Interior cathedral ceiling (C) Daniel FriedmanCathedral Ceilings Insulation FAQs

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Retrofit or add-on cathedral ceiling insulation questions & answers:

Frequently-asked questions and answers about insulating cathedral ceilings & other inaccessible or tight roof spaces.

This article series gives suggestions for insulating cathedral ceilings on older homes, providing under-roof ventilation for cathedral ceilings while obtaining higher insulation values or R-Values for these areas.

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Cathedral roof and knee wall insulation & venting FAQs

Two approaches for insulating cathedral ceilings and flat roofs (C) Carson Dunlop Illustrated Home

These questions & answers about how to insulate cathedral ceilings and un-vented roofs, were posted originally at CATHEDRAL CEILING INSULATION.

On 2017-10-23 by (mod) - super insulating a mudroom cathedral ceiling when we don't want to disturb the interior ceiling


It's often the most-expensive possible approach to tear off a roof from outside to address a venting problem; I would balance the cost of an outside tearoff and foam insulation vs R&R from the inside.

I'd also consider the total job cost vs. building energy cost and vs. the size of the space (and its value) that I'm rebuilding, and also I'd consider the inconsistency (presumed) between that tight Hi-R area of the home compared with the rest of the home.

I would not build a multiple layer roof, that is leaving old roof sheathing in place and adding 2xs framing and then foam then sheathing then new roof - it's likely to violate fire code.

On 2017-10-23 by Brady

am looking for best route to go. Heres the case. Thanks for your help if possible.

A mud room between house and garage. The ceiling was vaulted into catheridal ceiling. With tounge and groove knotty pine boards. Between boards and roof decking is fiberglass insulation packed between roof and knotty pine.

No vapor barrier between the two. No longer a sufficent venting system between the soffit and ridge vent. Removing tongue and groove is not an option. My thought was to have the problem taken care of from the outside.

Have someone remove shingles. frame over old roofdeck with 2×4's spray 2" of closed cell spray foam. Ply wood on top. Lay new roof. Remove ridge vent close soffit vents seal where roof meets walls. Would this be possible to prevent moisture issues in summer / winter.

And would it help remove heat loss. Looking for quote and advice. It is about a 600 sq ft section i would this done to. Located southren wisconsin. Thanks for your help

On 2017-08-07 by (mod) - Unvented air spaces in roof valleys: Should I provide leak paths or seal them?


You ask the key question indeed.

My concern is that if there isn't actually effective ventilation of the valleys into nearby better-vented roof space, then it's not going to work and just fool us into ignoring a trouble area.

I might be tempted to fully insulate these with blown in closed cell foam - that will prevent any air leakage into the space.

Pros: no air leaks so no indoor moisture leaks into the roof cavity

Cons: too expensive and you'll have trouble getting an insulation contractor to bid on a small, limited scope job,
and if there are future leaks from outside into the roof cavity they may be hidden from view and lead to rot - so the outside roof covering needs to be as bulletproof as possible (I like standing seam metal for that situation, again more $$)

Take a look at HOT ROOF DESIGNS: UN-VENTED ROOF SOLUTIONS and let me know what you think.

On 2017-08-07 22:24:30.138516 by C Charron

I have a new build with cathedral ceilings and dormers framed with 2x8 rafters. The roof is 12-12 pitch with 9/16" plywood, ice and water shield over the complete roof surface, 1x4 strapping and steel sheet roofing. The soffits and ridges are vented.

I was planning to install 1" furring strips on the top inside of the rafters and 1/4" plywood or hardboard to create vents, fill the remaining cavity with R24 Roxul mineral wool insulation, R6 mineral wool board insulation, 6mil poly, 1x4 strapping and pine T&G.

My concern is the unvented air spaces in the valleys. Should I provide leak paths or seal them?

