View Full Version : Ice dams, ridge vent-NOT ???

February 14th, 2005, 02:42 PM
I bought a new house this past summer, built custom in '97. The prev/first owner an apparently did a lot of stuff himself. For the most part he did good work, but a few things are puzzling.

I was on a biz trip for the big Jan 23rd Blizzard in MA. Later in the week my wife calls to tell me of massive icicles a nd ice damming on the front of the house. I'd have to show pics of the roof, it is somewhat complex. The back half of the house is vaulted all the way up to the 2nd floor level ceiling hieght, the front half is two floors with a "half peak" attic area (shaped like /|). Anyway, it is the roof over that attic area that the ice problems exist.

So I crawl up into the attic space (not having been up there since I bought the house, no pull down, only hatch in a bedroom). I am first releived to see light shining up from the soffits (perf vinyl) and the soffit vent "U channels" holding the insulation back. I look up at the peak and the decking seems to be applied as though a ridge vent was to be installed, but I see roof material rolled right over the gap!?

Outside I look up and see a ridge vent cap. Huh?

There is a power vent up there, near the peak that runs on a thermostat in the summer (AC unit up there too...). But that doesn't help in the winter. Could this guy have decked for a ridge vent, even nailed a ridge vent cap on but forgot to cut away the roofing material first?

It was way warmer up there than I expected too. It was in the upper teens outside, and seemed to be about int he 40s in that attic. Heat bleed? Insulation looked adequate (2x10 ior 2x12 joists, filled).

Anyway, sorry for the long post. The questions:

Is it obvious that the absence of the ridge vent is causing the problems? Would seem so to me.

If so, how to remedy? It would seem that I could either cut the material away from inside, but that would be tough, and might mess up the "gauze" (that is what I call it anyway) on top of the vent. Or yank the whole ridge cap off, with the gauze, cut open the vent, then put new gauze and vent cap on??

Lastly, how to tell if I have an insulation problem that is contributing to this ie: too warm attic. I can tell you that the last two gas bills have been shockers (but to be fair, it is way bigger of a house than we have ever had), but is there some other assessment that I can do? Or would it be normal for an attic without a ridge vent to just warm up over time anyway.

Thanks for any advice. I can get pics, measure temps inthe attic etc. Probably won't do anything structural until spring/summer anyway.

Run power vent when temps are near freezing?



February 14th, 2005, 03:39 PM
I would check your ductwork for leaks or lack of insulation. An attic in a well insulated ceiling shouldn't be that warm. I'm not sure what to tell you about the ridge vent -- were they just stupid, or were they missing some material and just covered it all over??? If the ridge material is the 3/4" thick honeycomb like stuff, you may be able to cut the underlying shingles with a retracting blade knife ("Stanley knife") and not damage the cap. But if you screw up, I'd make sure to have replacement ridge vent or a way to patch what you cut through.

With how your roof was done, a power vent shouldn't be required if the ridge vent could vent. Does it provide any venting when its not powered on? That should help if so, but your peak or gable venting is very inadequate with a blocked off ridge vent.

February 14th, 2005, 06:10 PM
The top of that attic is required to have venting as an outlet. If you have cathedral with the rafters enclosed by a ceiling not access to attic this ridge vent is required. Cathedral ceilings require insulation same as normal ceilings with a minimum 1" air gap for air to dry out the bottom of your roof decking. Only way this can be done is vents in soffit and ridge vent to vent each individual rafter space for that cathedral designed roof / ceiling construction.

If entire house has an attic then you may be able to take up plywood sheet by cutting a ceiling in a closet then lay out the plywood as a foot print to set a step ladder safely getting to the under side of that ridge vent. Use shears to cut away the roofing. I suspect the roofer made the mistake unknown to the builder closing off that ventaridge. Yes I suspect this is a major part of your problem.

Second way to cure if no cathedral ceilings closing off rafter spaces is to install square roof vents.

Third way to cure is to install a bypass switch using both a thermal switch for summer and a moisture switch for winter sensing moisture in that attic using the power vent to do all the work.

I would clear that ridge vent if it were me.

Next is the concern of warm attic. This tells me you have a mistake in insulation value.

