Another question on insulating metal roof

[cc-rider]

Another related question…. How do I get a decent R-value in the ceiling? I’d like to use reflectix, too, and a metal roof. And still have a cathedral ceiling. I don’t care if the rafters show or not. In fact, they probably won’t by the time I add whatever I need to add to get insulation up there, correct?

The main part of my house will have a "shed" roof (part of the clerestory plan....the other 1/3 will be the sunroom roof...which is flat because of the deck above it)

How do I insulate the roof? How do I get ventilation? On which side of the insulation would I put the reflectix.....under the metal roof, or on the inside side of the ceiling? My head hurts...I'm so confused!

Chris

[fantasymaker]

I'd want at least some blown foam

[ET1 SS]

I sprayed foam onto the underside of the metal roofing.

The metal rafters come down eight inches from the roofing, and then the girders, so the area between the rafters, I hung R-30 fiberglass batts. And underneath the rafters wood paneling.

So looking up. You see a 14 foot high ceiling, with wood paneling. Above that is eight inches of fiberglass batting, then one inch of styrofoam, then the metal roof.

Approx R-37.

[tamilee]

Originally Posted by fantasymaker

I'd want at least some blown foam

Hi;
Your locale says you are right smack dab in the middle of Il. I was born in Tuscola. You are the first member, I've notice from this area.
tamilee

[cc-rider]

Originally Posted by ET1 SS

I sprayed foam onto the underside of the metal roofing.

The metal rafters come down eight inches from the roofing, and then the girders, so the area between the rafters, I hung R-30 fiberglass batts. And underneath the rafters wood paneling.

So looking up. You see a 14 foot high ceiling, with wood paneling. Above that is eight inches of fiberglass batting, then one inch of styrofoam, then the metal roof.

Approx R-37.

Do you have an air space? Doesn't the metal roof sweat? I've heard that would be my biggest challenge....the metal roof sweating. Does the foam stop that?

Did you spray it yourself?

[ET1 SS]

Originally Posted by cc-rider

Do you have an air space? Doesn't the metal roof sweat? I've heard that would be my biggest challenge....the metal roof sweating. Does the foam stop that?

Did you spray it yourself?

I have 14 foot of air-space, between the floor and the ceiling.

Sweat? no.

Styrofoam epoxied right directly onto the metal, stops the condensation.

I did spray on the foam myself, it was rather fun.

[haypoint]

You can build a cathedrel ceiling and still have insulation space by having a sissor truss built. The roof is one pitch and the ceiling a lesser pitch. More space as it goes toward the top. Foam insulation has a higher R value and is less likely to have drafts or leaks than fiberglass batts. You should always leave a bit of space between the insulation and the metal roof so air can move from your ventilated soffit to your ridge vent. Otherwise it'll get hotter than blue blazes under there. I do not know how long sprayed on foam can expand and contract and stay bonded to the metal roof.

[cc-rider]

Originally Posted by haypoint

You can build a cathedrel ceiling and still have insulation space by having a sissor truss built. The roof is one pitch and the ceiling a lesser pitch. More space as it goes toward the top. Foam insulation has a higher R value and is less likely to have drafts or leaks than fiberglass batts. You should always leave a bit of space between the insulation and the metal roof so air can move from your ventilated soffit to your ridge vent. Otherwise it'll get hotter than blue blazes under there. I do not know how long sprayed on foam can expand and contract and stay bonded to the metal roof.

The house will have a "shed roof" so I'm not using trusses. I can put in deeper rafters, though, and hang the insulation. If I spray foam the metal, and then leave a gap, and then put pink foam or reflectix (or both) below the foam/metal, will that work?

ET1 - how did you spray it yourself??? Lotsa cans???

[ET1 SS]

Originally Posted by haypoint

You can build a cathedrel ceiling and still have insulation space by having a sissor truss built. The roof is one pitch and the ceiling a lesser pitch. More space as it goes toward the top. Foam insulation has a higher R value and is less likely to have drafts or leaks than fiberglass batts. You should always leave a bit of space between the insulation and the metal roof so air can move from your ventilated soffit to your ridge vent. Otherwise it'll get hotter than blue blazes under there. I do not know how long sprayed on foam can expand and contract and stay bonded to the metal roof.

When the two-components mix they form an epoxy.

It should stick forever.

When it sprays out, it will shoot for a good four or five foot away from the gun, though I do not see how to get it to stick to the metal roof and still: "... leave a bit of space between the insulation and the metal roof so air can move from your ventilated soffit to your ridge vent"?

