Converting attic space to cathedral ceiling


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Old 08-12-15, 12:29 PM
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Converting attic space to cathedral ceiling

Hello,

I am reinsulating the second floor of my home because, being built in 1945, there were not real standards to respect and it turns out that most exterior walls are uninsulated, and my attic is very poorly insulated and the eaves are completely clogged with loose fill packed in there by the previous home-owner.

With lack of a better way to explain the design, I have a gable roof with a dormer. All four slopes are 12/12.

Seeing as I am opening all my walls from the inside, and we are converting the 2 bed / 1 bath floor plan to a master suite, my spouse and I agreed that the best design choice would be to have a cathedral ceiling. This would permit us to remove all ceiling panels, and reinsulate adequately.

We are having the exterior walls done with urethane spray, because they are 2x4 walls and stud spacing is not consistent.

The question I have is as follows: to make this project fit within our budget, I can't go with the full 6+ inches of urethane for the ceilings - it adds about 5,000$ to the bill. I am looking for the most cost-effective means of insulating, and ideally have a non-ventilated ceiling - installing ridge vents, ideally, is to be avoided for budget reasons as well.

My current roof joists are 2x6 (unplaned - they actually measure 6" and not 5,5"). I would like to lose as little ceiling height as possible. There is also no vapor barrier or any other type of membrane other than the actual roof covering itself - asphalt shingles on tar paper. So this job needs to be done one way or another.

One of the companies I had come to bid on my project, suggested I could go with dense pack cellulose. I would be ready to do this, but I don't know what the best way to make that waterproof membrane between the subroofing and the insulation... If I put polyethylene or another membrane of this type, it will get punctured everywhere by the nails sticking out through my subroof.

Is a one inch foam board, up against the subroof, and sealed to the joists, an appropriate solution? And, do I still need to install a vapor barrier on the warm side of the insulation, or do I use unwoven fiber mesh?

Thank you for your time... My brain is starting to ache with all these unknowns.
 
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Old 08-18-15, 02:41 AM
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Bump? I would really appreciate some input on the subject. thanks.
 
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Old 08-18-15, 03:18 AM
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Sorry for not replying, I had trouble understanding what you wanted to do so waited for others to ask questions, none did, so I'll try.

I don't understand how you plan to convert the upstairs to a cathedral ceiling? You can't just remove the ceiling joists to open up that space.

Have you priced the spray foam, most shy away from it once they see how much it costs.

On the outside of those 2x4 studs, are there boards for sheathing? Some older homes have only siding nailed to the studs making insulation a bit more difficult.

Is the home framed in a balloon style?

What type of electrical wiring is in the house currently, knob and tube, 2-wire with no ground, or 2-wire with a ground?

Once you resolve the structural issues of creating a cathedral ceiling then we can discuss the unvented ceiling option. Code requirements must be met regardless of costs.

I'm not familiar with your codes, but here in the states no codes approve of cellulose against the roof deck. There must be a thick layer of air impermeable insulation or a vented air gap.

There are more questions, but as you can see we don't have a full picture.

I have installed scissor trusses to create a vaulted ceiling which can in some cases allow the existing ceiling joists to be removed, but best to have that engineered.

Bud
 
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Old 08-18-15, 05:52 AM
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Thanks for the reply!

So I don't plan on modifying the roof structure -- I am keeping the joist ties in place and will simply cap them with wood planking, and run my gypse boards up against the roof joists.

I have priced spray foam, and it is indeed expensive, which is why I am looking for viable alternatives. My insulation contractor (who specializes in urethane only) told me cellulose is no good for this application. I tend to believe him. And you as well.

As for the electrical wiring, I currently have two wire ungrounded, but this causes me issues and it will be dealt with by rewiring the whole second floor all the way down to the panel. Half the house (whole second floor, and living and dining and hallway of main floor) is on one 15 amp circuit. It will be rewired with new circuits and grounded 2-wire. This will be done while walls, ceilings and floors are opened up -- yes, I am removing the creaky uneven wood planking that makes up the subfloor to start over with tongue and groove 3/4"ply.


Another option my insulation guy told me was somewhat less of a bad idea, but still not ideal according to him, is stone wool (roxul). So, I hope I clarified what needed clarifying, and don't hesitate if you need more details. I really do appreciate your help!!
 
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Old 08-18-15, 06:16 AM
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I'm still having trouble with the description of the ceiling, "I am keeping the joist ties in place and will simply cap them with wood planking, and run my gypse boards up against the roof joists." and where you are creating a cathedral ceiling.

