Attic Frost

darren

To start with my attic has two gable vents and 2 roof vents.

A couple of weeks I blew in some new insulation. I went up there today to get a few after pics for myself and noticed that one side was frosty(the west side). The other side looks fine. I did notice a couple of places where the insulation could have been a little thicker but nothing to bad.

What may be causing it and what are some solutions.

I was thinking that soffit vents may help. With soffit vents do you have to separate them for best results or can they can be grouped together. The reason I ask is because one part of my house does not stick out as far the rest and could easily add them there without much work in the attic.

Let me know what you think
Darren

locofoco

I'd be looking for the source of the moisture. Make sure the bathroom exhaust fans aren't venting into the attic. I've seen a lot of them done this way. It's against code.
When you insulated your attic, you made it colder since not as much heat was escaping through the ceiling. This lowered the dew point on the underside of the roof. Excess moisture will condensate and freeze where it's coldest.
Is there any ventilation thru the soffit overhang?

darren

I did the bathroom fan myself and it is vented outside, actually its not even wired in yet.

There is no soffit vents just the gable and twp roof vents. If you reread my post i did ask something about soffit vents.

locofoco

Adding soffit vents will definitely help.

darren

First off i reread my repost and if i sounded kinda of snippy i did not mean it that way.

Should the soffit vents be spaced out evenly all around the house or could i put them in the one corner.

Scottsdale

You will definately need soffit vents. You need an equal amount of free space using intake and exhaust venting. For the soffit vents you will need to install a chute system. This consist of pulling out the birblock in sections. You will then install an cardboard or fiber chute. This is as wide and as tall as the birdblock space and about three feet long. With this the chute will pass the insulation and vent the attic. Supplied is a screen you will use to replace the wood you pull out of the birblock area. For proper venting go to www.Lomanco.com. This will tell you exactly how many intake and exhaust vents you need per square feet of attic.

Grumpy

Attic frost is almost exclusively caused by ventilation, or lack there of. I fix these kinds of problems every year.

When you blew in your insulation did you cover your intake, if you have intake? Soffit vents spaced usually 5' apart are a must in my opinion, and make sure they are clear of insulation.

If you only have two gable vents you may also want to consider adding a few mushroom vents on the roof for exhaust.

Attic ventilation is a science unique to the architecture of your building. There is no one size fits all solutions, and the advice we gave is really based on typical situations.

Does your bathroom fans ventilate into the attic? If so you need to vent them out of the roof.

Aceinstaller

yes grumpy summed it up.

I'm tired of seeing bath fans run into the attic with no connection to a roof vent. just think of all of the moisture in the roof every time you shower.

If you do have adequate soffit venting and the problem still occurs, have a local hvac company do a calc on the attic space and install a powered attic vent to accomodate. bye bye frost and condensation.....

Grumpy

Better idea is leave the roofing to the roofers instead of a HVAC contractor. The calculations are fairly simple to do, the problem is in making sure the fan is water tight. All too often I see fans just set in a bed of roof cement and leak after a few months.

Also if you install an attic fan you should install not only a thermostat but also a humidistat which will turn the fan on even in the winter when the humidity is too high.

Aceinstaller

I didn't mean that this isn't a job for a roofer either, hvac just popped into my head because the v in hvac stands for ventilation. While working with hvac companies I have installed many attic fans and would never do something as dumb as that.

If an hvac company doesn't know how to cleanly remove shingles with a flat bar and slide flashing under the shingles to where the shingles cover the flashing past the actual hole in the roof, they have no reason to be in business.

Seeing that you know about the humidistat trick is something that I would think most roofers would overlook.

River Rat Dad

add the needed soffit vents to balance the roof vents. Add roof vents as needed to get a 1/300 ratio, with half on top and half below. Close off the gable vents. Air follows the path of least resistence. The gable vents will act as intakes and short circuit the soffit vents.

jmorgan

Any chance that you "bumped" either the dryer or bathroom ducting when installing the insulation? Could there be a leaking joint in the ducting? How about recessed lighting fixtures in bathroom or kitchen. Make sure they are well buried in the insulation.
Jim