Helpful? 0

Dense Packing Slopes with 11.25 " rafters. Bad idea?

I did a lot of research when I built. Bottom line is that I chose the cheaper easier method and now I'm paying for it. I continue to hear that it's OK to dense pack cellulose in a slope and not vent it or not flash it with closed cell foam. This is incorrect and I can prove it now! Moisture has collected on the back side of the roof sheeting and ice chunks have formed, mostly on the north side of the house. Any where there's snow build up on the south side I have ice formation on the inside of the roof sheathing as well.

I just found this and my question is, "What do I do"? The issue is, that this is a hybrid timber frame home. So in one half of the house I can remove all insulation, dry everything out, then flash & batt (or densepack cellulose again). I believe "Building Science" approves that method and it make sense to me. Although how do I deal with the timberframe? There's 12" framing on top of a finished T&G pine ceiling with 3 dormers. The only thing I can conceive happening is foam injection from the roof side and replacing some shingles. I welcome any and all comments... Except that densepacking slopes in direct contact with roof sheathing works, because it doesn't over the long run.

Asked by James ODonnell
Posted Tue, 03/04/2014 - 16:41
Edited Tue, 03/04/2014 - 17:00


42 Answers

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Helpful? 0

As I wrote in my article, How to Build an Insulated Cathedral Ceiling, you can't fill rafter bays with cellulose insulation unless either (a) the roof assembly includes a vented air space above the top of the cellulose insulation, or (b) there is a layer of foam insulation of adequate thickness above the cellulose insulation. These rules make sense, and they are enshrined in most building codes.

If you can't access the problematic area from below, you'll have to access the problematic area from above. One option is to strip the roofing shingles, install an adequate layer of rigid foam insulation above the roof sheathing, followed by another layer of plywood or OSB and new roofing.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 03/04/2014 - 16:57

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Martin - Thanks for your speedy response. Do you feel that foam injection from the roof side would be a viable option. Cost is certainly a factor, but having a proper building envelope is too. What thickness of foam board would be effective in preventing this from happening again, if I chose to take that route?

Answered by James ODonnell
Posted Tue, 03/04/2014 - 17:13

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Q. "What thickness of foam board would be effective in preventing this from happening again, if I chose to take that route?"

A. The answer is provided in the article I linked to (How to Build an Insulated Cathedral Ceiling). According to the building code, this type of roof assembly (one that combines rigid foam above the roof sheathing with air-permeable insulation under the roof sheathing) must have rigid foam that meets the following minimum R-value requirements:
R-5 foam for Climate Zones 1-3,
R-10 for Climate Zone 4C,
R-15 for Climate Zones 4A and 4B,
R-20 for Climate Zone 5,
R-25 for Climate Zone 6,
R-30 for Climate Zone 7, and
R-35 for Climate Zone 8.

One possible contributing factor to your failing roof assembly might be that your assembly lacks an air barrier on the interior. Unless your T&G pine ceiling boards are backed up with gypsum drywall or a carefully installed airtight membrane, your ceiling probably leaks air like a sieve.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 03/04/2014 - 17:24

Helpful? 0

OK, I've read the article... which was very good, by the way. At this point it's looking like a flash & batt approach for the stick framed side of the house. I'm in zone 6 so if I understand this correctly I'll need 3.8 - 4" (R25) of closed cell foam sprayed directly to the underside of my roof sheathing. Is that correct? I'm sorry to question this, it's just quite a lot more than some contractors have spec'd in the past when I was building the house. Of course I realize that poor choice in contractors got me into this mess. That's not really a "Flash", it's more a of a belt & suspenders approach. Which I like, however, my bank account doesn't. Don't be offended, I'm just double checkiong.

Also, I'm still not hearing your opinion on the foam injection for the Timber Frame side. I visualize basically a flash & batt method except that the foam is injected from the roof side. Home Snuggers, here in Maine does this work. What do you think? I really don't want to repace the roof with foam board, and I can't do much about the t&g pine ceiling at this point. Both of those options are big projects.

Answered by James ODonnell
Posted Tue, 03/04/2014 - 18:00

Helpful? 0

Q. "I'm in zone 6 so if I understand this correctly I'll need 3.8 - 4" (R25) of closed cell foam sprayed directly to the underside of my roof sheathing. Is that correct?"

A. That's correct; 4 inches of closed-cell foam would meet minimum code requirements. There is some evidence that you can get away with less foam in some circumstances, but your case is a worst-case scenario: you already have a failure, you have no interior air barrier, and you have no interior vapor retarder. I wouldn't skimp on the foam if I were you. This is no time to cut corners.

Concerning "foam injection": if your cellulose is really dense packed (installed at 3.5 pounds per cubic foot), I don't know how a contractor is going to insert R-25 of rigid foam between the top of the cellulose and the roof sheathing. There is simply no room available -- unless you propose removing the existing roof sheathing and carving out a portion of the cellulose to make room for spray foam.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 03/04/2014 - 18:06

Helpful? 0

Thanks for the the answer about the flash & batt.