On 2017-07-30 by Josef Kissinger

Im looking to add insulation to my cathedral ceiling. I want to maximize the r value and add r49 or more if i can. Its vented. It has exposed beams that are around 8-10in thick that i want to insulate between and then add tongue and groove boards on top. I'll have to measure

. I guess i could add to the bottom of the beams to get more room for fiberglass, but i was thinking that foam would be a better option. I will do it myself. Can i sandwich multiple foam panels to achieve the proper r value and then spray some foam on the edges to seal it? Wold a combination of foam and fiberglass work? Cost is also a consideration.

My dad is a builder and he heard that it doesn't do much good to insulate with more than 5in of foam. It has diminishing returns, in other words. He recommended a few inches of foam and then fiberglass. I just dont have much space unless i add to the bottom of the beams.

IN summary, how do i maximize the r value per inch at a reasonable cost? Its still an option to add to the bottom of the beams. Especially since its probably a good idea to add foam on top of the beams since wood probably transfers a lot of heat.

On 2017-07-06 by (mod) - good venting options for a solid wall and roof log home

Yes, Art. See our articles on balanced whole house ventilation starting at

On 2017-07-03 by Art Van Houten

We have a 30+ yr old log home with dormers and cathedral ceilings in the upstairs.

The upstairs is not vented (except windows), the rafters are logs (@ 16 o/c) and visible to all, on top of the logs are 2x6 t&g, then plywood, then tar paper, then shingles (I think). There is no attic, no roof vents, no gable vents. Are there any good venting options?

On 2017-06-16 by Joe

I am replacing the three tab asphalt shingles on my 2.5/12 pitch hot roof - cathedral ceiling roof. The rafters are 2x6 with 6" fiberglass (8 foot sections) , paper faced (to the inside). All ceilings are drywall. The existing roof has conventional felt with plywood sheeting

. I plan to install ice/water shield on all of the decking to minimize water finding its way under the felt via nail holes or damaged felt.

The house is 40 years old so I imagine the fiberglass has sagged some, creating some airspace on top. I am considering a ridge vent with some companion venting of the soffit. I know the air flow will be limited, but believe that some of the closed (hot roof) cavity moisture will escape. What are your suggestions?

On 2017-05-17 by (mod) - solving trapped heat - no room to install a fan


We need to understand the whole situation before even speculating about what might be a good set of actions to take. Generally there will be two approaches

We either improve under roof ventilation and reduce roof Heat gain, or we insulate to prevent heat transmission into the interior. Or pozsibly both.

I would need to know more about the roof color, framing, possible venting space, dimensions, and the structure before I could have an opinion about how easily it could be ventilated. It would be helpful to know the climate the location and the insulation as well as roof framing structure that are already in place.

An onsite expert would be best.

On 2017-05-17 by Diane Wiggins

We recently had a metal roof installed. We have a cathedral ceiling in den. The heat is being trapped between roof and ceiling. This is a manufactered home. The heat is unbearable. Air conditioner running continuously. It gets to about 87 degrees inside.

There are vents right below roof on each end of the house. We had fans to pull air out over each end of the house on the roof.

The problem is the den/trapped heat. There is not enough space between roof and ceiling to install a fan. HELP!! Are there any solutions to this problem?

On 2017-01-21 by Joe M

Maybe I missed something written somewhere. But as simple as it sounds to put furring strips on the rafters and install rigid board between them. It seems to me that the rafters are possibly acting as thermal bridges. Would they not sweat one either side?

On 2016-10-29 by (mod) - insulating a salt box design house

I agree that foam insulation is an option, but I prefer to see that installed under a very reliable roof since leaks into a foam ceiling and be disastrous.

Please search for hot roof designs to read details about this approach

On 2016-10-29 by Franklin R.

Here in the Poconos (Pa.),I have a 30-year old saltbox with a new asphalt shingle roof. I want to improve the insulation on the "cape" (sloped) side of the roof, which of course covers a cathedral ceiling.

