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Tips on Insulating Odd Storage Room


noahpnw's Avatar
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Join Date: Feb 2014
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WA

02-07-14, 12:45 AM   #1  
Tips on Insulating Odd Storage Room

Hello all, Been working on figuring out a plan to insulate a storage room off of our upstairs hallway. The room is under the sloped roof in the corner of the house. A portion of this room also is above the covered porch which isn't sealed at all and is allowing cold air to freely enter the house.

The Previous owner added fiberglass Batt insulation directly between the floor joist to prevent air from coming through but this was not at all effective and I have removed this insulation. Also fiberglass insulation was added between the rafters which isn't doing a whole lot of good. Please see attached pictures to get a better idea of what I am trying to describe.

My plan is to frame, airseal and insulate a wall to separate the porch ceiling area from the conditioned space. The rest of the room i want to insulate with foamboard, tape the seams and fill the gaps with foam sealant. the rafters are not very deep, only 4" so I think I will have to lay the foamboard sheets over the top of them. To get it thick enough I may need to cut the foamboards to fit in between the rafters and add a second layer on top.

I was looking at R-Tech EPS Foam board with a foil backing for the job. Home Depot Recommended the Pink Formular XPS for a higher R-value and better vapor blocking performance.

I took several pictures of the room in question. Please take a look and let me know if you have any recommendations. I am new to all this insulation science and could use a few pointers. Thanks!

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calvert's Avatar
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02-07-14, 04:36 AM   #2  
Your plan is respectable. How are you going to insulate the new knee wall to close off the porch ceil. area from the room. If that is with foam sheets, fine, if it is with fibrous material make sure you put a solid sheathing material on the back side. Seal the new bottom plate to the floor with either adhesive or caulk.

When cutting the foam blocking material to go into the floor joist open bays and the slope of the roof you should cut them purposely loose to allow for a good firm seal with the can foam you would use.

I would use a foam that has the highest r- value . Typically that would be a polyiso core with a foil facing. Some brand names would be R-Max, Tuff-R, Thermax and there are others. They would usually have R-values in the 6-7 range/inch.

Since there is no source of heat specifically to this room and you are using it for storage I would not think it necessary to get crazy about the r-values, the concept of creating good air barriers is probably as equally important as the insulation. I am presuming the heat will emanate from the surrounding room and kitchen below.

One last point, what will be the lighting source.... Try not leaving any holes in the ceiling with a recessed fixture, maybe use a surface fluorescent and seal the wire hole.

 
Bud9051's Avatar
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02-07-14, 05:24 AM   #3  
Check local codes to determine what rigid foam will need to be covered with a fire barrier.

Also check code requirement for R-value.

What is the existing ventilation and what have you planned for the completed job.

A top objective is to create a thermal envelope with the air barrier and insulation continuous and in contact with each other.

Building Science Corp has many reference articles. I've attached one on vapor barriers but you can search their resources for more.
BSD-106: Understanding Vapor Barriers — Building Science Information

Bud

 
noahpnw's Avatar
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02-07-14, 10:46 AM   #4  
Thanks a lot for the replies and links, I'll read through that info.

What is the existing ventilation and what have you planned for the completed job.
There is some existing Ventilation. Where the sloped ceiling meets the hallway interior wall, there is a gap where it is open to the attic. Reference the first attached pic, if you enter the storage room door you can reach your hand up through a narrow opening to the attic. However there are no ventilated rafter bays that lead to this opening because of the shape of the roof. These rafter bays terminate at the roof valley which runs through the room and are unventilated. The soffit vents shown in the picture only ventilate to the ridge vent of the covered porch gable.

I had planned fastening foam boards over the rafters and leave a air gap between the foam boards and the ceiling. If necessary I would cut foam boards and seal them within the rafter bays as well, leaving an air gap for ventilation. The foam boards would be taped and sealed to provide a continuous barrier. The Product I was looking at was 2" thick R-Tech from Home Depot. From what I am hearing Polyiso may be a better way to go? R-Tech 2 in. x 4 ft. x 8 ft. Foam Insulation-310891 at The Home Depot

How are you going to insulate the new knee wall to close off the porch ceil. area from the room.
I planned on insulating the knee wall with the same foam board sheets as the ceiling. Planning on using "Great Stuff" Foam to seal all around the edges.
One thought, If I added a solid sheathing material to the back of the knee wall (cold side) I could add faced fiberglass batt in the stud bays, then put the rigid foam board over the top of that, then seal it up with foam sealant? Would that be a recipe for a moisture trap or would that help by filling the air gap behind the foam board with fiberglass. Thanks so much.

 
calvert's Avatar
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02-07-14, 02:41 PM   #5  
Regarding the foam on both sides of the separation wall, I would opt for thicker foam on the exterior side and fibrous insulation between framing and then the drywall with no foam on the interior side.

 
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