Regarding the foam injection, I may not be understanding it correclty. Here's a link to the Home Snuggers website. They use "RetroFoam" and it show's them injecting it from the outside wall. The foam is compressing the fiberglass, I guess I'm envisioning the same concept with the densepacked cellulose. Am I just wishful thinking here? Does the foam have enough compressive strength to do this to densepacked cellulose. Keep in mind, no core samples were taken and I have no idea if it was packed to 3.5 pounds/cf. I guess for this case we can assume it was.

Answered by James ODonnell
Posted Tue, 03/04/2014 - 18:17

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Non-expanding injection foams like RetroFoam will not do what you need here, since it's nearly as vapor-permeable as open cell polyurethane and not guaranteed to be air-tight. RetroFoam runs ~ 6.6 perms @ 1", so you'd need a minimum 7" of guaranteed depth to get it down to class-II vapor retardency. These foams have a tendency to shrink a tiny bit when they cure, which leaves a convection path for moisture to find it's way to the cold edge of rafter for the winter too.

Answered by Dana Dorsett
Posted Tue, 03/04/2014 - 19:31

Helpful? 0

"I did a lot of research" James, are all the bad roofs T&G inside? If so it is possible to pull it all down and start over. I know of shingles too that have actually all been painstakingly been removed and reused. What you may have done is build a home that was too expensive for you to properly insulate to what soon will be 2014 code. Roofs in our zone should be R 60 continuous if using blown in cellulose. If going with cathedrals and foam, get ready to double or triple or quadruple the square foot cost of your home. That is a fact. Beautiful homes.... but they cannot be built for starter home prices.

I would contact quite a few contractors in your area to price fixes. To afford all, do as much of it as you can. Or sell and cut your losses. You are in for quite a project. Dana and others here may have some ideas... My demo ideas may sound scarey but it's just labor and would go quickly.

Fix options or sell Fitch, not abandon. The sell option has to do with throwing good money after bad.

Answered by aj builder, Upstate NY Zone 6a
Posted Tue, 03/04/2014 - 20:06
Edited Tue, 03/04/2014 - 22:47.

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Seems these answers are too quick without knowing more and a jump to a solution without some options. You can’t tell a man to abandon his house.

I agree too, that there is a less costly solution than throwing Dow Chemical Company at everything that moves.

What is the sheathing material? What is on top of it and what is the finished roofing material? Where is the vapor barrier now in your roof or is there one?

Answered by flitch plate
Posted Tue, 03/04/2014 - 21:20

Helpful? 0

No, the problem area aren't ONLY subject to the T&G pine ceiling. However, it seems I can easily fix the stick framed section of the house with the Flash & Bat method (I would Densepack again).

The real problems issue I'm having is with the north side of the house that is Timber Framed. I've done minimal inspections but so far it looks like the south side is clear of snow and doesn't seem to have condensation on the inside of the roof sheathing. The north side definately does and I have three stick frame dormers on the north side.

So this what I've got from inside out.... Exposed timber frame, 3/4" t&g pine ceiling, 15# roofing paper, 2x12 rafters, 5/8" t&g Advantec, an extensive amount of Grace Ice & Water Shield, architectural 30 yr shingles. This is a 12x12 pitch and all bays were dense packed from the top of the bay. I had left a 1 foot strip of roof sheathing off for the insulation contractor to put their hose down. When I put the last 1 foot piece of sheeting on I had to pull it down with screws. It seemed be packed very tight.

Answered by James ODonnell
Posted Wed, 03/05/2014 - 09:20

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Also, I have an air exchanger pulling air from every bathroom and the kitchen. Air exchanger is sized for a home up to 6,500 sq ft. so I should be good here. My home is 32 x 52 with an attached garage 28x32. Foot print is 32x80 with garage. Foundation is ICF's. Garage floor and basement floor are insulated and have radiant heat. Garage ceiling is insulated, sheet rocked, & primed.

The three dormers on the north side have sheet rock and paint on them, not T&G pine. They are also densepacked with no vents.

Answered by James ODonnell
Posted Wed, 03/05/2014 - 09:36

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The link here:, is what I based my decision on in 2006 when I built the house. There are several technical references by what appears to be a reputable insulation company. What sold me was the several references to timber frames. I really thought this was the way to go for cost and efficiency. Below I copy & pasted the conclusion... comments welcome.

In Conclusion
Dense pack non-ventilated cathedral ceilings are, as a building science study entitled Report On Roof And Wall Details: Upper Canada Post And Beam points out, "nothing more than well insulated exterior walls with insulating sheathing which is sloped."

Cellulose has been used for years to dense pack cathedral ceilings with excellent results, outperforming the ventilated method. It is now being accepted as the preferred method of installation by building experts across the country.

To avoid moisture problems in the future, consult a knowledgeable insulation contractor.

