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Can Spray Foam Rot Your Roof?

In the Q&A forum, Nick from Louisiana asked why these icicles appeared after he spray foamed the underside of his roof.

Posted on Jan 14 2010 by Daniel Morrison

Ice dams are a familiar problem in New England and other parts of the country where winters are long and cold. Snow on under-insulated and under-ventilated roofs melts, pools and refreezes to form a dam. Water backs up under the shingles and much to the horror of homeowners often finds its way inside the building.

Spray foam polyurethane insulation is supposed to be a hedge against that problem. By forming an effective seal around rafters, and offering respectable R-values, foam should be blocking the migration of cold air into the roof where it can condense into water.

But a post by a New Orleans resident in our Q&A section showed just the opposite seemed to be happening.

Nick had hired a contractor to install open-cell foam on the bottom of his roof deck, converting the attic from a vented to an unvented space. When temperatures dropped below freezing, Nick noticed icicles forming at the soffit near an old, and by then unused, vent for a bathroom fan.

The roof itself was virtually new, and neither the insulation contractor nor the roofer could explain what was going on.

"This leads me to believe that it has to do with the cold weather on the asphalt roof and somehow the warm air in the attic is going through the insulation in that area to cause the problem," Nick writes. "The question is what can I do to stop the condensation?"

Open-cell foam is not a vapor barrier

Closed-cell foam, with higher densities and a higher R-value, can be an effective vapor retarder.

But not open-cell foam, It has a perm rating as high as 35 per inch, according to a technical bulletin from Fomo Products Inc.

And this, Robert Riversong points out, could be the source of the problem:

"The open-cell foam allows water vapor to diffuse through to the cold-at-night roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. where it condenses and runs down, possibly saturating the foam which does hold water," Riversong writes. "Open cell foam needs to be sealed with a vapor retardant paint. If the installer didn't inform you of that, he wasn't doing his job."

Riversong thinks the foam has the potential to absorb significant quantities of water, allowing it to pass through to a cold, condensing surface--the bottom of the roof deck. He argues the foam is a hygrophobic (water repelling) material that morphs into a hydrophillic (water loving) matrix as it cures.

When subjected to a standard ASTMAmerican Society for Testing and Materials. Not-for-profit international standards organization that provides a forum for the development and publication of voluntary technical standards for materials, products, systems, and services. Originally the American Society for Testing and Materials. test, he adds, an Icynene Inc. foam sample sucked up 34% of its volume in water after 96 hours of submersion. Installed at a density of 0.5 lb. per cubic foot, it has the potential to take in 2 1/2 gal. of water per cubic foot.

"I've heard of Icynene problems under leaking roofs, in which the foam soaked up water like a sponge," Riversong says.

Whoa, writes GBA advisor Michael Chandler. "Open cell foam is hardly hydrophillic. Leave a chunk of it floating in a bucket of water for a couple of days and see how much water it takes on. Hardly any, I've done it."

While Chandler thinks the ASTM test here is inappropriate, Riversong is undeterred.

"There are many examples of open-cell foam in walls and roofs that has become so wet from vapor diffusionMovement of water vapor through a material; water vapor can diffuse through even solid materials if the permeability is high enough. alone that it could be wrung out like a sponge," he writes.

"An anecdotal report on a blog told of Icynene in a basement ceiling under a bath that developed a leak. When the foam was pulled, the subfloor was black with mold and there were mushrooms growing in the foam."

The whole roof is not affected

If vapor permeance was the problem, wouldn't we expect to see evidence of water over the entire roof deck, icicles forming all along the eaves rather than in an isolated spot?

Rich Bev suggestions Nick look for a crack in the condensation line from air conditioning equipment installed in the attic, which may be contributing to a water and humidity problem.

"It may be just a direct leak from the A/C to a poorly installed spot in the insulation," he says.

A not-so-hot job of installing the insulation also could be playing its part.

