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-   -   Adding Attic/Roof Ventilation? (http://www.houserepairtalk.com/f34/adding-attic-roof-ventilation-3193/)

1parkpointer 12-07-2007 05:08 AM

Adding Attic/Roof Ventilation?
 
Our house is a two-story log, with a gambrel style roof. The second floor roof walls are actually trusses, which give flat 2nd floor ceilings and vertical walls with no knee wall; and the second floor end walls are conventional 2x6 construction.
The 2nd floor roof wall has a soffit vent at its base, which runs the entire length on each side of the house. Proper Vent is attached in between each truss and starts just above the soffit then runs vertically up the roof to the (gambrel) pitch change and then continues on between the top roof trusses for another 5 to 6 feet. The roof has a ridge vent along its entire length.
We live in Central New Hampshire, so we experience cold and snowy winter seasons.
We moved into the house in the late fall and were not aware of an roof ice dam problem. The first winter proved that the second story bedrooms which are on the ends of the house were really colder. The following spring we had a heating contractor install additional insulated heating ducts to the second floor bedrooms that travel up from the basement into the attic and then to the rooms exiting in the ceilings of the rooms. The additional heat worked, but the increase in heated air collecting in the attic has proved hard to get rid of. We've added insulation to the second floor ceiling from R-19 to R-38, but the attic is still not as cool inside as the outside air temp during the winter months. In winter, the heating ducts and any heated air from the second floor that find its way into the attic, warms it and the snow melts. Usually the roof vent is covered with crusty snow from the heat that escapes, but more often, it is covered with snow and doesn't seem to be venting at all. Elsewhere on the roof, the melting snow (water) collects along the pitch change of the roof (where it is cooler), and a portion refreezes, some drips over the edge and refreezes, basically creating a dam effect along the top edge and then along the most vertical part of the gambrel sections in various layers of freezing and refreezing. Additional problems occur at (3) roof windows on the more vertical section of the roof. Each roof window also collects a portion of the dripping snow melt on the top edge flashing and then the water refreezes onto the roof window. After and during each snow storm the melting continues. I have to put up a ladder onto the roof wall portions, and gently break off the ice.
My problem is, basically after each storm, the ridge vent gets covered up with snow and stops functioning until enough snow melts to expose the shingled style ridge vent.
Can I add gable end vents to help ventilate the attic/roof and lower the inside temp? I need to stop the melting, ice dams, damage to the roof shingles, and roof windows. Someone please help!

inspectorD 12-07-2007 05:41 AM

Wonderful explination...
 
Heating the great outdoors are you....yup, this creates a problem.
The areas where you get the refreeze are the areas where the insulation coverage is at it's least.
The basic idea is to let the roof be a constant temperature. The areas which cause problems have leaks . This is where you need to start. No amount of ventilation is going to help this issue, especially in the area you live in. My cousin lives near Dartmouth College, I know how cold it gets up there when we go for a dogsled ride.:D
The gable vents may actually cause more issues due to the cross ventilation you try to introduce. The venting you have now works like a chimney, cold air drawing up the roof traveling to the warmer area at the top. If you blow a breeze across this...you cancel out what is working.
Maybe you can seal the leaking joints better at the gambrel transition. This is a typical area we find issues with our Thermal Imaging camera. As for the skylight roof windows, there is no cure except removal, or lowering the temperature in the upstairs...bringing you back to where you started. Unfortunately This is the reality of roof windows, they loose large amounts of heat, you can always see this from the condensation on the inside...and the water staining which most folks think are leaks in the window.
To summarize, the design of the roof is the issue. The break in the roof design allows for an area which leaks the heated air into the attic space. I do not like to point fingers ...but the insulation company probably does not understand this issue...and some insulation is actually missing at the top hinge part of this design. The insulation touches at the bottom, where you see it , but not in that triangle hinge area above.
I hope this makes some sense, please ask away with anything you need clarification on.:D

ToolGuy 12-07-2007 05:57 AM

I think gable end vents are defianately worth doing. However, that doesn't help for heat that collects above them. This isn't my specialty so I'm just thinking off the top of my head. Maybe some sort of vent that stands above the ridge vent? Also, holes ~2" dia. drilled through the joists up near the ridge beam will help facilitate movement of the warm air between the joists. Just some thoughts, maybe someone can add to this or, better yet, has the perfect solution. It's early yet. You'll get a lot of replies to this.

ToolGuy 12-07-2007 06:03 AM

You might even get a reply as I'm typing mine.. :p

glennjanie 12-07-2007 12:08 PM

Welcome Gerry:
We are glad to have you. There is one other alternative to cure the ice dams. It is a heat tape which can be bought in lengths up to 1,000 feet, 240v and heats only where there is a freezing temperature; the remainder of the heat tape stays off until it is needed.
Folks in your area use the heat tape in a zig-zag pattern along the cold edge and it works real well. I don't know who else carries the heat tape but United Refrigeration does.
Glenn


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