Tell me the County and State you are in and I will tell you what the IRC requires for minimum insulation of your ceiling. Suspect your insulation is inadequate to meet code in ceiling making a heavy heat loss.

I have a cathedral ceiling in my living room up to and over loft with both a rafter and ceiling joist making the cathedral ceiling. I installed minimum insulation in that cathedral ceiling being on the north side of my home out of the sun in teh winter. This cathedral ceiling is the last part of the house that melts snow in the winter in my home showing proper insulation installation.

I would check out the above then start investigating other insulation envelope mistakes that may be present. Not hard to do and worth the money winter or summer.

Hope this helps


February 17th, 2005, 09:02 AM
All of the ductwork in the attic space is AC, and is insulated on the outbound ducts. House has forced baseboard HW, so no heat in the attic.

I really don't like the power vent anyway, I think a properly installed ridge vent will be all that is needed in summer.

As I said, the back side of the house is cathedral right up to the peak, but I believe it is air channeled between the insulation and the decking. I'll get back up there and take some pics. No real ice problems on that back side.

I'm in Dunstable MA WG. Just on the NH state line, eastern part of the state. The joists in the attic are either 2x10 ir 2x12, and filled with fiberglass insulation to their tops. It appears as though the insulation is adequate. If the ridge vent is totally blocked, is a slightly warm attic necessarily indicative of insulation problems? Or over time would it be normal for the attic to warm up just from heat bleed from the house below? When I was up there, the fron half of that roof was completely covered with snow, so I don't think there was any solar effect.

I'll get back up there and get some pics, and maybe a diagram of the design. Hard to descibe. Also, have a short "half roof" over the front porch that also ice dams. Not sure if there is even any way to vent that, no underside access exists today.....


February 21st, 2005, 06:47 PM
You are in a Zone 10 calling for R38 ceilings, R16 Walls, R17 Crawl, R19 basement walls. Use the above R values going to your local building supplier looking for the same insulation you have in your attic. Read the lable on the insulation and it should tell you how thick that insulatio is required to be to reach that R value.

The area where you ice bridging occurs is it 3/12 pitch or less. What pitch is the roof. Is the ice bridging showing where the warm attic ends and unheated soffit or porch begins. If so then heat loss in attic is your problem with low R value insulation. If you have a more flat roof this may be causing the ice bridging. I am leaning from what you have said that it is low insulation R value in ceiling or floor. May also be no fire blocking stopping warm air from rising by chimney effect inside the walls through drilled holes warming that certain part of the roof above.

Hope this helps


February 22nd, 2005, 04:35 PM
Ok, here's some pics. 1 day after a 4" snowfall, and the temp is 34.5 degrees. On the front of the house, upper roof, you can see some "warm attic" melting. Before the snow, the roof was bare front and back. The accessible attic space goes along the enter width of the upper roof. Are those melted through areas "hotspots"? Should that help me pinpoint a heat leak in to the attic? The lower front roof, over the porch has no access. The PO had vented a downstairs bathroom vent fan into that space. I have since removed the fan, but did not block off the duct. I plan to replace the porch lighting this spring, and may be able to cut an access. Obvious heat build up there too. How can such a cavity be vented???

Then you can see the back of the house. Much steeper roof pitch. On the upper right of that roof, you can see the area open to the attic area that spans the front. So a "smoking gun" for a warm attic. The entire area to the left of that slightly melted part is vaulted ceiling inside, all the way to the peak. The area below that area is an inaccessible space over the downstairs master bedroom. Unvented space, but no heat leak into there? I know there is no plumbing in there, but there are vertical AC ducts (supply and return). House heat is forced HW baseboard.

So an interesting day to take pics. I'll try to get up in the attic later and look around more and take some pics, but I have only 2 days before a couple back to back trips. So it may be awhile.

Comments? Observations???



February 23rd, 2005, 09:12 PM
The three round melt spots evenly spaced leads me to believe you have recessed lights directly below each of those round melt spots.

The warm attic will melt the snow. When the snow starts to melt the melt starts at the top of the roof and the snow shifts down as your melting progresses. Proof of that look at your skylight being a heat loss melting the snow from that skylight with melted snow running down the roof shifting the snow downwards toward your gutters. Then the melted snow hits the cold gutters causing refreezing when temp is close to freezing. Look under your skylight showing the melt tracking down toward your gutters.

