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Close up gable vent?

Bar44's picture

Hi.  As a follow-up to my earlier, somewhat open-ended post, attempting to solve my cold bedroom problems. 


My house has a hydronic hot air heating system.  The ducting to these rooms runs through an unheated attic (although mostly buried in blown-in fiberglass.)  There are the insulated flex-type.  There is  a continuous ridge vent and 1-1/2" plug soffit vents in every bay.  Is it possible that there is cold air coming in through the gable vent, and then blowing out the ridge vent and in the process cooling down the ductwork?  And also bypassing the whole purpose of the soffit vents?  WHat happens if I close  up the gable vent and there isn't enough inflow through the soffit vents? 


I live on Long Island, NY.  Thanks.

(post #111474, reply #1 of 51)

bar.. two things...


the gable end vents should have been blocked when the ridge vent was installed..


 they fight each other..


 the flow is supposed to be in from the soffits vents  and out the ridge vent..


the gable end vents interfer with this flow...


2d thing..


you should add insulation to your duct work one way or another.. blankets on top.. or blowing enough additonal to cvompletely bury the duct..


you might want to smoke test or pressure test you ductwork to make sure it isn't leaking also..


 


Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #111474, reply #2 of 51)

Thanks, Mike.


I was kind of hoping you would tell me not to bother closing it up, since it's going to be a PITA to do it - can't get into the attic.  Maybe somebody (Outwater?) makes a triangular decorative panel out of plastic that I can nail and foam into place from the outside.  Otherwise I guess I could make something up out of plywood. 


 


 

(post #111474, reply #3 of 51)

Soffit vents ,ridge vents, gable end vents,..they all let air in and air out. Its called circulation.


The gable vents do NOT intrefere with any ventilation streams of a soffit/ridge.
In fact, as long as there is sufficient  insulation in the attic floor area you can NEVER over-ventilate an attic.  The more openings (high, low, sides,etc) the BETTER.


Live and Learn.

(post #111474, reply #4 of 51)

hube... what do you base that on ?


if the gable end vent is left in place you will get a little transfer from the gable end straight to the ridge vent..


 there will be no drive on the soffit vents.. so they become useless.. and the area in the middle of the house becomes undervented..


 the gable end vents do,in fact, interfere with the flow pattern that ridge vents are based on..


 


in from the soffit... out of the ridge..


course you may have some website that will show that not to be true.. but i doubt it


now.. if ... you want to debate the question of vent   vs. no-vent... i'll buy into that


Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #111474, reply #5 of 51)

Rule of thumb, your vented attic should be as cold as the outside temperature, never block any circulation in your attic. Warm air ducts should not be installed in a vented attic in the first place if you can help it. You are asking for trouble if the attic isn't well insulated. Pile on the insulation but do not block any ventilation.

One problem that can happen is that heat from the ducts will melt roof snow, this water will flow toward the roof edge and freeze because that edge is cooler. Ice builds up causing "damming" this moves under your shingles melts again from the roof heat or warmer weather and flows into the building. Good venting prevents this cycle.

(post #111474, reply #6 of 51)

david... it sounds like you are advising NOT to block the gable end vents..


 which means  that you will ACTUALLYU reduce the amount of ventilation


a well balanced soffit / ridge vent system is the maximum amount of ventilation yoiu can acheive..


if you leave the gable end vents to short circuit that flow.. you will be reducing the ventilation in the attic


Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #111474, reply #7 of 51)

You will have to explain Mike because I just cannot see how opening up the attic for air circulation from gable ends, roof vents and soffit vents will cut down on the air flow. If you are saying that the air flow from the soffit vent and the ridge vent will be interfered with if you install gable vents then I would say that overall the airflow is still adequate.

On this particular house I think the '1-1/2" plug soffit vents in every bay' are too small, the soffit has to be vented more than that, I prefer perforated soffit material.

My experience is that the attic space should be as breezy as the outdoors.

Regards, David

(post #111474, reply #8 of 51)

here's one..


http://www.airvent.com/professional/whyVent/evaluate.shtml


 


and here's another... even better..


http://www.airvent.com/professional/whyVent/evaluate.shtml


the one i'm looking for but haven't found is the one that shows gable end vents short circuiting the flow..


instead of ventilating the attic.. they blow air in the windward end and right out the adjacent ridge vent..


all of the other vents in the attic become dormant because the short circuit takes over all of the drive..


the last link above starts to get into the other part of the equation.. which was always  FredL's contention.... that ventilation is useless.. all of the effort should go into controlling the moisture source and  sealing the heated space from the attic



Mike Smith   Rhode Island : Design / Build / Repair / Restore


Edited 11/14/2004 8:05 pm ET by Mike Smith

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #111474, reply #9 of 51)

Mike,


I agree with you...........ah..........sort of............


What happens when the ridge vent becomes covered in snow??


BTW, I HATE ridge vents. I think they look awful. And I don't think they work all that well even when properly installed which isn't a whole lot.


But, back to the issue. The gable vent is just below the ridge vent. By having both, the area of open ventilation is increased dramatically and theoretically should be sucking the crap out of the sophitt vents; provided they are not blocked.


