Rigid Foam insulation for ceiling?

[jeepmann]

I have a small 2 car garage with an 8' ceiling. I have a little over half of the ceiling insulated with the standard pink paper backed insulation but I want to cover it. I originally planned to put osb up to match the walls, but I noticed our pole barn at work has the foil backed rigid foam on the ceiling. This would be close to the same price as the osb, add a little more insulation and be very simple to install. Has anyone else used this in a garage with a short ceiling?

 

[MoonRise]

Foam board insulation (or spray foam, or any other type of foam insulation) is almost never 'rated' for exposure. Mostly due to fire reasons (the stuff burns and usually makes really nasty smoke if it does burn) but also due to UV breakdown (foil-faced reduces UV problem, but still has the fire 'issue').

Cover it with drywall IMHO.

 

[SINISTER]

Non covered batt insulation in between joists, vapor covered with poly plastic sheeting overlapping by at least one bay when joining sections, and ridged foam extruded poly on top. Use sealant on any joints.

Cheap easy way to have a somewhat super-insulated envelope, aside using a dual stud setup filled with batt, double RFI with a 2" air gap.

 

[kevin206]

It would go up in flames if a fire started. And I'm not sure if the foil reflective side would give any 'good' light reflection. I nailed a 6" strip of plywood to the bottom of my rafters to make an upside down T shape. I then dropped in styrofoam panels. I got some insulation and still had access if needed. In my dad's paint booth we nailed styrofoam sheets to the bottom of the rafters. I think that we used the nails that had the large plastic washer to provide support. As an aside, He later painted the ceiling with a flat latex white paint. The stryofoam held up well.

 

[NUTTSGT]

The foil face will get duller with age but paint will stick to it. It canalso give abit more insulation than OSB. I hung some with plastic cap nails. Then cover the orange heads and seams with foil tape.

 

[Big Bad Dad]

An easily combustible material like insulation paper backing or the styrofoam is required by the building codes to be covered. This is a fire protection measure, and is usually printed on the insulation backing.

 

[K'ledgeBldr]

Garage attached? Or detached?

The plain simple truth is- any type of insulating material left exposed (other than unfaced f/glass) is a fire hazard; along with OSB.
Drywall, IS a recommended and fire rated wall covering.

 

[bazzateer]

Insulate the ceiling (leaving an air gap at the top), vapour barrier (seal all joints) then dry-wall and paint drywall white.
Proper job!

 

[deuces2]

MY 30x40 has been styrofoam 3/4 foil both sides and has been up for ten years now .I added 2x4s between joist and taped -ductape the seams,it is real easy to heat with kerosene heater.this is not the prettiest ,**** I was able to hang it all by mysef.I do have plywood down the center above for light storage. I dont have moisture or rust problems,I got a trailer load of this as seconds and its been a good deal. I also used this in a 24x28 stickbuilt eor ceiling and have yellow fiberglass batting above also with plywood laid down for storage. this has been up fro 15 years,I heat with the 220 volt electric e/z.

this garage is 15 years old and the foi back still reflects pretty good

 

[Dan in Pasadena]

Resurrecting this thread to ask a few questions:

My situation: I have a low (< 8 ft) relatively flat,but sloped ceiling in my 13x28 shop w/ 2x6 joists 16" o. c. It was badly painted white by a previous owner and is chipping & peeling badly now. It would be a LOT of work to sand/strip working overhead so I just want to cover it with foam insulation panels. maube that silver bubble wrap type stuff Home Depot sells. Yes, it gets hot in there in summer but my PRIMARY INTEREST is covering the nasty paint.
I will sand/paint the 2x6's.

If I'm using thin (1/2" or 3/4") panels do I actually gain anything by leaving dead air space behind? Or is it so little as to not concern myself? How do I create this space between the 2x6's? Spacers of some type? I've thought of using 3/4 round along the edges of the 2x6's but that adds a lot of cost & hassle. Knowledgeable opinions please?

 

[Kevin C]

A dead air space should add about R1 of insulation value. It would work behind the insulation, or if you added drywall, a 1" gap behind the drywall also adds about R1.

 

[Dan in Pasadena]

Thanks. Definitely NOT adding drywall. Just not necessary from an aesthetic point of view, cost, AND it would lower an already low ceiling. Doesn't sound like it adds much insulation value either. So I guess that means I should only consdier it a cosmetic cover up for the lousy paint afterall.

 

[Kevin C]

Thanks. Definitely NOT adding drywall. Just not necessary from an aesthetic point of view, cost, AND it would lower an already low ceiling. Doesn't sound like it adds much insulation value either. So I guess that means I should only consider it a cosmetic cover up for the lousy paint after all.

The 3/4" foam would add about R3 (low cost white foam, closed foam Dow would be R 3.75, Polyisocyanurate foam gets you 4.8). Combined with the air gap you get a total increase of R4. If its straight foam with no thermal bridging, you get the full R4 (cheap foam), R5.8 for the Poly with an air gap.

Good article that shows it on the outside, but the effect is the same when on the inside walls.

http://www.engr.psu.edu/phrc/training/Building%20with%20Exterior%20Rigid%20Foam.pdf

 

[Gary S]

I did what deuces2 did. I put up 1" thick foil faced foamboard to cover my blankets. I llike it far better than drywall. Drywall would add almost no R value while the foam adds another R6.5. Drywall wouldn't reflect light nearly as well as the foil.
I highly recommend the foil faced foam for a garage ceiling.

 

[Old Moparz]

Insulate the ceiling (leaving an air gap at the top), vapour barrier (seal all joints) then dry-wall and paint drywall white.
Proper job!