The ice bridging on the gutters is normal to a degree. However the warm attic seems to be your problem melting from the top down then refreezing at the gutter line. If the insulation was high enough R value to meet minimum at least the melting would be pretty well stopped. My attic is cold and the roof is snow covered after a snow until the air temp goes above freezing. When this happens my gutters also are above freezing allowing the water not to freeze over the unheated soffit and gutter line allowing that water to drain away down the gutters limiting ice buildup.

I would go to the building supply house and look at the packages of the insulation matching that in your attic. Find how many inches meets the R value I gave in prior reply. Then measure your attic insulation. Suspect your insulation is inadequate over your ceiling.

Hope this helps


February 23rd, 2005, 09:49 PM
Again, thanks. There are recessed fixtures on that upper floor however. When I get up there, I will look very closely at the area under those melted spots.

Do you think that it is possible that the attic is reasonably well insulated, but because the attic is not vented at the ridge, or any high spot, there is a normal heat "bleed" and buildup in that attic that would cause that? If that is the case, correcting the (absence of) the ridge vent would seem to fix that.

I would like to believe however that there is some signicant heat leak up there as my last gas bill was $400. Much bigger house than our last, but that seems high. Would love to find some culprit and be able to fix it.

I know that the between joist insulation is at least 9.5" thick (2x10 joists) maybe 11.5 (2x12s), so R-38 seems probable. Of course there could be other "leak" areas....


February 24th, 2005, 06:58 PM
It is not uncommon that blown in insulation is installed 8 to 12" above the ceiling joists. I think if you went to the supplier and look at the blown in insulation you have on the package it will tell you how many inches is required. You will find your insulation is short of enough.

Both the insulation R value must be reached to save heat loss inviting melting and the ventaridge need opened up as we discussed before. Both need corrected to solve your problem.

Don't forget that unless those recessed lights are in contact rated to be in contact or covered by insulation you must keep them open to the air above them to allow heat to escape. If you don't have IC rated recessed light tanks you should replace them with IC rated tanks so you can cover them and limit that heat loss. Never cover over a recessed tank with insulation unless the manufacturer lists them to be covered. If you do you are at high risk of a fire. Those non IC rated recessed tanks may be cheaper but they lose enough heat to pay the difference in about 1 year.

Good Luck


February 28th, 2005, 01:46 PM
Opps, I left a "not" out of the last post, I do not have any recessed lights in the ceiling of that upper floor. Also, the insulation is not blown, but yellow fiberglass (not corning pink) between the joists. My experience has been that with fiberglass, 10-12" thick will get you R-38 pretty easily.

I'll try to get back up there this weekend and look closer....


January 9th, 2008, 10:30 AM
Well I'm still in this house, and still have this problem, although I'll confess to not having done much about it since I posted last.

One question however, that has been in my mind.

My AC unit is in the attic (AC only, no heat) and I am wondering if that is a common source of heat bleed into the attic? I know it is a closed system, with the return ducts into the house, but should I be concerned about this as a source of heat bleed into the attic?

We put magnetic covers over the AC vents in the winter, but cannot get to a couple of them as they are about 18' up on a 2 story wall....



January 9th, 2008, 10:51 AM
I doubt you a/c unit in the attic will be a problem being a closed system as long as your plenum and heat ducts are insulated.


January 9th, 2008, 11:00 AM
I'm also in MA, south of Boston
R30 = usually 10" joist
R38 = usually 12" joist

I prefer to over insulate
My mom's house has insulated 2nd floor ceiling, older house, not enough insulation. Smaller joists, plywood in the attic
So, when I re-roofed I put ridge vent in with rafter vents
Then I added insulation to the slanted roof

Roof is now insulated, snow & ice no longer a problem
The roof deckis insulated against the warmer attic
The attic is now warmer which cuts down on the heating bill
The attic area itself is still vented with gable vents

Prior to this I added a power vent to one gable to exhaust heat out of the attic. With added insulation on the rood deck the attic does nto get as hot in the summer

Your problem will continue until you take action to fix it
Always amazes me about un-insulated attic space - I know - builders like to keep the costs down
Properly vented attic properly insulated will stay warmer in the winter & cooler in the summer. This saves on heating & cooling

I have a 15 x 17 sunroom nearing compeltion on the back of the house
Finished insulation, started sheetrocking. There isn't ANY heat out there & it stays about 55 degrees. On a sunny day it goes up to 65-70

January 6th, 2009, 03:52 PM
Well nearly 5 years after I posted, I finally solved this problem. So I thought I would post.