Answered by James ODonnell
Posted Wed, 03/05/2014 - 10:06

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A roof is not just a sloped wall. Walls in cold climates (almost) never have vapor-impermeable outer layers such as Grace Ice & Water, nor do they sustain snow-loads for weeks or months on end. Anybody who says a roof is just a sloped wall is simply wrong. The exterior layers matter

From top to bottom you currently have:

-30 yr shingles.
-Grace Ice & Water (less than 0.1 perm, a true vapor barrier)
-5/8" t&g Advantech (less than 1 perm, a class-II vapor retarder)
-dense packed cellulose (highly air & vapor permeable)
-#15 felt ( 5+ perms, and nearly impossible to make air-tight.)
-3/4" t&g pine (about 2 perms when dry, rising with moisture content, but without an air barrier, extremely air permeable)

Had you slipped a "smart" membrane type vapor retarder such as Intello Plus or Certainteed MemBrain between the t&g pine & cellulose instead of the #15 felt, and detailed it as an air barrier it would probably be working just fine, as long as you keep the average interior relative humidity at 35% or lower during the winter. (You might have been OK with air-tight gypsum painted with ~3 perm standard latex too, since it would block the air infiltration, and have only half the diffusion moisture, but it would be marginal, relying on the moisture buffering of the cellulose to manage the load.)

Had you installed rigid insulation above the Grace Ice & Water to the IRC prescriptive minimums for your climate zone (as summarized by Martin in response #3) you'd also be fine, even without the interior side vapor retarder. Alternatively, 1-2" of closed cell spray polyurethane(0.5-1.2 perms) applied to the underside of the roof deck prior to dense packing would also get you there, as long as you keep the relative humidity at 35% or lower during the winter.

If you install a smart vapor retarder on the interior side of the 3/4" pine taking pains to detail it as an air barrier and install another layer of interior-finish (either more pine or painted gypsum, your call) it'll probably be a cheaper fix than ripping up the shingles and adding the requisite R-value of exterior insulation plus a nailer deck above the Advantec. Smart vapor retarders are sub 1-perm when the proximate air on both sides of the membrane is under 35% RH, but become vapor open when the air becomes more humid. So in winter it will limit the rate of moisture accumulation, but when warmer weather arrives heating up the roof deck and releasing it's stored moisture burden raising the RH of the entrained air in the cellulose, it passes that moisture inward at a rate limited only by the permeance of the other interior-side layers. With 3/4" t & g pine as the interior side finish it'll dry at a rate 2x or more quickly than it'll take on moisture through the smart vapor retarder.

Answered by Dana Dorsett
Posted Wed, 03/05/2014 - 11:54

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Dana, thanks for taking the time to help me out. Your response is excellent and something I considered, but didn't have the technical expertise that you appear to have. I have a problem with wanting something that isn't economically feasible and plunging in head first allowing my bank account to suffer. Unfortunately I'm never going to get the performance I wanted out of this timber frame and may be stuck with the suggestion you made about the smart vapor retarder and gypsum. Although it bothers me a bit choosing the less robust option, I feel reducing the air flow and applying a vapor barrier that will limit moisture getting to the cellose & back side of my roof sheething is probably the smartest & least cost option at this point. Since I already will have an insulation contractor onsite, this will allow me to drill into the t&g and check the densepack before applying the smart vapor barrier and gypsum.

Answered by James ODonnell
Posted Wed, 03/05/2014 - 12:14

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Have you had an energy auditor in? A blower door test? The problem may be the insulation, but it also might be bad air sealing, esp. between the timberframe, T&G, and 2x12's - sounds like a lot of potential pathways that might be short-circuiting your insulation.

Answered by Dan Kolbert
Posted Wed, 03/05/2014 - 12:22
Edited Wed, 03/05/2014 - 12:23.

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If I choose this method (#14), can anyone comment on adding some amount... 1,2,3,4" of Polyiso (not foil faced), XPS or EPS foam board first and where would the smart vapor barrier go then, still under the gypsum board I assume? My fear by adding insulation like this to the inside is that I'm moving the condensation line if moisture does get in. So if I add insulation does moisture now condense closer to the middle of my roof cavity instead of the back side of the roof sheathing? You all can probably tell I'm nervous about all of this and maybe over thinking it a bit.

Sometimes I wish I had WUFI software to check all this, but I'd probably really drive myself crazy then.

Answered by James ODonnell
Posted Wed, 03/05/2014 - 12:51

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your home is
what climate zone
when was it built
how wet for how long while built
when did you move in
do you dehumidify
do you humidify
do you have lots of plants
have you checked the humidity in your home
is humidity the main problem along with the home being recently built and not finished drying out and lowering it's wood moisture content

what would happen if you
ran a dehumidifier
snow raked the snow off the roof

As to ice and water shield
has it been put down on your roof extensively and everywhere your roof frame would be generating melted snow.

Dormer sidewalls, wood framed chimneys all other sidewalls valleys all when I build have ice and water shield, skylights and stove flues get it too all the way to the eaves.