One contractor declined to give me a quote because he could not guarantee being able to insert fiberglass batts into the 14'-long rafter bays due to nails protruding through the sheathing above. Fair enough.

Another contractor recommended spraying in closed-cell foam. I've been wary of the foam (no vapor barrier, no venting) but now I read that it would make sense because the foam is its own "vapor retarder" and no ventilation would be needed. It's an expensive solution, but seems to be right.

This typical salt-box also has a small, low, ventilated attic area that can be improved with new cellulose blown in right over the existing fiberglass batts. Thoughts?

On 2016-10-10 by (mod) - raise a cathedral roof to add insulation?


I'm unclear on what you're doing. If you mean, for example, lifting one side of a cathedral-ceiling framed roof to add an additional floor of living space, the project is sufficiently disruptive that leaving or retaining ceiling drywall will probably be no consideration.

Generally, a cathedral ceiling-framed structure is going to rely on either a structural ridge, wall ties or some other structural component to keep the building walls from spreading from the roof load. You wouldn't just "raise" such a roof. There'll be structural changes required.

On 2016-10-10 by p giles

is it possible to raise a cathedral roof, without taking out the ceiling been removed so no mess inside

On 2016-09-07 by (mod) - builder installed a ridge vent on a hot roof

Before "fixing" the problem

I'd want to see what's going on with more detail to diagnose accurately the stain cause and thus to be confident of the solution. We don't know if water or snow are blowing in the ridge vent or if moisture is entering the roof from inside the home. (I agree that a ridge vent with no eaves intake isn't going to do much good).

Adding soffit vents to feed the ridge vent won't work unless there's adequate air space in the roof cavity. IE it's either a hot roof or it's not.

The bit about tearing the whole roof apart to warrant it is an OPM problem - spending your money to reduce my risk. Search for OTHER PEOPLE's MONEY to read details.

On 2016-09-07 by JS

Four years ago, replace cathedral hot roof. The roofer installed a ridge vent, but neither of us had the sense to consider that there were no soffit vents. Now I have dark stains on the drywall ceiling, emanating about 2 feet out from the ridge.

I cut a hole in the soffit and can see that the fiberglass is drywall to deck... no air gap.

I considered two options:

(1) Remove the ridge vent, and while the ridge is open, reach into the gap and pull out some amount of insulation, spray the area with bleach, let dry over night then seal the ridge back to hot roof design.

(2) Install soffit vents and hope that over time, enough air will slowly pass through the insulation to dry out the moisture and escape through the ridge vent. A highly experience and reputable roofer recommended I try this first.

He would not simply seal the ridge because he could not warrant it, unless decking was removed and insulation was replace.

I'd sure appreciate your opinion, or a load of dynamite to level this place.


On 2016-09-03 by (mod) - use a test cut to investigate un vented cavities

Chris I would be tempted to make a strategic test cut with a hole boring bit that cuts out a round disc of about 1 1/2" to look through the materials to see what's going on - provided you can find a most-suspect area to test that is also not going to be an eyesore when you put the plug back into the hole.

On 2016-08-31 by Chris

I recently moved into a 30 year old true log cabin. My roof has 1" tongue and groove ceiling boards with 4" X 12" main support beams every 4 feet. The roof was replaced 2 years ago and I am getting "dripping" from the ceiling causing water spots on the tongue and groove and dripping on to the floor etc.

At first I thought it was only when it rained but now it can happen as long as 24 hours later. At first I thought it was the chimney since the chimney is made out of stones so when the roof was replaced the did not flash the new roof but "caulked" it instead

. I couldn't see any obvious cracks or holes but resealed around the chimney anyway. We do not have air conditioning in the cabin. We do keep the cabin closed during the day to keep heat out. At night we open the windows and use a fan for comfort.

And yes, we let all that humidity into the house also. We also have noticed one of our closets is allowing mold to collect on shoes. I am attempting to contact the company that replaced the roof to ask exactly how the roof was replaced.

