As a Home Inspector I have been seeing an occasional attic where the inner side of the roof sheathing has foam insulation sprayed on. There is no apparent ventilation. The attic space is essentially sealed, but there is no insulation between the living area and the attic space other than 5/8″ drywall. Although I have not yet seen a problem caused by moisture accumulation, unless I am missing something, it seems almost inevitable.
Any clues on where I might get info to read up on this or words of wisdom by those installing this type product would be appreciated.
Marshall in MN
Edited 2/7/2004 1:38:25 PM ET by Marshall in MN
Replies
I believe the foam insulation sprayed in is moisture permeable. In other words it stops air infiltration but allows moisture to pass through. That is what I have always read.
Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
"If yer gonna drive fast on the highway why not go as fast as you can? Like... a hundred miles per hour or more lol."
There have been a lot of discussions about foam insulation here lately. I believe that closed cell foam acts as a vapor barrier, whereas, open cell does not. Some of these foam insulation vendors recommend spraying it directly on the underside of the roof deck, with no ventilation. Here we have not heard of any evidence that it is good or bad. I believe most people here, like I, are suspicious. Personally, I can't make any sense of having a non-vented attic, running the risk of moisture accumulation up there, and at the very least, increasing the volume of air that your HVAC system has to condition. Also, at least in my state, by code, foam insulation has to be covered for fire safety reasons. I believe this is per the IRC.
Not trying to be mean but what is the point of getting a home inspector if you don't know right from wrong?
If we demanded that home inspectors know everything, how many of them do you suppose there would be? It doesn't surprise or bother me that a home inspector might be unacquainted with a technique that's seldom used where he works, especially if it turns out that the reason it's seldom used is because it's a bootleg. There are lots of ways to do things right, but not nearly as many as there are ways to do things wrong.
Also, wouldn't you rather have an inspector post his questions here than silently ignore things he doesn't understand?
Edited 2/7/2004 5:21:35 PM ET by Uncle Dunc
OK - so why don't you answer the question... :-) BTW - I'm a home inspector and I do know everything. I have a crystal ball. My inspection fee is $10,000. That covers my time, expenses, and the rest goes to support my rather opulent live style :-)
Seriously though, we are all here to learn. Personally, I'll be interested to see what this thread turns up.
Matt
Edited 2/7/2004 5:40:45 PM ET by DIRISHINME
There is no subject in all of the topic of building science that generates more controversy than that of venting, insulation, and vapour barriers. There is no one right or wrong answer for all situations. As the details of a house and the location it is built in change, the methods and theories of how to deal with the issue change. For instance, there are times and places where no VB is needed. Other times and situations where failure to use one wqell installed is clear negligence.
What we have here is an honest person looking to further his understanding.
If you already know it all, more power to you.
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The straight up answer is that no Home Inspector knows everything and when he/she confronts an unknown he defers to a professional in that field. A home Inspector is a generalist not a specialist.
I am an electrical engineer who spent the twenty years before becoming a Home Inspector as a construction project engineer for the worlds largest oil producer. Been there, done that, and still have a lot to learn and questions seem to be one of the better ways of finding answers.
I have two reasons for asking about the spray on foam. One is I have encountered it and want to know how it works and how I might tell if it isn't working as it should. The second is that I have a 100 year old Victorian in MN where today it got very close to zero - on the way up! I have huge ice dams and 10-12 foot icicles. This is not good. First time conditions were right for that since I bought the home.
Marshall in MN
Marshall, Your ice dams are likely the result of too much heat getting to the underside of the roof deck. Once the melt freeze cycle begins the ice dam formation, it snowballs (no pun) from there. You have had very severe conditions this winter. Moisture in the attic is not the cause of the ice dams on the roof. Hopefully you can get better sealing of all air leaks into the attic, including steps up, lids, pull downs, pass throughs etc., and some more insulation. If and when you replace the roofing, I know you will be generous with ice and water shield as the first layer. How far up from the eaves do th ice dams extend? Don't break your neck to find out...PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Paul,
It's a little difficult to say how far up the ice dams go. I still have a foot or so of snow on the majority of the roof. I would guess 3-4 feet.
The attic space has historically been used for storage and I know the openings leak warm air like a sieve. My thought was that, if the foam is a good solution as I have seen it installed, I could basically seal the attic at the sheathing and soffits and then no longer worry about losing heat to that space or ice dams.
