OT, roof insulation question

seems to be allot of insulation knowledge here.

my Girlfriend has a house with a cathedral ceiling, house built in 1950, 2 x 6 rafters, little or no insulation in that area. Syracuse winters range from very cold to warm which causes ice dams and water damage and its getting worse. anyways priority is to prevent water damage first with energy savings secondary.
different contractors are saying different things:
one guy wants to remove decking in that area , lay in 4 inch fiberglass with baffles over it, then re deck with proper ventilation. two others say no ventilation and pack area with blown in cellulose.

what say you?
thanks

surplusjohn said:

seems to be allot of insulation knowledge here.

my Girlfriend has a house with a cathedral ceiling, house built in 1950, 2 x 6 rafters, little or no insulation in that area. Syracuse winters range from very cold to warm which causes ice dams and water damage and its getting worse. anyways priority is to prevent water damage first with energy savings secondary.
different contractors are saying different things:
one guy wants to remove decking in that area , lay in 4 inch fiberglass with baffles over it, then re deck with proper ventilation. two others say no ventilation and pack area with blown in cellulose.

what say you?
thanks

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6 inches? Best bet is closed cell spray foam. another good way to go is to remove roofing externally install 6" of rigid foam installation add sheeting and re-roof. There a guy on youtube watch his talks


dee
;-D

Rigid foam in a closed cavity without a perfect moisture barrier is a recipe for disaster in Syracuse. Moist air will get by the foam and condense, with no means for escape.

2x6 rafters do not give much room for insulation, standard out here is 2x10. So I do not like the idea of reducing the amount of insulation that is there. That guy is right about needing an air channel though. You do not say how big the roof is or what it is. I am guessing not to big and comp shingles since 2x6 wont span much.
If it was me I would pull the old roof and sheeting off and put rigid foam insulation in the cavity. This could be spayed in or foil covered sheets. It has incredible R-value and is light weight. Then the plywood roof sheeting, and then lay 2x2 furring strips on top of the 2x6 rafters with a second layer of plywood to take metal roofing. It is important that the entire roof be vented, a continuous ridge vent and low eve vent so that air can flow between the two roofs. 2x6 will only give you 5 1/2" of insulation so any heat inside the house will not take lonng to get through that thin insulation. This is where your ice dam is starting. Cathedral ceiling probably makes it worse because all the heat will gather up at the peak. The melted snow water runs down the warmed from below roof and re freezes when it gets off the warmed roof and hits the cold roof at the edge of the wall where the eve starts. This is why it is so important to have the air channel. I dont care what kind of insulation you put in there, 5 1/2" is not thick enough to stop heat flow. (always warm to cold) So you know heat will be melting the snow and you know what happens. The way to fix is to remove the heat going through the roof before it melts the snow and that is to allow it an escape path up the air channel and out the ridge vent.
This also works in reverse in the summer by not letting heat from the sun soak down into the living space. Heat goes down into the air channel and is then vented up and out the ridge vent.
I have a standard attic that I did the second roof inside and ridge vent the entire thing and the attic temp in the summer time (110F) will stay maybe 5 degrees above ambient temp. So on a 110F day the attic temp is 115F. I have no air conditioning and do not really need it. Happy to answer any questions.

wheels17 said:

Rigid foam in a closed cavity without a perfect moisture barrier is a recipe for disaster in Syracuse. Moist air will get by the foam and condense, with no means for escape.

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This is exactly why there needs to be an air channel for the warm air to escape out a ridge vent.

Your roof has to breathe. Meaning the plywood/osb needs air flow. If water gets under the shingles/metal/whatever, it will stay there and rot out your roof.

I would install the air vent foam strips, usually pink, on the roof. They're about 1 1/2" thick. This will create an air space between the roof and insulation and then install whatever you want for insulation. I like roxul insulation. Think if fiberglass and bread mixed. Non itchy, cut it with a bread knife, stays in place by itself. Little heavier, but has a slightly higher r value.

