The Prodex R Value claim is based upon heat flow not thermal mass. They do explain it some here: http://www.insulation4less.com/Insulation4lessTechnicalArticles-267-Reflective-Insulation-Fact-vs-Fiction.aspx
Todd Miller
2017-02-19 05:43:32.000000
remodeling a 14 x 60 oakwood mobile home with a metal 3/12 pitch mobile home seamed roof
i started remodel from inside out .. removing the old insulation from the ceiling and replaced with roxul R30
I also removed the cardboard the manufacturer had between the top of the scissor style truss and the bottom of the metal roof (now i realize this was a mistake)
i have boxed the trusses with plywood glued and screwed to the sides of trusses togive them strentgh to hold 1 x 6 tongue and groove pine
once i got ceiling finished in the pine i noticed on mornings after it had got down to freezing or under the following morning as the sun hits the roof i get condensation dripping down the walls
now i have been told to go on top of existing metal with osb sheathing , tar paper , and a new AG panel metal .
but i dont see how this will stop my moisture that is collecting in the existing air space .as i believe i need to give it a route to escape
i have added a roof vent and a gable vent and even a 250 cfm fan in the existing roof to try to get airflow but this hasnt helped
the humidity in the living space is a fairly constant 34 to 36 %
im at a stand still on remodel until i get this condenation under control ..HELP
thanks in advance for any insight
DAVID MCCOMAS
2017-02-16 16:28:54.000000
i was afraid that is what it would come too lol well i was planning on putting AG OR 5 V on after i was done on the inside so im gonna say tearing the original seamed roof .. but where do i go from there ... i think if i tore original metal off i could gain a airspace for soffit and ridge vent type of ventilation ... so should i remove original metal roof .. put osb sheathing on top of trusses .. underlayment ..then a new metal 5 v or ag panel roof ? with ridge vent and soffit ventilation ?
DAVID MCCOMAS
2017-02-16 20:36:31.000000
What do you suggest ?
DAVID MCCOMAS
2017-02-17 09:22:55.000000
ok thank you for that information ...my take is that in my situation the unvented roof on the last page best suits my situation ..that being said
i should strip off the original metal seamed roof
put rigid foam board on top of roof truss (thickness ?)
plywood /osb decking on top of rigid foam (thickness?) (truss spacing is 24" oc)
underlayment
1x4 purlins run horizontaly
new metal
no soffit vent ?
DAVID MCCOMAS
2017-02-17 11:32:29.000000
here are some pics i have
will show after i stripped mobile home insulation out and the cardboard
put osb to the side of trusses glued and screwed (pic doesnt show but i have drilled 3" holes in osb hoping for air movement )
install of R30 ROXUL insulation i believe it is 7" thick i tapered it some so it would fit down to the wall
cieling is now completely covered with 1 x 6 tongue n groove pine
pic of outside of roof i had laid 2x4 up there just to get idea roof sags in between joist
DAVID MCCOMAS
2017-02-17 14:37:21.000000
OK COULDNT LOAD MORE THEN 1 PIC
ROXUL R30 INSULATION INSTALLED 7" thick tapered down to fit to wall
DAVID MCCOMAS
2017-02-17 14:39:37.000000
CEILING WITH 1 X 6 TONGUE N GROOVE
DAVID MCCOMAS
2017-02-17 14:40:31.000000
outside of roof 2x 4 just messing around roof sags between trusses trusses are not sagging
DAVID MCCOMAS
2017-02-17 14:43:16.000000
looks like i could get alot of R value using PRODEX TOTAL insulating underlayment (WWW.INSULATION4LESS.COM) i dont see how but it claims to have a R value of R16 and is only 3/16 thick foil covered on both sides . anyone familiar with this product ?
DAVID MCCOMAS
2017-02-18 18:41:46.000000
no sheathing on the underside now ... yes the cardboard apparently was the vapor barrier they used
DAVID MCCOMAS
2017-02-19 09:20:49.000000
well if i would have done more research before getting rid of the cardboard maybe i would have avoided this situaton lol live and learn ...
ok so im good with what you stated above.. what R value am i needing on top the deck ? im near greensboro north carolina not alot of snow but we do get some time to time from the chart in the publication you posted link to earlier looks like im in zone 2 or 4a so that would indicate R5 to R15 ...R5 is not that hard to do with rigid foam board (1" thick if i remember correctly ) but R15 would break the bank in rigid foam .. and thank you for all your expertise on the subject
DAVID MCCOMAS
2017-02-19 09:42:02.000000
ahhhh good news finally lol how about the roof decking thickness ? t russes are 24 " on center local lowes tells me 7/16 osb is fine ?? seams thin to me but obviously i dont know lol
DAVID MCCOMAS
2017-02-19 09:48:45.000000
ouch ... plywood is atleast double the price but i am not a fan of OSB either .. and i have to do it right this time i have advantek sub flooring thank goodness it has held up to the rainforest i have created very well i cant say enough good things about it . ok ... so would spraying under side of metal with closed cell foam be a viable option ? would that be better ? just trying to get all my ducks in a row here and figure out what i can afford to do .. no i dont want to take the tongue n groove down but seams to be the cheaper way . however the new roof was in the plans just not this soon . which way would be better ? if i put plywood sheathing on top of the trusses i could come up with a little more then a 1" air space between insulation and bottom of plywood and incorporate a soffet vent as i would like to build a 6" (atleast) overhang on the new roof . would this be beneficial ? also i could blow in more insulation and fill the cavity up ..and go ahead and blow in on the ends of the trailer where i have a flat ceiling and havnt done any remodel (have not took ceiling down or added roxul insulation on the ends only 24 ' in the center where the 2/12 ceiling is )
DAVID MCCOMAS
2017-02-19 22:17:16.000000
Whats easier to tear off...the ceiling of the roof?
Eric Novotny
2017-02-16 17:23:08.000000
Just putting on sheathing may not solve the issue. You are going to need to incorporate some insulation on the roof deck prior to the metal to make sure the framing is staying warmer (i.e. closer to interior temps) and therefore not having the condensation issues.
Eric Novotny
2017-02-17 08:20:39.000000
I would suggest removing the roof, cladding the current structure with a rigid foam of sufficient thickness, covering the foam with plywood, strapping the new roof to that new substrate.
http://www.finehomebuilding.com/pdf/021221068.pdf
Eric Novotny
2017-02-17 09:24:48.000000
If the roof is unvented, vented soffit is not required. If there is an overhang, you will need soffit to provide a finished edge.
Can you post up some pictures? I can walk you through the process.
Eric Novotny
2017-02-17 13:35:05.000000
+1
I would not trust the underlayment with the insulation value.
Based on the pictures that you submitted, I am assuming that you will treat this as a "conditioned" roof (i.e. sealed and unvented).
Obviously you would prefer to not tear off the T&G at this point.
Is there any sheathing under that metal or was the cardboard the effective vapor barrier they were using?
Eric Novotny
2017-02-19 09:10:47.000000
You don't want to pull down the T&G I take it?
The honest truth isn't the best here.
If it were my home, I would plan on tearing off that metal and putting down plywood and covering that with foam, strapping it with the purlins, and venting the roof above deck.
That metal will still be cold unless you get perfect coverage with the foam and will still radiate temperature at the edges and be a condensation potential.
Eric Novotny
2017-02-19 09:24:09.000000
I think you are going to be good with 1-1.5" of polyiso foam.
Eric Novotny
2017-02-19 09:43:51.000000
Not much of a price spread there. I would go with 5/8 plywood, 4 ply. It is only going to be a bit cheaper per sheet and you have about 30 sheets there.
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