To the best of my knowledge the installed 2x4 runners (every 2 feet) on top of the tongue and groove. Then filled those areas with foil faced styrene insulated sheets. Then placed sheeting over the top of that and then shingles. To my knowledge no vapor barrier was installed. From the amount of water stains on the ceiling, it appears this has been happening quite frequently but its hard to tell if it was from the old roof. My thought is this.

The roof gets extremely hot (outside temp ahs been averageing 85 with high humidity)for over a month now. When it rains it causing the roof to "cool down". However the inside of the cabin is still the old temperature and very humid. I believe this is causing condensation between my tongue and groove and the 2" of foam insulation or between the insulation and roof sheeting.

As it gets wetter it is trying to find a way out. The would explain why it is "leaking" in several areas and not just one.

I hope someone out there can give me some insight on this issue. My biggest fear is this winter when the cabin is nice and toasty and the roof will have snow on it and the issue will just get worse. PLEASE HELP ME!!!!

On 2016-08-08 by (mod) - find the moisture source before trying a fix

I'd look for the moisture source;

Is the foam open-celled or closed-celled?

Where on the ceiling? Near what? We're also thus looking for roof leaks, ceiling penetrations, condensation within the ceiling/roof cavity.

On 2016-08-08 by Pepper

I just built my home. I have vaulted ceilings, closed cell spray foam with metal roof. I have condensation forming on ceiling. Any suggestions????

On 2016-07-23 by (mod) - sagging roof repairs

Sorry I can't make a specific referral.

I agree that you can't really assess what's needed until some exploring has been done. My view is that it's best not to leave wet, rotting, or moldy mateirals in place in a building;

On 2016-07-23 by Mike

Thanks for your comments on my sagging roof. You did make me feel better about the closed cell insulation. WE can now proceed with making my roof a vented roof. WE do not know if we have rot and mold until we open from the top.

Planning on putting good quality 2x6`s back in where needed ( I was thinking cedar if I can get them the length I need) next to other rafters. I know this will cause more thermal bridging but cheaper than putting a whole new roof on and all new sheet rock inside. If I have major rotting that may have to be what I do.

I suspect rotting because I do not see sagging on the inside with present sheet rock. The other major problem is getting this all done quickly because house will be open to weather.

Do you have any other though? Do you know of any one in Omaha Lincoln Nebraska area that would have some experience with my problem?

Mof, thanks for your comments on my post about sagging Cathedral ceiling. You made me feel better about the closed cell spray foam, so now we can proceed to make the roof vented. Now we need to open the roof from top to see if there is major rotting and if so how to proceed

. If I take all the rotted boards out I will have to take sheet rock down inside house. ( big job). I was thinking of putting in new rafters ( using good quality 2x6`s) screwing sheet sheet rock to new rafters, then taking off the rot if it is there.

I know this will cause more thermal bridging, but will be cheaper than rebuildig the whole roof and redoing all the sheet rock. Do you have any thoughts? And do you know of anyone in Omaha- Lincoln Nebraska area for consultation.

On 2016-07-22 22:41:43.004007 by (mod) -


Hot roof and vented roof are two different approaches that don't mix, I agree;

I'm not sure about a foam shrinkage problem - that's not a common complaint that I've come across with modern foams; it was a problem back in the 1970's with UFFI.

Closed cell foam is ... closed cell. If the roof cavity were filled, typically builders don't bother with a poly vapor barrier as the foam is already a vapor barrier provided it was properly, smoothly, uniformly installed without holes and defects.

A closed cell hot roof design would not normally be ventilated; While I think too much of his opinions miss real world problem conditions, Joe Listburek - more famous and more degrees than I - would argue that a proper hot roof design insulates the roof cavity and doesn't try ventilating above the foam.

