Attic ventilation for a gambrel roof?

[mamakat]

Our home was built in 1960. We moved in 4 years ago with a relatively new roof. We have since had issues with ice dams and mold in our attic. We've had several roofers come to inspect and advise. It is our understanding that we have several issues:

1. Not a true ridge vent
2. No soffit vents
3. poorly flashed valley where the addition meets the main house

We do have two gable vents.

The plan is to put in a new ridge vent, add soffit vents and install a power vent with therm/humidstat. The mold will be removed and we are replacing all of the insulation.

Questions:
1. Is this adequate or too much/too little?
2. What size power vent would be recommended for 800 sq ft.?
3. Any other considerations?

Thanks for the comments!

[catmanacman]

i would consider foaming the attic then you dont need the ventilation.or the insulation

[genduct]

is used to make the "attic" a potentially habitable space. Are your ceiling joist strong enough to support a real attic use? If so then call a real insulation contractor because foam, although at first blush a really good thought, may stop you from using the attic in the future as habitable unless you cover so as to reduce fire hazard. And if you are going to cover and use then conventional fiber glass may be the answer.
Don't have the answer, just another question

[tipsrfine]

Find someone that is BPI or RESNET certified and has experience to come out and perform an energy audit of your home. The ice dams are likely forming due to air leakage from your conditioned areas that is blowing right through your insulation and is warming your roof up in that area, but it then re-freezes as it gets out to the eaves. Without proper training in Building Science, as are BPI & RESNET certified people, even experienced insulators will likely not know how to remedy problems such as yours.

[54regcab]

Most "ridge vents" are junk, good luck finding a "true ridge vent" that actually works.

[motoguy128]

+1 on spray foam. No need tobastadize the soffits and roof and punch more holes in it and burn electricity trying to vent it. As for a habitable space. There are coatings that can be applied later if needed.

You will need to still fix the flashing of course.

[energy_rater_La]

gable vents
ridge vents with soffit vents
and pav's..

that is every method of venting an attic
with the exception of passive vent (whirlybird)

doesn't sound like anyone is solving the problems
but instead throwing every ventilation strategy known
into your home.
I'd get better opinions for your home.

best of luck..

[tedkidd]

i would consider foaming the attic then you dont need the ventilation.or the insulation

+2. Very least air seal attic penetrations.

On the moisture, jumping to treatments without diagnosing cause? Where is the moisture coming from? Where is the heat coming from?

Moisture doesn't magically appear on your roof deck, it gets delivered there. Likely your fart fans dump shower steam into your attic, along with other plumbing and wire penetrations delivering humidified air from your furnace. Mold more predominant in attic adjacent to bathrooms?

Its this heat which causes ice problems. Gable vents allow free exit path for air to leave after delivering heat and moisture to your roof, allowing a continuous supply of fresh heat and moisture.

Cure your problems once and for all and see your energy bills go down or treat by removing heat in winter and see them go up.

If you add venting don't be surprised if the ice doesn't resolve itself, as more venting may mean more area for heated air to exfiltrate up and out of your house. Oh, and if you have comfort issues, expect more venting to make them worse.

[tipsrfine]

This is a link to a great video on how to prevent wet attics. http://ecw.mediasite.com/mediasite/SilverlightPlayer/Default.aspx?peid=ef5fffc781c0464f93f675f089096f9b 1d