Sent from my 2PS64 using Tapatalk

surplusjohn said:

one guy wants to remove decking in that area , lay in 4 inch fiberglass with baffles over it, then re deck with proper ventilation.

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After thinking a little more this guy is on the right track. I would NOT use fiberglass but use 4"ridgid foam with foil facing, shiny side down to reflect the heat back into the room. (as opposed to shiny side up to keep the suns heat out) All edges should be filled with canned spray foam so there are no gaps. Fiberglass is going to be R13 to R15? and foam is about R7.5 per inch so the rigid foam will give you double the R-value. if you can keep the venting in the existing bays it will be cheaper and also you should be able to have this part of the roof still match the rest of the house. I liked metal in previous post due to it being light weight to offset the added weight of second layer of roofing to keep max insulation in the 2x6 bay.

Found it:
This is a very good booklet that explains what you are needing to know. Years ago when I did my roof I asked them to send me a paper copy of it, maybe still available?
Talks about ice dams and how to stop them in one section.
https://www.airvent.com/index.php/v...1-principles-of-attic-ventilation-course/file
Title is: principals of attic ventilation.

Before signing any contracts, you should check with the building department or a construction engineer about the 2x6 rafters, especially with a cathedral ceiling whether it will support the additional weight of a second roof. As far as an additional roof I would again consult with someone in your area as to the proper insulating structure.

Tom

TDegenhart said:

Before signing any contracts, you should check with the building department or a construction engineer about the 2x6 rafters, especially with a cathedral ceiling whether it will support the additional weight of a second roof. As far as an additional roof I would again consult with someone in your area as to the proper insulating structure.

Tom

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Very good insight. This is why I think it best to use 4" rigid foam isulation in the existing roof structure so no additional weight is added. Should be a simple re-roof at this point. With the addition of better insulation and proper venting.

you know, you can fir the ceiling down to create any size cavity you need. Vent space is mandatory, without question. I would look into the spray foam insulation first. The rigid foam boards second. Keep in mind there are different types of boards and the R per inch, along with the price, vary considerably.

surplusjohn said:

seems to be allot of insulation knowledge here.

my Girlfriend has a house with a cathedral ceiling, house built in 1950, 2 x 6 rafters, little or no insulation in that area. Syracuse winters range from very cold to warm which causes ice dams and water damage and its getting worse. anyways priority is to prevent water damage first with energy savings secondary.
different contractors are saying different things:
one guy wants to remove decking in that area , lay in 4 inch fiberglass with baffles over it, then re deck with proper ventilation. two others say no ventilation and pack area with blown in cellulose.

what say you?
thanks

Click to expand...

You need ventilation UNDER, even with a steel and concrete roof or a commercial carpark. There's your starter test as to which contractors "understand" the tasking.

Roof-within-a roof works well for controlling heat loss. Outer/upper is for weather, is not insulated, hopes to not have too damned high an upper surface/lower surface temperature differential. That just "cooks" the roofing and distorts the joints. Then they leak. Not news.

Lower/inner is basically undisturbed by weather, is aimed at control of thermals. Pretty standard, actually - it is commonly the batting or chopped crap over yer living spaces, drywall under, open air, end or roof or ridgeline vents, soffit vent as intake, underside of the roof over. Vanilla, IOW.

Blow-in anything is a cheap-out on installation cost and aggravation. Looks best to hit-run, find next vict.. 'er "customer" installers. All blown-ins have one form or another of degradation, even weight-gain drawbacks.

Cellulose, its degradation and moisture absorption over long time spans make it one of the worst choices, long term. Scratch those two opportunist who pushed it and move-on.

Blown-in are otherwise not as predictable or as good as properly placed and edge sealed materials.

"Get it really good" and you'll want make-up air, too, BTW. Too tight a house is not a healthy house.


3CW, ....and in the midst of this very issue for the better part of a year and still plotting and scheming the nuances and options of parts of it. Because.. "what is under" has significant effect as to what works best for the "weather" choices OVER, too.

