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Old 03-25-2011, 09:51 PM   #1
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Not venting a metal roof.


The retrofit of our roof was done August, 2010.
Our house is a Lindal Cedar Home built in 1973.
It is chalet, open inside with a loft, and large windows. We heat with a wood stove.
My roof is a 12/12 pitch, and a cathedral ceiling.
Here is a synopsis of the project starting at the top:
26 gauge pole barn type metal roofing (dark brown),
Next, one side foil bubble wrap with the foil on the upper side (facing the metal roofing.
The roof is framed with 2X8's. The metal roofing is screwed to the 2X8's over top the foil bubble wrap. The 2X8's are filled with fiberglass insulation (R-30). [We realize we are not getting R-30 performance because the insulation does not have enough space.]
This framing is fastened to the existing roof with wooden blocks and lag bolts.
The existing roof is a 2" thick tongue and grooved Ponderosa pine ceiling deck with 1" of compressed styrofoam insulation. The styrofoam insulation was saved by the contractor. The 2" thick Ponderosa pine is also the ceiling of the house.
So, to conclude, here is my roof starting this time from the bottom:

2" tongue and grooved hardwood pine supported by 4X10 beams.
1" styrofoam insulation.
8" fiberglass insulation inside framed 2X8's.
foil bubble wrap (with the foil facing up).
26 gauge pole barn roofing.
The roof does have a ridge vent, and pole barn roofing has ventilation channels.

The roof does not seem to have any moisture problems. We had 60 mile an hour winds this winter with no problems. The house is now much easier to heat and cool.
I welcome any comments.

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Old 03-26-2011, 11:26 AM   #2
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Not venting a metal roof.


I don't think that's the way I would have done it(for obvious reasons)
Ron

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Old 03-26-2011, 02:44 PM   #3
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Not venting a metal roof.


Ron6519,
Thank you for the comment; I appreciate any input.

I finally got three estimates for the project. Most contractors and roofers would not even look at it because of the pitch of the roof.
The contractor that finally did the job admitted: 'two years ago I would not have "touched this job", but we need work, or I will have to lay off my crew'.
The other two contractors wanted to use ventilated insulated nail board with asphalt shingles.
I wanted a metal roof, and I wanted the roof framed for added strength and less weight. [We had two layers of asphalt shingles which weigh much more than the 2X8 framing and metal roofing.]
Lindal Cedar Homes uses this paradigm of framing at the present in their "green homes".
Once again, thank you for your input.
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Old 03-26-2011, 06:28 PM   #4
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Not venting a metal roof.


A picture of the framing of the roof might help. Note the following:
2 inch thick tongue and grooved ceiling deck.
1 inch compressed styrofoam insulation (saved by the contractor).
Framing attached to ceiling deck with blocks and lag bolts.
Attached Thumbnails
Not venting a metal roof.-framed.jpg  
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Old 03-26-2011, 08:05 PM   #5
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Not venting a metal roof.


With that construction, how does the hot air go from the eves to the ridge?
Ron
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Old 03-26-2011, 09:28 PM   #6
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Not venting a metal roof.


Ron6519,
I must begin by admitting: I originally posted this chat under another person's thread (not venting a metal roof, penny0322). Someone recommended I start a new thread.
Basically, my roof has very little ventilation.
I do have a ridge vent, and it is probably venting the top section of framing. The metal roofing does have ridges that are venting a minimum amount of air between the metal and the bubble wrap.
But, being objective, my roof is basically without ventilation.
After doing a lot of research, I discovered that the "real experts" in the roofing field do not feel ventilation is necessary if metal roofing is used.
The Johns Manville company makes two types of nail board. One is ventilated the other is not. The non ventilated nail board is for use with tile, slate, and metal roofing.
http://www.jm.com/insulation/buildin..._nailboard.pdf
According to research I have done on the Internet, commercial building metal roof construction does not use ventilation.
Other research I have discovered relates that the air in one's house is the main factor. The research states that "ventilating a roof will not solve your moisture problem if the air in your house is bad".
Since we "battle dry air" in the winter and run air conditioning the rest of the year, we feel that we have good air in our house.

At the same time, I am open to criticism and comments.
That is why I posted on this blog.
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Old 03-26-2011, 10:29 PM   #7
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Not venting a metal roof.


Roof ventilation keeps the heat generated from the Sun from radiating down into the living spaces. It also keeps the building materials from super heating, therefore extending their lives.
It has nothing to do with venting the living spaces, which should be isolated.
From the pictures, the construction resembles a "cold" roof, but without the ventilation. The cold zone under the sheathing and the roofing material isolates the living spaces from the exterior heat and keeps the snow from melting due to heat loss from the house.
Ron
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Old 03-27-2011, 08:16 AM   #8
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Not venting a metal roof.


