Roof Ventilation and Insulation - Midwest - Gable and Ridge vents only, no soffit vents

Question

I have a 1920's home in Ohio, and have NO soffit venting in the house. There are 2 gable vents, with one small temp-controlled fan (set to turn on ~95 F or higher). There is also a ridge vent.

The attic is unfinished, with some insulation on the attic floor and some sub flooring installed, but it's not perfect. I can see light from outside in a few spaces, but they aren't "supposed" to be there =).

There is a lot of discussion on the net of soffit + gable + ridge, or gable only, but nothing about gable + ridge.

First off, with 2 gables and a ridge vent and this small fan, is this sufficient for airflow in the space? I do not see any mold or moisture problems, but it gets incredibly hot and is very tough to cool my 2nd floor (attic is on 3rd floor). In the summer, with AC on, I have a ~6-10 degree F differential between 1st and 2nd floor. In the winter, heating the 2nd floor isn't so bad.

Because of this, I bought some thin R11 radiant insulation, it's basically aluminium foil wrapped on both sides of some really thin insulation. My plan was to attach this stuff directly to my rafters, in order to keep the space cooler in the summer. This would also leave a ~4" gap between the roof deck and the insulation, so if there IS any air flow there now, hopefully it would remain.

Is this going to cause any problems with my gables + ridge as it exists already? Even without this insulation, do I have any existing problems I may want to try and take care of?

I do not plan to put soffit vents in and don't want to get that answer back =).

Thanks!

Answer 1

Here is your problem Gable Vents and Ridge Vents do not go together period.

Your Gable vents are acting as Inlet Air Ducts for your Ridge Vents.

So your air flow comes in through each gable and flows immediately to the closest air outlet the ridge vents NEAREST the gables.

So the Air flow in the center of the Attic is basically NON-EXISTENT . And the Actual cooling from Gable to ridge vent is very limited.

Either one or the other but not both.

So here are some options:

Option 1: Close your ridge vents.

Option 2: Close your Gables and Install Soffits (I know you don't want to hear that - keep reading though) - these would need to be properly installed - a soffit guide is best - so your insulation and critters do not block them.

Option 2 will allow you to get rid of your Electric Fan as well, saving you money on the electricity of the fan. As for how much difference Ridge Vents vs. Gable Vents I can not tell you if there is a savings or not a savings, getting that info is like getting an act of congress for something that matters.

With Option 2 you have direct line air flow from outside upwards to the roof all working by convection - $aving you $$ .

Now if you do this a vent here and there might be expensive and time consuming aside from calculating how many and what size .. Instead of doing that - they make Continuous Aluminum soffit that is pre-drilled/cut with holes. You basically lay it in like aluminum siding and it is very easy to install. When I was living in FL my house there had it. This type of soffit is inexpensive, it works great and as I said easy to install. I had to replace a couple 3 foot x 6" sheets; if my memory serves me right - I think it had cost me somewhere around $8.00 - I think it was so much cheaper than what I thought I had bought a couple extra with out skipping a beat. Probably a bit more expensive than that now - I went to a local metal soffit fabricator shop and purchased it.

Answer 2

It sounds like you bought what's known as "double bubble". It's nearly worthless and I'm sorry to say that you were the victim of a scam. Throw this stuff out. In a cold climate like central Ohio, it will only cause trouble. In an attic that's improperly vented and not well air-sealed, moisture will condense on its smooth and impermeable surface as if it were a bathroom mirror, causing liquid water to pool at the eaves.

There are many ways to properly ventilate, air-seal, and insulate an attic properly, but it's a complicated subject and hard to go over here. But the general gist is as follows:

• If you plan to finish the attic, then you want to insulate at the roofline: either spray-foam from the inside, or install rigid foam or mineral wool on the outside (usually when you re-roof).

• If you don't plan to finish the attic, then you want to add soffit vents to slightly exceed the airflow of the ridge and gable vents, add rafter channels to keep insulation from clogging the soffit vents, air-seal the attic floor/ceiling below it, and pile on cellulose insulation until there's a fluffy insulation blanket about 16" thick on the attic floor.

There are many nuances ("what if I don't have the roof overhang necessary to add soffit vents?" "What if I have ducts or mechanical equipment in the attic?" "What if I'm afraid of spray foam or worry about it being toxic?" "What if I just replaced my roof last year?") but those are the basics.

Answer 3

Whoever built your house screwed up -- here's how to fix it

Instead of putting a piddling R-11 of dubious quality insulation in, and under the roof deck too -- I would recommend cathedralizing the roof system with insulation over the structural deck after laying a fully adhered or liquid applied air barrier down on the structural deck, to R-50 (yes, this will take a few layers o' foamboard or rockwool -- stagger the joints in both directions!). This high R-value lets you get away with not having any attic venting to the outside whatsoever (as it is now inside the insulation-box), and lets you pull that insulation out of the bottom of the attic, too. However, this does mean you'll need to air-condition the attic in order to deal with the moisture problem up there -- you'd need massive amounts of vent air to deal with the moisture problems, and it's not a very good way to dehumidify a house, so mechanical dehumidification is generally a better idea.

Otherwise, you are likely gambling with the ice dam queen come winter without soffit venting, as the whole idea behind a vented attic (in the winter, at least -- in the summer, the idea is to pull in not-so-hot outside air to replace even hotter attic air and thus cool the roof deck down) is to pull in gobs of cold outside air under the roof deck to keep the roof deck below freezing and prevent ice dam formation. (Columbus doesn't quite get average snow loads that make it "ice dam territory", but you're getting fairly close to it).

For more info on how to vent (or not vent) roofs, check out BSI-046: Dam Ice Dam.

Answer 4

I am not a roofer but I also have your situation. Ridgevent and front and rear gable vents. This is actually a doable situation as I understand it if the gable vent is opened further to reach the floor of the attic. That way the air will flow across the floor allowing the uptake into the ridge vent. If the gable vent is higher than the floor then it is not doable. Easy enough to make the gable opening larger or shift it lower. You need to look into this and you need to do your own research.