Insulating a Vaulted Ceiling?

[burger]

Hey!

Thanks to everybody for thier responses to my first two threads. I have a lot of questions about designing and building my garage and I'm glad you guys (and gals) are here to answer.

I've been thinking about a hip roof with a vaulted ceiling on the inside.

This would be on top of a 2' of cinder blocks and 8' stud walls (10' o'all.

I have everything modelled in Google SketchUp and I think it looks great... just curious how I'd go about insulating it.

I have a Taunton book on framing techniques, and they recommend 2x6 rafters with insulation for 2x4 studs to allow and air gap on top of this insulation. This would work in conjunction with vented soffits and a ridge vent.

Sound good? Any other ideas?


Thanks,
Ed

 

[PAToyota]

The air gap method is one way. Another is to use the spray in foam - like http://www.icynene.com/ - and you can spray it solid and not worry about the venting.

 

[JMURiz]

I am just going to use some R-19 paper backed battens and staple them to the rafters...should give me ~ 4" space for the air to vent from the soffit to the ridge-vent. Since you'll be using 2x6 (instead of my 2x10) you'll need something thinner, might want to look into that styrofoam stuff one guy on here has been touting.

 

[burger]

JMURiz: The 2x6 size came from the example drawing in my framing book. I may use a different size based on the requirements for my span. Sorry if that was a little unclear in my original post.

PAToyota: Maybe I'm dense, but doesn't the roof NEED to vent to work properly? Sounds like a neat idea if it would work.

 

[kbs2244]

If you go with paper faced fiberglass, then you need ventalation behind it. The paper is not a good enough vapor barrier and some will get through and need to be vented out.
The foam stuff forms a crust when it dries that is a pretty good vapor barrier, so you can spray it on directly without any venting needed behind it. It works pretty well at pluging up any little air leaks as well. But it is pricey.
Which ever way you go, get one of those 20 x 20 inch, $15.00 window fans, set it on low, and hoist it up in the peak at one end of your garage. About 2 feet from the end wall. You will be amazed at how much that low but constant air movment evens out the temp. Both winter and summer.
I am a big beliver in ventulation. It solves all kinds of rust, condensation, and comfort problems.
If you are located where it gets hot in the summer I like those ball shaped wind turbins to get the heat out of the garage. They are quiet, need no power, and move a lot of air. For the winter you can either make a plug of some kind for the hole in the celing, or go up on the roof and wrap a garbage bag around it. (I have even seen molded plastic winter shields. Just one more thing to lose in my mind.)

 

[PAToyota]

The spray in foam doesn't give any place for the dewpoint to create a problem. The moist air vapor doesn't go through the insulation. So you can do it without venting. Take a look at the Icynene website - I think they have the diagrams on there.

 

[Vicious_Cycle]

I vote for doing it just as you propose, with fglass batts and room for air circulation.

I have seen homes with vaulted ceilings where the builder didn't leave room for air circulation (i.e. R-19 in 2x6 joists), and they invariably wind up with moisture issues. Usually sooner than later.

 

[CraigFL]

You could consider SIPs -- Structural Insulated Panels

http://www.r-control.com/sips.asp

 

[realz]

Wind turbins

If you are located where it gets hot in the summer I like those ball shaped wind turbins to get the heat out of the garage. They are quiet, need no power, and move a lot of air. For the winter you can either make a plug of some kind for the hole in the celing, or go up on the roof and wrap a garbage bag around it. (I have even seen molded plastic winter shields. Just one more thing to lose in my mind.)

From an upper midwest carpenter;
It is recommended to keep air moving year round in an attic space.
Don't cover the wind turbins in the winter. Moisture can be caught and do damage to the building.

 

[1320stang]

I think you still need to have an air gap for venting, not for the winter, but for the summer. Roofs get really hot, the air gap helps to keep from cooking the roof and reducing it's lifespan.

 

[burger]

What's the best type of vent? Ridge vent, or one of those mushrooms/wind turbines/etc?

I have an old ceiling fan that I plan to mount on the interior side.


Thanks,
Ed

 

[JMURiz]

I personally like the ridge vent, if nothing more than you don't have a huge turbine on top of your house.

 

[z28toz06]

Re: Wind turbins

From an upper midwest carpenter;
It is recommended to keep air moving year round in an attic space.
Don't cover the wind turbins in the winter. Moisture can be caught and do damage to the building.

I agree, use the pink or blue thin foam panels that you staple in between the roof joists. This creates a vapor barrier that lets moisture escape up the inside of the sheathing from the soffit to the ridge vent. There is no need for a 2" gap using the r-19 vs the r32 insulation. Heat rises and that's where you do not want to skimp.

 

[burger]

Re: Wind turbins

I agree, use the pink or blue thin foam panels that you staple in between the roof joists. This creates a vapor barrier that lets moisture escape up the inside of the sheathing from the soffit to the ridge vent. There is no need for a 2" gap using the r-19 vs the r32 insulation. Heat rises and that's where you do not want to skimp.

Hey!

Thanks for the reply. I'm really green with this stuff, so would you mind telling me what you mean by, "the pink or blue thin foam panels that you staple between the roof joists?" Is this what you mean?

Ed

 

[burger]

How does the electrical wiring for the lights, fan, door openers, etc figure into all this?


Thanks,
Ed

 

[kbs2244]

No argument on keeping the attic vented in the winter!
But this is a vaulted celing, no attic space.
So the idea with the turbin is to vent the hot air that gets trapped up there in the summer. Close them off in the winter so you don't lose any heat.
Even if you go with the batts, with space above them going to ridge vents, (which is a fine way to go) I would want the turbine for summer comfort.
In this application, the turbine has nothing to do with vapor venting. It is for venting the whole garage.
And you can put it on the back side of the ridge, so it is out of sight.

 

[mpraddict]

The SIPs work because there is no concealed space....one side of the panel is exposed to the roofing and the other side exposed to the interior space. I would feel uneasy about not having any ventilation and a small amount of airspace above the ceiling. You'll still be trapping heat up there. IMHO continuous ridge and soffit vents are the best. If you use these, do not install gable end vents, they will only interfere with the proper airflow.
The picture Burger posted is an insulation baffle. They're installed to maintain the air gap between rafters where there is minimal space at the bearing walls.

 

[wheelz]

Re: Wind turbins

Hey!

Thanks for the reply. I'm really green with this stuff, so would you mind telling me what you mean by, "the pink or blue thin foam panels that you staple between the roof joists?" Is this what you mean?

Ed

Those are what I used. Liked them very well. My main shop is 30 x 40 14' high with a 14' wide room on the right side 8' high for a tool room/bathroom hvac room. The slope of the roof over the 30 x 40 area was continued over the tool room using 2x6's creating the sloped ceiling I used the foam panels (easy to cut/ staple in place) then 6" kraft faced insulation stapled between the 2x6's then drywall over that. I plan on adding another room to the other side just like it for a waiting room / office area.