[ET1 SS]

Originally Posted by cc-rider

The house will have a "shed roof" so I'm not using trusses. I can put in deeper rafters, though, and hang the insulation. If I spray foam the metal, and then leave a gap, and then put pink foam or reflectix (or both) below the foam/metal, will that work?

ET1 - how did you spray it yourself??? Lotsa cans???

Each pair of tanks covers 600 square foot.

My 2400 square foot house [required 2400 square foot of foam for the roof, plus about 2600 square foot for the walls], so I used like nine pair of tanks.

Each pair of tanks costs about $400 delivered.

I sprayed it all myself.

It was very easy to do.

[cc-rider]

How deep did you spray it? I'm wondering if it would be cheaper than putting 4" thick foam against the metal (if I can figure out how to make the foam stick in the first place!). Would the heat of the metal roof ever melt the foam or make it "unstick"?

I'm braindead and can't figure this out. If my floor is 24 foot long, (36 foot wide, which doesn't matter at this point).....and the roof is a simple shed type with a 6/12 pitch.... that makes a triangle with one leg 12' and the bottom 24'..... what would be the length of the actual roof because of the angle??? All I can remember is "3,4,5"....but not what to do with them!

Once I have that number, I can multiply that times the 36' length to figure out my square footage for the roof. Can't I?? It's too early in the morning!

Were your walls metal, too?? I'm using standard stick framing for those, so probably don't need to spray foam??

CC

[cc-rider]

Another thought....
Is there anything toxic about this spray foam?

CC

[ET1 SS]

Originally Posted by cc-rider

How deep did you spray it?

I sprayed it so that as it expanded, it cured at about one inch thick [R-7].

You can spray it on thicker, or you can go back over to for as many layers as you wish. You could build it up six or ten inches if desired to.

... I'm wondering if it would be cheaper than putting 4" thick foam against the metal (if I can figure out how to make the foam stick in the first place!).

Good luck getting it to stick. My metal panels have ripples, a foam board would not fill those ripples and shapes, so you would have an air-gap. Air-gaps allow condensation, and water may work to dissolve glue.

I do not have full confidence in glued-on foam panels holding indefinitely.

... Would the heat of the metal roof ever melt the foam or make it "unstick"?

No.



[quote]... I'm braindead and can't figure this out. If my floor is 24 foot long, (36 foot wide, which doesn't matter at this point).....and the roof is a simple shed type with a 6/12 pitch.... that makes a triangle with one leg 12' and the bottom 24'..... what would be the length of the actual roof because of the angle??? All I can remember is "3,4,5"....but not what to do with them![quote]

Look at your plans.

... Once I have that number, I can multiply that times the 36' length to figure out my square footage for the roof. Can't I?? It's too early in the morning!

Were your walls metal, too?? I'm using standard stick framing for those, so probably don't need to spray foam?? CC

Yes, width times length would give you the square footage.

It sounds like your house will have about 864 square foot, and the roof will be close to 900 square foot.

My walls are metal.

Metal buildings are much cheaper to build than stick buildings. They are pre-engineered and guaranteed to meet building codes.

Spraying foam seals all air drafts.

Living inside of a styro-foam ice chest, is draft free and much warmer.

[ET1 SS]

Originally Posted by cc-rider

Another thought....
Is there anything toxic about this spray foam?

CC

To my understanding they out-lawed CVCs in the 1970s.

Foam uses nitrogen as a propellant. It does 'outgas' for 24 hours, mostly nitrogen.

It totally cures hard within 2 minutes.

[idahodave]

Originally Posted by cc-rider

I'm braindead and can't figure this out. If my floor is 24 foot long, (36 foot wide, which doesn't matter at this point).....and the roof is a simple shed type with a 6/12 pitch.... that makes a triangle with one leg 12' and the bottom 24'..... what would be the length of the actual roof because of the angle??? All I can remember is "3,4,5"....but not what to do with them!

Once I have that number, I can multiply that times the 36' length to figure out my square footage for the roof. Can't I?? It's too early in the morning!

CC

The long side of a right triangle is equal to the square root of the sum of the sides squared, or in your case square root(144+576) or about 26'-10". Don't forget any overhang at the eves when you multply it by 36" for the roof area.

[Beeman]

www.metalroofing.com

This site has a lot of info and manufacturers contacts that are glad to provide info.