A closer look at the insulation up there revealed that the existing insulation on the floor of the attic was poorly installed and some very large gaps and open spaces. Those melt spots I had seen were directly over the AC duct "drops" to the first floor. I could see bare drywall in most of them.

I had been monitoring the attic temp with a remote thermometer and the very coldest I think I ever recorded was 38... in winters with sub zero (F) temps.

So decided to take insulation from my basement ceiling and after fixing the open spaces in the existing insulation, put a perpendicular layer of batts over it. I would have done blown insulation, but with my AC up there, I need to get up there yearly to change out a filter and didn't want to have to walk through/around it. May basement has no walkout and usually is 59 degrees in the dead of winter. 57 is the coldest I have ever seen. So I really don't think that insulation is all that necessary... and I was tight for $$.

So I fixed the existing insulation (R30 on either 10 or 12" joists), tucked some smaller squares of the basement R19 into the eaves (but keeping the vent sheets clear) and then laid R19 over the whole space perpendicularly. I spray painted a line on the pieces that cover the narrow plywood walk to the AC so I can either walk on it, or just move them out of the way to get to the AC then put them back. I finished by putting a 4" layer of Styrofoam on my hatch board.

I was thrilled to see a reading of 29 degrees this morning on the thermometer and it was only 20 degrees outside. I am sure if I measure temps in the 20s in the attic, I won't be melting snow on the roof and having huge icicles and dams in the winter.

Now I am just hopeful for a decent drop in my gas bill this month. I paid OVER $500 last Jan!!!

January 6th, 2009, 06:51 PM
All the info that everyone provides really helps out the next guy.

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January 6th, 2009, 07:22 PM
All the info that everyone provides really helps out the next guy.


Yeah, that is why I came back and posted. I don't know how many times I had gone looking for a solution, found someone who asked about, got advice tips, and .......... THEN WHAT HAPPENED!!!!!! :twisted:

January 13th, 2009, 11:25 AM
Ok, hold the phone........ I don't think this problem is resolved after all.

In the last couple days, the attic temp has not dropped below about 36, that after creeping up very slowly from the 20s I saw before. Andi it was 9 degrees outside this morning. At first I was baffled, but last night it hit me...

Sat night, Sunday morning we got 8+ inches of show... the roof is completely covered..... including the ridge vent....

I just did some googling on ridge vents and snow and while they are known to work very well in the summer, I guess it is very common for them to clog up with heavy snowfall. When I saw 20s in the attic with 20s outside, there was no snow on the ridge. Now with snow last 2-3 days, the temp has crept up....

Makes sense. Yes, I probably reduced the heat bleed by adding/fixing insulation, but I am sure there is always some heat bleed in every attic and without "high" venting, and the insulating factor of a good layer of snow on the roof, I can see how attic temps can creep up.

I have icicles again, but not as big as I have seen in the past.

So I am thinking 2 things, one is to put gable vents in. Although I was reading one forum that said that ridge and gable vents were bad when the ridge was not snow covered, as it makes an imbalance between high (ridge and gable) and low venting (soffit) and can pull makeup air out of your house (more exhaust than intake).

Add big gables and remove the ridge vent? In my previous house I had limited soffit vents, an a couple 12"x16" gables, and no ridge, and in 13 years never saw an icicle off the roof.

My other option is to run my power roof vent. But that seems kind of stupid in the winter. I'd have to wire a manual switch of some kind, right now it triggers at 140F on a thermostat. The geek-solution would be for it to com on when there is a certain differential between inside and outside temps, regardless of the actual temps.

Ideas? Comments?

If I do install gable vents, I'd have to wait until the spring....

January 13th, 2009, 12:54 PM
Turbine vents are the other possible solution. Same problem when I lived in Minnesota. I ended up using a powered vent because the roof pitch was 1 1/2" in 12. I've used turnbine vents and they have worked out quite well. They tend to clear themselves, and they stand proud of the roof surface.