My first concern would be trapping of moisture between the foam and the sheathing. If the foam allows moisture to move through it, it would appear to condense on the cold sheathing. The sheathing in my case is board with air gaps left from the days when it had a wooded shingle or shake roof covering.
In working with projects I learned that many, maybe most, great sounding solutions are really just different shaped problems. I know what the problem I have now is, I might not recognize a problem caused by the foam.
Marshall
Try http://www.buildingscience.com
One reason that it is big in the south is that they stick a lot of HVAC equipment and duct work in the attics. Much better to have then in conditioned space rather than in unconditioned space.
Where that is not done I don't see the advanatage except for valulted ceilings.
Marshall, I believe I would spend my energy dollars on the attic floor, not the underside of the roof. Otherwise, you could spend a lot of money and still not have a much warmer house. An inch or two of foam sprayed on the backside of ceiling below, would stop the house air leaks of both moisture and heat. Then fill with something less expensive like cellulose for more R-value.
I am afraid that if you foamed the roof, and still had the moisture/heat leaks, whever there was a thermal bridge sufficient to transfer the dew point inside, you would have moisture problems. That would be an expensive way to relocate the problem, with no bottom line good news.
PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Part of the problem is that the third floor is mostly finished, floored, and it would be difficult to get foam into the space between the joists, although at one time someone did get loose cellulose in. The storage areas in each corner of the attic space are floored but the walls and sheathing are unfinished and mostly visible.
I tried to order the book but....
Marshall,
I like the idea of sprayed closed cell foam under the roof but have heard some objections.
1) You have to have ventilation between the shingles and the insulation or the shingles will break down from overheating. On new shingles it will void the warranty. Don't know if this is true or not. May not be a problem in MN.
2) It is expensive.
3) You have to stop up the soffit vents. You also have a much larger conditioned space to heat.
On the plus side:
1) You can get a much better insulation value per unit thickness.
2) You dont need a vapor barrier
3) It expands so you don't have any little gaps that can generate convective losses.
Seems like open cell foam would allow moisture to collect on the underside of the roof.???
Harpo
Your house appears to be balloon framed and I would guess that most of the warm air leaking is from within your walls.
If I were spraying foam in your attic, the first place I would try would be in between your studs to try and seal the flow of hot air escaping to the cornice or soffit overhangs.
Gabe
Edited 2/8/2004 7:02:51 PM ET by GABE_MARTEL
You're right about the balloon framing. The walls are double plastered with blown in cellulose fiber that is very old, I'd guess, and has settled.
I really hadn't thought of the walls being part of the problem since I'd been told that the double wall structure was really a very good form of construction. I'll have to scratch my head and see how that can be approached.
Thanks for the input.
Marshall in MN
Marshall,
When I looked at your picture of the house and noticed the apparent age, the balloon part was easy. By the amount of ice formations at the corners where windows did not interupt the flow of warm air to the attic, it seemed obvious to me that you had major leaking inside the walls.
You have to expose the studs at the attic floor level and block the air flow.
Pull the loose insulation out, about a foot down, pack with rigid insulation and caulk all around.
Essentially, you have to create breaks similar to the windows in your walls and thereby prevent serious heat loss into your attic and out into mother nature.
Gabe
Marshall, just got home, saw your house picture. Very nice house. My grandparents had a similar house in Massachusetts a few decades back.
Their non-insulated walls let heat flow to the attic, then to the under side of a slate roof. Although I don't recall any serious roof leaks, I do recall 10' icicles every where except over the windows, so we could't reach them. Your walls are doing the same. There is some insulating value to a dead air space in a wall, and will help more in the summer heat than winter cold. In your case, the walls are convecting house heat to the attic, and you know the rest of the story. Gabe points out a solution on stopping the air flow that will likely reduce or eliminate your ice dam after this cycle is over. If it does not, then you have other leaks(air) from heated space to attic. I would spend my effort from attic floor down, not up.
In the land of insulating, stopping air movement is king. Without air control, a lot of insulation is worthless, and both heat and moisture get where they should not be. Keep us posted. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Since this one seems to be under control, I'd like to ask about a variation on it. My mom said that this year she has condensation on the underside of the roof sheathing. Enough that it drips and gets the ceiling beneath a little wet. Theory of people who've been in the attic is that the stone fireplace going through the ceiling and roof heats that general area and thus the condensation for a few feet around the f/p.
