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Old 07-09-2012, 08:13 AM   #1
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Help with Ventilation


My house was built in 94 and recently here in VA we have been having extreme heat. Yesterday the temp got to 102. My house has dual zone air conditioning/heating system (one for upstairs, one for downstairs) and both systems were completely replaced last summer. However our upstairs will just not cool down! The temp upstairs would not fall below 85 yesterday so it is miserable to go upstairs . While the downstairs is nice and cool. Two friends of mine that are in construction told me that the reason for this was because my home does not have ridge vents on the roof. I went up into the attic to check it out and see that all we have is gable vents WITHOUT fans. So I am curious is ridge vents would seriously make a huge difference in the temp upstairs? Below is a pic of my home.

Another issue that we have had ever since living in the home is the unbearable temp difference in the room above the garage. We had our 3 year olds bedroom there but had to change it because in the summer the room is literally 10 degrees hotter than the rest of the upstairs. So for instance when it was 85 yesterday in my upstairs this room was around 92-95 degrees. Now I know rooms above garages are going to be warmer, but my friends also said that this room is so much hotter/colder because it has a "seperate" roof from the rest of the house. If you look at this picture on the left side of the "garage roof" has a gable vent but I thought that in order for gable vents to even work properly they needed one on each end of the roof. While my main roof has a gable vent on each side this roof only has the one is that right? If someone can tell me that putting a ridge vent on my main roof and the garage roof will make a big difference I am all for it I just want to make sure before I spend the money. Thanks for any help and I am going to be posting this on the roofing and HVAC forums just in case.


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Old 07-09-2012, 08:45 AM   #2
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Help with Ventilation


Ridge vents will vent the whole roof not just on the ends.
Once the ridge vent is installed the gable vents need to be covered up from the inside.
Both style vents are useless unless you also have vented soffits. They draw the air in the soffits and the hot moist air exits out the ridge vent.
If there are no soffit vents or there covered over with insulation this also needs to be addressed.

How much insulation is in the attic?
http://www.energystar.gov/index.cfm?...sulation_table

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Old 07-09-2012, 08:50 AM   #3
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We have soffit vents around the whole roof and there is tons of insulation in the attic. I went up there and made sure I could see the light coming in from the soffit vents into the attic. While I did see most of the light I would say maybe 10% of the soffit vents were either blocked by dirt or Im guessing covered over with insulation. Also its a pull down attic with a ladder. Ive heard that you should insulate the door with a attic tent or something similar. But I didnt know if anyone knew if this would make a huge difference in the temp upstairs.
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Old 07-09-2012, 08:55 AM   #4
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It will help some but the ridge vent would make the biggest differance.
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Old 07-09-2012, 09:45 AM   #5
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Most "continuous" soffit vents are the perferated or lanced type. They aren't worth the pennies you'd get for them at the recycling yard! A much more effective soffit vent method is some type of screened louver. It doesn't have to have louvers, that's just more readily available - here anyway. The obvious purpose of the screening is to keep out the bugs! You can make the call as to the "screen hole" size. This "flaw" with those type of "continuous" vented soffits is always overlooked by the average homeowner/prospective buyer. It looks great and makes sense on paper - but is simply uneffective in practice. Most contractor couldn't care less how it "feels' inside after they have installed the product and are long gone!

Make sure your even on the right page with the correct "amount" of venting.

From the code books (I own most of them), they apply the 1/300 rule. That's 1~SF for every 300~SF of attic area.

Half of that for intake, the other half for outtake. It's good practice to have some 25~% more intake than outtake also.

"In the field", this is the way to calculate it,

INTAKE:

NFA~in^2 = ( Attic area~ft^2 / 4 ) + 25%


attic area is,


wall-to-wall width~ft of the building perpendicular to the ridge


x


wall-to-wall length~ft of the building parallel to the ridge.


OUTTAKE:



NFA~in^2 = ( Attic area~ft^2 / 4 )

You can split up the area and calculate as you see fit.