Insulation, I dig. Ventilation, I dig. Male up air, I dig.

Roofing material, Metro DC has growing challenges, OTOH.

Wind gusts - several times - from changes, be they "glow ball worming" or wotever - have torn brand-new 30-year roofing off in its third WEEK after install.

I'm looking at the materials rated for the Florida hurricane alley already. More folks may need to start doing the same. Legacy asphalt shingle is no longer a good gamble.

Still air 364 days of the year are zero help if 80 MPH + gusts tear the roofing to flinders that one out-of-step day.

Goods already proven better are "out there".

All the roof outside the walls and 3' up should have the rubber underlayment not tar paper. I would suggest the rubber underlayment on the entire roof. At least do the bottom and the ridge. That*will help with ice dam leaks.
Bill D.

Keep in mind that rafters/joists are thermal breaks and there are a lot of them. Foam on either side of the existing ceiling/roof would be much, much better than foam in the cavities and a lot easier to apply.

Rigid foam is also a lot cheaper than spray foam. Leave a gap between sheets and foam the joints.

surplusjohn said:

Syracuse winters range from very cold to warm which causes ice dams and water damage and its getting worse. anyways priority is to prevent water damage first ..............

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If that is the case, pull the shingles and felt and install this:

GRACE ICE & WATER SHIELD(R) | GCP Applied Technologies

That will take care of your water problem and needs to be done no matter what you decide on insulation.

Personally I would seriously question some of the advice you are being given here. Joe Lstirubek has done a large amount of formal studies on this subject. Lots of info at buildingscience.com and some of the other web sites like energy.gov. Go with what you learn there.

Steve

neilho said:

Keep in mind that rafters/joists are thermal breaks and there are a lot of them. Foam on either side of the existing ceiling/roof would be much, much better than foam in the cavities and a lot easier to apply.

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Except that shingle manufacturers specifically state that shingles are not to be nailed onto foam boards. So don't do that.

Steve

SteveF said:

Except that shingle manufacturers specifically state that shingles are not to be nailed onto foam boards. So don't do that.

Steve

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Who said anything about nailing shingles into foam? Foam furring strips would be 1 1/2" wide and lyed on top of either existing framing and new plywood nailed THROUGH the foam into the framing OR foam layed on top of the existing plywood in line with the framing below and again new roof plywood nailed through the foam into the roof rafters. In both cases the shingles are nailed directly to plywood/osb roof sheating. We do not even know that the OP's girlfriend's house has comp shingles. Good chance it does though.
Are wood shingles common in that area?

I find a couple things interesting as of late.
With the rise in re-roofing with steel "ag Panels"
they are doing them all over the place.
The manuf's new recommendation to NOT put the screws on the "peaks",
including the overlap peak.

I can see someone stuffing a heat tape in that "v" peak every 9"
ending at the gutter (loops slid up the slope maybe 1/2 the total roof length)

Unlike heat tape applied to shingles (on top) no penetrations, and no
getting ripped off as ice dams slide off.

should make a nice, protected install, that should last a long time.

SteveF said:

Except that shingle manufacturers specifically state that shingles are not to be nailed onto foam boards. So don't do that.

Steve

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Of course not. All those nails compromise the R value of the insulation and don't hold the roofing material on.

My point was that a continuous layer of insulation is much better than one penetrated by thermal breaks.

Anyway, surplusjohn, a few questions:

Roof pitch, roofing material, roofing condition, roof deck condition? And would your girlfriend entertain the idea of building a horizontal ceiling inside the house? Is there a budget? Help available from grants/weatherization folks?

Rob F. said:

..... Foam furring strips would be 1 1/2" wide and lyed on top of either existing framing and new plywood nailed ..................

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What you are saying is completely true and would be a good solution. However the OP has given us little details about the existing roof structure which may not be happy about the weight of a second roof deck or the budget available.

I see neilho is trying to get some of the details that would make this a little easier.

Steve