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Spray foam insulation questions


chrisexv6's Avatar
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12-10-15, 08:54 AM   #1  
Spray foam insulation questions

Recently got a quote for spray foaming our attic. We're located in Milford, CT (which I believe is zone 5? zip is 06461). The price is immaterial right now, I have questions about the application:

1. Installer said they would use open cell and spray foam the underside of the roof deck. He did not mention anything about the need for a vapor retarder over it. Here in the Northeast, is it something that should be required?

2. The building science docs I read said the first vapor retarder needs to be the one in contact with the insulation. What does this mean for the plastic sheeting that's already in place between our ceiling drywall and the joists in the attic? Does it need to be removed?

3. Can the existing fiberglass insulation stay, or does it HAVE to be removed?

4. Are the concerns about moisture getting trapped and rotting the roof deck actually valid concerns or just a lot of FUD? Or both?

Thanks in advance.

-Chris

 
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12-10-15, 03:31 PM   #2  
Can the existing fiberglass insulation stay, or does it HAVE to be removed?
If there is existing insulation, what's the reason for the spray insulation? Is the existing insulation, only between the floor joists or between the rafters too? Are there ridge vents & soffit vents?

 
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12-10-15, 06:02 PM   #3  
As Pulpo is asking, we need to know more about what you want to do. Converting from a traditional insulated ceiling to an insulated roof is not something that improves your homes performance. It usually is associated with a reason for doing such. I.E. finishing that space for some purpose, converting it to conditioned space because there are ducts and or hvac equipment up there.

Generally, as was probably mentioned in the building science article, you do not put permeable insulation directly against the bottom of the roof. You don't want moisture finding its way through to a very cold surface where it will condense.

More info please.

Bud

 
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12-10-15, 06:10 PM   #4  
I had wanted to air seal everything myself, then use blown in cellulose in place of the fg. But the material and time cost (mostly the time cost) made me search out alternatives.

I figure spray foam would be a better option vs paying someone to just blow cellulose (no one I asked seemed interested in also air sealing before blowing the insulation). At least after spray I can take my time air sealing if I want

I do have HVAC ducts up there and the space is currently vented with ridge and soffit vents.

 
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12-10-15, 06:18 PM   #5  
Here's some more reading:
Will Open-Cell Spray Foam Insulation Really Rot Your Roof?

Bud

 
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12-11-15, 05:54 AM   #6  
Thanks for that link. I've actually read that article (and the studies and other articles that one referred to). As mentioned in your link, its all very confusing and seems to contradict itself all over the place, especially if you read the comments.

So I agree open cell foam is "safe" and per that article a vapor retarder is required. I have someone literally living on the same street as me that had spray foam applied to the underside of the roof deck and they were told the vapor retarder is NOT required.

I would go so far as just adding it myself (if a contractor wouldnt) but would worry about the requirement that it be in complete contact with the spray foam. I assume there will be voids leftover after the foam is cured and cut to the joists. Dont those just end up trapping moisture?

 
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12-11-15, 06:25 AM   #7  
@ Chris <So I agree open cell foam is "safe" and per that article a vapor retarder is required.>
I'm not sure I totally agree with that approach as being safe. It can be done, but there is a lot more to it.

Creating an unvented attic (conditioned space) is more involved than just applying foam insulation to the bottom of the roof deck. The gable ends must be insulated and sealed. The ventilation, soffit and ridge or gable vents, must be removed or sealed. And the attic space conditioned, which may involve removing the current attic floor insulation. The risk is, if the moisture level in the attic is allowed to rise too high, that moisture may condense on a cool roof assemble even though there is plenty of insulation.

Next is, how much insulation are they proposing? R-38 is your 2009 code minimum which would be 10 plus inches of open cell foam. That is more than one application will allow so either two applications or they talk you into one being enough, even though it doesn't meet the minimum code.

Then there are those rafters at r-1.25 per inch. If they are not covered with sufficient insulation they become a thermal bridge reducing your total roof assemble performance.

Extending your hvac system up to that space, installing an ignition barrier along with a vapor barrier, and more gains you a conditioned storage area. Yes, there may be some energy savings, but greater savings can be achieved for less cost using a more traditional approach and without risking your roof. Shingles can leak, but with foam applied below you won't know it for years.

Bud

 
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12-11-15, 06:37 AM   #8  
Thanks for the advice.

Im starting to agree with your assessment.

While its nice to have someone else do the work, and say that the attic is "sealed", Im not sure I could verify that it is indeed 100% sealed (blower door test could do it, I suppose)

They proposed R-30 because that's the depth the joist size allows for. They also included R-21 on the gable ends, so at least they recognized the need to seal those as well. I presume the soffit and ridge vents would end up sealed off just by nature of spraying the foam over/around them.