Chandler suggests that some installers plug up rafter bays at exterior walls with plastic film so the foam doesn't leak out the soffits as its applied. But that keeps the foam from sealing wiring and plumbing penetrations in the top plateIn wood-frame construction, the framing member that forms the top of a wall. In advanced framing, a single top plate is often used in place of the more typical double top plate., he adds, and allows humid air to collect in soffits where it can condense.

Taking short cuts as the foam is sprayed can result in voids in the foam between the rafters and the roof deck--another channel for warm air. He suggests a look inside the soffit to make sure the foam has completely sealed the top plate in the wall, and to check that foam has completely filled the rafter bays.

"So much of this stuff is about caring enough about the building science to get the details right the first time," Chandler ways. "Spray foam is 'hot' and there are a lot of get-rich-quick types going into green building with little care for quality or integrity."

GBA senior editor Martin Holladay is thinking along the same lines: "Is there any chance that the spray foam has shrunk away from the rafters, leaving cracks that permit warm humid air to contact the cold roof sheathing?" he asks. "Perhaps the moisture transport mechanism isn't diffusion--perhaps it's air movement."

Our expert weighs in

We invited Peter Yost, the Director of Residential Services for BuildingGreen, to provide his expert opinion on what might be causing Nick's icicle.

Peter Yost's advice:

To identify the source of the moisture, the first step is to determine if the dampness problem is local or general. If the problem is vapor diffusion, the moisture will extend to all (or most) of the roof sheathing. If the moisture is due to a roof leak or an air leak, the dampness will be localized.

A clue: The exhaust fan looks awful suspicious

Nine times out of ten, moisture problems are caused by bulk water or air leaks. I bet this is one of those nine times. If the moisture occurs in just this one spot — a spot that has a soffit termination for a bath exhaust fan and a condensate line — it’s hard to imagine that this is just coincidence. Even though this exhaust vent was abandoned for a through-the-roof route, are there enough obstacles in this section of the attic at the eave to make the spray foam application in this section less than complete?

Pete's bet: An incomplete foam job

My first bet would be that the spray-foam installer had a hard time getting a proper airtight application of the foam in this area of the attic. My second bet would be he or she saved this tough section for last; contrary to popular belief, spray foam installations are quite quality-dependent (and even more so with open-cell foams because their expansion is more than three times greater than closed-cell).

The pictures of the opened soffit are too close up to really tell us much — other than stuff is wet and probably moldy. Does the opened soffit suggest that spray foam installation in this section of the attic at the eave was deficient?

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Jan 19, 2010 8:08 PM ET

Apologies to those with an aversion to 'moist'
by Lucas Morton

Is that an exhaust fan vent I see there?

Jan 20, 2010 7:33 AM ET

Warm, moist air, right?
by Micah

Has to be some warm, moist (relatively speaking) air getting to the cold side of that sheathing, right? That has to be the cause of this - but where that warm, moist air is coming from is anyone's guess with the info shown. Could be that exhaust fan, poor job of foam install, penetrations not fully sealed, all types of stuff. But the root cause has to be warmer, moist air condensing on the sheathing... I think...

Jan 20, 2010 9:51 AM ET

I agree with Micah
by Martin Holladay

I agree.

Jan 20, 2010 11:26 AM ET

Brick Siding = older home ?
by John Brooks

How does the brick veneer indicate an older home?

Problem MAY be related to the vent in the depends

Another possibility is air leaking from wall to brick cavity to soffit
..............rather than from attic or top plate to soffit.
The whole thing is a 3d network of possible air paths....
Air sealing that attic does not air seal the walls.

Jan 20, 2010 11:37 AM ET

What Dan may have meant ...
by Martin Holladay

Perhaps Dan meant something like, "The brick siding looks old to me, so I think this is an older home."

Jan 21, 2010 2:51 PM ET

Looking like a case of not venting humid air
by Alex

As I understand it, this is a hot roof installation. I wonder how the roof/attic space is ventilated. The spray foam also working as an air barrier would prevent the humidity from escaping through the roof. Excess moisture will condense when it reaches the dew point and follow gravity down to the eaves where is appears to be freezing. I wonder if a mechanical ventilation system was added during the renovation work. I'm guessing active mechanical ventiation might solve the issue.

