Retrofit or add-on cathedral ceiling insulation questions & answers set #2.

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.

Cathedral roof and knee wall insulation & venting FAQs

These questions & answers about how to insulate cathedral ceilings and un-vented roofs, were posted originally at CATHEDRAL CEILING INSULATION - please check out the advice given there.

On 2019-01-25 by Redsail - why we replaced the roof to deal with a bat infestation

Thanks for your prompt response. Replacing the roof may seem extreme, but I battled this issue for 4 years,spent about $2500 and did countless hours of research, all with little success.After talking to other that had similar roof styles and bats I finally was advised by a pest exterminator that the only way to keep them out is to use composition.

Bat exclusion companies are rare, expensive, and most roofers and pest companies don't want to deal with the problem. Bats have one baby/yr and they return to their previous home so the flock just gets bigger each year. They can squeeze into less than .25 in. opening so sealing is impractical and not advisable.

I did have foaming done as seen in previous pictures, but that is when the cracking sounds began due to the probable reduced air flow. I have included a video of a bat pulling his body between the tight seam of two tiles. Watch carefully in the left corner of the video and you will see him pull himself through. One man I talked to spent 2 wks removing hundreds of pounds of guano from under just part of his shake tile roof. They are a big problem.

Anyway, I just want to clarify a couple of things. The mesh opening on the two prows is probably 2" by 30 ft and 2"x 20 ft and the gable has 2" x 30 ft. It seems that would be enough open area for intake air and when it heats up in the summer the air would automatically move up to the new ridge vent.

Also, the mesh is covered by a metal flashing which the roofers tightened up to try to discourage the bats and that also seemed to have increased the noise.

There are no holes in the tongue and groove ceilings and when the roof was opened in a couple of places to check, it was clean and dry under the sheathing. I'm looking for the least expensive option and ridge vents and opening the flashing and installing better mesh seemed like a solution to me.

Also considering some of the newer long strip vents that being used in newer homes. Do you think any of these possibilities will work? Lastly, what do they call the old fashioned ridge vents you prefer?
Again, thank you for you help with these questions.

On 2019-01-23 by (mod) - replaced entire roof to keep out the bats: venting problem remains

Wow - replacing an entire roof to keep out the bats sounds expensive and extreme.

Was that advice given to you by a professional pest control or animal control expert?

I'd have looked for specific entry points to be repaired and I might have added some separate bat -houses on the same property to encourage the bats, a useful and important species, to live peacefully nearby but out of the house.

Your photos show moisture stains that, if they're from inside the building, suggest that under-roof ventilation has not been adequate.

You might also want to look for and correct moisture sources indoors and air leaks into the ceiling from indoors.

Mesh type ridge vents do not pass as much air as the older, uglier, but in my opinion more-effective aluminum ridge vents.

And no ridge vent will help whatsoever (and may simply make matters worse) if there is not also adequate air intake at the building eaves or soffits as well as an air path up under the whole roof.

Generally we want to be sure that there is more than a 50:50 ratio of intake to outlet venting area, otherwise you risk sucking conditioned air out of the occupied space, sending it out at the roof venting outlet.

See PROBLEMS with PARTIAL ROOF VENTILATION

Our primary question is: is your building design one using a "hot roof" that was designed to be insulated but not vented? Or is this design supposed to be vented?

And see ANIMAL ENTRY POINTS in BUILDINGS to keep bats out of the cathedral ceiling

On 2019-01-23 by Redsail - bats and moisture under my roof

I have a 1976 Justus cedar home that has prow facades on both the 2nd and 3rd levels and a flatter gable in the back on the 3rd floor. The interior on the upper two floors is tongue and groove cedar cathedral ceilings.

I replaced a shake style concrete tile roof with composition last summer because bats were getting under the tile roof.

Since then the roof began having loud popping and cracking noises during the summer particularly on warmer days here in the Pacific Northwest and they are frequent enough to seriously interfere with sleep.

During the re-roof it became clear that the roof was not unvented as I thought, but instead the prows and gable had about a 2-3 inch wire mesh strip over an opening between the sheathing and rigid foam insulation that had been pushed in by the animals for entry.

The roof is constructed like a hot roof with 2-3 in of rigid insulation and about a 3/4 in of air space between the furring strips and upper sheathing. This construction evidently met venting standards when the house was built.

The ridges have no ridge vents and there are no soffit vents.

I am thinking of adding Cobra ridge vents to allow for better ventilation but continuing to use the existing new metal mesh areas as the intake.

Does this seem like a reasonable approach?

I have read that the ratio of intake vs. outflow should be 50/50 or up to 60 % for intake if necessary.

I'm not sure how to calculate this accurately and would appreciate any suggestions you may have for addressing these issues. I will try to upload some pictures for clarification.

On 2018-12-09 by (mod) - venting a cathedral ceiling with open webs between rafters.

I think the general approach that you describe sounds pretty good. I don't know what the climate and the heating load is where your building is located so I can't comment on the total adequacy of insulation.

If you are adding structural insulated panels on top of an existing roof search but you have solid insulating material I'm not sure that there is actually a moisture trap issue.