I agree, & drywall is cheap. If perfection isn't an issue with appearance, cut the boards down to an "easy to work with size" & install it. I did a portion of my garage with 48" squares, not full sheets. Put the tape & mud on, then paint when dry.

Drywall comes 3/8" thick.

 

[MoonRise]

Dan,

Almost flat but slightly sloped garage ceiling? Just the exposed 2x6 joists/rafers and the underside of the roof sheathing? And all that 'ceiling' is (badly) painted white, and the paint is now peeling? And the only thing above the ceiling' is the actual roof?

Got a picture?

First off, how old is that building/paint? If it goes back to the 1978 or so, you may very well be dealing with lead paint. Uggg. If the building/paint is newer than that, you-should- be OK from the lead paint aspect. Check if you are not sure (I think H-D and such have a DIY lead paint test kit).

http://en.wikipedia.org/wiki/Lead_paint

Moving on past the possible lead paint.

If my understanding/description of the layout is correct, then you really can't/shouldn't just put up insulation panels on the bottom of the roof/ceiling rafters.

If you do that, without putting in soffit and peak ventilation, you would just trap heat and moisture between the insulation panels and the roof sheathing. Which would cause the sheathing and the roofing (notwithstanding tile roofing) to rot and/or deteriorate -much- faster.

And it's your 'space' and all, but leaving exposed foam insulation panels in a garage (or anyplace else) is soooo against Code. Fire hazard.

 

[Old Moparz]

Just remembered that a friend of mine had a big condensation issue after he sealed off an attic space with insulation & drywall that wasn't properly vented. He had beads of water collect on the bottom side of all the drywall on the ceiling. It dripped on everything, so he had to rip all the drywall down from the ceiling to access the space so he could vent it. Not just double work, but now a big mess from the demolition.

 

[Flange]

Here in the UK we use insulation backed plasterboard (sheet rock) quite a lot. It is sheet rock with rigid phenolic foam insulation bonded to it. It can be got with various thicknesses of insulation, from about 1 inch to about 5 inches. See an example here

http://www.kingspaninsulation.co.uk...herm-K18-Insulated-Plasterboard/Overview.aspx


You must be able to get this type of product in the US.

 

[nehog]

I'm thinking of doing the same thing, foil based. I don't want wood or drywall because of weight considerations. I figure foil backed, paint the foil side that is down a bright white to reflect light.

Problem: The spacing of my purlins is about 4 ft. I wonder how much 1 (or 2) inch foam might sag between them?

 

[Gary S]

Problem: The spacing of my purlins is about 4 ft. I wonder how much 1 (or 2) inch foam might sag between them?

I don't know how it would handle 4'. My 1" thick foil faced foam works very well on 2' spacing of my rafters, and supports the R19 blankets above the foamboard as well.
I expect that 2" would handle the 4' span quite well. The foil faced foamboard sold here is the isostyrene type which is very rigid. And, the foil facing reflects light much better than a white ceiling.
My foam is attached with drywall screws and fairly large fender washers to it doesn't start slipping down.

 

[Dan in Pasadena]

Dan,

Almost flat but slightly sloped garage ceiling? Just the exposed 2x6 joists/rafers and the underside of the roof sheathing? And all that 'ceiling' is (badly) painted white, and the paint is now peeling? And the only thing above the ceiling' is the actual roof?

Got a picture?

Below is a bad cell phone photo (pardon the mess, I was/am in process on resetting everything yet again - GJ driven angst to get it "right"! lol
Obviously I wasn't trying to photograph the ceiling. I don't remember WHY I took this shot.

...First off, how old is that building/paint? If it goes back to the 1978 or so, you may very well be dealing with lead paint. Uggg. If the building/paint is newer than that, you-should- be OK from the lead paint aspect. Check if you are not sure (I think H-D and such have a DIY lead paint test kit).

http://en.wikipedia.org/wiki/Lead_paint

I honestly hadn't even thought of lead. I'm just too lazy to get up&down, up&down, yada, yada to sand and paint it properly. The house is from the late '20's but this shop is probably from the 70's; no way to find out. It was not permitted but IS grandfathered in - I checked.

If my understanding/description of the layout is correct, then you really can't/shouldn't just put up insulation panels on the bottom of the roof/ceiling rafters.

I have no intention of putting these panels ON the rafters/joists. I planned to put them IN BETWEEN the rafters/joists to cover the peeling paint and still leave some head room since it is low in there already.

And it's your 'space' and all, but leaving exposed foam insulation panels in a garage (or anyplace else) is soooo against Code. Fire hazard.

Yeah, I know I shouldn't consider this. I SHOULD strip it, prime and paint white - all while wearing appropriate personal protective gear, of course - to maximize the height and provide a pleasant looking, reflective ceiling - DAMN you guys! Making me be responsible and adult.

 

[MoonRise]

Ahhh, trying to stuff the foam boards in between the rafter and up against the roof sheathing.

Nope.

As I mentioned, unless you leave an air space (and have air entering into and leaving that space) you will just trap heat and moisture inside that area. Which will cause the sheathing and/or roofing to rot out and/or deteriorate much faster from the build up of heat and humidity.

Hmmm, 16" OC and just want to cover it up?

How about just getting some 1/4" pre-painted white pegboard and putting that up on top of (well, actually on the bottom of) the ceiling joists/rafters?

It's thin, not too expensive (less than $10 per 4x8 sheet IIRC), has 'vent' holes in it already, just put it up with a few screws through those nice holes and into the joists/rafters.

(also no having the 'exposed' flammable foam boards there)