Jan 21, 2010 9:04 PM ET

one more thought...
by Micah

I just read the update. Lots of "gas powered appliances" up in that attic (as told by the new info posted). I recently had a really, really scary situation with a client where they had new (and extensive) levels of humidity in the home which was showing up in the form of condensation on the window's interior (with temperatures in the low 20's here in Indianapolis). I "scratched my head" for some time and took multiple moisture readings until I thought to check his combustion appliances. Yep... sure enough, there sat the HWH with the direct vent exhause pipe 1/2 way off the rubber boot. This was 2+ years into his owning the home (with previously no condensation issues) so we all assumed the client knocked the vent loose with the lawnmower outside or something...

So, sorry for the novel, but I would DEFINATELY check the gas appliances and how they are vented in that at attic space. It strikes me that Nicks says the "roof was converted... 1 1/2 ago" and (I'm assuming) that this problem is just now showing up. Maybe it didn't get cold enough last winter to reach the dew point at the roof sheathing? Don't know - but the issue has to be warm, wet air hitting that roof sheathing... The question now is where is it coming from?

Jan 23, 2010 8:33 AM ET

What the IRC says
by Ned Pelger

I learned on a recent project that the IRC allows the foam, without venting the sheathing, if closed cell spray foam is used. The less expensive open cell seems to be the problem here, I think.

Jan 24, 2010 6:13 PM ET

Type of spray foam in rooflines
by Carl Seville

Referring to Ned's comment, the 2009 IRC allows open cell foam in climate zones 1-3, and closed cell foam in zones 4 and higher. There are exceptions to this if alternate vapor retarders are used.

Jan 24, 2010 8:39 PM ET

Your Roof is Leaking
by Anonymous

Is that photo a speaker or a vent? I see a a/c condensate drain with frozen water too. Has the A/c been running here? Why is there ice in the drain? There is definitely a lot of moving water to make an icicle this big. Is that a bathroom window or a bedrrom or a house window? If its a bathroom, maybe your condensation / mositure theories hold up, but if not, this is from a leak somewhere. It is not the foam's job to stop leaks, that is the roof's job

Jan 26, 2010 7:06 AM ET

Fresh air
by Dan

Open cell insulation is not a vapor barrier. If the air inside the house is humid then the open cell insulation needs an air barrier to prevent the moisture from rising up through the open cell insulation and condensing upon reaching the plywood and then working it's way down the roof and out through the eaves.

Jan 26, 2010 7:32 AM ET

Ice Damns
by David Brooke Rush

It is possiable that warm moist air is moving into the exterior walls and behind the brick veneer and right into the soffit area. Once the spray foam was installed, the air became trap at the bottom of the soffit and now condenses on the roof sheathing at the bottom of the roof. When trouble shooting a problem "The first place to look, is the last thing you did". Good luck.

Jan 26, 2010 8:43 AM ET

The picture tells it
by rcartiva

If the roof is a hot roof, then why are the sofit vents still in the house (pic 1). You either vent a roof or completely seal it "hot roof". You have something in the middle. The vents are allowing warm moist air in the attic during the day and when it gets cold out at night it is condensing on the under side of the colder roof. I would also check to see that all the duct work in the attic is sealed as wells.

Jan 26, 2010 9:07 AM ET

Condensation from insulation next to roof
by Steven O. Suessmann

Sounds like a problem I had in my 1920's bungalow. I put fiberglas insulation next to my tyne roof, there was ice build up inside between roof and insulation, which later melted and dripped. there needs to be ventilation gap of two to three inches between roof and insulation. In my house the rafters were not consistantly spaced, so I put 2x2's next to the roof for ventilation gap, and recycled plaster lathes to keep the insulation from touching the roof. Worked well. No more condensation problems. I think too many times we try to seal a house up too much.

