foam board insulation

My question is in regards to the use of foam board insulation on the interior of my kitchen ceiling. I live in a house that is 104 yrs. old. It has new electric and all other modern conveinences. I recently took down the drop ceiling in my kitchen and I am going to finish the original plaster ceiling with stainless steel. I would like to insulate the original ceiling and I was wondering if the use of foam board was acceptable. There is one light fixture and I read to keep the insulation 3 inches away from that. Is it ok to use the foam board and then cover it with stainless?

I'm not sure about the foam board but I would sure like to know the specifics on the the SS you are going to use to cover the ceiling.Sounds interesrting and I haven't seen that type of ceiling in almost 45 years.

Just finished doing this on a computer room addition that had termites. Pulled the old ceiling down and found no insulation 2x4 rafters so. Used cut a nd fit 2" foam between rafters then 2" below the rafters. then drywall for R30. make sure you allow at least 1" air space above the foam and ventilate, no problem if this kitchen has a open attic above. Note the higher price foam has almost double the r value of styrofoam. They do make ceiling fixtures rated for direct insulation contact called, I think IC fixture. consider using flourescent fixture for less heat into room and save energy. They make diamable flourscents.
Bill D.
Bill D.

Most foam board is flammable, so you have to cover it. Wallboard, or even stainless would count as covering.

Are you adding this over the plaster? Or are you putting it in place of the plaster?

I would cover the hidden side too, so that in case of an electrical problem the foam board doesn't get lit by the sparks etc. (My in-laws had an arcing fault start a garage fire, I may be over-sensitive).

the ss would not be a good enought covering by itself, you need sheet rock over the foam, the lighting fixtures that are rated for contract with insulation are ment for fiberglass not foam. the idea is not protecting the insulation but withstanding the heat build up in the can, these things get hot! long term exposure can cause the foam to burn at lower temps than you would other wise think.
I don't know what the code is on foam exposed in the attic space but once you have a fire that will encourage it to spread allot faster.

Dow brand Styrofoam (trade name) was sold with a little brochure that stated that in inhabitabed living space it was necessary to cover it with 1/2 drywall or continuous sheetmetal. I don't recall there being any metal thickness specified and I heard it jokingly put forth that maybe household Aluminum foil would qualify. I don't know about the foil - I rather doubt it. Is the National Building Code on-line to check this?

Bill D, what higher cost foam (name and who sells it) has twice the r value of Dow Styrofoam (r of 6 per inch)?

In the past, the 2 primary foams on the market were polyurethane, and polystyrene. Now there is a 3rd, sort of, Polyisocyanurate. Actually, polyurethane is a reaction between polyisocyanate and polyol....as is "Polyisocyanurate". But "Polyiso" has been branded and apparently developed to have even better fire resistance.

Traditionally, urethane had the much greater R value, but it is more subject to degrade from light, and water (damp) will deteriorate it over time. You want to use polystyrene (blue board) under a concrete slab, e.g., as the urethane will deteriorate. In cooler boxes, where the foam is blown in between 2 metal skins, urethane (or Polyiso) is used for the maximum R value with the thinner walls.

Urethane (or polyiso)is harder to get to burn, and it doesn't "melt". It is often sprayed on, at least in industrial settings, right onto ceilings and metal side walls, etc. I believe if it is involved in a fire from other causes, it gives of cyanide gas. But it is difficult to ignite and doesn't really support combustion on by itself.

Styrene melts easily, and will burn pretty readily, too. It has less R value per inch to start with, but it is les subject ot degrade from light and moisture, and it is usually cheaper, even on a per R basis.

These are generalities. I haven't had to spec the stuff for a dozen years, and there may even be new things on the market. I gather the polyurethanes marketed as "polyiso" also have gotten the costs down somewhat compared to polystyrene.

Anybody remember cork insulation? I've worked in some marvelous houses from the 20's that were state of the art at the time, and all that stone and brickwork has a 2" layer of cork either between courses, or under the plaster. Makes thing really difficult to fasten new work to the walls, though, as there is often a good 3 - 4 inches to solid masonry.

smt

Anybody remember cork insulation? I've worked in some marvelous houses from the 20's that were state of the art at the time, and all that stone and brickwork has a 2" layer of cork either between courses, or under the plaster. Makes thing really difficult to fasten new work to the walls, though, as there is often a good 3 - 4 inches to solid masonry.

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Ours has hollow tile as the inner-most course. Works pretty well as an insulator. Everywhere is plenty warm (hot water heat) except the one room with 3 walls and the roof as outside exposure on the north side.

That room I have been considering stripping plaster and putting blue board and wallboard over the hollow tile. One little radiator doesn't cut it in there.

Just curious, why not use blown in cellulose or fiberglass OVER the original ceiling (in the attic). Cheap, easy, and seals pretty good to the framing.
Up in that part of the world, you need to be real careful about the position of your vapor barrier, or accidentally having more than one "vapor barrier" in an insulated assembly, and probably more so in a wet kitchen than elsewhere.
In the north, the vapor barrier needs to be on the warm-in-winter side of the insulation, or you'll get condensation IN the insulation, followed quickly by rot.
You can buy vapor-retarding paints for the interior face of gypsum board and plaster, and then seal all penetrations (outlets, fixtures, etc. and you have an optimum position of your vapor barrier. This is a PITA, so in most new construction, it's plastic on the inside of the studs. What surplusjohn said about the fixtures is dead on.