Are you sure those gable vents are really vents and not just "dummy vents" for the visual balance. The Ridge Vent is great, but issues typically lie in the installation and specific type. I usually do the roof louver vents. They are fine too.

The dormers (when they are actual living space) should be treated as "mini attics" too. An exhaust vent and soffit vent for them as well.

Radiant barrier might be a solution too.

I just redid my soffits and will be doing the roof louvers, when the roof temp is about 90~deg instead of 150~deg.

Last edited by kevsprojects; 07-09-2012 at 05:23 PM.
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Old 07-09-2012, 10:04 AM   #6
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Thanks for the responses! I am not sure how to tell if the gable vents are dummy vents because I am not really familar with the process of roof vents except for what I found out recently after researching through the internet. I went up into the attic and the vents are open and you can easily see outside. They also have a screen Im guessing to keep bugs out. These are the gable vents I am speaking about. Now the strange thing that I noticed going around my neighborhood is that NOBODY in my neighborhood has ridge vents at all! My neighbor directly next door doesnt even have soffit vents on their upstairs roof! I see a few circular soffit vents on their lower roof but thats it. (Mind you they have the exact same setup as my home except they have a fireplace as do most homes in the nieghborhood, I am one of the few that does not have a fireplace) I have been told contractors were probably trying to save money . Its just confusing because upon searching the net I see conflicting answers about wether or not to get fans put on my gable vents or get a ridge vent installed. You guys think that this is a roof issue (the heat) and not a HVAC issue?
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Old 07-09-2012, 11:17 AM   #7
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You need to have the home looked at by a qualified contractor that understands roofing, ventilation, and energy efficiency in total.

I can guarantee several things:
  • Too much air leakage
  • Not enough insulation
  • Massive connectivity with the living space
  • Poor venting dynamics
  • Improper kneewall insulation in the garage bonus room
All of these things can be fixed with relatively surgical measures and proper technique.


That home looks like the Stafford/Fredericksburg area.
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Old 07-09-2012, 11:57 AM   #8
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WoW,

I am having new shingles put on my roof. I found a GC that is doing roofing, and other things now that the building market has slowed. The trouble I have found is that all the "experts" have conflicting expert opinions. I have a post on this forum from when I started thinking about the roof that ranges from close every hole and heavily insulate to vent everything. My GC is installing ridge vents but said I don't need to close off the gable vents.

kevsprojects, a couple of posts up, is saying that the continuous soffit vents (which I have, from a previous siding project, and I made sure they drilled holes in the wooden soffits before they installed the vinyl ones) are flawed, but not why.

I am not a professional builder but I consider myself competent enough to understand these processes. Unfortunately, I can't find any experts that will agree on a right way.
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Old 07-09-2012, 12:09 PM   #9
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I am not sure what he is referring to from the ineffectiveness standpoint.

Perhaps as it pertains to the venting underneath the vinyl soffit at the framing side???

The vinyl soffits that are out there provide enough ventilation in most cases but only if combined with a properly uncovered overhang and ridge vent.

Soffit and Ridge vent venting is the most effective. Closing off the gables is not a must but the system should be balanced with the slight nod going to the intake venting.

If you have a vented attic, stay with the ventilated design if it work right. Most sealed attics are for scenarios where there is not enough depth to get a proper insulation layer up there.
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Old 07-09-2012, 02:26 PM   #10
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Sorry about that, I was a bit pressed for time on that initial post. The gable vents really don't need to be closed off. They'll just "share" the balance of the exhaust. By the numbers, you could subtract out the gable vent area from the calculated exhaust NFA for the ridge vent, the ridge vent would be shorter than had the gable vents not been there.

The flaw I was speaking of is concerning the actual perforations in the vinyl/metal panels. It's WAY to restrictive. A little dirt and some spider webs and there practically closed up. These are an easy way to fool the buyer and often the "inspector". Legally you can "say" the soffit is vented - but in reality, "it ain't do'in much"!

