Hot Porch Roof

[Tony]

I have a large front porch with a roof about 8 feet up. It is open on the bottom so you see the sheathing and joists (2x6's). When the sun is on it the heat really radiates down to the porch area making it hot as hell even though you are in the shade.

I am considering putting up a "ceiling" but good circulation won't be easy without a fan. The porch roof extends about 10 feet over the original roof and shingles of the house so I suppose I could close it up and add a fan. If I do it I'm thinking of using 3.5" insulation so there is plenty of room for air circulation between the insulation and the sheathing.

Any other ideas before I get broiled?

Tony

[HeyBub]

Forget the insulation.

Radiant barrier. Cheap, 95% effective, easy to install.

[ransley]

Obama says white paint everything

[Tony]

What kind of radiant barrier? I don't want it to look like aluminum foil. Maybe I could use the radiant barrier instead of insulation then the sheathing under that for looks.

Tony

[Stormin Mormon]

Staple up a mylar foil space blanket? To the bottoms of the rafters?

[Stormin Mormon]

Look good. Cook in the summer. What a choice.

[1D10T]

1" Styrofoam, backed with aluminum foil, foil side up, against the sheathing. Cut it into strips, making a snug fit pressing them between the rafters. Available in 4 x 8 sheets. The white Styrofoam will look good too.

[HeyBub]

You could do that. You could cover the radiant barrier with almost anything - even paint.

You should probably also plan on some way for the hot air to escape...

[gfretwell]

Why not just put in a fan? Blow that hot air out of there. ... and paint the roof white

[Tony]

A fan doesn't stop *radiant* heat.

I have been tempted! That part of the roof can not be seen from ground level anyway.

[Larry The Snake Guy]

Not directly, but by conducting heat away from the sheathing, wouldn't a properly placed fan lower the temperature of the sheathing thus reducing the amount of heat it radiates?

[HeyBub]

If you can't see it, that's a good trick. It's often done on commercial buildings with flat roofs.

The reason you don't want to do it if the roof's visible is that turns an icky color and stains from the junk in the air.

[Tony]

I've considered ceiling fans but I don't know where I could properly place them to do the job. I think ceiling fans would just blow hot air all around me. If I'm lowering the temperature of the sheathing then I'm transferring the heat from the sheathing and into the air. I just don't see any easy way to use fans without a lot of turbulence, so I'd be blowing hot air all around. I'm tired, does that make any sense? BTW, the roof is 28' x 12' and a little more than a 1:12 pitch.

[Tony]

Do they use actual paint or the white stuff for mobile home roofs?

[Larry The Snake Guy]

Sort of. If they're doing it right, they're using "roof paint" (not sure about the exact name). It's a thick, insulating, reflective paint. I've seen it in white and silver at the local DIY stores. It may come in other colors, but if heat is your main issue, you want one of those two.

Now, of your roof is in good shape and you're just looking to reflect more heat, there may be other options I'm not familiar with.

[Larry The Snake Guy]

Yeah, ceiling fans without also insulating the roof probably wouldn't help. I meant a fan/fans somewhere where they could blow/draw air across the underside of the roof and out. That may not be possible depending on the design of your roof, and is probably not your best option by itself. I was just giving an example of how fans could prevent radiant heating, in response to this statement: "A fan doesn't stop *radiant* heat."

[Stormin Mormon]

Foil is useless as condunctive insulation. Touching the hot roof accomplishes nothing. The styrofoam could help.

[1D10T]

With the foil-side up it reflects the radiant heat. Perhaps I wasn't clear, or you're not familiar with the product - the foil adheres to the Styrofoam. I believe it's often used under vinyl siding.

[HeyBub]

Right. But it's 95% effective against radiant heat. You've got to have an air-gap and circulation to remove the heat, but it's a cheap and effective solution.

[Stormin Mormon]

If you put the foil side "against the sheathing" then the heat will conduct from the roof to the foil.

You could put the foil side under the rafters, facing in the direction of the sheathing. It would also be a lot easier to install, you don't have to cut the foam to shove it in between the rafters.