In your case the whole installation sounds like a mess - leaks, rot, sagging. I would be slow to simply build another roof over the existing one: I don't like leaving wet, rot, mold in building cavities as there's a risk that it's going to make more trouble down the road;

So before deciding on a repair plan I'd want a more thorough investigation of the present roof condition; Ultimately it may be more economical and end in a better design to demolish and replace than to simply build-over. But that's just speculation - and arm-waving - until an actual on-site investigation of the condition of the roof and the structure are completed.

Keep me posted.

On 2016-07-22 by Mike - cathedral ceiling house problem diagnosis and repair

I need immediate advise. I have house ( ranch) built 1950`s, it has 2x6 cathedral ceilings through out the house. Eleven years ago I had re roofed the house and not checking out what a hot roof was, I put ridge vent on and opened all sofitts. Thinking roof should breathe. Now we had hail storm and roof was damaged.

Since its poorly insulated ( fiberglass batts) I decided this was opportunity to add closed cell foam and using osb sheathing. Insulating contractor says to spray 4" closed cell foam leaving 1-1/2" ventilating channel. I also have roof sagging over 20x15 living room and 15 x 12 bedroom.

After all my research I could have rafter rot and mold. Will need to put new rafters next to the old when we open from top side. I consulted structural engineer that was willing to talk on phone without a charge ( could still hire).

He did not recommend vented roof with closed cell foam, he said the foam will shrink and I will have future moisture problems. He said I need some type of moisture barrier against sheet rock. He said put hot roof back on.

Insulator says foam will not shrink. Who is right? He said we could do 2" foam and spray fiberglass to fill whole cavity and go back to hot roof design. Do not put ridge vent in and close off soffit. My research say for hot roof design must fill entire roof with closed cell insulation.

Does anyone have an opinion on what should be done. I have read so many articles I am now very confused.

The one article I was following

shows retrofit correction of cathedral ceiling. New roof scheduled to be put on in about a month.

On 2016-07-14 by (mod) -

Yeah, and our spell checker sometimes does us in too.

You can take down the ceiling, taking care to inspect all of the trusses for damage; often factory truss parts are joined using a pressure plate that can peel away if the trusses are bent askew during installation or renovations. If that happens some repair is needed before proceeding.

You need to decide between a HOT ROOF design - no ventilation, perhaps with spray foam insulation - and a vented roof design; the latter will probably require a bit of added framing as if your trusses are 2x4 you won't have enough space to get decent insulation in the ceiling space.

Search InspectApedial for HOT ROOF DESIGNS to see some opinions about making a bullet-proof roof and using foam insulation . Of course you'll have to cover the exposed foam with fiberglass.

I'm not sure I'd take any of this approach, as you certainly can't eliminate the truss chords and diagonal braces without a complete roof re-framing job. With the ceiling down when you stare up at all of those truss parts you might think differently about leaving that space open.

On 2016-07-14 by plumfieldcirca1868

Wow, if I could only edit my after I write a comment! "kind of" and "your time"

On 2016-07-13 by Sandy

I was hoping you could direct in the right direction. I have read so much on your website, which is amazing by the way, but I can't seem to find what I'm looking for. We have an existing house that was build with factory made trusses.

The house was completely gutted because the previous tenant was horrible and now it's an open structure. I would like to turn it into part "class room/gathering room" with about 1/3 of it a kitchen. I would like to take the drywall ceiling down, parts of which are moldy and keep the ceiling open. What is the best way to insulate the roof? Or is it better to just replace the drywall and insulation if need be.

I think I would prefer if I could leave it open, but someone told me it would look bad. I kinda of disagree.

Thanks for you time!

On 2015-10-08 by John How do I insulate a cathedral ceiling with a scissor type truss

How do I insulate a cathedral ceiling with a scissor type truss

On 2015-06-09 by (mod) - dark spots on ceiling - thermal tracking?


found at the More Reading links above and there you will find

that may explain what you are seeing

On 2015-06-09 by Kim

Darken spots on ceiling. From one end of house to other. All on ceilings that face sun in afternoon. Have tile roof. Home Depot said I had plenty of insulation, but there is none from the end to about 6 or 8 inches in. It's in ever room that the back of house gets full sun in afternoon.