Domes don't have attics, so I don't know much about insulating v not insulating them, etc.
Does a heated f/p sound like a reasonable explanation for condensation under the roof? If so, what's the preferred solution? Maybe insulate the f/p in the attic?
Cloud, not sure I can buy into the chimney causing the problem. It takes excess humidity for the chilled surfaces(below dew point) for the condensation. Houses built to minimum attic ventilation specs often have problems when extreme weather happens, as this winter has. She has some air flow leaks carrying the moisture to the attic, and not enough ventilation to remove the excess humidity, thus it is sleeting in the attic. Look for blocked vents(snow?), and air leaks at steps to attic, whole house fan enclosure, wiring etc. What type of framing is the house?
Unless the chimney is leaking combustion air (carrying water vapor), I don't think it is the problem. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
35 yo one story ranch. Condensation new this year. Just in vicinity of chimney. I can't remember the attic insulation details.
Cloud, do you suppose there are house air leaks around the chimney fit that are pulling humid air into the attic? Settling of fireplace may have opened up some space, and extreme cold this year revealing problem. The hot humid air then hits roof deck just above, and presto, rain! Can you stuff some rock wool around the chimney fit? PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Paul,
Please don't mention my name or post or advice or comments or any part of, when you post for fear that anyone would get the impression that I sanction or agree with anything you write.
And I can assure you that I will never mention your name in anything that I write to others.
With all due respect,
Gabe
Great looking house!
This week I am insulating an addition by spraying 6" of open cell foam on top of the drywall ceiling. IC potlights wrapped with FG, all visible holes and gaped duct taped. I am told that it will give an air seal and R28 insulation. Depending on the quality of the floors in the attic, you could remove a plank or bore some holes to get the foam in between the joists.An ex-boat builder treading water!
Bob:
Why did you wrap the IC cans in fiberglass? Can't spray foam directly on air tight IC cans?
While I am using foam and like its properties, the point that it does burn is always in the back of my mind. The IC cans that I am using do have a number of small holes and openings between the two shells. It seems prudent to keep the foam away from the bulb. So I've wrapped them with FG.
The same point was just made by Paul Hayden in the IC Cans thread.
Bob B.An ex-boat builder treading water!
No attempt should be made to seal fixtures that were not designed to be sealed, period.
They will overheat and could result in a fire.
Pots should be boxed with drywall if you want to spray foam over them.
Gabe
NOOOOOOOOOOOOOOOOO
You don't want to drill any holes between any two layers and spray foam in between unless you want the ceiling to fall down.
The foam is very adhesive in liquid state and as it expands it grabs hold of any surface and pushes away.
Gabe
I don't know everything but I do have a big head to contain all that I do know
;)
So maybe by spilling a little out here, I can vent the pressure on my brain a little, LOL
What you describe is a conditioned attic space. The foam used for such is a vapour bar so moisture remains contaioned within.
Sometimes, this means that the house should have a recovery systrem, sometimes not.
The conditioned attic is more common in the south as I understand it, because design and climate conditions there place air conditioning units and ducting in the attic and because the VB should be on the outside of the space in a predominantly cooling climate.
Corbond makes a good case with their studies and tests for installing to the outside of the building envelope in all locations, as long as the while house is dealt with. They do one day classes, but much of their info can be found in print and online. Their product is a pink colour instead of beige, white, or brown. Try to search the web for "Corbond" + insulation to find more.
Welcome to the
Taunton University of Knowledge
FHB Campus at Breaktime.
where
Excellence is its own reward!
Please clarify: Is this attic space heated and cooled or just allowed to swing as it will?
MERC
DJ, you're back. The place didn't fall in like all of those other naysayers said!
I knew you could do it!
In the Jan 2004 issue of FHB there an article about insulation in general and touches upon Sprayed insulation. In a nut shell Open cell foams have high perm ratings ( perm stands for permeance, how easily water vapor passes through a material) , in the range of 9 to 10. Closed cell have a rating of less than 1. (anything below 1 is typically considered a vapor retarder). It goes on to say for roofs, climate dictates which is preferable. Cold climates should have low perm foam and hot climate high perm foams are better. Hope that helps....