So James is there a chance that new home moisture is all or part of the problem?

Answered by aj builder, Upstate NY Zone 6a
Posted Wed, 03/05/2014 - 13:22

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I have not done a blower door test. That's a good point. It's been on my list to get an energy audit done, but keeps getting put at the bottom of the list for whatever reason.

Just an FYI. Mr Applegate called me back (link from comment #12) and we spoke for quite sometime about this issue. He was very informative and helpful. This method of dense packing slopes has been used in Michigan (similar climate to Maine) since the 80's with little or no failures. However, he stressed that it is critical to have a good pack. Reducing air flow and moisture inside the building is critical to success. A loose pack will create a situation like mine. He has many years in the business, but does agree with Dana's suggestion of adding a smart vapor retarder and gypsum board "If" a problem truly exists. Re-packing to ensure a good dense pack would be smart as mentioned.

We've had unsually cold temperatures this year and Aaron feels that may be part of the issue. Although you can't ignore a problem like this, it may simply dry out as the temperatures rise and I may not have a problem like this for many years. I'm still looking at adding a vapor retarder and possibly foam with gypsum board and would like to hear any comments folks have regarding that.

Answered by James ODonnell
Posted Wed, 03/05/2014 - 13:23

Helpful? 0

Southern Maine
Climate Zone 6
2006-2008. Long Project. It was dry when insulated. It did get wet while we were building but I feel it had sufficient time to dry before sheet rock or t&g pine was installed.
Finished 1st floor moved in, then finished 2nd floor the next year. 2nd floor was heated and insulated while finishing.
Air exchanger only. We don't humidify or de-humidify. No I haven't checked the humidity level. Good call on that, sort of embarrassed I didn't think of it.
Ice & water shield on the entire North side, including up dormers, inside dormer windows, dormer roofs, etc.... Most of the south side has ice & water. No issues on that side.
I don't think new home moisture is the issue, but I do feel that if I got all the snow off and ran a de-humidifier it would help dramatically. I will first check the humidity level.

Great suggestions. Thanks to everyone contributing.

Answered by James ODonnell
Posted Wed, 03/05/2014 - 14:53

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If you put foam on the interior side of the assembly it won't appreciably change the average temperature of the roof deck which is the only critical factor beyond the vapor permeance of the interior layers. But it WILL improve the overall thermal performance.

In that approach don't go lower than about 1-perm on the interior foam or you potentially create a moisture trap between the Grace Ice & Snow and the foam, which is what you DON'T want. All facers on polyiso are sub 1-perm, and XPS is under 1 perm at 1.5". The highest R thermal break you'd be able to achieve there reasonably would be R12.6 using 3" of unfaced Type-II (1.5 lbs/cubic foot density) EPS. In that instance doesn't matter which side of the foam the smart vapor retarder resides on, and it might even be OK to use housewrap instead of the vapor retarder, since 3" of Type-II EPS is a minimal class-II vapor retarder.

Where you went astray of the Applegate recommendations ( was in two places. Note the diagram 2/3 of the way down the page:

- It specifies a VAPOR PERMEABLE underlayment for the shingles. In that instance #15 roofing felt works, #30 felt or Grace Ice & Snow are definitely too vapor-tight. Ice & Snow is a true vapor barrier, #30 felt is under 0.2 perms, which is about as tight as it gets for Class-II vapor retarders, so you have effectively zero drying capacity toward the exterior, even on a sunny day in July when the temperature of even the north side roof deck breaks 120F.

-Also spelled out in the diagram is gypsum on the interior side, which is orders of magnitude less air-permeable than t & g pine with #15 felt under it, since it's nearly impossible to air-seal #15 felt at the seams, and absolutely impossible to air seal 3/4" pine planking, whereas gypsum it's almost a done-deal (though detaining the seams & edges still matter.) In the text they correctly note: "Air leakage is now considered to be the prime cause of most condensation problems in walls and roof spaces. "

Not spelled out (but actually important) is that the gypsum also needs to be painted with at least one layer of latex, bringing it's vapor permeance down to the 3-5 perm range, since the vapor permenance of paper-faced wallboard is typically on the order of 50 perms and higher (though "moisture resistant" wallboard can run as low as 20 perms), which is way to high to make it in a zone 6 climate.

Answered by Dana Dorsett
Posted Wed, 03/05/2014 - 15:57

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Diagnosis, diagnosis, diagnosis ….

James … you said something here:

“This is a 12x12 pitch and all bays were dense packed from the top of the bay. I had left a 1 foot strip of roof sheathing off for the insulation contractor to put their hose down.”

Are you aware that to achieve 3.5 to 3.7 PCF the hose has to be within and to maintain about 18” distance from the face of the blow as its pulled backwards by the installer?

Are you sure you have the density necessary to fulfill the standard necessary for air and moisture control in your insulation. The NuWool and the Applegate warranties (solutions) require the density to be assured. Before you take any action, conduct spot audits to determine if you have the density across the deck in each rafter bay would be wise.