I need hElPoo. There are no water leaks, no rotten wood? The spots are not even that dark, but are noticeable
Thank you

Question: What is causing drip marks from leaks out of cathedral ceiling in a Northern California House?

wrote: July 21, 2013 Hello,--> I read through your very complete article about roofs, venting, etc. Thank you for all the was very educational. I'm not sure if I have answers to my specific issue solutions, so I'd like to give you some background and ask your opinion. Northern California summer home in the mountains (about 4800 elevation)

Closed for winter months until about end of April, snow on roof melting at that time Cathedral ceiling on upper floor (2-story house)

Discovered drips from center beam in interior (April was still dripping with liquid on horizontal surfaces, etc) The builder replaced roof ridge with vented ridge (shingled roof) and sanded off drip marks on interior beams

A year or two later, drip marks on beams are back (p.s. there is also a big bat problem that everyone here wants to have an air-tight home)

I don't want to replace roof yet, but what can I do in the winter? Leave central heat on low? Open some windows an inch or two? I'm open for suggestions, and thank you very much! - J.H. 7/21/2013

Reply: Here are things to check to track down a roof leak vs. interior air and moisture leak

A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. You will find additional depth and detail in articles at our website.

That said, I offer both a guess and some suggestions:

I agree that it makes no sense to replace the roof covering before we have a clear diagnosis of the cause of leakage; Worse you could be wasting a lot of money re-roofing only to discover that "leaks" continue because the cause was improper venting, soaked insulation, air leaks, or that there is moldy drywall and wet insulation that need replacement in the ceiling.

Guess: the home has either one or more leaks into the roof cavity (cathedral ceiling) or condensation accumulating in that cavity.

In a cold climate and depending on the level of roof insulation, water entering the roof can freeze, accumulate as ice, and thus return to the interior as leaks and drips that continue for quite a while in thawing conditions.

Worse, once the insulation has become wet the cavity has lost insulation value so the problem is likely to be worse, especially if the source is condensation from inside.

You said the house is shut down but did not say whether heat is left on or off. If heat is off and the house interior is at freezing temperature (not my first choice for building preservation), the water source in the ceiling is more likely to be an exterior leak.

If heat is left on the water source could be an exterior leak, ice dam leaks, or interior air leaks carrying moisture into the roof cavity.

If the water source in the roof cavity is from air and moisture leaks from the interior, the passage points into the roof are most often at penetrations such as around light fixtures. The percentage of moisture that moves directly through solid drywall into a building cavity has been shown to be quite small.

The cure for such interior to roof air leaks is to seal penetrations and provide functional roof cavity ventilation. To that end, a ridge vent is ineffetive if there is not adequate soffit intake, and if the total ridge vent outlet is sufficient. For example a plastic mesh fabric type ridge vent covered by shingles does not move much air out.

We also need enough air space between the insulation and the underside of the roof deck for air to flow freely. And the ridge vent needs to be tall enough to vent through snow cover.

I would first inspect the roof surface with care from outside to look for obvious leak points or damage; I would next determine exactly the state of under-roof ventilation: soffit intake, roof spacd, ridge outlet;

Then I would go to the two most-suspect areas in the roof cavity and make a test cut sufficient to inspect the insulation for signs of wetting and mold, the cavity side fo the drywall for water and mold, and the roof sheathing for water, mold, and to confirm the air space.

In any event I would be cautious about leaving windows open in a home with heat off because of security risks, animal entry risks, blown snow and rain damage risks etc.

I do like eaving heat on to keep the home above freezing, say at 40 or 45F which can avoid building damage that comes from extreme temperature swings inside - conditions that are not anticipated by most modern construction; But as I suggest, let's wait on the cure until we understand the disease.

