How to insulate a flat roof garage?
I have a 13 by 20 foot flat roof garage with 3 by 7 inch joists on 24 inch centers, 1 by 6 tongue and grove sheeting and white roll asphalt. The region is S.E. Florida and was built in 1957. It was a carport at one time and got closed in. it does have a 7 by 9 garage door (no insualtion) that faces east, and a flat 2 by 6 stud wall that faces west (no insulation). It gets very hot in there and want to insulate the ceiling.
My local big box supplier has 2 inch white Styrofoam sheets as well as the pink ones and a foil version too, and of course batt insulation.
I want to get the temperature down so I can work in there what would you recommend I do to to insulate. One more question what about painting the roof white with elastomeric paint?
Thank you for your time.
Replies
I suspect that your best bet would be to apply foil-faced foam across or between the bottoms of the joists and then somehow ventilate the space above to the outside.
Without going to spray foam, poly sheets are probably going to give you the highest R value per inch. Do the roof first since that's where almost all your heat load is coming from. However, without AC the room will still get just as hot as it does now, just more slowly.
Does the foil face of the insulation face up?
Thank you for the replies. Does the foil face of the insulation face up twords the ceiling? I assume it would to reflect the radiation from the roof.
There is no air moving in the garage so I will add some louvers up high and some low to get air moving
. Thank you for your time.
If there's only one foil face it would face upwards.
I'd out the foil up. As far as your louvers go remember that the air you'll be moving will be the outside temperature and the hotter the garage gets the less air you'll move.
The venting needs to be ABOVE the insulation. The air up there will be plenty hot, even compared to the outside temp.
Venting above the insulation?
Thank you all for the replies but I don't understand about venting above the insulation. I do not belive I can.
I have a 3 by seven joists and I install poly foil faced insualtion in between the joist up against the roof sheeting. I do not see how to vent above it. I assume I can lower the insulation an inch or two but I have no where for the the aire to flow to. The ends of the joists are blocked.
As for other venting , I thought I can mount a louver high at one end and another low at the other end and get the cooler air to flow up. Maybe use a solar powered roof vent.
Last option I want to use is a vent in the center of the garage because it can be see for the street and would not look that great. But if its the best option in this case then we have to do it. I assume a vent for a flat roof on a small curb.
Thank you for your advise.
You will note I originally suggested installing the insulation on the BOTTOM of the joists, or between them and flush with the bottom. At the very least, 2" of space between insulation and roof. And then some sort of ventillation of that space to the exterior. Yeah, it's not easy, but will be far more effective than simply plastering insulation to the roof.
Ok, understood thank you. I will see about venting at one end and will try and do that. I will post results when i complete the work.
Thank you to everyone that replied.
It would work to vent to the outside on one end and from the inside on the other. In fact, might kill two birds with one stone.
Great idea!
I can make that work with some simple boxing and insect screens. Thanks again.