I say this from experience. I have all six sides (including floor, and cathedral ceiling) of my house dense packed. Behind drywall and behind subfloor. We used an infrared camera to monitor installation density. After each day of blowing, we found voids that were not palpable or visible at the leading edge/face of the blow. So we would go back in the next day. Voids and insufficient densities are masked by the good density at the face of the blow closest to the installer.

This is why blowing behind drywall and other solid faces is not reliable; and why transparent webbing is preferred by some installers. Quality assurance and warranty compliance.

Infrared cameras cost a couple of grand but can be rented. I think you will be more confident and better equipped with your diagnose if you do this audit first.


Check your densities.

Answered by flitch plate
Posted Wed, 03/05/2014 - 16:58

Helpful? 0

Even 4lb cellulose would not have saved this roof, with a sub 0.05 perm exterior and an air leaky interior cladding.

But with smart vapor retarders or insulation above the roof deck the absolute density of the cellulose simply matters less (a LOT less). Even 2.8-3lb cellulose would be sufficient if it had the requisite R25 (for climate zone 6) above the roof deck and an air-tight interior.

But I'm not sure how they'd blow to even that density with a foot -wide hole- half the cellulose would have ended up all over the yard.

Answered by Dana Dorsett
Posted Wed, 03/05/2014 - 17:53

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James, you have a good useful thread going.

Dana, my logic and armchair brain says dense pack cells over felt... was talked about a few years ago... anyway the felt is an air barrier. So now you are saying overlapped seams of felt forced together by 3.5#/sqft of insulation is leaking air???? Maybe but the problem has to be other to my logic.

First stop for interior moisture is definitely air with too much moisture getting to where it is found condensed. That we all agree on... right?


James, Doing Dana's fixes on just the North... and dropping the humidity... sound like a plan?

Answered by aj builder, Upstate NY Zone 6a
Posted Wed, 03/05/2014 - 19:49

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Do You heat with Propane?
A few years back I stumbled upon the answer to a customers condensation issues which they had spent 22+k trying to resolve hiring multiple hvac and sprayfoam contractors.
Their problem ended up being with the Propane boiler which was venting into the basement not out side. No poisonous gas with propane.....but a lot of water vapor.
The humidity of the home did not feel alarming but the house was kept at 72-74 degrees....too hot IMO
Humdity levels were checked at that point to find they were WAY high.
Yet another hvac guy rewired the boiler exhaust to work properly.....problem solved.
That was The last winter I can remember where temps were this cold in NE and snow piled up on roofs....Jan/feb 2011 I believe.

Answered by Dirk Gently
Posted Wed, 03/05/2014 - 20:39

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Agreed that some type of vapor retarder and gypsum painted will be a big improvement. I would likely spot check or simply re-pack the cellulose.

I can't say I was aware 18" was required, but the hose was snaked to the bottom of the cavity and filled upward as the machine "stalled" so to speak. I was onsite for that, you could hear a change in the machine when they pulled the hose back another foot or so. This makes me believe the densepack was done correctly, but I'm also onboard with the thermal imaging camera. The original contractor used one and found some issues... then never came back. The check was already written.

I heat with oil, but good suggestion about the propane. I will be buying a humidity monitor and checking that very soon. I'm trying not to jump to conclusions as this has been a very cold winter and no water damage is present at this time. The only reason I checked the timber frame section was because of what happened in the other side of the house.

You all have been so helpful and I will most definately be visiting more often. I feel much more relieved about the situation and prepared for what ever repair option is feasible. I am grateful for folks like you, keep it up. I was always told that there are only really two reasons you feel stress, 1. You don't have the proper tools, 2. You don't have the proper knowledge. Fix either or both of those things and the stress disappears. I'm on my way to feeling less stress. Thanks so much everyone.

I'll keep checking if anyone has any further comments. Please feel free.

Answered by James ODonnell
Posted Wed, 03/05/2014 - 23:04

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James - I'm in Portland. I can recommend some good auditors if you want - dan at kolbert building dot com.

Answered by Dan Kolbert
Posted Thu, 03/06/2014 - 12:17

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A permeable cathedral ceiling cavity can dry to the inside provided there is (1) effective whole house ventilation and (2) the vapor drive into the ceiling is minimized by detailing that keeps the bulk flow of stack effect air out of the assembly in the first place.

I agree with Dana on the detailing and permeability issues but don't agree with the Dow Chemical solution (i.e. XPS on top of the roof deck) as necessary and it is not a requisite for the Applegate or NuWool warranties. DP cell density and a void-free blow are the primary requirements.

Granted, the T&G pine without a vapor control is a problem. The roof itself seems to offer little room for a fix. As pointed out, it sounds to be a water tight, airtight membrane (over the deck area).

By the way, are you sure you have no ridge vent?