My original plan was to seal the ceiling and top plate penetrations myself, remove the fiberglass and then blow cellulose back in. The goal being reducing as much air movement as I could by myself. Its just a lot of work, the materials cost isnt too bad. Spray foam is no work (for me) but is obviously more expensive.

Weighing putting the effort into it vs. risking a roof issue, Im leaning towards just putting the effort into it myself and going with the original plan. My house isn't THAT loose (last blower door test done about 5 years ago said 1.3 air changes per day, I think recommended was 1.1), but we do have a few areas that seem cold but shouldnt be (i.e. interior walls and outlets that have cold air coming in)

 
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12-11-15, 07:08 AM   #9  
A blower door test would have difficulty confirming the vapor barrier is completely sealed. The BD is installed at the front door and involves the entire house and it only identifies air leakage, not necessarily moisture all paths.

If you have 2x6 rafters the R-30 implies a higher r-value than I would use. What did they claim for r-value per inch? What are your rafters? And in any case, how do they justify not reaching the code minimum?

< My house isn't THAT loose (last blower door test done about 5 years ago said 1.3 air changes per day, I think recommended was 1.1)>
Not sure what they were telling you, but a normally well sealed house would be 8 air changes per day, one every 3 hours. Less then than that and you would be experiencing condensation on the windows in the winter and high humidity readings. The target for air leakage is often 0.35 air changes per hour. Here is some wording, although not the latest.
""The home shall meet minimum ventilation requirements of ASHRAE 62-1999, “Ventilation for
Acceptable Indoor Air Quality”. (.35 ACH by natural or mechanical ventilation)""
http://www.energystar.gov/ia/home_im...Spec_v1_0b.pdf

Going with the traditional approach would allow you to better target your approach. One of our posters rented an infrared camera and used that with regular window fans to direct his air sealing.

Bud

 
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12-11-15, 07:17 AM   #10  
Ill take a look at the blower door test results....it might not have been listed in air changes per day, Im pretty sure about the numbers themselves but obviously its not per day, or not "complete air changes"

Havent talked to them about the minimum code, etc. Since Im really leaning away from it Im not sure Ill even bother questioning.

If Im going to seal and reinsulate myself, it wont be happening until the Spring. Don't like dealing with a cold attic! So I have plenty of time to research, etc.

Interesting idea about a regular window fan....I wonder if that could be used in conjunction with a gable end vent to try and pull air through the house ceiling and "follow" it with the infrared cam

 
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12-11-15, 08:36 AM   #11  
You would be very impressed with what a first time user can see with an IR camera and, if you snap some pictures and need help interpreting them we and many others can help. Get a camera that snaps the IR and also a digital so you/we can see what the camera is looking at.

Then enhance the normal convection with a fan and air leaks will look enormous. During the winter is the best as you have days with a great temperature difference.

Jobs like air sealing the attic floor can can be reduced to just a few problem areas.

BTW, any moisture issues, like a small leak in the roof will glow cold with IR. I have found many unanticipated leaks, which is actually good as the sooner they get repaired the better.

Just read another article and several times they repeated, the most important energy improvement is now air sealing. Obviously there has to be some insulation, but if you have just 6" in your ceiling you have (wild guess) 80% of what you need as it would take 18 more inches to get just 10 more percent. The first inch saves the most. After that more insulation decreases in what it can save.

The new way to express air leakage is at 50 Pascals depressurization. Numbers like ACH50 = 6. That's 6 air changes per hour at 50 pascals pressure. 50 pascals is very small. Suck on a straw until you lift the water 1" and that is 250 Pascals of negative pressure.

Bud

 
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12-11-15, 08:59 AM   #12  
Posted By: chrisexv6 ". . . I have someone literally living on the same street as me that had spray foam applied to the underside of the roof deck and they were told the vapor retarder is NOT required . . ."
Maybe that neighbor had a closed cell material like isocyanurate applied ?

 
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12-11-15, 09:00 AM   #13  
Ill definitely look into that. I knew a long time ago but forgot that Home Depot has started renting out Flir cameras in some locations (two of which are near me). I could probably do a good amount of sleuthing with a day on one of those. Even considering getting the Flir One made for smartphones, it isnt the cheapest in the world but its far cheaper than any other Flir camera.

 
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12-11-15, 09:03 AM   #14  
Maybe that neighbor had a closed cell material like isocyanurate applied ?
Nope...confirmed with them they went with open cell per the contractors suggestion. Ive also seen pictures of their job and its yellow in color which Ive read indicates it isnt closed cell.

 
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12-11-15, 10:02 AM   #15  
Yellow in color sounds like it wasn't covered with a thermal barrier.

The reports on the Flir One haven't been impressive but sure better than what we see without the IR. Way back when, my Flir was 8 grand. The carrying case was $400 all by itself. Today, $4000 would buy 10X the camera I have now. Maybe someday .

Bud

 
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