No Frost on roof - good or bad?


Old 12-01-06, 01:59 PM
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Question No Frost on roof - good or bad?

I seem to be the only one in my neighborhood who's roof does not frost up during these colder mornings (around 30 degrees).

Is no frost on the roof good or bad?

To me, reason dictates I am letting more heat dissipate through the roof then heating my house. However, I recently had a new roof installed. This includes a plywood 4x8 sheeting (sheething?) and composite roof material. Because of the additional sheething (was not there before), the roofer suggested he add more ventilation holes for summer heat escape.

Built 1990 (Single Story - tall ceilings)
Northern California (Sacramento area)
Blown-in insulation on easy access areas. Laid in insulation in hard to reach areas.
Temperatures around 30 at night lately.
Heater turns on about once an hour at 69 degree settings.
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Old 12-01-06, 02:00 PM
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If my attic is venting well, would this mean I do not get frost on the shingles?
Is the frost on the shingles and indication of a temperature change in the attic vs. the shingles?

When the roofers were installing the new roof, they removed the old roof and my insulation was exposed just after the sheet rock from the inside. I have blown-in insulation, and asked them their opinion on the insulation. The roofers said we have the most insulation they have seen in our neighborhood. I added some more blown-in to be sure. I have also "re-fluffed" the insulation in most of the areas I could easily reach. I usually check my duct work and confirmed that all the connections to not appear to be leaking. Yet it is a house built in 1990, and nothing has been done to the HVAC other than general maintenance.
Old 12-01-06, 02:30 PM
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Frostless roofs and frostless areas on a frosty morning are indicative of heat loss. Is there a vapor retarder beneath the blown-in insulation? Did you seal all gaps along perimeter of attic, chimneys, vents, etc. where warm, moist air from below can escape into the attic? Are ducts insulated? Are you sure you have adequate ventilation? Adequate insulation? What is your R-value? R-value requirements can vary from R-19 in the southern states to R-49 in northern states. Is attic access door insulated? Are bathroom vent/fan units or anything else ventilated into the attic?
Old 12-01-06, 03:32 PM
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Thank you for replying.

The heat loss is what I am afraid.

There is NOT a vapor retarder beneath the blown-in.

I did not seal gaps along perimeter of chimney or attic area, I presume the builder had...

The attic entrance is not insulated.

The duct-work is mildly (if not minimally) insulated.

This is only a 1900 sqft house. If it makes a difference with your helping me.

The adequate ventilation includes to gable ends vents (about 12 x 24") Four vents in top of roof with two 5 inch holes each. 3 x 16" vents every other roof overhang area, sorry I am not sure how to describe these, you can see these from the outside of the house looking up under the roof overhang.

The attic is VERY cold almost the same temp as the outside air on a cold night, when I go up there at night.

Bathroom and vent fans go through the attic and vent to the outside of the roof shingels.

I suspect my R value is only around R-19. It MIGHT be R-24. Most areas the blown-in is a little higher than the 2x4s... Hence about four or five inches.

I was thinking of blocking some of the vents during the winter. As I seem to really need these to vent out during the summer (over 100 degrees) for my A/C to work well.

Should I pursue more insulation? Or perhaps more sealing around different areas?
Old 12-01-06, 03:43 PM
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Dont block any vents no way. You need them summer and winter. More insulation is what you need. Id go for a R25 with no paper on it. Put it down across the rafters on top of what you have
Old 12-01-06, 03:53 PM
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I was thinking of putting some on the roof side, as opposed to the ceiling/sheet rock side.

I just want to be clear, you say, basically add more insulation, correct? Put it on top of the blown-in on the ceiling side???

So the "no frost on the roof" (when everyone else has frost) is a bad thing, right?

Thanks In Advance.

Old 12-01-06, 08:07 PM
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Just to cover all bases ...

Do you get sun on the roof before your neighbors? Or do they have more tree coverage? Could the frost on your roof be melting before theirs?
Old 12-02-06, 10:23 AM
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I have a BIG oak tree on my north side. I also have some "Dwarf" Redwoods (down to seven of these) on my south side. They are pretty close to the house about 20 - 30 feet away and they are around 70 feet high.

I get sun on the south side, but I usually see the frost on everyone's roof just as the sun is rising, but I don't see the frost on my roof.

Thanks for the reply.

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