Insulating Cathedral ceiling w/ addition

Started by JeffnTN, January 29, 2005, 01:13:37 PM

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I really could use some constructive input on this.

I thought I had it all figured out.  Well, now I see that I may have missed something.  

I have framed John`s 20xx30 and added 2 feet to the length and then added a 12x20 MBR from the enchilada plans.

My dilemna is:

I framed a small walk in closet in the MBR where the two meet.  I was originally just going to insulate all exterior walls with R-21, all ceiling space with R-30, and the floor (I-joist) with R-25.  The closet is framed with 2x4.  The ext. walls with 2x6, and the rafters with 2x10.  But where the two roof systems intersect this leaves an area that is not well insulated.  (This is due to the continous 1 inch plastic attic vent channels needed for the R-30-C insualtion required for the cathedral ceiling)...
The vent channel at the intersection of the two roof systems leave a void in the well insulated plan .....This occurs because of my closet design.

Because of the closet ceiling and the resulting gable inside the MBR being made of 2x4, and the fact that I have already insulated  the LR ceiling with the R-30 (and the 1 inch vents,) this leaves a weak spot in my insulation system.

I know this is very hard to visualize so I took pictures this morning and hope they help explain the long winded verbal description that I just spent forever typing.  (Typing is not my strongest point)  ;D

If anyone could help me decide how to handle this I would be grateful!

I am considering:
1) removing the last portion of the vents in the LR (these appear as the black things in the lower portion of the roof line in pic #1)

2)insulating the closet ceiling and the closet gable in the MBR with R-13 and insulating the 2x6 interior wall with R-21 (originally I was not going to do the interior wall) (pic #2)

3) or just insulating the area in front of the vents  in the MBR closet with R-30 and framing/boxing that in to close off the air flow..... (pic #3)  (again these are the black things barely visible in the picture)

Thanks for any input and I want you all to know how much I owe John and everyone on this site for the help and advice I have received over the past few years of planning and building my cabin!

Oh yeah, in case you are wondering, (and I would if I were  you)...  The view of the OSB (looks like a floor) in picture #3 is  the temp platforms I constructed in order to get up there and have the space and safety needed to do all this by myself since the work surface is 10 feet 4 1/2 inches above the subfloor.


John Raabe

If I have the thing figured out you have the main house roof which is sheathed and will be a cathedral ceiling. Then the bedroom addition will also be cathedral? Is that true? Pic 3 looks like an attic over the addition but it is the scaffolding, right?

If that is true (a big if), then you could build up a 2x4 wall on top of the roof at the join line and up to the peak. Insulate it (R-21 sticking out the back) and let the sheathed area we see in pic 2 be vented to outside air (w/ a ridge vent).
None of us are as smart as all of us.


John, Thanks for the reply.

Yes you have it figured out.

Obviously I am not a professional photographer

That is scaffolding I have put up to work off  of.
The scaffold ends at the framing you see in pic #3.

The MBR wil be open ceiling cathedral with built up beams  (after I remove that UGLY scaffolding)   just like the main house section.The framing is the area I chose to cover the walk in closet for the MBR.  This closet lies between the 20x32 and the 12x20.  At this roof junction, (THE LOW end) is  where my question lies.

What to do with the vents?  They are a done deal.  Should I insulate the  MBR closet ceiling (2x4) and MBR
gable wall with R-13 or frame an area along the  continous vent edge where the 20x32 ridge vents (bottom)
connects to the 12x20   with R-30?


Hope to hear from someone who sounds like they MAY know what to do as I am an impatient person and cannot sleep well with unsolved problems.  I think I will just follow my instincts on this one and frame a chase in the closet ceiling and put in R-30.

 Might cut the vents I left exposed on the downhill slope of the main 20x32 where the 2 roofs intersect.  

I Gotta move on as this monster will not build itself no matter how hard I kick and prod it.   It is even beginning to wear the leather out of the end of my steel toed REDWING  BOOTS!

Adios y vaya con dios.

Habla espanol?



I didn't put the time in to understand exactly what the problem is,  but I'm guessing you have most of the roof well insulated,  and some of it can't be to the same R level,  also venting may interfer with with beefing up the insulation in the area you want to increase.

Well in hopes of calming your fears:  Nobodies insulation is even!  You know those nice Low-E Argon windows?  They have an R value of 2.5!  Heat loss is a funciton of area and R value, if most of your ceiling has a large R value, and there is a little part with lower it is not going to be much different than if it was all the same R value.

Please don't lose sleep over this,  insulate the best you can and  try to eliminate any leaks.

John Raabe

When you wall up the junction wall between the two buildings you can eliminate the lower vents that are now in an interior space and just drill 1" holes into the roof sheathing to bring in air above the insulation. That cricket area would be open to outside air.

If I'm seeing it right, I would let the closet ceiling be a shelf in the MBR and it would not need insulation. It looks like it is on the MBR side of the junction wall.

If needed, you can always beef up the insulation levels with an inch or two of foam sheathing under the interior finish.
None of us are as smart as all of us.


John, Thanks for the reply,  

Yes you are seeing it right.  How would do the hole thing at this stage?

Hole saw?

I am completely dried in and do not/ will not penetrate that 12/12 metal roof at this stage of the game.  

