Roof Troubles - frost in attic


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Old 01-09-04, 12:29 PM
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Roof Troubles - frost in attic

Over the past few weeks, i've noticed what i think might be a big deal. while getting out and puttin away Christmas decorations in the attic, i noticed water spots (small ones like what a single drop of water would leave) on the plywood flooring and cardboard of boxes up in the attic.

there are some damp spots on the interior sides of the plywood of the roof and then the other day, i noticed something even more disturbing (to me at least). wed. morning, when it was barely 20F outside, i heard what sounded like crumbs dropping onto the attic pull down door in the hallway. i cautiously pulled down the door/ladder to see what it was, more than half expecting a mouse or squirrel to come flying down at me. i didn't see anything at first but when i went up the ladder to take a closer look, i noticed that all the nails points (holding the roofing onto the plywood from the outside) were covered in ice or frost and with the morning sun heating up the roof, the ice was starting to slide off the nails and fall the the attic floor and door/ladder.

so far, luckily, the amount of moisture coming down from above has not seemed to penetrate more than just the top of a few boxes and dry up pretty quickly - not making any stains in the drywall below but still, i'm wondering what i'm dealing with here.

the roof is at least 7 or 8 (could be as old as 10) years old and is on the second layer of asphault shingles. so i'm kind of expecting to have to get the whole roof done probably within the next year anyway but the frost/ice kind of threw me - is that leakage from above or condensation from below? we don't have any kind of vents leading into the attic space that would be bringing in any water vapor from the house below up there and there are 2 vents in the attic itself that allow outside air to circulate. one of the vents has a fan but that is thermostatically controlled to come on only when it gets hot up there....

any ideas? i have a roofers coming out this weekend to have a look/give esitmates but i wanted to be as educated as i could be before i speak to them.

thanks in advance...

austinpm1
 
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Old 01-09-04, 01:17 PM
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If it is condensation, then most nails will have the frost. Chances are that the wood around the nails will look dry, however. It it's leakage, then the water may be getting in via the nailholes, and you should see the wood around the nailholes being quite wet. As well, when it's leakage, it would be unusual to have the leakage distributed over a large area. Leakage usually starts around a roof penentration (chimney, plumbing stack or air vent), and runs into the attic in a rather narrow stream (or drip).

Your description leaves me to suspect condensation. Since you're using the attic for storage space, I would also suspect that the trap-door you use to access the attic is not sealed air-tight, and some normal warm air from the home interior is leaking into the attic and causing the condensation. You may also have other sources of moisture such as bathroom vents that are not vented to the outside.

You currently have a power vent which is heat-activated. You don't really say if you have any soffit vents. The normal ventilation that one would want to see would have air coming into the attic through soffit vents, and exit through the roof vents. When properly sized, you will have passive ventilation that dries out most condensation. As well, you should have a vapour barrier that prevents the warm and moist air from the home's living space from entering the cold attic.
 
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Old 01-09-04, 01:43 PM
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Lightbulb vents

With pgriz all the way here. Id have to ask about the insulation you have up there do you have V/B under it on the ceiling. if not there is a paint that you can get and put on the ceiling to help. Also they are now building like a box around the attic stairs out of fiberglass ductboard to help insulat it . last you have to get vents cut in the over hang. For now you could put a humidistat on that fan there so it would run now to help out. Get that moisture out of there now.
We tell people to just think of that roof as some thing that is there to keep the rain and snow off the insulation and should be open all around ED
 
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Old 01-09-04, 01:58 PM
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i kind of suspected condensation more than leakage (although leakage might not be too far off if my plywood decking is beginning to rot from either side).

2 vents - one motorized, one just open. both are side facing (one in the front of the house one on the side so theoretically above both of these vents, moisture could accumulate which is where i think the most frosty nails were...

i won't know about the shape of the plywood i guess until someone starts pulling off shingles, though, right?? and then what kind of costs does that add to a roof job?

thanks again for the input.

Austin
 
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Old 01-13-04, 02:50 PM
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Anyone notice the number of "frost in the attic" posts increase since the weather turned cold? Seems like too many people don't have proper ventilation or insulation.
 
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Old 01-13-04, 03:19 PM
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Yuppers, sure is a problem in this extremely cold weather. Plus with it this cold out everyone is overheating their house with woodstoves or LP inserts/etc which makes the problem more noticable. It doesn't help with the crappy ridge vents they installed about 5-15 years ago either. My other personal favorite is the solid soffeting installed on houses that covers the vents.
 