Jan 26, 2010 9:08 AM ET

Several possibilities and two culprits
by Dirigo

I agree with all the comments about condensation but I'd be looking into the heating units, how they're exhausted, and why open cell foam (absorbs moisture) was used instead of closed cell foam.

Jan 26, 2010 9:34 AM ET

Condensation from warm air inside house.
by Chris

You mentioned that the bathroom vents through that "speaker grill" on the eave. I think that the roof area is so confined that when the foam was sprayed they shot right over the vent hose from the bathroom on the other side of that window and it has created an evelope allowing warm air vs cold roof situation. You can get lots of condensation from a warm vent pipe and cold roof over a period of 48-72 hours.

Jan 26, 2010 9:57 AM ET

Where does the brick veneer and withe end....
by Phil in MN

I like a good mystery! Could the withe between brick veneer and sheathing be "venting" excess moisture into this space? brick and other masonry cladding can hold water. Sun can heat the brick work driving the moisture out as vapor into the withe. Cold surfaces can collect moisture- think dehumidifier. On a cold night the roof deck will generally drop below dew point and pull water to condense on the surface. Why not the underside too?

Jan 26, 2010 10:12 AM ET

by Michael

Is it in the bathroom area that you have condensation??? ("its now vented through the roof") If it is in that area, you could stop using the bath for a week and see if it dries up?? If it stops, then you know a vapor barrier or more ventilation at the bath. However from the water I see from the pictures, you are simply not getting it vetilated! Check the vetilation!

Jan 26, 2010 10:34 AM ET

moisture issue
by Biff Harter

eliminate the source of the moisture and you will eliminate the problem. Seal the subfloor with closed cell foam. Paint the interior walls and ceilings with a vapor barrier paint. Seal the open cell foam with a vapor barrier then make sure vents are installed and used each time they cook or shower. Dehumidify and add a 4" supply and return to the attic air handler. This should eliminate any possibility of moisture being the culprit.

Jan 26, 2010 10:57 AM ET

by Brian Owens

I am building a house in Houston where we will be using open cell foam in the walls and roof line. This will seal the building envelope. The gas furnace and tankless hot water heater are in the attic. The furnace and hot water heater are designed for this situation with speacial vents that not only vents exhaust but brings in its own combustion air. Perhaps this is where the problem lies in an older house that has been retrofitted with foam insulation but is still using and old furnace and hot water heater sucking combustion air into the soffits.

Jan 26, 2010 12:18 PM ET

The poster claims a new roof
by Boats234

The poster claims a new roof and eliminates that possibility BUT I would revisit it. We had a record breaking 25+ "s of rain last month and we all know open cell absorbs moisture.

Most spray retrofit jobs are dammed/blocked at the top plate, so moisture from inside the brick veneer should have free comunication to the soffit vents.
As another poster noted the back up AC condensate vent appeared to have ice coming from that also. It is not unusual in our area to run the AC and the heater on the same day so a clogged condensate line is also likely along with the possibility of a poorly vented gas furnace. But that would cause high humidity levels through out the attic area..... maybe this is the path of least resistance.

Jan 26, 2010 12:21 PM ET

wrong foam...
by Don

Open cell will suck moisture ... recommend closed cell or if possible sealing the open cell as Robert Riversong has suggested. Providing the roof has no leaks, this should resolve the icicle problem..... this doesn't mean that there still isn't a broader humidity problem in the home that may need to be addressed. .

Jan 26, 2010 12:29 PM ET

more information needed
by Owen Sechrist

Phil's comments about the brick cladding and withe caught my eye. If the house is cooling down overnight and presumably cooler during the day than the outside tempurature then sun heating the brick creating water vapor which would then drive inward because the house is cooler is logical. Where this theory gets fuzzy is I have a hard time believing a 1960's house is going to have an effective vapor barrier beyond the withe forcing the vapor to move upward. We need more info about the wall assembly or assemblies.

