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Old 03-13-2010, 09:45 PM   #1
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need advice: to insulate or not to insulate?


i am going to replace my rubber flat roof and i am trying to decide between 1) white vs. black 0.60 mil epdm membane, and 2) 1" or 2" of polyiso insulation underneath the epdm.

I live in a 100y.o house and the 3rd floor (top) is HOT and stifling in the summer. I thought maybe adding insulation under the EPDM membrane will help with that, but i'm getting mixed answers (ie, 3rd floor will always be HOT, unless install an a/c there; small roof area so adding insulation won't help with electric/heating bills; adding insulation will make it even hotter!).
Then i thought getting white epdm would be better than black because of reflectivity, but again, getting mixed answers (ie, white epdm works if you live in the south, but won't make that much difference in the north...i'm in wilmington, delaware; white epdm efficiency decreases as roof gets dirty with dust and dirt over time, so have to clean roof every so often)

oh! and i have no attic space at all. i don't know what space there is between roof deck and my bedroom ceiling. i was hoping NOT to have to install insulation in the ceiling, that adding insulation in the roof is good enough...

please advise!!

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Old 03-14-2010, 07:38 AM   #2
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need advice: to insulate or not to insulate?


You want to use a layer of insulation under the EPDM for mechanical reasons, such as protecting the roofing membrane from nails backing out of the roof sheathing.

The insulation may also prevent some heat transfer but not enough to make a difference because heat rises, there for your problem is ventilation rather than insulation.

Before removing the roof look at adding Intake & Exhaust vents and once you have the roof off pull the sheathing up with it and hopefully install air baffles in between the trusses.
If you can not install the baffles from the roof down than you'll need to cut into your ceiling.

It's a pain and will cost a few bucks, but if you can get proper,
Intake installed at the eaves or in the lower portion of the roof field,
Un-Obstructed air flow in the ceiling cavity,
Exhaust vents at the higher points of the roof,
you will lower utility bills and increase comfort levels.

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Old 03-14-2010, 10:40 PM   #3
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need advice: to insulate or not to insulate?


thank you, slyfox, for your advice. i will look into possible ventilation options. my roof does not have eaves or soffits that i can tell. anyway, what is your opinion on white vs. black epdm?
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Old 03-15-2010, 10:38 PM   #4
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http://www.fpl.fs.fed.us/documnts/pdf2002/rose02a.pdf

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Old 03-26-2010, 09:43 AM   #5
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need advice: to insulate or not to insulate?


You'll need to check what kind of ventilation scheme you have, or perhaps there is no roof venting at all, very common with flat roofs.

If the roof is not vented, then I would go with a thick layer of ISO above the deck. 3 inches minimum if you wanna make an impact. There is no better way to insulate an unvented flat roof. If there is no insulation below the deck, I'd make the ISO thicker to compensate. You could additionally add some ins. below the deck between the rafters. This makes best use of your constrained ceiling/attic space but only do it if you also have ISO above the deck. Its best for the structure to not have ins. below the deck at all.
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Old 03-26-2010, 12:44 PM   #6
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need advice: to insulate or not to insulate?


I am not sure about the capability of your HVAC system, but a little air circulation throughout the house may also alleviate some of the temperature discrepancy between lower and upper levels. For the record, I would expect insulation to have a noticeable impact, though (as Mr SlyFox stated) there are probably mulitple sources of heat transfer to the inside. My choice of colors would be dependent on where I live. In warmer climates, I would opt for lighter colors. In cooler, darker (a little solar energy is a good thing in the winter, right?).
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Old 03-27-2010, 11:36 PM   #7
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need advice: to insulate or not to insulate?


Quote:
Originally Posted by rodeo View Post
If the roof is not vented, then I would go with a thick layer of ISO above the deck. 3 inches minimum if you wanna make an impact. There is no better way to insulate an unvented flat roof. If there is no insulation below the deck, I'd make the ISO thicker to compensate. Its best for the structure to not have ins. below the deck at all.
These are not accurate statements. The best available insulation for any building top is polyurethane foam. There is no thermal bridging, and no seams.

The decision to insulate above or below the deck depends on the construction of the building itself. If you have a warm roof construction, then by all means add insulation above the deck, OR to the underside of the roof deck.

If you have a cold roof configuration, then adding insulation above the roof deck would be a complete waste of money.

A hundred years ago, they nearly never (if not never) built any building with a warm roof configuration. They were nearly all cold roof applications with the building's insulation above the ceiling (if they had any insulation at all).