When we've done enough inspecting that we are confident of the cause of the drips you describe, only then does it make sense to start "repairing".

Question: insulating cathedral ceilings in a Saskatchewan Bungalow

(Mar 13, 2014) Shane Harris said:

I'm updating insulation on my cathedral ceiling on a 1966 bungalow which currently has no vapour barrier. The shingles need replacing so I will be tackling this from the outside by removing the roof sheathing. I plan on using closed cell spray foam to provide the vapour barrier and insulation.

How much foam do you recommend and what R value should I aim for? (rafters are 2x6, 16o.c.) Is their any way to prevent the thermal bridging through the rafters? Will spraying the sides of the rafter and adding some rigid board insulation between the rafter and sheeting work? Is it even worth the trouble versus the benefit or cost?

Shane Harris
Yorkton, Saskatchewan



You could add a layer of high-r foam insulation IF you are building a hot-roof unvented design.

Otherwise the foam layer atop the rafters and under the roof sheathing will have its R-value wasted since ventilating air would be moving between the underside of the foam and the upper side of insulation between the rafters.

With 2x6 rafters (under-sized by modern standards) you can only get about 5 1/2" of insulation - not the greatest R value though the R varies by foam type.

If interior space permits I'd consider adding solid foam on the interior ceiling and new drywall over it to increase the total R.

I pose that the total project cost to R&R intact roof sheathing for this project is higher than insulating from the interior.

Check for bids from professional insulators.

Reader follow-up:

(Mar 13, 2014) Anonymous said:

I'm unable to tackle this from the inside do to decorative wood paneling in the cathedral part of the roof that I don't want to disturb. Should I look at going with only 2" of spray foam to provide the vapour barrier, add batting and then the rigid board insulation to cover the joists before sheeting? From your articles you still recommend a vented design to keep the roof cool in the summer and prevent premature wear on the shingles.


Okay, makes sense. Yes it's a cold climate , similar to Minot, ND. So, I have to use spray foam or rigid board(sealed around the edges) between the rafters vs the batting because of no vapour barrier correct?


Rigid board between rafters -which I've done -is a lot of cutting and fitting and sealing, and costly compared with spray-foaming the whole cavity. Because it's just 2x6's, the addition of a layer of 1 or 2" solid foam Hi-R insulation improves the total R value; you'd secure the roof decking to the rafter tops through the Hi-R.

While we prefer the vapour barrier on the ceiling warm side, it's less critical than sealing around any ceiling penetrations on the inside (lights for example).

Question: drop ceilings, sagging from wet insulation

(June 22, 2014) Deborah said:
We have a drop down ceiling in our office about 1200 sq feet with only one wll return for the ac. The last 3 months we have notice a sewer smell. The ac is in a small 1/2 bath size room with a door. We've had a lot of ran, high temps and humidity.

Also the insulation is now weighing down the ceiling tiles. Someone told us we needed to insulate the system and replace some of the tiles with plastic egg grates. This would allow the proper air flow and venting for the system. Please advise before I spend a lot of money?



You need an onsite inspection by a competent HVAC or other building professional to first understand how your system is designed. If the office ceiling space above the drop ceiling is being used as a return air plenum you don't want to subvert the design by adding addtional vent openings.

Separately, if you are seeing sagging and moisture or condensation problems that is a potentially serious issue risking mold contamination and even ceiling collapse - conditions that need to be inspected as part of answering your question.

Question: low pitched dormer roof insulation

(Aug 15, 2014) jerry said:
I am located in Zone 4 . I have a second floor low pitched dormer where the HVAC is located. All the ducts are insulated (R-3) and I have R-48 fiberglass between the ceiling joists. The 3 inch furnace flue vent (not insulated) is in the attic.

