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Jim F 05-04-2010 09:59 PM

Another roof ventilation question
I have gone through some of the recent posts and have enough information to raise more questions in my head so here goes my specific situation.

Historically the previous roof on my house failed prematurely due to overheating from inadaquate ventilation. There was also mold on the inner decking.

Three different estimators suggested three different solutions for ventilation. The roofer I hired cut a wider ridge vent but did not go end to end so the attic now has that and gable venting on both ends. I realize that is not the best combination and that ideally the ridge vent should be paired with balanced soffit ventillation. The problem is that the soffit vents were previously boarded up and insulation was blown down into that space. This space goes down about 2 feet and the other side of that is a vaulted section of the second floor living space. The solution would be to get that blown in insulation out of there and the soffits opened back up with foam baffles to seperate the insulated ceiling side from the soffit vent side. That is a long-term goal.

In the meantime, I would like to prevent my new roof from cooking over the summer months. There is currently a power gable vent fan with a failed thermostat and the fan itself doesn't sound too good. It can be replaced easily enough with a 70 dollar replacement fan from Home Depot.

I guess my questions are:

1. How hot is too hot for the attic space before it starts cooking my new roof? Which I can find out by placing a thermometer in the attic.

2. Is it worth my while to replace the gable fan? Which would depend on the answer to the first question.

waterman1971 05-04-2010 10:12 PM

There is a product you can install that goes under the first course of shingles. it is like a 7" wide drip edge with built in air channels. You cut a vent near the bottom of the roof to allow air flow. I'm sure someone has a link the will post shortly.

AaronB 05-04-2010 10:24 PM

I don't like the idea of using smart vent too close to the roof edge in ice dam areas.

Slyfox 05-05-2010 06:07 AM

The goal of proper ventilation is for the attic space temps to be equal to the exterior temps. If the interior temp is warmer or colder than the exterior problems occur.

You said correcting your intake & unobstructed air flow is a long term goal,
I would replace the power fan now, it will not correct the venting issues but will help.

Installing eave or field "in the roof several feet up from the eave" are both options, but, you still have to deal with moving your current insulation back to install baffles to allow free air flow from the point of intake to the exhaust,
so if you have to spend money doing that part anyhow than you might as well hold off and do the eave intake being that it is the safest and most productive of the intake methods.

Jim F 05-06-2010 10:35 PM

I've been meaning to follow this up with pics just to give a better perspective of my unique situation but too busy as usual. Took time away from my ongoing bathroom project to take care of this little side project and am glad to get it out of the way.

Bought the gable vent fan at HD for $79.00 today and installed it (same day imagine that). There is always an unexpected snag and this time it was trying to pry out the supersized romex staples in very cramped quarters. Still only took 1.5 hrs and finished just in time to grab a quick shower and get to work for my evening shift.

As I said this is a temp fix just to prevent my new roof from cooking. Truthfully, I don't really know how the newer enlarged ridge vent will perform yet. The manufacturer recommends setting the thermostat at 105 degrees f, I have mine set at 100. I will have to wait to see how often it kicks on over the summer. Greatful that it is indeed temporary since I just learned in another post that it can cost 2-3 dollars a day to run this sort of fan.

Jim F 05-13-2010 10:33 AM

Pictures as promised
5 Attachment(s)
Here is what I am talking about in this thread. as you can see from the inside room picture the ceiling vaults somewhat and in between this vault and the roof is a space completely blown in with insulation. I believe the particle board sections nailed to the eaves cover vent holes but not sure about that. Somebody must have thought it was a good idea to button up the attic to save on heating costs. There are no soffits, only eaves. As you can also see there have been mold problems resulting form the lack of ventilation. I also have unfaced attic batts to reinforce the blown in which has settled quite a bit over the years. I hope this helps with the ice dams in the winter.

I am assuming that once I reestablish proper eave ventillation it would be appropriate to block the gable vents on each end and turn off the fan so as not to "short circuit the proper air exchange between the eve vents and the ridge vent. Is that a reasonable assumption? Also, is there a benefit to building actual soffits to cover the eaves?

All comments are welcome.

MJW 05-13-2010 12:07 PM

These types of homes cannot be insulated and ventilated like the newer houses. There is no room between the wall and roof trusses to insulate or ventilate from the soffits. Without alot of major reconstruction, you should close the gable vents, keep the ridge vent and install box vents lower on the roof allowing intake for the ventilation. This can all be done during or after blowing in new insulation. Once this is done, you will need a dehumidifier at least, and better yet, an air exchanger. This will all cost more money, but it will be fixed and possibly save you a few bucks over the years on heating/AC.

IMO, this "savings" attitude with these older homes will only pay off if "Energy costs neccessarily skyrocket" to quote our late Pres.

Also, I really hope they resheathed that roof before new shingles were put on. This also contributes to holding in more moisture.

Jim F 05-13-2010 05:18 PM

I did have them resheath it with CDX don't remember if it was 1/2 or 5/8 inch now. It had old barn board sheathing and I really wanted something more solid to nail the new shingles onto. I am trying to stay away from box vents if possible plus that doesn't sovle the problem with thermal wicking along the edges and ice dams in the winter. I really think there is space enough between the ceiling and roof decking to remove the blown in, put some type of insulation over the ceiling and leave a venting space above that in the rafter bays. But I will have to do some tearing out and vacuuming to really get a good look.

seeyou 05-13-2010 05:45 PM


Originally Posted by Jim F (Post 441563)
I am trying to stay away from box vents if possible plus that doesn't sovle the problem with thermal wicking along the edges and ice dams in the winter.

If you install the box vents low enough, it should help eliminate ice dams.

I'm not real crazy about this product (I'm sure it works, but I'm afraid it could leak - just a gut feeling), but it could be an option:

This vent would likely work in your case as well:

Oh yeah, I'm the one that posted that $2-$3/day power vent operating cost. I got that from a reliable source, but I'm pretty sure that's a very worst case scenario.

Jim F 05-13-2010 07:51 PM

That Raft-a-vent looks promising after I get the insulation cleaned out of that space. Hopfully, it will not run too many days.

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