I'm interested to know how many sides of the house have what appears to be an acrylic finishing system on them. Obviously the side with the soffit issue does not, and if I'm reading the description right seems to be the only soffit area afflicted with moisture problems. If that is the only exposed brick wall of the house I would consider that a clue suggesting inbound moisture is the culprit and that the inbound moisture is coming through the brick.

On the other hand the inconsistency could be based on a foam insulation gap in that area of the roof. Does this attic have a floor and if so was the perimiter removed so the insulation could be sprayed between the attic floor joists at the perimeter and over the top plates?

I'm leaning toward one or more air gaps in the insulation, possibly involving the disconnected bath fan vent(is the old duct still connected?) or an insulation installation issue that is causing water vapor to drive outward as the outside tempurature cools.

I don't think the existence of the old soffit vents is a significant contributing factor, although they certainly ought to be closed up if for no other reason than to reduce air penetration and improve thermal efficiency. I hope I don't eat those words. :-)

Jan 26, 2010 12:56 PM ET

Unvented roof deck
by gary55

The IRC may allow this installation; but it also requires that roofing materials be installed according tothe Manufacturer's installation instructions; one of which is benerally a minimum of one inch of vented space beneath the roof deck - check with the shingle manufacturer to see if this hasn't already voided the warranty on the shingles.

Jan 26, 2010 1:24 PM ET

spray foam rot a roof
by Ed De Medeiros

Going by those photos.Major ventalation issue.Adding foam spray to the attic is a good practice,but at the same time you have changed the dynamics of the attics airspace.
#1 Interior home pressure air test ! Find the air leaks in the building envelope
#2 seal interior air leaks windows,attic hatches etc.(1st picture shows a window at he test spot big time leak at the window.
#3 Supply indepentent source of combustion air at furnace and hot water tank as discribed located in the attic(this will help equalizing the negative air pressure in the attic.
#4 .Those old soffits got to go foresure, install maintenance free aluminum vented soffits,roof vents.
#5 exterior brick make sure the weeping holes are clear.Brick also needs good air movement .
Hope my suggestions help .GO SAINTS all the best at The SUPER BOWL

Jan 26, 2010 1:26 PM ET

by Harry Applin

Insulating under the roof deck will trap warm moist air in the attic and you don't want that. The ceiling should have been insulated. I lived in the N.O. area and am quite familiar with this problem. Who ever suggested that the roof deck be insulated is in the wrong, you want to keep the warmth and cool in the living space and not in the attic. If systems are in the attic, water, a/c, then protect them.

Jan 26, 2010 1:27 PM ET

How about that abandoned bath vent?
by T.C. Feick

If the old bath vent still has a path to conditioned space, or worse, the path exists but the hose was re-routed to the roof, an awful lot of bathroom moisture would have a nice path to the soffit. I also would definitely check the mechanicals as I have had a vandalized chimney cause the same condition described above. A CO detector would've alerted me to the problem sooner...

Jan 26, 2010 1:30 PM ET

Unintended Consequences
by John Brooks

I believe A Not-So-Complete Air Control Layer is concentrating air flow at the weak links.
Before adding the spray foam the house had more places to leak.
Incomplete spray foam and or lack of structural backer behind spray foam does NOT provide a complete Air Control Layer.
I believe that Spray Foam "the product" did not cause the damage...
An incomplete Air Control layer did.

Jan 26, 2010 1:34 PM ET

ice mystery
by Gary

Based on what info we have to go on I would have to look to the A/C unit installed in the highly insulated attic as my first major problem. I live in Canada and we install them outside,I have actually seen units run so long to try and cool a poorly insulated(almost none) house, and when they run this long the copper pipes that the gas charge runs through actually forms ice build up on it meanwhile it is 95degrees outside .Our units have condensate lines hooked to them to pumps the condensate created by the process of converting the warm air to cool air, is there a pump line on the unit in the attic and if so where is it being drained to ,is the line sweating and dripping out the soffit and meeting the cooler air as it drips outside and freezing. Bizzare as it seems remember the air in the attic will be hotter than the outside ,even more so with the new roof and the appliances installled up there adding even more heat. these are only a few of the issues I can point out based on the info we have to go on.