Power exhaust venting (whether in the gables or on the roof) does indeed work! But there's more to that process than just goin to lowes and buying an exhaust fan. The temperature in a typical attic can easily reach 130~deg F (and higher) in peak summer. This miracle fan has to be able to withstand these brutal temperatures and still operate within it's own specs and not melt down. There is a German company that makes a fan specifically for this purpose. They are apparently well known to the farming communities for their deployment in chicken houses and the like. I think they cost around $300'ish or so. But even at that, I'd be afraid to trust my own home to a $300 chicken fan. If the chicken house torches - we all eat fried chicken for a while . If your house torches well, different story.

Proper ventilation and HVAC are a part of the same equation. If your home is properly ventilated, you'll realize the benefit in less energy required to heat & cool it. If you have a crawlspace that's vented to the outside world - button it up as soon as you can and make sure have a minimum 6~mil vapor barrier (I would always double that) on especially a dirt floor and even a concrete floor. By doing that, you will prevent gallons (yes measurable in gallons) of moisture from entering the living spaces above where that moisture not only causes the usual decay & mold problems, but has to be "handled" by the HVAC system. More work to heat it, cool it, extract it etc. The crawlspace venting scheme is outdated, old technology, old outdated theory. I have tons of pdf's on this and other matters. Ive' seen the principle work in my own house too. a few years ago, my HVAC ductwork in the then vented crawlspace use to "rain" all day long. If I could of had lightning effects with the sound of thunder I could have made a documentary on "tropical climatology". After the vapor barrier on the dirt floor and the stem walls, as well as closing off the original vents and a few more holes to boot like left overs from a deck attached to the band joist, and some perfectly drilled holes about 2~in in diameter - for what I'll never know, now all is quiet in the jungle!

I'm told some builders still build with vented crawlspaces because they just won't "get up to date" with current technology.

My soffits were also completely closed up. Just gable vents for exhaust. And where was the intake supposed to be coming from!

I'm convinced my house was built as a high school project, or maybe a couple of guys after a few cases of Bud Light!

Anyway, you could keep the soffits you have and put in your own additional screened louvers, or other styles that may suit.

See the pic for the one I used.
Attached Images
 

Last edited by kevsprojects; 07-09-2012 at 02:31 PM.
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Old 07-11-2012, 09:52 AM   #11
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"The crawlspace venting scheme is outdated, old technology, old outdated theory. I have tons of pdf's on this and other matters."

Can you provide links to some?

After I suit-up and rake the blown fiberglass insulation out of the overhangs where I can't see light, and fluff-up the rest, I need to head into the crawlspace. Crawlspace has temp controlled vents. Insulated HVAC lines are sweating some too.


Oh the joys of home-ownership...
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Old 07-11-2012, 02:00 PM   #12
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Here's a few to digest. When you DO close up the vents and vapor barrier the floor, don't insulate the floor joist. There should ideally not be a vast temperature difference between the crawlspace below and the living space above.

Well, problem - I see that I can't upload a file > 100Kb. I'll keep working at and see if I can get more uploaded, or some links.

Ok, here's some links,http://www.advancedenergy.org/buildi...2008-07-15.pdf


http://www.advancedenergy.org/buildi...pportunity.pdf


This one pretty much has it all!
http://www.crawlspaces.org/

Look on the Knowledge Library, Ventilation tab -

A good reason for NOT using powered attic/exhaust fans. Negative pressures back-drafting of gas water heaters in particular etc.

ASHRAE has a pdf download for this too.
http://www.rlcengineering.com/csfallacies.htm

Sealed Crawlspace specs
http://www.rlcengineering.com/csspecs.htm
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File Type: pdf CrawlVenting.pdf (72.5 KB, 41 views)

Last edited by kevsprojects; 07-12-2012 at 08:10 AM.
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Old 07-21-2012, 06:28 PM   #13
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