As for cathedral ceilings, they seem simple at first glance, but must be built to rigid standards. You CANNOT use any air permeable insulation directly against the bottom of the roof. Many extreme failures where moist inside air finds its way through, even Roxul, to condense against the cold roof, ie the roof rots out. Depending upon your climate zone there is a ratio of rigid foam against the roof deck that can then be covered with fiber insulation. Just guessing, but in CA I would guess a minimum 2" of rigid then the Roxul. BUT, you need to be targeting your code required minimum insulation level which could require more rigid, it is a ratio where the inside surface of the rigid needs to remain above the dew point in your climate.

Note, if you create an unvented space above that 2nd floor ceiling it also must be conditioned, meaning it becomes part of the living air space. If you do not heat it and circulate the air, then it will grow mold.

Any chance of pictures.

Also, let me apologize for sounding uncooperative, it is difficult to properly advise via long distance and from our point of view it is very important you pull permits as required and meet minimum codes. Any variation should be approved by local code officials.

Bud
 
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Old 08-18-15, 06:27 AM
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I agree, some pictures would be really helpful.
http://www.doityourself.com/forum/li...rt-images.html
 
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Old 08-18-15, 08:09 AM
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I understand your difficulty to understand properly my project... it is not one of those simple open-insulate-close projects.

I don't have the means to get photos up right now, but I will try a different way of explaining.

I have a two-pitched roof - 12/12 slope. it has an attic space. the upstairs floor right now has pitched ceilings from 40" off the ground (low wall) to 7'6 (following roofline) and as of 7'6 the ceilings are flat - the gypse is hung off the joist ties that cross from one pitch to the other. my roof joists and ties are set at 24" intervals.

I plan on removing the flat ceiling gypse, and the insulation that is in the attic, and the gypse on the pitched ceilings because the insulation is inadequate - my attic is not well ventilated because my soffits are packed with cellulose right now.

After removing all my gypse, I will be left with exposed roof framing and subroofing from inside. The subroofing is slat, from circa 1945. (as are my exterior walls, to answer an earlier question).

I want to insulate between my roof joists, so I can bring the gypse up to the ridge beam following the pitch of the roof, basically taking the current attic space and making it living space air, leaving me with the joist ties crossing open air every 24" from one pitch to the other.

If this fails to illustrate the project, I will make a sketch and try to upload it.

And if this is not what is called a cathedral ceiling, my apologies ... I'm not extremely well versed in architecture and construction design terms.
 
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Old 08-18-15, 08:32 AM
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The best way to insulate between your roof rafters is to do what is called a hot roof. (google "hot roof" and you will get lots of info) You mentioned that spray foam (what you called urethane) was too expensive, but did you look into any DIY foam kits?

Another thought, and Bud would be better versed on if this is an option, you could cut some layers of rigid expanded polystyrene and fit them into the rafter spaces, then use some cans of spray foam to fill the gaps.
 
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Old 12-02-15, 05:54 PM
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For the benefit of people who may be in the same situation as me, I will update my project.

We ended up removing (against suggestion of a forum member, I agree) all ceiling joists. I was very (VERY!) comfortable removing them once I had removed all the blown insulation that was supposedly insulating the attic. When you see your ceiling joist is actually five different pieces of 2x4 that span from one slope to the other, and offers absolutely no structural support, you get into researching - and realize that you have a self-supporting ridge beam / hip and valley roof.

The smaller of the two ridges (about 12 or 13 feet long, and it tapers down to 7 feet at the knee walls) is only 6'6 high, and has no collar ties or anything of the sort.
The larger of the two is the main part of the house, at 12 feet in height, 22 feet long. We ended up replacing the front 10 feet's worth of ceiling studs (actual full length 2x4's, instead of nailing five different pieces together!) because we wanted to have flat ceilings at this part of the floor (for bathroom and walk-in closet).
We ended up fabricating pine casings to create decorative beams for the remaining 12 feet.

Attachment 59544

And, well as for the insulation... We bit the bullet and dished out the 6k for urethane spray foam. only one thing to say about this : TOTALLY WORTH IT.
There are things that I am willing to compromise on or to go cheaper, but as everyone here says, and I agree with it wholeheartedly, the bare bones and structural stuff is nowhere to go cheap or half way.

So, thanks for the input, it was really appreciated! it helped a whole bunch.
 
 

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