Jan 26, 2010 1:39 PM ET

That vent
by Gary

Is that an old bath vent or is that vent being used to vent the a/c unit if it is it may not be powerful enough to vent the unit properly and it could have major condensation build up on it ,which is slowly dripping out the soffit and freezing up in the process.

Jan 26, 2010 1:44 PM ET

Spray Foam Cannot Rot Your Roof But Water Can
by Mac Sheldon

I hate to be cynical, but the title of this blog point misguided. Spray foam cannot rot anything, including a roofdeck. Moisture CAN lead to rot if given a food source and mold spores along with the proper temperature a modicum of oxygen.

The problem here is obvious; moisture is migrating with air currents from under or within this house to a condensing surface where it's forming liquid water. There appears to be a substantial amount of water in an isolated area which makes troubleshooting relatively simple. The author did not mention that the entirety of the roof insulation was laden with liquid water. This would happen if the foam had allowed water vapor to diffuse through it where it condensed to saturate the foam. Instead, a relatively small area is shown and it's located near the bathroom. If the bath fan vent pipe is damaged or displaced, the fan could be discharging into the attic. It's also likely that since the attic above the bathroom is very small and there could be numerous obstructions that caused the spray foam applicator to miss or under-spray the area in question. This is my guess.

The pipe stub coming out of the eave is likely the pressure relief valve discharge and the icicle formed on it is from the opening in the eave and not from within the pipe.

The bottom line is that moist air is moving to a condensing surface; probably through large voids in the foam or missing foam at the point in question. Air flow has to be stopped, the affected area dried, then a proper foam job applied. The gypsum board on the ceiling of the bathroom should be removed and a thorough repair must be made.

And, by the way, open-cell foam is an air barrier material (air-impermeable) at 3.5" in accordance with ASTM E-283 and E-2178. Air is not flowing through the foam.

Jan 26, 2010 1:48 PM ET

10 X 3 affected area
by Gary

Where are the aplliances sitting in relation to the area of condensation / ice build-up.

Jan 26, 2010 1:50 PM ET

Hi Mac
by John Brooks

I believe that may be a condensate drain...that is acting like a pressure relief valve.

Jan 26, 2010 2:15 PM ET

by Linda

This is a MESS!
I don't have the same humidity problems, in my locale, as Louisiana, but I wouldn't have let an installer do this to my home!
Open cell foam, otherwise known as a big sponge, is a big no no in the Bay Area for all kinds of things, even in backing rod for sealant. Was the the brand certified for this use? What kind and composition is it? Hopefully, at least it is not Polyisocyanurate?
When the vents were sealed off, what accommodation for venting was designed? I didn't see much on the roof. Where is a vapor barrier?
Is the house air conditioned? What is that condensate drain for?
As others above referenced, gas appliances put out a lot of moisture. The venting design should have included that.
The problem is not a incomplete foam job. The photos clearly show that water is able to concentrate in the foam and at the roof line. Get it OFF Now!