I still maintain that you need more analysis and hard facts. I encourage you to complete your diagnoses and first try to optimize the performance of the current insulation and HVAC system:

- Ensure you have the void free density throughout the entire assembly (IR camera audit, re-blow where necessary, from the rafter bay centre, not from one end)
- And as per James' recommendations/questions, an analysis on moisture levels in the ceiling by monitoring various spots with a moisture meter for a couple of weeks, keeping a corresponding log of types of home activity and outdoor climate).
- Test the effectiveness and possible conflicts in the air movement in your ventilation infrastructure (including testing the equipment performance).

Answered by flitch plate
Posted Thu, 03/06/2014 - 12:54
Edited Thu, 03/06/2014 - 12:58.

Helpful? 0

Before going too far down the path of replacing your oil-burner with propane, not that at the recent 5 year average pricing of heating oil & propane pricing and typcial ME electric rates, heating with ductless mini-split heat pumps would pay for themselves in less than 3 heating seasons in a southern ME location. If even one large zone could be handled by the heat pump it would be worth it. Heat source by the mini-split will cost less than half what it's costing with the oil-burner, and if you are on a lower-cost municipal power company it could even be less that 1/3 the cost (!).

Run a room-by -room heat load calculation (if you don't already have that info handy) on the largest contiguous rooms where a point-source heater would not be a problem and we could come up with an appropriate model or three. (Do NOT leave this to the HVAC pros to get the sizing right- there isn't enough margin in it for them to run the necessary calculations unless you pay them a few hundred $USD.)

As a sanity check it's worth doing the room-by-room calc for the whole house, then comparing that with a heat load calc based on the "K-factor" stamped on the billing if you have a regular oil delivery service, or gallons per heating degree-day if you're more of a spot-market fill-up type.

Here is some bed-time stories to read while pondering it:

A short & readable policy piece comparing lifecycle heating costs & carbon footprints using heat pumps vs. oil / other in New England climates: (Take note of Table 6 on p.6 mini-splits are highest efficiency air source heat pumps.)

Specs on a couple of cold-climate mini-spit series that work great in your climate:

Third party bench testing of a couple of popular 1-tonners (older, and slightly lower efficiency than current models)

In-situ performance testing of dozens of units installed in real houses over multiple climate zones (the most relevant to you would be the Eastern Idaho clustering, which is a slightly colder climate than yours.):

The 10 units in the Idaho Falls cluster were all 1-ton Mitsubishi MSZ-FE12NAs , and the cluster averaged a coefficient of performance (COP) of 2.96. In your climate the same unit would nudge a shade north of 3.0. But then newer MSZ-FH12NA is about 15% more efficient and you'd be in the mid-3s, which is about the same all-in efficiency of ground source heat pumps (with all pumping & air handler power factored in). It''ll comparable to (even cheaper than) heating with condensing natural gas.

Answered by Dana Dorsett
Posted Thu, 03/06/2014 - 12:59

Helpful? 0

Fitch, your approach is currently the one I am taking. I have ordered a humidity monitor and will be taking a log as suggested. I then plan to find a place to rent an IR cammera or get an auditor in here .

I definately do not have a ridge vent. I followed the Applegate process, however, missed a couple of very important details as mentioned in an earlier answer.

I feel the only solution to this problem, if a problem truly exists, is re-dense pack & install a vapor retarder with painted gypsum. If it was 20 years down the road I would be looking into 4" of nail base EPS vented.... but it's not and that's far too costly at this point. Of course knowing what I know now, I'd be removing the Grace Ice & Water layer first. Doesn't matter, it's not happening.

Dana, I don't intend to replace my oil burner. You may have misread something. Dirk mentioned it considering that it could be a moisture source. Although, I do like all your advice about heat pumps & mini splits. They've come along way in recent years.

Answered by James ODonnell
Posted Fri, 03/07/2014 - 09:30

Helpful? 0

One last question... I think. Can anyone recommend a smart vapor retarder. This I'm hoping would apply to the stick framed section (closed cell foam layer, dense packed cellulose) of the house and possibly the timber framed section (see answer #13). This industry seems to change a lot. I've seen MemBrain, Pro Clima, and DB+ by Pro Clima. It seems the DB+ has a high perm rating (5.5) high levels of humidity. That doesn't really seem like a good idea with my situation... just a thought. Let me know what you guys think.

Answered by James ODonnell
Posted Fri, 03/07/2014 - 14:03

Helpful? 0

James, long thread, but if you haven't checked moisture you may be missing the right and least expensive fix.

Check humidity. Check foundation incoming moisture. Check moisture the occupants are producing. Check your exhausting of moist air systems and if they are being used enough.

If your home had no moisture entering it, there would be no moisture in your roofs since you have stated that the exterior of the roofs are well covered with ice and water shield.

How deep was the snow on your roof? I have been on roofs with very deep snow and found that the roof level of snow was a pond of water because that much snow really insulates. Roofs that never leak can have problems when there is 3' snow on them.

Good luck, I will stop being a pest. Hope to see you tell us that you have this fixed someday somehow.