From the "get go", I realized this project was going to be compromise. I accepted that my goal would have to be: improve the situation, not solve all the problems.
Having said that, I must admit the roof has improved the appearance of the house, and the house is much easier to heat. I used mush less firewood and electric heat this winter (and we had a hard winter).

My goal in entering this blog was to get input, and you have given me some. Thank you.

At this point, I wondering if you would take the time to relate to me how you would have "tackled" this project.
Thank you again.
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Old 03-27-2011, 09:39 AM   #9
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Not venting a metal roof.


Quote:
Originally Posted by maestro View Post
From the "get go", I realized this project was going to be compromise. I accepted that my goal would have to be: improve the situation, not solve all the problems.
Having said that, I must admit the roof has improved the appearance of the house, and the house is much easier to heat. I used mush less firewood and electric heat this winter (and we had a hard winter).

My goal in entering this blog was to get input, and you have given me some. Thank you.

At this point, I wondering if you would take the time to relate to me how you would have "tackled" this project.
Thank you again.
If the house is engineered to carry the load, I would have put insulated Panels(SIPS) on the roof. On top of that, I would have built a traditional cold roof and then the metal roofing.
Ron
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Old 03-27-2011, 02:38 PM   #10
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Not venting a metal roof.


Your proposal is excellent, and it is obvious you have done your research.
According to the Structural Insulated Panel Association (SIPA) website:
http://www.sips.org/content/index.cfm?pageId=269#33

"Does a building with a structural insulated panel roof need to be ventilated?
"Some building science experts, such as Building Science Corporation Principal Joe Lstiburek, have advocated venting the roof by providing an air space between the SIP roof panels and the roofing material (known as a “cold roof”). This practice is not a requirement for SIP buildings, but an extra measure to improve the durability and moisture resistance of the building."

A friend has a timber frame home with a roof that is insulated with SIPS. The company that supplied his home did not recommend ventilation, and his roof is not ventilated.

Thank you again for your input.
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Old 03-27-2011, 06:47 PM   #11
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Not venting a metal roof.


Have you read this, step #4: http://www.buildingscience.com/docum...r-all-climates

Find your Zone on the map or the closest city below map; http://publicecodes.citation.com/ico...001_par001.htm

The Zone # establishes the insulation requirements and v.b.; http://publicecodes.citation.com/ico...006_par003.htm

Where are you located?

Gary
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Old 03-27-2011, 08:16 PM   #12
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Not venting a metal roof.


Quote:
Originally Posted by GBR in WA View Post
Have you read this, step #4: http://www.buildingscience.com/docum...r-all-climates

Find your Zone on the map or the closest city below map; http://publicecodes.citation.com/ico...001_par001.htm

The Zone # establishes the insulation requirements and v.b.; http://publicecodes.citation.com/ico...006_par003.htm

Where are you located?

Gary
We are in Indiana at 5A, on the border of 4A.
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Old 03-27-2011, 09:20 PM   #13
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Not venting a metal roof.


So you need R-20 of rigid foam board. With the remainder in f.g. (or other) to total R-38; http://publicecodes.citation.com/ico..._11_sec002.htm

That Code is based on this, pp.11, step #3,4; http://docs.google.com/viewer?a=v&q=...J6MkJknmaD7nGQ

This will help on the fiberglass, I put together a while ago; The "biggest loser" in fiberglass insulation....

Gary
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Old 03-28-2011, 09:55 AM   #14
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Not venting a metal roof.


GBR in WA,

Thank you for all the great information.
So, to have "done it right", I would have needed approximately 3 inches of styrofoam, and enough fiberglass to get me "the rest of the way" up to R-38 (probably 6 inches).

Like I said in an earlier post, this project had a budget. And it would have doubled or tripled the cost to get me up R-38 with styrofoam and fiberglass and the extra framing. I would also have had to deal with the extra weight on the roof.

Most of the contractors wanted to use ventilated insulated nail board. There is no way I could have reached R-38 going "that route".

Thank you again for all the information, research, and especially for taking the time to share with me.
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Old 03-28-2011, 11:21 PM   #15
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Not venting a metal roof.


Glad we could help! The thicker foam board should be next to the metal, not at room side, to stop the moist air from reaching and condensing on the metal. The bubble-wrap needs a 3/4" air space from the foil, otherwise it's only R-1 rather than R-3; http://www.energyvanguard.com/blog-b...diant-Barriers

Not really for a heating climate; http://www.healthyheating.com/Page%2...g_sys.htm#MNEC

http://www.homeenergy.org/archive/he...0915.html#fig5

Anymore questions, ask away....

Gary

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