the ceiling. The flooring consist of in order; laminate, cover, sub-flooring, and decking boards. I am going to place a vapor barrier underneath and then install batt material. The bottom is not an issue, its the roof that I cant get a straight answer.

The roof is 200sq ft and slopes off the house. It consists of 2X8 rafters and has a soffit in the front. The question I have is that I only have about 7.5 inches of depth in the rafters and will require 1 in of space for air in ordeer to vent and then 10" for a batt to reach an R-38 Value. I am thinking about using 1-2 inches of spray foam and some type of batt material. Besides the soffit there is no other way for the air to flow out. Should I use a combination of material or is there something I can do to insulate the ceiling. Also, can someone please recommend what would be best, within reason $, to use as a ceiling. I have had many recommendations from wains, vinyl siding (seriously considering), to drywall.

I am going to have a zoned heating and air duct into the room off my existing system.

I have pics of the porch and rafters if it would help

Any recommendations on the insulation and ceiling material would be greatly appreciative.
 

Last edited by kevinoz; 02-26-10 at 03:01 PM.
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Old 02-26-10, 03:19 PM
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Hi Kevin and welcome to the forum.
Easier if we know where you are. You have a couple of options for the ceiling, one is no venting at all, called a hot roof. The secret to that option working is a perfect air seal so no moist inside air gets up there. Not a pro on the subject, but it is being done more and more. Be sure to discuss it with your code people to make sure they will accept it.

As for the limited depth near the soffit, my understanding of the required R-value is that it is an average value or sometimes just the cavity itself. I'm sure if you achieved an overall average of R=38 you could make a good argument. Especially if you are adding extra to make up for the thermal bridging which they are most likely not including. In other words, go to R=42 everywhere you can or something like that. Again, ask the code people.

For the floor, air sealing is critical as any heat will go up and the cold stay down. Depending upon where you are, Georgia or Minnesota, R=19 may not be enough. Several recent threads here on the forum discussing the challenges of cold floors over unheated spaces.

Bud
 
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Old 02-26-10, 04:33 PM
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Just another jump-in. When you mention your floor, I am assuming this was a deck at one time. How high off the ground is it? Will air move beneath it freely? If so, be sure to include in your materials a covering. We usually cover it with 4x8 sheets of 3/8" plywood and apply 1x3's over the seams. This will keep more air infiltration from entering the room and will keep animals from pulling down your insulation. We also use solid vinyl soffiting to cover under an insulated deck/converted porch/sunroom.
Bud, how 'bout pushing the insulation as far as possible, leaving it at the edge of the room. This should allow enough soffit venting to enter above the insulation, while allowing the insulation to, well, insulate the room below. I have done it with a closet rod with a nail run in the end of it to help coerce the insulation to slide across the ceiling into the bay. Not sure it would work with the OP's situation.
 
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Old 02-27-10, 05:55 AM
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Forgive me for being a little lost. From what I read and understood is that the order would be my flooring, sub-flooring, decking boards, insulation, and then 4x8's with a vapor barrier covering the ground underneath. It was an existing deck, approximately 2 feet off the ground.

As far as the soffit, would that also go beneath the deck. I apologize, I like doing projects but walking in unchartered waters.
 
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Old 02-27-10, 06:14 AM
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OK, is the area under the deck enclosed from the outside, or exposed to air currents? Vapor barrier should go to the living (warm) side. However, in your instance, if the deck is enclosed, there should be a 6 mil vapor barrier on the earth.
 
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Old 02-28-10, 06:31 PM
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The joist below, where I was going to put the insulation are open 4X8's. I origionally planned on putting the insulation, with the paper on the insulation away from the floor, and then putting a vapor barrier on the ground MIL-6. If I understand correctly I am to put more wood at the end of the joist to close it in and then put a vapor barrier covering the ground. I know I may sound stupid, but how else are we to learn. If I put the plywood underneath do I need to put holes in it so it may breath or seal it off? I really appreciate your help. I thought the floor issue was done, the room is the one I am racking my brains over.

I am in Fayetteville, NC
 
 

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