I have ridge vent and last year added more sofit vents so that I have a 12 inch vent every third rafter. I continue to have ice damning issues every winter. Considering two options; (i) foaming all of the HVAC ducts , better sealing all of the can lights and vents, then putting 4 inches of additional fiberglass (blown in) or extending the vent chutes to the ridge - in each rafter and spraying foam to the underside of the deck-removing the R-48 from the ceiling rafters. Thoughts, ideas recommendations?


Thanks for the question Jerry.

As you still see ice damming we've got these topics to check out:

1. there may still be inadequate intake or outlet venting - I want continuous soffit vents not intermittent vents, and I want a continuous ridge vent.

The "vent chutes" may also be inadequate - I'd like 2" of clear space between insulation top and under side of roof deck at the soffit openings - for the full width between every rafter pair. Some of the flexible vent chutes are too soft and may give just 3'4" of space.

2. there may be abnormal amounts of heat leaking into the roof space from below - sealing openings such as around lights (you may need to go to DCIC ceiling pot lights if you've got older recessed lights there) will addresses this

3. there may be too much in-attic or under roof heat generation or heat source from ducts or the metal exhaust vent.
Check first for duct leaks.
Next consider more duct insulation. R-3 isn't much in a cold climate. That will improve heat delivery to the occupied space, reducing heating costs too.

4. Finally: consider (but defer) using an insulated chimney from the ceiling up through the roof.

Keep us posted - what you find will help others.

Question: Big Beam House insulation

(Sept 10, 2014) Anonymous said:
I have a Big Beam house with all rooms, except bathrooms, with exposed ceilings of 2 x 6 Douglass Fir.

The insulation on the roof is 2" solid foam with an attached nail based. There is no venting. I may have to re-roof - Has modern technology suggested a new method to vent a Big Beam home? Any recommendations? Thanks Jerry

Question: insulating or going to a hot roof cathedral ceiling after roof leaks

6 Feb 2015 Fred William said:
Just read your comments about hot roofs in cathedral ceilings and have a question. We recently bought a 1928 home that has a new addition. Last year we had water leaks from ice dams underthe older sections.

From talking to 4 insulation contractors, one main problem is the tight space, only 4 inches, between the slanted ceilings in the 2nd floor closets that flank our staircase and the roof sheathing. 3 of the 4 contractors really don't want to deal with my problem, said they would get back to me, and never did.

The 4th guy said he sees this all the time for older homes. His recommendation: blow in cellulose from the top down into this 4 inch wide space and then go into the closets and blow cellulose through the interior walls between each stud making a top and bottom hole. I just looked up R values and 4 inches of cellulose is only about 10;

probably not good enough to prevent all future ice dams. But an R-10 is better than what I currently have which is zero. I called a general contractor and he said that I don't want to give up that flow of cold air from sofit vents to ridge vents by filling that space with insulation.

Bottom line: if i go with this insulation contractor I will get some insulation but will eliminate the winter cold air ventilation that is also nice to have under the roof sheathing. (The contractor will also blow in cellulose throughout the house in all areas to stop heat from escaping into the attic. He said that he found gaps around the chimney, around lights and around ceiling fans) Your comments are appreciated, thank you.


Fred I'm not sure what comments you seek.

The article series above discusses
- insulation options
- ventilation options
- Hot Roof design options for non-vented cathedral ceilings

Certainly I would not do anything about your ceilings nor add insulation before doing some investigating. It would be a shame to simply blow insulation into a cavity only to find later that you have to remove the whole shebang to get rid of moldy drywall that nobody attended.

I'd go to the most-suspect point where leaks occurred and make a small opening, say 2x4" to look at the cavity side of the drywall, the wood framing, the existing insulation.


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Or see INSULATION LOCATION & QUANTITY for ATTICS to discuss the relative benefit of adding insulation to a cathedral ceiling versus building walls in the same area.

Or see ROOF FRAMING TIES & BEAMS for a discussion of proper framing of a cathedral ceiling

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