Jan 26, 2010 2:46 PM ET

Tesing and Inspecting!!
by Eric Smith

I agree with Mac Sheldon. Additionally, as a building consultant who has been working with homes insulated with spray foam insulation for many years, I would also look at the following:
1. The gas fueled aplliances wihtin the attic should all be sealed combustion. If they are not, then you are introducing moisture into the attic every time they turn on (ie.. furnace during heat and hot water heater year round.) You may not notice a problem in the summer months simply because nothing wil freeze when you are looking at an ambien temp of say, 100 degrees fahrenheit mixing with an interior temp. of say 70 degrees fahrenheit.
2. Even if it is caused by moisture from these appliances, the air has to mix (hot/cold) Which would mean that the attic air is mixing with the ambient air which means there is a leak around that area of the eave.
3. The bathroom exhaust vent may have become disconnected from the soffit which means the air being discharged from the bathroom is no longer dumping outside but into the soffit. The air from within the building envelope is warmer than the ambient air and if it reaches dew point, which it probably did do, then you will definitely introduce condesation which will freeze (winter) mold if not dried out quickly (summer).
4. I would ABSOLUETLY NOT insulate the attic floor. In fact, if the spray foam was installed properly, the previously installed attic floor insualtion should have been removed. If not then you are trapping moist stale air within the attic.
5. You should have a minimum of 5.5 inches of spray foam on the underside of the roof deck and ALL wood should be completely covered.
6. You need to maintain soffit ventilation. The brick wall still needs to breathe. Depending upon how the soffits were connected to the home, the soffit vents will allow the wall to breathe. The intake of the wall would be the weep holes at the bottom and the soffit vents will be the exhaust. (very important).
7. If the attic has ben done properly and the correct appliances are installed, the attic should maintain a temperature of not more than 15 degrees fahrenheit difference from the indoor temperature.
It is encouraged to have someone come out to your home who understands open cell spray foam and have them conduct a thorough inspection of everything and run a blower door (air infiltration) test as well as a pressure differential test between the main body of the home and the attic and the attic and ambient.

Jan 26, 2010 2:50 PM ET

Open Cell vs. Closed Cell
by Eric Smith

You will find that closed cell foam is typically used in colder climates and open cell foam is used more in warm climates such as yours. The decision to use open cell foam was a good decision and the type of foam you chose has nothing to do with the condesation problems.

Jan 26, 2010 2:59 PM ET

by Mike Schulz

I see a fan and I see a condensation pipe. Not enough pictures. locations of foreseen rot and so forth to come to a conclusion or possible cause. Blaming material until resolved is myth.

Jan 26, 2010 3:05 PM ET

Energy Flow Accross Enclosures
by Tom Falik

There is a need for more research on potential negative effects of foam inulation in wall or roof cavities preventing energy flow to and from exterior sheathing, and thereby preventing proper drying of the sheathing. We need to make sure that this unintended consequence of foam insulation doesn't turn into an "EIFS" type disaster. Joseph Lstiburek at published a provacative and alarming article in December, 2009 at He raises important questions. We need for the foam producers and suppliers to respond to these warnings, if they can.

Jan 26, 2010 3:15 PM ET

Gutter/fascia leak
by Doug

Looking at the condensation you'd have to guess a potent vapor source as many have suggested...but I'd also say the brown stains to the left of the icicles in the first picture indicate water running between the gutter and fascia board. That could indicate a roof-edge leak (poor drip edge detail, inadequate lap of starter shingle & first course, poorly sloped gutter, leaking gutter joint...) which is letting water behind the fascia into the soffit area.
Depending on conditions that could be part of the story.

Jan 26, 2010 8:12 PM ET

I know exactly what is going on here.
by Johnny Boy

SPF Contrator here - and I know exactly what is going on.

That low pitch roof offered limited opportunity for the SPF installer to ensure the foam reached the end of the soffit and sat above the wall assembly. He/she could not reach and decided to block it off . From the attic it looked sealed - but the reality is, warm thermal energy from the home was cascading over the cold roof deck sheathing near the soffitt and causing condensation. Condensation leads to ice.

Building science novices need not hypothesize about vapor diffusion and closed cell versus open cell, etc, etc, etc. This is a very simple case of a lazy installer.


Jan 26, 2010 8:31 PM ET

gas combustion
by Robert Sanders Jr

Gas appliances are in the attic, they consume oxygen and must draw air from somewhere. That air is bringing in the moisture.

Maybe the gas heater and tankless water heater are providing some of that moisture. When gas combusts one of the byproducts is water.

Jan 26, 2010 9:39 PM ET

type of insulation?
by Don Winslow

What would be the negative aspects ,if the insulation was poly-isocyanurate?

