Addition Question: venting roof/crawlspace

supton

Disclaimer: I am not a carpenter. I'm just trying to get rid of an ice damming issue.

My house was built in the 40's as roughly an 18'x18' structure, 2 story, no attic. Roof is like a 12 in 12 pitch? [looks 45 degrees to me.] Shortly after that, a 12'x18' single story (with a short crawl space above) addition was added. The roof for this part is more shallow, like 30 degrees. Anyhow, I have issues with ice damming on this "new" roof, due to ventilation: this roof has a single 4"x6" vent.

Now, at the end of the original rafters there is fascia, untouched after all these years. The previous house owner redid most of the interior, including insulation and sheetrock; he did put the pink foam tray under the roofing and a ridge vent. On the original portion of the house, that is. The addition has the old crawlspace, untouched basically. The crawlspace is insulated from the rest of the house; it cannot vent into the venting on the steeper roof; as a result, this roof isn't vented either (no air intake).

My question is: can I drill holes into this fascia, so as to allow venting to occur? This isn't some form of fire blocking? I have to go get a photo of the crawlspace, but below are exterior photos.

Photos:
Back of house, faces east:


Side of house, with leak, faces south:



Front of house, faces west:



Last side of house:

supton

Crawlspace, as attached. You can see the original siding, which was white; looks like they nailed a support across that to support the new rafters. If you look above that, you can see the blocking (old fascia?).

on edit: the hole in the bottom right is the crawl space entry. The backside of the original siding is all insulated (you can see a bit of insulation in the entry); not shown is the batting that I'm laying on to take this photo.

Attached Thumbnails

 

supton

Today I removed that blocking. I think it was installed either as fireblocking, or to just prevent airflow. In some places it was held in with just a nail, so I don't think it was installed for structural reasons.

Jack of most

If you want to just ventilate the addition attic space. Add a couple roof turbines or soffit vents. I don't think this is causing your problem. Pitch is. Also is it damming at the point where the 2 roofs join or at the bottom of the addition roof?

supton

It was damming in the middle of that shallow pitched roof.

It seems to be doing better this year, after I removed the blocking. There was a storm or two that I could not get up there until a day or so later; when I pulled the snow off, it was still fluffy on the bottom. I still pull the snow off, though, after each and every snow storm.

Jack of most

I'm not positive, but by removing the blocking you may have opened up enough space to allow a little warmer air into that attic space keeping it from damming.(melting just enough) Or, just the opposite, cooling off that space reducing the temp difference in that attic as to not melt snow/frost to turn into ice when temp drops.(the reason the snow was still soft this year) Sun can cause this problem also. Warming the roof during the day and freezing at night.

The way it's supposed to work is; the attic spaces of a house are to be the same temp. as the outside temp. They should also have at least 150 sq. inches of ventilation.(Depending on your local building codes)

Insulate your living space from the attic with the recommended R value for your area. It pays to insulate. I think 25 - 30 is good.

This should help but I still feel that pitch is the problem. The reason for steep roofs in northern climates. I used to have to shovel low pitched roofs on the farm as a kid.

supton

Well, there is a 4"x6" gable vent in the crawlspace, so there is some air intake, just not good enough. I might look at making it bigger, and adding a second one to the other wall; but as you said, it's shallow. I suspect that, as long as i keep the snow off it, I should be all set. I simply cannot get any airflow from the eves without ripping out the ceilings, and I'd prefer not to do that right now.