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Venting options for 1910 brick home with renovations

I recently purchased a 1910 Victorian in Montana. The house is brick on a granite block foundation with a full semi-finished basement with garage under the house. The walls are mostly lathe and plaster on the first floor, which is 90% original.

The house is heated with gas-fired water radiators and provides excellent heat. The house sits with full southern exposure on one side and great east and west exposure in the front and back.

Recently we've had a week of very low temperatures (-20s) with it only getting to 0 or the teens during the day (don't worry, I'm an East Coaster and this weather is great. Yesterday it was 16 and I was doing yard work in a t-shirt. Back east I'd freeze to near-death at 40 degres!)

Coming with that I ended up with ice dams in one of the new additions to the home. On the second floor what was formerly the attic has been expanded with new gable roof and drywall on the inside. There is still the "old" attic area as well as the two new gable attic areas that increased the living space. The entire attic is very well insulated. All the new additional areas have been corebonded with insulation at the lover levels. There is 12" to 16" of blown in insulation on the attic floor.

Yesterday water was leaking down to the living space on the second floor. I went into the attic and noticed the entire inside of the roof structure was wet and dripping. I did my research and discovered it was due to ice dams. A contractor came over and went through the attic with me and confirmed the attic is well insulated. Too well insulated it seems as it is air tight and there is no air flow.

There is a ridgeline vent that is in good condition and is not blocked.

However there are no soffit vents and they likely could not be installed. The areas where they would need to be installed are blocked by the corebond. It would require a major reworking to get them installed in there.

Short of soffit vents are there other options? One of the new gable additions faces East. The second one (and the one with the major leak problem) faces South.

The attic is very warm - liveable warm. It's not flowing from below due to the great insulation on the attic floor and the fact that the builders added 5/8" thick drywall on the 2d floor ceilings. All seams and joints from the 2d floor to the attic are either covered in insulation or have been sealed with that yellow spray stuff. Heat transfer from the 2d floor to the attic is minimal at best.

The heat is coming from the full southern exposure. 70% of the roof area gets full sun. 30% is on the back half and is the older part of the house that does not have the new addition. No ice dam problems there that I'm aware of.

So long post and short question:

Will gable vents help the situation at all? The contractor who came by is looking into some options for me. The two additions that were built have cedar shakes on the sides of them. The roof is newish and asphalt.

We are thinking that a gable vent on the east side and then one on the southern side would help with air flow. Right now there is none. I ensured the ridge line vent was free and clear along its entire length but there is no fresh air coming in from anywhere.


ETA: the roof pitch is very steep. There are overhangs extending past the heated living areas that are about 1' to 1.5"

I tried to attach a photo but am getting an error that it isn't a valid image file, even though it is.

Re: Venting options for 1910 brick home with renovations

Yes, that will improve air flow in the attic. Too bad about the soffit. Also, look into dormers vents, which can be installed on the lower portions of the roof.

Re: Venting options for 1910 brick home with renovations

A Ridge vent needs soffit vents to function correctly. Adding a gable vent may be enough, but the best answer is probably going to be creating soffit ventilation, even if that means re-doing some other work which is already done. Alternately you can move south where we don't have to worry about ice dams, only about keeping enough ice for drinks in the summertime. :cool:


Re: Venting options for 1910 brick home with renovations

Thanks for the replies. Gives me some things to think about.

Move south? I grew up in the Mountains of Georgia, I've lived in the Shenandoah valley of Virginia, I lived in Washington DC in a lovely old row house and I recently lived on Coronado (San Diego) in California.

Montana beats all of them hands down. A few ice dams here and there are definitely worth it!

Re: Venting options for 1910 brick home with renovations

I'm not sure your are going to "vent" your way out of this. Are your attic rooms they type with knee walls and a slanted wall formed from the roof rafters? If so,does the foam insulation extend all the way up the slanted walls? If so, was a plastic form to make a gap between the foam and the underside of the roof sheathing installed before the foam was applied so that air can flow from the knee wall area to the attic?

If all the answers are yes, you are not going to "vent" your way out of this one. You will have two options, rip out all the sheet rock and remove the foam insulation, then re-insulate properly, or put heating elements on the roof sections where the ice dams are forming to melt the ice.

One other thing that mightwork would be to recover the roof in question with a metal roof, but the metal roof will need two layers of furring strips, one vertical, one horizontal, under it so that air can flow freely under the metal. You may also have to rip out the sheet rock on the slanted wall and add 1/2" foam boards (4x8 sheets) and then re-sheetrock and finish. The sheet rock will break the conduction between the sheet rock and the rafters which act like s short circuit for heat to the roof.

A little test you can do, after a snowfall, or frost forming on the roof, check to see where the snow melts first. If you see vertical bands forming in the slanted wall section of the roof where the snow melts first, this is where the water for your ice dams is coming from.

Re: Venting options for 1910 brick home with renovations

12 or 14 inches of insulation in a climate where temps commonly get way below zero is WAY under insulated! You need much more insulation and more ventilation to bring that attic temp down close to the exterior temps. If the attic is colder, your daytime melting will be lessened. Snow on the roof is actually a good sign!

If you have boxed gutters, consider getting rid of them and using old fashioned hung gutters that don't contibute to the damn at the bottom of the roof. They don't build those Swiss Chalets to look cute and idylic, they build them that way because they are perfectly suited for snowy Alpine climates with cold nights and sunny days, the perfect combination for ice damns.

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