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Old 01-13-04, 04:34 PM
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what do you mean by crappy ridge vents? currently the house has no ridge vent but my first contractor had one in the estimate and i want to make sure it's not a 'crappy' one
 
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Old 01-13-04, 06:33 PM
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BTW - on a hunch, i lowered my humidifier on my furnace from 50 down to about 30 and, as if by magic, 2 or 3 hours later, the windows in the house are clear (no fog), the doors shut more easily, and i think the frost in the attic is down too (we'll see tomorrow morning - supposed to be down in the teens again tonite).

getting estimates for replacing the roof either way...

how does $5k sound for removal of old roof, ridge vent install, and gutter replacement + 6ft ice shield at bottom of roof? i this the first guy is going to cut soffit holes (there are none presently)

the house is pretty small (3 br ranch + attached 1 car garage) maybe 1000 sq ft...
 
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Old 01-14-04, 01:56 PM
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Austin, some of the ridge vents from about 10 years ago were a very bad design and worked about as well as a saw without teeth. Heavy wind would force water and snow into the house and make it look like a roof leak. Luckily this design has disapeared. The guys i work with do not use ridge vents and use those round roof vents, i can't remember the proper name of them for the life of me. It all depends on the codes in your area on what is required and allowed.
 
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Old 01-14-04, 02:21 PM
Grumpy
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If it's a 1000 sq ft ranch 5k is a bit high, for the Chicago area. Not only make sure the soffit vents are cut, but make sure that insulation doesnt block the rafter pockets. This is a common problem. Insulation is stuffed into the rafter pockets so no fresh air can get into the attic.

The round roof vents can be turbine (moveable by the wind) or mushroom, which are the typical breahter vents. Turbines are unsightly and don't work well in low wind. Ridge vent is *usually* the best way to go, but when it comes to ventilation it's not a matter of personal preference. Ventilation is a science. Check www.rollvent.com and www.airvent.com for more info. You can also look for lomanaco, which is another large manufacturer of attic ventilation products.
 
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Old 01-22-04, 03:01 PM
It Wasn't Me!
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Ridge vent is the way to go BUT you must also have soffit vents and adequate insulation. If your roofer is worth his salt he will do ventilation calculations and install what is needed. The best ridge vent I have used so far is shingleVent II by airvent.
www.airvent.com Also I do not use nails to install the ridge vent I use galvanized screws and then nail the ridge caps on. Make sure to block off gable vents if you have them they will short circuit the ventilation process.
 
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Old 01-22-04, 07:07 PM
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Ridge vents on semi-flat roof design

IWM,
You mentioned ridge vent calcs. I have three questions, but first a quick roof description. My home's roof is a BUR, tar-gravel composition, and has a pitch of less than 2" per foot - not flat, but very low pitch. It currently has soffit vents and pretty large eaves - about 16" minimum. However, the soffit vents are only a few inches wide. The roof has no other ventilation.

1. Can a ridge vent be installed on a roof with this low of a pitch?
2. If not, what other type of upslope ventilation can be accomplished?
3. What is the formula for determining proper ridge ventilation?

My aim is to rid the second floor of summer heat. Luckily, I haven't had problems with ice dams, but don't want to deal with that either. I am getting ready to reroof this spring.
 
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Old 01-23-04, 10:59 AM
It Wasn't Me!
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Hi MattG

1. Ridge vents are not recommended to be installed on a roof pitch of less than 3/12

2. Not being able to look at the roof and answer this question is very difficult. This type of roof system is generally not designed for exhaust ventilation. The intake ventilation in your soffit area is now acting as a flow through type system which is not the best. The best way to reroof this would be to remove the flat roof and install trusses.

3. Most codes recommend a minimum of 1 square foot of net free ventilation area for every 300 square feet of attic floor space, If its balanced between exhaust vents on your roof and intake vents in your soffit and If there is a vapor retarder installed.
Otherwise the recommended minimum is 1/150
For the best ventilation system performance we recommend 1/150 no matter if you have a vapor retarder installed or not.

A typical ridge vent has a net free area of 18 sq. inches per foot. Therefore your soffit net free area should be 9 sq. inches per foot on both sides of the building which equals 18 sq. inches per foot net free area. This way your ventilation system is balanced.
 
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Old 01-31-04, 07:08 AM
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If your venting ratio is 1:300, or better, you most likley have a source of warm, moist air entering the attic space. Weatherstrip the hatch, look for other sources of interior air....leaking dryer vents, bathroom fan ducting, etc.
Jim
 
 

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