Answered by aj builder, Upstate NY Zone 6a
Posted Fri, 03/07/2014 - 14:39

Helpful? 0

No kidding about the roof snowpack issues! I've shoveled waist-deep snow out of the roof valleys after near record-setting Nor'easters in recent years. Anything over 15" on the roof is prone to becoming ice-dam hell for my place in it's current less-than-ideal state of roof insulation (to be rectified when I re-roof in shot years). Most storms I can get by with just raking down the snow from about 2' above the wall intersections, but there have been several where the only recourse was to get up there with a snow shovel.

Answered by Dana Dorsett
Posted Fri, 03/07/2014 - 16:54

Helpful? 0

So I'm back. Looks like the insurane company will cover the damaged insulation on the stick framed section of the house.

Just looking for a little feed back on the fix for this (Stick Framed Section). All the insulation will be removed and the enviroment dried out. The plan is to spray 2" of closed cell foam on the back side of the roof sheeting, then dense pack with cellulose, then a layer of vapro retarder (Pro-Clima), last sheet rock the living space & paint with latex paint. Comments? Does this feel like a solid fix to everyone. Keep in mind, that most of this area is a valley so venting the roof isn't really an option for a large majority of the roof.

Answered by James ODonnell
Posted Tue, 03/18/2014 - 20:59

Helpful? 0

The ProClima smart vapor retarders (INTELLO/DB+) that we distribute in the USA with can work well with cellulose insulation and should be a suitable solution for your situation - These reinforced vapor variable retarders do need to be installed airtightly on the interior of the enclosure - ideally not be penetrated by outlets, lights etc. Hence we recommend a service cavity, for more tips please see our our blogpost regarding INTELLO Plus and cellulose installations. If not using a service cavity, all outlets etc need to be integrated into the airtight layer and require closer staple distances (1" or less) to prevent staple blow outs/leaks etc.

Please note that the DB+ smart retarder has a vapor variability (0.8 to 5.5perm) which offers a great benefit, but doesn't offer the best in class protection that INTELLO Plus (0.17 to >13 perm) vapor variability offers.
DB+ is paper based and contains recycled content - so is even more sustainable, but INTELLO offers the best protection against moisture damages (if installed correctly of course, so use TESCON tapes and follow other recommendations).
Below a photo of a cathedral ceiling, without service cavity by BLDGTYP in a WI project where they blew cellulose behind T&G after most of them boards were installed over INTELLO Plus (preventing needing a large amount of staples).
Let us know if you have any other specific concerns regarding application etc.

Answered by floris keverling buisman
Posted Tue, 03/18/2014 - 23:26
Edited Tue, 03/18/2014 - 23:29.

Helpful? 0

You are in Climate Zone 6. Since an insurance company is involved, you might want to follow the building code. In the 2012 edition of the IRC, the relevant section is section R806.5; earlier versions of the code have similar sections.

Your approach is called "flash and fill," and the code spells out minimum requirements for the layer of spray foam that you plan to install. In your climate zone, the spray foam layer needs a minimum R-value of R-25. That means that you need at least 4 inches of closed-cell spray foam on the underside of the roof sheathing to meet code.

All of this is spelled out in my article, How to Build an Insulated Cathedral Ceiling.

There is a reason for this requirement; the intent is to keep the interior surface of the cured foam above the dew point during the winter.

Your plan to install a smart vapor retarder on the interior side of the assembly will lower the risk, and may (arguably) allow you to go with thinner spray foam -- but that possibility is not spelled out in the code. Whether or not you can proceed as you intend depends on the interpretation of your local code official.

Answered by Martin Holladay, GBA Advisor
Posted Wed, 03/19/2014 - 04:41
Edited Wed, 03/19/2014 - 04:47.

Helpful? 0

That's great advice and I like that the code specifically spells that out. Thanks again Martin, I'll take that stand and see what happens.

For anyone interested, I'm still evaluating the Timber Framed section. Currently the humidity level has not risen above 30% and is typically at 25%. I checked the insulation in one area last night and it was dry. I plan to check the bottom of the rafter bays today. I'm able to do this since I have a front porch and there's no T&G to ruin under there, like the interior of the house.

Answered by James ODonnell
Posted Wed, 03/19/2014 - 09:34

Helpful? 0

Great news, I don't see any damage in the TF section. I drilled several holes in the bottom of rafter bays on the North side and see only dry dense pack cellulose.

More great news, I had code coverage. They're paying for me to go back with 4" of ccSPF and dense packed cellulose in the stick framed section of the house. Phew!!!

I've gotten some great advice here that's put my mind at ease with this unvented roof assembly. I have yet another question about this assembly to keep those bright minds thinking. I recently spoke with my brother in law who is a veteran builder in the Lake Placid, NY area. He recently had to demo a roof that was ruined with this similar assembly. I don't have all the details, such as thickness of foam, but what is everyone's thoughts about the roof sheathing rotting with this assembly. If a leak occurs or if moisture gets into the roof sheeathing do I risk rotting out the roof sheething? I've been racking my brain once again and scouring the internet for proper ways to vent a valley. I've come up with the hole drilling method, new designs such as "ValleyVent" (not an option for me), and the use of metal roofing (also not an option).