If it were me, I would check to see where your insulation lies. I bet you would be best served insulating your 3rd floor ceiling, keeping the conditioned air in, and the sun/cold out. There is no reason with today's technologies that you can't easily accomplish your insulating goals if you're willing to do what has to be done to get there.

Anyone telling you that it can't be done is feeding you hooey.
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Old 03-28-2010, 09:26 AM   #8
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need advice: to insulate or not to insulate?


ISO board, short for polyisocynate is practically the same thing
as polyurethane foam, if not identical. The R values are the same,
depending the weight of the foam.

An unvented flat roof in cold climes preferably should be insulated as a warm deck roof
though its not always done.
If its a cold deck roof, then it needs to be vented, or be uninsulated compltely.

The problem is unvented insulated cold deck flat roofs, lots
of ignorance rooted there.
Many times these roofs relied on poly/visqueen type
of vapor barriers on ceiling. This is almost always a recipe for
wood rot if there is fibreglass insualtion.
This type of VB needs to be perfect with no holes, something rarely achieved.

This type of ignoramus unvented cold-deck flat roof construction was quite common until
ISO board/polyurethane foam was invented in the 70's.
Warm deck construction now became much more feasible but there are still
alot of professional roofers that dont take this seriously.

If you're flat roof is unvented and its coming time for you to reroof,
think seriously of putting foam ABOVE the deck. There is no below deck
insulation schemes (FB batts or even cellulose) that are as robust.

It is more expensive, but its your once chance to do it.
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Old 03-28-2010, 10:07 PM   #9
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need advice: to insulate or not to insulate?


Most flat roofs here are unvented, with no condensation issues.

I disagree.. it is better to put the insulation below deck because it will not be likely to be removed when you next tear off the roof, saving the recurring expense of insulation replacement when re-roofing.

With a cold roof assembly, above the deck insulation doesn't do you any good. You still experience thermal loss due to the cavity above the ceiling and uninsulated structural members. Most times, there were no vapor retarders besides the original plaster and lathe ceilings, and never an issue with condensation...

You're right about the chemical makeup of ISO board... its identical to SPF,. but SPF was around in WWII, maybe longer.

Where are you located, rodeo? How long ya been in the roofing biz?
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Last edited by AaronB; 03-28-2010 at 10:10 PM.
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Old 04-04-2010, 05:53 PM   #10
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need advice: to insulate or not to insulate?


So are you saying, Aaron, that a warm deck design is not worth it?

If I have a cold deck, unvented flat roof, are you saying that laying foamboard above the deck during a reroof is not worth it?
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Old 11-02-2010, 12:51 PM   #11
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need advice: to insulate or not to insulate?


bump!

I found Aarons last few posts in this thread to be confusing.
Aaron appears to be an established experienced contractor so I ask him to clarify himself. He can start by answering the last post above.

edit: looks like aaron hasnt posted since may. end of that thread.

any other takers that want to defend aaron or dissect his insulation advice?

Last edited by rodeo; 11-02-2010 at 12:55 PM.
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Old 11-03-2010, 07:09 AM   #12
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need advice: to insulate or not to insulate?


Quote:
Originally Posted by rodeo View Post
bump!

I found Aarons last few posts in this thread to be confusing.
Aaron appears to be an established experienced contractor so I ask him to clarify himself. He can start by answering the last post above.

edit: looks like aaron hasnt posted since may. end of that thread.

any other takers that want to defend aaron or dissect his insulation advice?
AaronB is simply saying it's better to have the cavity 'dead space' between the ceiling and roof sheathing insulated and if that area is insulated properly than insulation on the roof is of little importance as far as preventing heat loss, etc.
If for some reason you can not insulate that 'dead space' area properly than the next best solution is to have insulation on the roof.
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Old 11-03-2010, 09:00 AM   #13
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need advice: to insulate or not to insulate?


so its better to do it underneath the decking to seal it off- is that right?
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Old 11-04-2010, 03:41 AM   #14
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Placing fiberglass insulation against the roof sheathing in cold climates is a bad idea unless:

1. the deck is ventilated ie: cold deck design
-OR-
2. there is also some/enough rigid insulation above the deck ie: unvented design


Aaron seemed to be saying that an unvented design was still OK without placing rigid on top.
I hope he isnt thinking to put visqueen plastic on the ceiling to stop moisture from entering the batt filled rafter cavity - horrors.

This is what my stupid durolast roofer did for me and said to me
He made me an unvented roof without the rigid on top. Then told me to put plastic against the ceiling if I was so worried about condensation.

"85% of all building lawsuits involve roofing issues"

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