I think the question is whether or not we're going to reach the dew point in the ceiling structure under the range of temperatures they are going to occur in your Club.

On 2018-12-06 by David Anstatt

I have a cathedral ceiling with open webs between rafters. The rafters are wrapped with chestnut trim and the sheathing (interior) is also planks of varying widths of 1x chestnut. these are all laid on top of the rafters and finished on the inside with stain and varnish.

Above them ii a layer of 1/2 in perlite followed by 3/4 in T&G planks of sheathing.

Heavier than 30 wt. paper was applied over this assembly followed by the original asbestos "slates'. This 90 year old roof has done it's job and now replacing it with composite "slate" roofing material.

The room below is approximately 30x20 and heated in winter and cooled in summer. There is no insulation other than the 1/2 perlite and no ventilation other than what seeps through the 90 year old house. The ceiling is by no means airtight. In taking up the old roof the decking is in near perfect shape, no rot , no mold.

Here is my dilemma:

I'd like to take this opportunity to add some insulation but don't want to mess with the beautiful natural wood finish in the ceiling. I was thinking of adding a layer of ZIP insulated decking over the existing sheathing which will gain me up to an R9 using 2 in. Zip panels.

I don't want to go any thicker because it will negatively effect the rake line , and overall look of the house.

The seams will be taped to provide a vapor free barrier on the outermost layer of roof underneath the roofing tiles. While I'll gain some (small as it may be) insulation in the roof, will this create a moisture trap in the roof where none seemingly existed in the past.

Or, will this "sealing of the roof prevent the drawing of moisture through the decking system? I think the draftiness of the 'as-is" roof naturally vented any moisture in the past as evidenced by the sheathing condition. Does anyone have any similar experience in this type of situation and/or suggestions /input on the direction I'm headed?advise

On 2018-09-17 by SAm

I have a roof area, an addition by a previous owner that is one sloped plain, about 600 sqft. In the spring, there is dripping through some penetrations in the vapor barrier such as screw holes for the smoke alarm...

so I know there is water resting on it. However, there are no leaks during inclement weather. I'm assuming that the insulation is inadequate, and moisture is accumulating and freezing inside the roof space, especially around the bathroom vent ducting, which is where most of the leaking is.

It is a very small space, maybe 8" at the low end, and 30" at the high end... filled with very dirty fiberglass batts.

However, the condition of the roof sheeting and interior ceiling are still sound. My plan was to blow in fiberglass to make it into a hot roof.

This would give me the added insulation in the roof, as well as insulating around the bathroom vent.

I am paranoid about hot roofs, but this is the only solution I have come up with short of ripping apart the roof from the bottom or the top. Am I missing anything obvious?

On 2018-03-16 by (mod) -

Yes

On 2018-03-14 by spydox

I see the 2 designs for the cathedral ceiling (vented and unvented) at CATHEDRAL CEILING INSULATION but I wonder, can there be say a 2-3" airspace on the house side of the insulation? That greatly increases the R value.

On 2018-01-06 by (mod) - dripping from the peak

Amy

Do you think we could be seeing indoor moisture condensing under the roof and leaking back into the home?

I might make a test cut into the stained area to see if I can trace the water to its source.

On 2018-01-06 by Amy Kenworthy

I have a cathedral ceiling dining room that was an add-on to a home - we purchased this home after the fact.

The ceiling has exposed wood beams with drywall in between and slight water staining was noted by the wall and near the peak in previous years.

However, one year ago we replaced the aged cedar shake roof with architectural asphalt shingles and last spring and summer we had a steady dripping from the peak and near the peak of this ceiling almost constantly.

We live in the high mountain desert of Wyoming so had precipitation only into June - the dripping persisted for a few months after the precipitation ended so I think that condensation is the problem.

A stream does run by just adjacent to this portion of the home. Being in a rural area, our options for consultation on this problem are limited. How should we tackle this problem?

On 2017-10-23 1 by (mod) -

Brady,

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

Brady,

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?

CC

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 DESIGN PROBLEMS 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

https://inspectapedia.com/BestPractices/Ventilation_Whole_House.php

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

Diane,

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 inspectapedia.com 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?

P.

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 InspectAPedia.com 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.

Thanks

...

Continue reading at CATHEDRAL CEILING INSULATION - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CATHEDRAL CEILING VENTILATION
• CAPE COD ROOF & KNEE WALL INSULATION & VENTILATION
• CATHEDRAL CEILING INSULATION
• HOT ROOF DESIGN PROBLEMS
• HOT UN-VENTED ROOF DESIGN SOLUTIONS
• HARD to VENT ROOF SOLUTIONS for HIPS & CATHEDRAL CEILINGS
• INSULATION LOCATION & QUANTITY for ATTICS
• PROBLEMS with PARTIAL ROOF VENTILATION
• ROOF FRAMING TIES & BEAMS proper framing of a cathedral ceiling
• ROOF NOISE TRANSMISSION
• ROOF VENTILATION SPECIFICATIONS pros and cons of hot roof designs

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