With asphalt shingles, Grace Ice & Water, sheething, then 4" of closed cell foam... I can see the potential for rot. How would that moisture leave the roof sheething? I will say the home he demo'd was seasonal and not heated during the coldest months & highest snow pack of the year. Could that be the issue and since my home is heated year round to a minium of 60 deg F, am I worrying for nothing? I'm not reading a lot of positive feed back about the hole drilling method due the air flow getting lazy and not flowing through the drilled holes.

Answered by James ODonnell
Posted Fri, 03/28/2014 - 20:09

Helpful? 0

Non vented rigid foam roofs that had T&G ceilings... rot... drip water... and are nightmares at least that is what I have run into here just below your brother...

Spray foam is not the same. You are stopping air with spray foam that the afore mentioned assembly is not even though the original builder thought it did. Time and experience has shown to many of us around my parts that rigid foam roofs systems need venting above the foam.

CC spray foam, DP cellulose is far superior to unvented rigid foam.

It's all about air, moisture, condensation, and lobster traps. Don't build lobster traps unless you want lobster. (one way in and no way out for moisture)

Answered by aj builder, Upstate NY Zone 6a
Posted Fri, 03/28/2014 - 22:05

Helpful? 0

There are lots of ways to rot a roof, and roofing doesn't last forever.

If the moisture comes from the exterior (as rain or melting snow), your only protection is the roofing and good flashing. After 15, 20, or 30 years, most roofs start to leak. At that point, you have to notice the leak before you have extensive sheathing rot. Otherwise, the roofer who is hired to install new roofing will replace the sheathing that is rotten.

Sheathing replacement during a re-roof job isn't that unusual. However, if a building has closed-cell spray foam on the underside of the sheathing, it's quite possible that the owner won't notice that the roofing is shot for quite a while -- meaning that more of the sheathing will need to be replaced as part of the re-roof job than usual.

Answered by Martin Holladay, GBA Advisor
Posted Sat, 03/29/2014 - 05:42
Edited Sat, 03/29/2014 - 05:43.

Helpful? 0

So I'm about the insulate this area. 4" of spray foam with....? I'm seriously considering going back with Kraft Faced fiberglass batts. I'm so tired of the mess that cellulose makes. Not to mention if it does get wet, it's an even bigger disaster trying to remove it.

Can anyone discourage or encourage me if this is a good idea. I know fiberglass insulation is used all the time, however, I like dense pack cellulose for a lot of reasons.

To re-cap: Unvented cathedrals, 12" rafters, 4" of closed cell spray foam and fiberglass or dense pack cellulose. I want to apply a vapor retarder which kraft face batts already have on them. If I used cellulose I'll need to then apply a vapor retarder like Proclima. All I see is additional cost, mess, and more work.

I have the worst possible situation such as north slope with a large valley that does not typically get shoveled off and can accumulate 2 foot plus of snow. I don't want to risk another moisture/icing issue on the underside of the 4" spray foam (Now), but I'm not real sure cellulose vs fiberglass would really make a difference with this. Comments?

Answered by James ODonnell
Posted Fri, 05/30/2014 - 10:33

Helpful? 0

Either fiberglass batts or cellulose can work in this location, but cellulose is easier to install well, more likely to fill all of the nooks and crannies, and more likely to reduce any air leakage.

That said, if you choose to install fiberglass batts, it's possible to do a good job, as long as you are conscientious and work slowly. The denser the batts, the better. (Look for batts with a high R-value per inch.) To learn more about this topic, see Installing Fiberglass Right.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 05/30/2014 - 10:50

Helpful? 0

The ratio of foam-R to fiber-R matters. The prescriptive R25 for Zone 6 presumes R50-ish for a total center-cavity R, or a 50/50 ratio. But if you keep the ratio at 50/50 or better you do not need an interior vapor retarder- standard latex paint is good enough.

A 2 x 12 rafter is nominally 11.25". So with installing the 4" of foam (R25 ish) 7.25" of cellulose or high-density batt (R27- R29) you're looking at a total R slightly greater than R50. If you backed off and used a standard density R25 designed for 2x8 framing it's compressed performance in a 7.25" cavity is R24, which would be somewhat safer from dew point control point of view than dense-packing cellulose (R27-ish) or splitting/compressing HD fg or rock wool batts in there, or dense-packed fiberglass (R30-ish).

Mind you, the code prescriptive values will work, but in reality with 4" of ccSPF and dense-pack you can "cheat" the prescriptive ratio by quite a bit without much risk:

Even 2" of ccSPF and dense-packed fiber is very low risk in zone 6, if you look at Table 3 in that document, provided you don't have a light colored "cool roof" material as the exterior roofing.

Answered by Dana Dorsett
Posted Fri, 05/30/2014 - 16:24

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