Ceiling vent for covered porch


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Old 08-04-14, 11:00 PM
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Ceiling vent for covered porch

We have a one-year old home in Florida where the main house roof (hip with attic space) extends over the screened patio on the back of the house. In addition, we extended our patio further out from the back wall of the house with an insulated-panel roof and screened walls on two sides. So half of the patio (nearest the house) is under the house roof with a sheetrock ceiling and the outer half is under just the aluminum insulated panel roof.

It's on the South side of the house and therefore quite hot much of the year. We have a ceiling fan but it often feels like all it's doing is moving hot air around. I'm wondering if there is some way to add ventilation in the ceiling of either the part under the house roof or the added panel roof to help hot air trapped on the patio rise up and out. It would of course be quite easy (and less risky for rain leakage) to put vents in the sheetrock porch ceiling (portion under the house roof), but I don't know if that is a bad idea for any reason. I would think it would simply act like more soffit venting and just suck the cooler air from the patio (well, cooler than the attic air!) up into the attic which has a number of mushroom-type vents to exhaust its own hot air outside.

Would this help relieve some of the hot, stale air trapped on the patio and help to lower the air temperature on the patio at all?

Are there any negative impacts of such a change (code-related or otherwise)?

Thanks in advance for any feedback on this topic...
 
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Old 08-05-14, 06:31 AM
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I can't speak about codes, too far away, but adding ventilation through the sheetrock sounds like a good idea. If you have soffit venting all the way around, the limiting factor may be the "mushroom-type vents" up top. Air in must equal air out, so if the exhaust vent area is limited the new vents will not add a lot. But they should add something.

If you have ever visited (or seen pictures) the Caribbean you should recall all of the white roof tops. Limiting heat into your porch area, and the entire house, should start with the color and reflectivity of the solar surface. To that end, newer shingles are addressing the solar gain so perhaps an option down the road.

Your ceiling fan is doing exactly ar you described, blowing the hot air down to where you feel it. Table top or floor fans directed at you would feel better than that ceiling fan.

What color is the ceiling, sheetrock and panel above the porch? The heat from above moves by radiation and convection. Relative to radiation, convection is very slow. But the radiation is instant and dark colors are the worst. The best would be a shinny metal surface, a radiant barrier.

Shading is another aspect to keep in mind. Whether it be nature made (trees) or man made (canvas) blocking the sun from shinning directly onto the roof will make a big difference.

Bud
 
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Old 08-05-14, 08:50 AM
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Thanks Bud. The paint color of the patio (exterior concrete house walls) and ceiling sheetrock is a light taupe or beige-ish color. Definitely not dark. I specifically chose a light color for my house when building because I've noticed here in FL that the darker colors fade more quickly and require repainting sooner than lighter colors.

The roof shingles on the house-roof over part of our patio has black shingles, so I'm sure the attic just over the patio is quite warm, although there is a roof vent at the peak of the rear hip over the patio which should help ventilate the rear part of the attic.

The aluminum insulated panel roof over the outer half of the patio is white aluminum on both sides.

Because it's a hip roof on all sides, I don't know if I could get back in the part of the attic covering the patio to staple up some radiant barrier on the roof trusses, but I could possibly blow in some insulation similar to the rest of the attic. Would that help keep the heat from the attic coming down to the porch? I guess as long as there is sufficient roof venting, there should be more convection going up and out than down and onto the patio.

I would imagine the white insulated aluminum panels are not radiating a lot of heat into the patio since they are white and insulated (about 3" of foam). I'll have to step out there and feel the underside of the white roof panels this afternoon when it's about 90 degrees out to see how much heat is being radiated by that portion of the porch covering.

Thanks again...
 
 

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