Insulation, Radiant and Vapor Barriers - To Warm or Just Right?
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AS
01-30-03, 07:54 PM
I was hoping people would offer their opinions or comments.
We have made some improvemenets in ventilation and insultaion to our attic this winter in an attempt to reduce the temprature and prevent further ice damming on our roof.
We have been closely watching the temprature and have come up with some specifics. The house temperature remains at 70 degrees. The attic temprature is approx 15 degrees warrmer than the outside air temp.
I have heard different comments about what the ideal temprature should be in comparison to the outside.
Any comments if the 15 degrees is adequate or still to high?
We have made some improvemenets in ventilation and insultaion to our attic this winter in an attempt to reduce the temprature and prevent further ice damming on our roof.
We have been closely watching the temprature and have come up with some specifics. The house temperature remains at 70 degrees. The attic temprature is approx 15 degrees warrmer than the outside air temp.
I have heard different comments about what the ideal temprature should be in comparison to the outside.
Any comments if the 15 degrees is adequate or still to high?
resercon
01-31-03, 10:08 AM
My reply here is not to discourage others from providing their input but for others that may want to know my opinion on this forum.
The 15 degree difference is not bad provided it's not above freezing and the outside temperature is below freezing. This is because if you had snow on your roof and it was below freezing outside and above freezing inside the attic, the temperature inside the attic would melt the snow from underneath it. The melted snow would go down your roof to an area where it is below freezing, like your eaves, overhangs and/or gutters and freeze. This would create a dam and any subsequent melted snow there would build up and you would have what is known as ice damming. To avoid this, it is recommended that the attic temperature be at or below the outside temperature.
Adequate free venting usually will accomplish this for you. Probably one of the biggest problems today is the advent of ridge vents. When they get covered with snow, you don't have adequate free venting. The ridge vents may be in your roof but they're not venting anything when they're covered with snow.
However, the 15 degree difference does suggests there is more than just adequate free venting. On a sunny day even though it's cold outside, there could be that difference. Try taking the temperatures at night. If the temperature difference is still 15 degrees, then look at the nails on the underside of the roof. Touch them to see if they're wet or have black stains surrounding them. Heat will condensate against the coldest part of the attic and the roofing nails are it.
If this is the case, then it's probably the attic by-pass phemonea that's causing it. This is where heat from the house is by-passing the insulation. Examples of it is whole house fan louvers in attic floors, recess lighting, uninsulated pull down stairs, drop ceilings above tub encolsures, ceiling penetrations for electrical, telephone and cable wiring, plumbing stacks and chimney chases and much more. Prohibiting heat from the home from entering your attic does more than prevent moisture problems like ice damming, it will also reduce your heating cost a lot.
The 15 degree difference is not bad provided it's not above freezing and the outside temperature is below freezing. This is because if you had snow on your roof and it was below freezing outside and above freezing inside the attic, the temperature inside the attic would melt the snow from underneath it. The melted snow would go down your roof to an area where it is below freezing, like your eaves, overhangs and/or gutters and freeze. This would create a dam and any subsequent melted snow there would build up and you would have what is known as ice damming. To avoid this, it is recommended that the attic temperature be at or below the outside temperature.
Adequate free venting usually will accomplish this for you. Probably one of the biggest problems today is the advent of ridge vents. When they get covered with snow, you don't have adequate free venting. The ridge vents may be in your roof but they're not venting anything when they're covered with snow.
However, the 15 degree difference does suggests there is more than just adequate free venting. On a sunny day even though it's cold outside, there could be that difference. Try taking the temperatures at night. If the temperature difference is still 15 degrees, then look at the nails on the underside of the roof. Touch them to see if they're wet or have black stains surrounding them. Heat will condensate against the coldest part of the attic and the roofing nails are it.
If this is the case, then it's probably the attic by-pass phemonea that's causing it. This is where heat from the house is by-passing the insulation. Examples of it is whole house fan louvers in attic floors, recess lighting, uninsulated pull down stairs, drop ceilings above tub encolsures, ceiling penetrations for electrical, telephone and cable wiring, plumbing stacks and chimney chases and much more. Prohibiting heat from the home from entering your attic does more than prevent moisture problems like ice damming, it will also reduce your heating cost a lot.