Jan 26, 2010 11:24 PM ET

by Craig Townsend

If the "abandoned" bathroom vent still has some ductwork attached to it, it may have presented an obstacle to the foam installation and resulted in gaps between the duct and the roof sheathing. If moist attic air, warmed by the HVAC, were to come into contact with the leftover duct, filled with cold outside air, condensation would be the result. The moisture would build up and travel down the exterior face of the duct and pond in the soffit. This might be one reason that the problem is occurring at that particular location.

Jan 27, 2010 8:08 AM ET

Agree with Craig
by John Brooks

Craig....I also believe that the abandoned duct could be contributing to the problem.
I have to wonder if the homeowner has tested the flow of the new bathroom ventilation.
What if the spray foam has jamed the damper?

Jan 27, 2010 8:26 AM ET

Low tech flow testing
by John Brooks

Some tips at the bottom of this blog for homemade flow testing

Jan 27, 2010 4:19 PM ET

Installation Error - NOT the wrong product
by Paul LaGrange

Nick, when performing diagnostic testing or performance inspections I often see spray foam insulation improperly installed. One sure way of determining if outdoor air is entering your un-vented attic area and identify exactly where it is entering is to perform a blower door test in conjuction with a infrared camera. When the home is under a negative pressure and is allowing outdoor air to enter the attic area the IR camera will show the differing temperature of the incoming air and easily identify where the air leaks.

When an attic is completely sealed off with spray foam insulation, whether open or closed cell, vapor is not ussually a big issue here in the Gulf South. Good Luck.

Jan 28, 2010 8:35 AM ET

Air is Escaping NOT Entering the attic
by John Brooks

You probably already know this.....
In this case
Warm Moist air is escaping and causing damage.

Jan 29, 2010 12:35 AM ET

Mac Sheldon and Eric Smith are correct
by Jeff White

Warm moist air is migrating from within the home into the eve (clearly). This is not an open cell foam verses closed cell foam issue. Probably, difficult to access due to low pitch roof and bath fan mechanicals in the way. We always start in the difficult areas. IMPORTANT: Use a Jet tip on gun to make sure the thermal envelope is complete and in-line with exterior drainage plane (complete above the 2 top wall plates). Old bath fan vent pipe should be completely removed.

Jan 29, 2010 1:17 AM ET

Permeability of open cell foam
by Matthew Cantrell

Open cell foam has a perm rating of 11 compared to .6 for closed cell foam (based on a standard ASTM test units are liters per square meter at 75 pascals.) It is also 9 times as air permeable as closed cell foam. Warm moist air is leaking into the attic from the living space(or coming from unvented gas appliances), probably a lot of air is leaking around the vent opening, passing through the foam and condensing on the cold sheathing. Open cell foam also holds water very well, like a sponge and it looses its insulation value when it is wet. This increases the rate of condensation. Open cell foam should not be used in an unvented attic application. Closed cell should have been used.

Also note that all foams are very flammable and have a low ignition point. It is very dangerous to have foam unprotected in an attic with combustion appliances. The foam should be covered with a flame retardant.

Jan 30, 2010 9:06 PM ET

several good points
by greg

Before I go on my rant I suggest the soffits be removed so you can inspect the foam to see if it created a good seal. On some shallow pitched roofs we have actually started our jobs by spraying from the exterior of the perimeter of the house once the sofftit was removed to ensure we were able to achieve a good air seal. You can also tell by water marks if you have a roof leak which I doubt. I too am a spray foam contractor and we do both types of foam. The type of foam used is not your issue as most open cell foams are considered air barrier at a thickness of 5 inches. Sounds more like an application issue if the foam is causing the problem. There is no need to apply a vapor barrier over the foam this is not your issue. In regards to gas appliances in your attic most codes and manufacture's ES Reports state if there are heat producing (gas fired) appliances in the attic an ignition barrier must be applied over the foam. Also we tell our customers of retro jobs that the house is a system and changing the insulation you are changing how the house works and therefore they should consult with an A/C contractor who is knowledgeable of foam insulation, Changing to spray foam will have a direct impact on how your a/c works as this is also how we dehumidify houses in the south.

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