Attic Vent... do they really work?

[Overhaulin63]

I've read several articles about attic vents and some say they are great and some say they are a waste of time and money.

I live in Ohio and while the heat problem here is not year-round like other states the attic seems to get really hot.

I was once on another roof that looked to be in nice condition, but when I walked on it, it was like walking on a waterbed because the plywood was cooked and I just don't want to have that happen to mine.

The garage has a light grey shingles with roof and soffit vents, not clogged, but still gets pretty hot. Sorry I don't have an actual temp, but I'll try to get one.

Either way, would an attic vent help prolong the life of the sheathing/structure for my application or would it be a waste of time and money?

Thanks in advance for any help!

 

[jam022316]

I think they do work. My roof has no vents except the gable and soffit and it has that waterbed issue. I'm getting ready in two weeks to replace the roof and I assume by the way it feels I'll be replacing the decking as well.

 

[NUTTSGT]

Part of the waterbed feeling may be coming from sheathing that is too thin. I believe there must have been a trend to use 3/8" plywood as roof decking a few decades ago.

If you're replacing the roof, check out the sheathing while the shingles are off. There is no better time to replace it than when the present.

 

[yeldogt]

Most attic venting does not work -- in a dry climate venting creates fewer problems.

There are endless studies showing why -- also measuring roof temps with closed systems.

The biggest problem with open attics -- they create pathways for conditioned air to escape. Especially with any powered vent.

Also -- low structures ... single floor dwelling in wet grass climates can actually suffer from damp attic problems. In the AM with dew on the grass -- moisture can be driven along the siding as the sun heats the building .. into the attic through the vents. There was a development down near the coast where many of the OSB roof sheathing was actually wet.

 

[strutaeng]

It seems logical that it would work. I mean the picture that you see with cool, fresh air entering the soffit leaving at the ridge as heated air looks good.

I was shocked when a coworker went to some building envelope seminar in Wisconsin or somewhere up there and told the "new" thing was a sealed attic. How was this possible, if ALL of the books that I had read had attic venting. Technically, it is called non-vented, and this was like 10 years ago!

Historically, venting was a "fix" for condensation in conditioned spaces and it has worked; buildings were just really drafty/leaky. However, with newer building systems that are more airtight and with some good detailing, you can build a non-vented attic.

I'm a big proponent for non-vented, provided you understand the concept of vapor transmission, dew point, etc. You eliminate the source of dust, noise and bugs into the attic as a benefit. Non-vented attics are always going to be cleaner. Non-vented IS allowed by the code.

So to answer your question. Does venting work?

If are asking about condensation control, then yes, venting works very well.

If you are asking about keeping the attic cool, then not really. The tests have found that it is somewhere around 3F difference on a vented vs non-vented. So it is like a 125F vs 128F comparison. A credible GJ member here stated that shingle color alone has more impact on attic temperature!

Greenbuilderadvisor website is an excellent source on the subject. I hope this helps.

 

[yeldogt]

When you look at the diagrams for a vented roof structure -- they have these pretty pictures and air flow arrows. Well -- air is not on rails that can be controlled .. it's also not water. People have a visual of what they think air will do -- but it does not follow what people think is going to happen.

Just add one variable -- wind. What do you think happens when air moves across a roof -- does the air say .. OH wait ... I can't go in that ridge vent -- it's only for exhausting air. No -- it goes in. What really happens with vented structures -- they pressurize and depressurize all day long. Mostly depressurize -- sucking air out of a house. Pulling crawl space air out of a dwelling -- often wet air from the ground.


Go into almost any builder development -- look at the bath fan. Often to save money they install it in the best place for the light. This is often in the middle of the room -- with the toilet further into the space ... often the outside wall because that's where the stack is. Since the only real space to pull air is from the door area -- the fan is really not exhausting odor from the toilet in a practical way. The fan should be far from the air source. That why the remote fans where you can have two intakes work the best -- one in the shower ... the other in the far corner close to the toilet.

The same with make up air in a kitchen (now being code in many places) -- people think that putting the intake in the floor behind/near the stove is going to make all the air going out of the building -- naturally flow into the building from the new intake. Now ..think about that. What really happens?-- you just draw cold air along the floor and pull from both the intake and the rest of the house.

 

[DC73]

If you're talking about any kind of powered vent, they typically use more electricity than they save by lowering the attic temperatures. Most building scientists won't recommend them.

One of the best options is a properly designed unvented attic assembly with insulation under the roof deck. That can be pricey and hard to implement on an existing structure but is certainly a possibility.

For a regular vented attic, having plenty of intake and exhaust vents is the key. There are calculators online that will help you determine the minimum ventilation your attic needs. Continuous soffit and ridge vents are very effective for some roof designs. Hip roofs are more problematic.

DC

 

[danski0224]

Nope.

 

[jbwilkins]

.... the fan is really not exhausting odor from the toilet in a practical way.......

Bath fans are there primarily to exhaust moisture, not odor.....While the toilet does generate some moisture (water sitting int eh bowl), the real culprit is the shower and the fans should be located closer to them....

 

[yeldogt]

Bath fans are there primarily to exhaust moisture, not odor.....While the toilet does generate some moisture (water sitting int eh bowl), the real culprit is the shower and the fans should be located closer to them....

You find this in 1/2 baths all the time -- so not water vapor. It also occurs with long baths where the tub is at the back wall ... some thing. The fan is set for the light ... not what it's designed to do.

 

[gungatim]

You find this in 1/2 baths all the time -- so not water vapor. It also occurs with long baths where the tub is at the back wall ... some thing. The fan is set for the light ... not what it's designed to do.

off topic but funny story: I put an exhaust fan in our half bath on the first floor when I built (it is in the center of the first floor). with the bath located between the kitchen and dining, with family rm on the other side I thought the noise of the fan would block any annoying "noises"...

the builder ran the vent straight to the back of the house, exiting the back wall just to the right of the patio door, which of course leads to the deck.

first summer we had a little party, a dozen people many on the deck, some inside. every so often i'd smell an uncomfortably nasty odor. no one mentioned it, but I could tell others smelled it...you guessed it, whenever someone went #2, the odor dumped straight over the deck where people were trying to relax....at least the house didn't smell.

moral is, think where that thing is going to exit!

 

[Overhaulin63]

Wow... great info and thanks everyone. I think I am going to stick with just the gable and ridge vents for now.

I love this site!

Thanks again!

 

[jkuro]

The biggest problem with open attics -- they create pathways for conditioned air to escape. Especially with any powered vent.

WHAT, this makes no sense. If the home was built correctly it wont have any pathways for air to escape!

 

[yeldogt]

The biggest problem with open attics -- they create pathways for conditioned air to escape. Especially with any powered vent.

WHAT, this makes no sense. If the home was built correctly it wont have any pathways for air to escape!

What's built correctly?

Every house leaks .... even spray foam houses leak (just less). The amount can be determined using a blower door.

Typical builder construction -- USB/batt/ 1/2 drywall .....leak..leak...leak. Add any recessed lights -- fan boxes .. more leaks from conditioned to un.

In many areas .. making a closed attic is the best

 

[LS6 Tommy]

Attic ventilation is not really about lowering the temperature. It's about reducing moisture.

Tommy