Yes I am almost done with insulating the ceiling.  It is tough and I cannot WAIT to get back on the ground/floor!

John Raabe

Get a 1" round hole saw that fits in your drill chuck. You only need one hole in each rafter bay, (down low) and of course you aren't going through the roofing, only the OSB inside the protected cricket.
None of us are as smart as all of us.


John, Thank You so much for the advice.  
Just want to make sure I am on the same page here.  Where the MBR overlaps the main living area, (the overlap roof area being referred to as the "cricket") ... I should drill an opening through the 1/2"osb to allow venting where there is no soffitt?  There are continous ridge vents, by the way....

Would you do a chase along the top of the closet ceiling (which is my first idea) or do the entire closet ceiling and 11'1" interior wall? (chase will be R-30 as are  all the ceiling areas...)

If I did the holes and the chase I should be good, right?\Hope so .

That is the game plan as of kickoff time tomorrow


DARN IT!   ???

I finished insulating the @#$% cricket this afternoon.  I Know  I could go back and drill, but do I really need to?

John Raabe


It is likely the actual situation you have is more complex than I'm visualizing. There are also, most likely, several ways to do this.

If the cricket is insulated then you wouldn't drill holes into the lower roof sheathing. That would be the weather and heat barrier and then the lower roof doesn't need insulation in that area.

The basic idea to follow is to build a continuous insulated plane. That's why it seems simplest to use the common wall between the main house and MBR and just carry it up to the peak. Insulate that, the main roof and then vent the cricket.

But like I say, there are other ways to do it if you are already committed.
None of us are as smart as all of us.


Hello everyone.  I hate to sound like I am beating a dead mule, but I have more questions concerning Well,
this topic.  I think I may have figured it out finally.  I took new pics to help describe what I have done.

#1 I closed off all open vent areas in the main 20x32 area where the two roof systems meet.  I did this by nailing the openings shut with OSB from the 20x32 side, caulking completely and then removing the attic vent up to about 30 inches (sealed with metal foil tape) measured along the rake of the roof. I think convection will still vent this upper area of the main 20 x32 roof if what I have read is correct.  

#2 this is the closet ceiling in the MBR  (12x 20 addittion ) portion. I am furring it down to 5 1/2 inches to accept the R-21 instead of the R-13 I originally proposed.  

#3 This is the MBR gable (12x20 portion) I will also furr this out 2 inches to accept R-21.  (and frame for a stained glass window to be backlit by the attic light) .

#4 This is the attic (John called it the cricket), which has been thoroughly insulated with R-30C (as has the lower main roof portion below it (the underlapping (20x32)roof  

I think I should be fine here now but PLEASE tell me if you see any potential problems!!!

For instance, do I need to pierce any of the overlapping kraft vapor barriers?  They are separated by framing but I am unsure about this.   I have totally isolated any air movement from conditioned to un- conditioned space but now am wondering about moisture concerns.   Thanks.  
Need advice  soon as sheetrocking will happen ASAP

glenn kangiser

I dont  know if this will help any or not , Jeff, but Charlie Wing wrote about making your own dual pane windows and stated that if you sealed the inside window and allowed the outer window to be vented to the outside there would not be a condensation problem because the moisture could not get to the outside where the cold was to condense.  I should think that you would want to keep the warm moist air inside of the insulation rather than venting it to where it can contact the cold surface and condense.  Warm air can carry more moisture than cold air so when it drops below it's dew point moisture happens.  Just think about where this may happen and you can answer your own question.   I know- what a load of -------   ;D

In some areas sides may change in the summer so it doesn't really matter anyway because all of your work is defeated by the reversal of the warm moist air.  In this case it is mainly important to stop the flow from one side to the other I read somewhere-  ???
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin

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Glen, thanks for the input.

I have double glazed windows with a thermal break so I am not worried about condensation on the windows (they are Aluminum) so much as I am about condensation/moisture accumulation  within the insulation and framing which comprise my roof system.

Appreciate your input as always though!

glenn kangiser

I probably didn't make it clear that the same applies to moisture wherever it is as far as dew point and condensation  go.  When the air reaches it's dew point the moisture will condense.  This would also apply in a building cavity.  If the moisture stays on the warm side it won't condense if insulated from the cold so that it doesn't reach its dew point.  If the warm moist air makes it through to a cold area it will condense.  Air flow with lower moisture content can remove the condensed moisture if it's not trapped.
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin

Please put your area in your sig line so we can assist with location specific answers.


I understand the basic physics of this, however I am a little weak on the mechanics.  I have built many dwellings, but insulation/moisture was never part of my job.   I am just a simple carpenter.

 Am I doing anything wrong here?

glenn kangiser

I went back and reviewed your pictures individually and I don't see anything I think would cause any problem.  It seems that the closet area ceiling is  already internal so should be more of a sound or individual room heat issue but not a moisture problem.
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin

Please put your area in your sig line so we can assist with location specific answers.

John Raabe

Almost all moisture problems come with airflow issues. Thus blocking airflow through an insulated assembly is the first priority. Do that and it really doesn't matter where the vapor barrier is.

Forget it and there will be condensation and potential moisture problems.
None of us are as smart as all of us.




At this point I am continuing on as there is little room to turn around on this mountain road.