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Ventilation and ice dam problem

Bobatc's picture

This past summer we had a new roof (architectural shingles) and vinyl siding installed on our 1972 colonial.  We live in zone 6, so snow is a part of life.  The previous siding was concrete-fiber shingle and the insulation in the walls was original.  All of the windows have been replaced within the past six years and attic insulation has been upgraded as well.  The attic originally had gable vents at either end with soffit venting under a 10 x20' main entrance overhang.  There is an unvented six inch eave overhang in the front but none in the back; the siding abutts a fasciaboard which borders the roof.

The roofing contractors installed ridge venting the entire run of the roof (approx 50') but closed off the gable vents.  The siding was installed with 1" foam but no vapor barrier.  This winter we have had two large snow events followed by freezing temps.  We have had an ice dam form and water infiltration above the same bedroom window each time.  This beroom has a sloped ceiling due to the roof design. 

My question is whether to remove the gutter and vent the fascia in the back of the house?  Or, don't worry about venting the base of the roof and re-install the gable vents at each end of the house?

Thank you in advance.

Bob

If you have no soffit venting (post #207485, reply #1 of 14)

If you have no soffit venting then the ridge vent does little good.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Bob (post #207485, reply #2 of 14)

Could you take a some pictures of the window and post them.  Show a bit of detail, but some shots away that show roofline,gutter and the vinyl detailing.  While venting might be the problem, the water entrypoint might be a better way to correct the damage.

thanks.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


Lack of insulation between comfort zone and roof. (post #207485, reply #3 of 14)

You do not have enough insulation between your comfort zone and the roof.

The heat is escaping from your comfort zone through the ceiling and the door to the attic, causing the snow to melt. Where the roof overhangs the walls the roof remains frozen and the snow doesn't melt, this leads to snow melt backing up the roof and running into your home.

Forget about roof ventilation, concentrate on keeeping the heat inside your home, by adding more insulation to the ceilings. Venting attics is old technology, we understand now that the passing wind creates a low pressure area above and down wind to a home, this causes the warm air to be pulled from the home, causing high heating bills. All holes and cracks in a home need to be blocked to keep the heat in, all drywall ceilings need effective insulation to save heat.

Once the whole roof is cold the snow will gradually blow off or evaporate in time. Look at it as a challenge, you want to be the last home in your area with snow on the roof - proving you have enough insulation.

A useful tool, is a wireless weather station, preferably one with two remote monitors, you place one in the roof and the other outside then you can read  on your computer how the temperature in the attic compares with that outside and with that inside your home, making it clear if you have enough insulation. The joy of having the right information is, you can add insulation whenever you feel like doing it...and you can lower your heating bills.

Lack of insulation between comfort zone and roof (post #207485, reply #4 of 14)

I was thinking along the same idea, so now the question is do I try to fill the area with fiberglass batting or have an insulation contractor come in and spray foam the tight spaces.  Has anyone tried to spray foam themselves? 

Ice dams (post #207485, reply #5 of 14)

I have almost the same issue. My roof has not been done and has no airspace or room for airspace because it is living space. Can I seal it with sprayfoam and not worry that the sun will still cause icedams?

i have heating cables to keep the backup to a minimum.

Sun and ice dams. (post #207485, reply #7 of 14)

Ice dams are caused by heat rising from inside the home and warming and then melting the snow that is pressed against the outside of the roof. It has nothing to do with the sun!

The heat from the home melts the snow, the water cannot escape downwards as it is blocked by the snow sticking to the overhand, this is still frozen, the water rises under the snow covering until it finds a hole in the roof, then it runs into your attic.

If is a good idea to use foam between the rafters, as done properly the foam will keep the water vapor in the air away from the roof. To make this work, you have to fix sheets of polystyrene under the rafters, to stop the rafters acting as a heat bridge and passing your heat to the outside of the roof.

Then cover with drywall.

Perry (post #207485, reply #8 of 14)

You may be an expert in your field which I don't know.

But while I agree with much of what you say, this one about the sun not melting the snow which cannot get past snow filled or frozen gutters is wrong.

It happens.

It happens in unheated buildings.

Don't dismiss it.

 

Just a dumb carpenter from cold dismal Ohio.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


Yep. I've seen it too. It's (post #207485, reply #9 of 14)

Yep. I've seen it too. It's not as common, but with the right conditions it can happen.

Andy Engel

Never try to teach a pig to sing. It wastes your time and annoys the pig.

I've seen it too.  The sun (post #207485, reply #10 of 14)

I've seen it too.  The sun can warm the exposed southern slope and heat the attic to the point that the northern slope (still snow covered) begins to melt.  The water runs down to about the lower 1/4 of the roof deck at which point it freezes again, because the roof is cooler that far down.  So you can get an ice dam a foot or two up from the start of the eave overhang.

Doesn't happen too often -- requires precise conditions -- but it does happen.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

The gospel according to (post #207485, reply #6 of 14)

The gospel according to Lstiburek says that having more ventialtion at the ridge than at the soffets is a bad thing. What happens is that the ridge vent depressurizes the attic. If you have adequate soffet venting (it doesn't sound like you do), the pressure differential is balanced by air coming in from the soffets, which is how the system is supposed to work. Lacking adequate soffet venting, the depressurized attic will pull air from inside the house, through recessed lights, attic hatches, up through the walls by way of holes in the plates, etc. This heated air warms the roof sheathing and is likely what's causing your ice dams.

There's a lot to say about this, but it's all been covered in the magazine or over at Green Building Advisor.

Andy

Senior Editor, Fine Homebuilding

Calvin, Andy Engel, Dan H (post #207485, reply #11 of 14)

Thanks for your comments. I have never seen this or have read about this in my 43 years of pulling homes to pieces.

Being interested in all things to do with home renovation I would like to know more. Can you remember when,  time of year would be important as for this to happen the sun will need some large amount of heat, probably May?

I don't recall for sure, but (post #207485, reply #12 of 14)

I don't recall for sure, but I would guess the sun-on-the-roof events (maybe 3-4 significant cases in 36 years) occurred about this time of year -- early March.  That's when we can get fairly heavy snow, and the sun is also high enough to hit the roof full-force (and also clear the neighbor's house up the hill). 

Our roof ridge runs east-west, so the north side gets no sun this time of year, while the south side is fully exposed.  You wouldn't likely see this scenario on a north-south roof.

(It has been known to snow here in May, but it doesn't last very long -- usually melted by noon.)


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Perry (post #207485, reply #13 of 14)

Here, in NW Ohio I would say it happens often enough for most anyone to notice.  Dark roof not totally covered-after a wind driven snow.

Rain after a snow that melts part of it.  Sun the next day.

Snow that still sits down low on the roof traps the water-it freezes overnight.  Continue with more rain/sleet, refreeze..........Where can it go?

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


If I recall, there's a (post #207485, reply #14 of 14)

If I recall, there's a significant amount of snow, cold weather, and plenty of sun. Later in the winter would make sense because of the higher sun angle.

Andy Engel

Never try to teach a pig to sing. It wastes your time and annoys the pig.