The kitchen of my house has a cathedral ceiling. The room is cold in the winter and hot in the summer. The house was built in the late 70s and I'm reasonably certain, there is little if any insulation between the ceiling sheet rock and the roof. I can't get into the area between the ceiling and roof to inspect. Any frost or light snow on the kitchen roof melts quickly whereas all the other areas of the house with a flat ceiling and 13 inches of cellulose above, do not. I would like to insulate the ceiling from the inside and then install either a suspended ceiling about 8 foot from the floor. I'm looking for suggestions.
John, a flat ceiling is fine. You can install a drywall suspended grid, this is the same type system as a commercial drop ceiling with slightly wider faces made to screw drywall to. You would need to do the insulating before installing the gyp. You might want to consider a more decorative approach as long as you have the cathedral height. Look through this Trim Tex site for some ideas:
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especially the drywall art section: look for the gallery section and the videos
I think a cathedral ceiling is a nice feature and I would hate to give that up. I would explore other possibilities such as removing the existing drywall to install better insulation and maintain air flow or at the very least look into blown-in insulation. After that I would install an additional layer of drywall with a radiant foil in between drywall layers. I would also install a suspended paddle fan to keep heat from accumulating up there. Perhaps for the summer a small exhaust fan at the peak would help with the heat load or locate an A/C return vent up high.
Do you have any ceiling light fixtures in the kitchen? If so, you could turn off the power and remove the light fixture. This should let you see around the electrical box to see if there is insulation behind the sheetrock.
You may also be able to measure up next to the electrical box to see how deep the rafters are. Standard R30 fiberglass insulation would need at least 2x12 joists (11-1/4" deep), though foam insulation may not need as much depth.
This doesn't offer any "solution" to the problem, but at least you would know what is currently there.
This is a very good point. My garage building (steel, fully insulated) can be 80 degrees at the peak, and 55 at the floor. It really amazed me as to how much heat was trapped above head level.
In my case we installed ceiling fans to move the heat from the high peak into the working area. Major difference, totally changed the wayt we heat the building.
Radiant foil between two layers of drywall is useless. In order for foil to be a radiant barrier, it must face an air space (and not face up, where dust would accumulate against it). If you have no air space, then the heat will simply conduct through the radiant barrier, it won't be a barrier at all.
Cathedral ceilings are nice, to keep it restud over drywall on the studs then use foamboard, Polyisocyanutate Dow foilfaced is R 7.2 per inch with radiant barrier, its the highest R value insulation you can get. with 2x4 you will ger R 25.2, but thats not enough,2x6 will get you R 39.6, Finish anyway you want I use T&G pine planking
I agree with this approach, with a slight variation and added details.
1 - if you have recessed lights in that ceiling, rip them out and seal up the holes. Recessed lights in cathedral ceilings should be illegal. They're a huge energy waster and worse, they are responsible for more moisture entry into the cavity than any amount of permeability of the ceiling material. If you do that, and close up any other holes in the ceiling, moisture will not be an issue in there.
2 - for optimal insulation, fill the cavities with dense packed cellulose. Forget what they're saying about ventilating under the roof deck. If you seal the holes, you don't need to worry about that. The only place moisture will get in the ceiling cavity during the winter is from indoors. You'll have less ice damming and better insulation all around if you just forget about it and seal up the cavity. For a typical 2x8 rafter, you'll get about R-25 insulation from the dense packed cellulose.
3 - Affix the foil faced polyiso board directly to the existing ceiling, 2" thick, taped at the seams Then, attach nailers over that, perpendicular to the original rafters. This will give you a high quality thermal break to minimize thermal bridging through the 2x4's. The foil faced polyiso board is also a complete vapor retarder, so this further ensures no moisture will get in the cavity. This will add R-15, bringing you up to R-40.
4 - If you want to go the extra mile, fill in the space between the
2x4's with another 1 1/2 of polyiso board, giving you another ~R10. Stagger the seams with the layer below, which again reduces any chance of moisture getting through the layers. Add sheetrock below, attached to the 2x4's.
If you're afraid of filling the primary cavity because of the ventilation propaganda, leave it as is, but do the rest of the steps. But now you're going to want a total of 6+ inches of polyiso board in order to get sufficient insulation. This will be much more of a pain to install.
Keep in mind that sheetrock is pretty cheap and easy to work with (for a pro), so don't be afraid to rip it out to get at the underside of the roof deck above. Another option besides the above one is to rip the ceiling out, then spray high density polyurethane directly to the roof deck above. Fill the cavities and seal up all the way down to the soffits. This will provide a complete vapor barrier and excellent insulation. No ventilation required or desired. when you're all done, this solution may be less expensive than the previous ones because it's just a couple steps - rip out ceiling, spray foam, replace ceiling.
For more details on roofs, venting, etc., consult:
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You'll hear a lot of arguments about venting. Venting is needed when a structure is poorly built and it needs venting to remove the moisture carried by the warm, humid interior air leaking into the cavity. This warm air then cools, and when it does, the moisture condenses and rots out the roof. If you seal up the ceiling so that moisture can't get in there, the problem goes away. During the winter, when moisture is the big issue, the moisture must come from the inside. The outside air during the winter contains very little water, and will tend to dessicate the roof assembly rather than add to the moisture.
During the summer, people will argue that venting is required to cool the roof. But the amount of cooling provided by venting in the normal fashion is vastly too small to actually be useful. Even a properly vented roof, with continuous strip vents at the soffits and large ridge vent provides minimal cooling, so that argument is bogus as well. The worst are the nominal vents that most people add - those
2"-3" holes drilled in the soffits and filled with "vents". The free area (amount of space open to allow air flow) is so tiny as to be totally worthless. Worse, during the winter, south facing walls heat up and the warm air from the walls will travel up and into the soffit vents. This then warms the roof, melting the snow and leads to ice dams. Current building practices are a series of band aids applied to fix other problems. If it were done right in the first place, with proper consideration for the physics involved, these problems would go away.
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