January 13th, 2009, 01:14 PM
If you have a lot of snow you can resolve the problem by installing a couple or even a few cupola at the ridge. These are little houses mounted on the ridge that have roofs with hangovers and screens to limit influx of snow. Then when the snow builds over the ridge vent the cupola is still above the snow build up on the roof allowing continuous ventilation. I suspect you can buy the cupola at lumber stores prebuilt just needing installed on the roof. Does the same as ridge vent, gable vents without the two fighting each other.

Just my idea


January 13th, 2009, 01:24 PM
If you have a lot of snow you can resolve the problem by installing a couple or even a few cupola at the ridge. These are little houses mounted on the ridge that have roofs with hangovers and screens to limit influx of snow. Then when the snow builds over the ridge vent the cupola is still above the snow build up on the roof allowing continuous ventilation. I suspect you can buy the cupola at lumber stores prebuilt just needing installed on the roof. Does the same as ridge vent, gable vents without the two fighting each other.

Just my idea


Excellent alternative to a Turbine Vent and better looking too, if the style fits which I expect it would with his roof.
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January 21st, 2009, 08:54 PM
Ahhh, a friendly forum. You even allow the resurrection of old threads. That is so important for people who come after us looking for information. They can view a complete discussion and any new developments years down the road.

Zinfendel - You are to be commended for returning to your post.

You are facing the exact thing that I've been concerned about with regard to ridge vents. I posted something at DoItYourself Forum (http://forum.doityourself.com/roofing-gutters-waterproofing/337173-adding-gable-end-vents.html#post1507014) that you may find helpful. Even though I've seen many references to ridge vents clearing themselves of snow, I don't think I would risk my project on it. Check that link above for other venting options.

I don't think mixing your venting will be a problem unless you have significant winds. If conditions were just right you might find that your venting causes a vacuum in the attic and it might draw air out of the living area. Also, if you do get significant winds and fine wind driven snow, it might get into your attic through the gable vent. I've had that problem here on the Minnesota prairie. As an illustration for the need for balanced venting, I have a large wood frame, gable roof outbuilding. Years ago a roofer installed 3 wind driven turbines on the roof with no intake anywhere. After a big windstorm I found the heavy attic access hatch had moved significantly. The vacuum was so great that the hatch was sucked up into the attic.

January 22nd, 2009, 10:25 AM
Also, don't forget that while the snow covering the vent may be a problem, the snow cover itself will provide a pretty good layer of insulation, effectively raising the r-value of your roof! It *will* get warmer in your attic when there's 8" of snow on the roof...

January 22nd, 2009, 06:14 PM
good point on the wind and gable vent ie snow getting blown in. I live on a lake and put gable vents on both sides of my house, including the side that faces the lake. During windy rain storms, about twice a year, a significant amount of water gets blown into the gable vent facing the lake, I am rectifying this year. But they do work great for cooling off the attic space.
The place next door has a ridge vent and has the problem of it getting covered with snow too. It's a vaulted ceiling and when the vent gets covered the whole sheathing surface heats up enough to melt a layer over the whole roof, then it freezes. This causes an ice dam over the whole roof. They need to remove the shingles and put down that sticky layer of ice and water shield. I digress... some solutions I've seen for the ridge vents getting covered are raised ridge vents, along the entire length of their application. I'm not sure if they are a custom job or not but they look ok, like long cupolas. They're built up about a foot and a half above the ridge. I don't have any pics. That solution might work on my neighbours place since the wind would shave off the snow on the top and the any snow on top would be minimal anyway and easily melted if the attic temps got too high, that's the theory behind the ridge vent anyway, doesn't always work, obviously. Anyway, hope some of that helps. D

January 22nd, 2009, 10:15 PM
My ridge vent is free, but that's because my 2nd floor isn't fully insulated & sheet rocked yet. Wind can also blow rain into a ridge vent. That is true for any opening in your house. Wind can also blow rain up under your shingles

My entire roof is Ice & Water shield to the ridge under the shingles
That will not prevent snow & ice from forming a layer over the ridge vent. There is heat loss thru the roof, venting will not stop that, only redirect it to the ridge vent. Under the right conditions you will get icicles, you will get the ridge vent covered

On my addition I will have a cupola