My lesson in attic ventilation came as a newlwed, renting a ranch house with small windows at either end of the attic. being por as we were, i decided that the windows should be closed up in the winter; that is until I went up there one frosty day and discovered 2" icicles hanging of the roofing nails.


I do agree that he needs to insulate his ducts well, and it wouldn't hurt to have them tested.


Eric


I Love A Hand That Meets My Own,


With A Hold That Causes Some Sensation.

 

 

"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." — Sherlock Holmes, 1896

(post #111474, reply #10 of 51)

i've never seen them get blocked... but i guess i t could happen..


 that 2d link  says that if that does happen , the flow will be from soffit to soffit


Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #111474, reply #35 of 51)

If you've never seen ridge vents (or any other type of roof vents for that matter) covered, you've never seen snow before either.

(post #111474, reply #36 of 51)

" I,ve never seen them get  blocked, but I guess it could happen" ...


lol. duh.  ya, they do get blocked,especially after a 2' snow storm.

(post #111474, reply #11 of 51)

no... no.. no....  it doesn't increase the flow .. it short circuits it.


 i've seen pics of smoke test..


 if you leave the gable end vents it decreases the overall flow


Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #111474, reply #12 of 51)

Now smoke tests I understand, if they show the air flow being short circuited then I am a believer. Thanks, DT

(post #111474, reply #13 of 51)

Now see; if you were right here in front of me, I would say "Really!..........hhmmm!"


That's interesting, and something I will look for in the future anytime I read about attic ventilation.


Thanks Mike.


Eric


I Love A Hand That Meets My Own,


With A Hold That Causes Some Sensation.

 

 

"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." — Sherlock Holmes, 1896

(post #111474, reply #14 of 51)

i had a partner that used to use a similar phrase.." i hear you"..


 what it really meant was "BS.. i've listened to you, and you're wrong, but we're not going to discuss it"..


it took me a long time to figure out that he wasn't agreeing with me... hah, hah, hah


Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #111474, reply #18 of 51)

.." i hear you"..but we're not going to discuss it"..


nnaahh, I politely agree, but I would still like to form my own opinion based on my own research! ;~)


I think what Blue said made it home. I hear you're a gambling man.........maybe we should make a wager............seems you're not doing to well lately...........hmmm!


Eric


 


I Love A Hand That Meets My Own,


With A Hold That Causes Some Sensation.

 

 

"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." — Sherlock Holmes, 1896

(post #111474, reply #20 of 51)

I think he owes me some hard cash on that Kerry Bush race...I gotta go check the archives.!


blue


Warning! Be cautious when taking any framing advice from me. Although I have a lifetime of framing experience, all of it is considered bottom of the barrel by Gabe. I am not to be counted amongst the worst of the worst. If you want real framing information...don't listen to me..just ask Gabe!

"...

keep looking for customers who want to hire  YOU.. all the rest are looking for commodities.. are you  a commodity ?... if you get sucked into "free estimates" and  "soliciting bids"... then you are a commodity... if your operation is set up to compete as a commodity, then have at it..... but be prepared to keep your margins low and your overhead  high...."

From the best of TauntonU.

(post #111474, reply #21 of 51)

I think Pete and Buck have pretty much cleaned him out!

I Love A Hand That Meets My Own,


With A Hold That Causes Some Sensation.

 

 

"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." — Sherlock Holmes, 1896

(post #111474, reply #15 of 51)

I recently had a new roof with ridge vents added....Had to ask for soffit vents, nobody puts them in unless asked.... My point: I have a window that's been stuck closed for 50 years and I thought of getting it open/replacing so I could open it in summer and get some ventilation.... ahem, well, even with ridge vents and soffit vents, the attic is as hot as ever in summer time.... This article and your argument are, leave it closed, that stuck window is your friend?

(post #111474, reply #16 of 51)

I gotta agree with Mike on this one. Closing the gable vents isn't new knews. They started doing studies back in the early eightys as a result of severe energy crisis .


The theory is that the hot air will rise, escaping out of the highest outlets, while drawing in cooler air from below. If the "below" source of air is the gable vent, then the soffits will not deliver as much as they would in the absence of that gable vent. Additionally, gable vents are prone to creating positive and negative air flows when the wind direction is hitting them. They will actually suck in substantial amounts of blowing snow under some wind conditions.


Just plug them up and balance your lower and upper vents.


Food for thought....the last house I lived in on the Lake had no vents..high or low. I checked in occasionally and saw no frosting...


blue


Warning! Be cautious when taking any framing advice from me. Although I have a lifetime of framing experience, all of it is considered bottom of the barrel by Gabe. I am not to be counted amongst the worst of the worst. If you want real framing information...don't listen to me..just ask Gabe!

"...

keep looking for customers who want to hire  YOU.. all the rest are looking for commodities.. are you  a commodity ?... if you get sucked into "free estimates" and  "soliciting bids"... then you are a commodity... if your operation is set up to compete as a commodity, then have at it..... but be prepared to keep your margins low and your overhead  high...."

From the best of TauntonU.

(post #111474, reply #17 of 51)

Worked on an old early 1900s two storey with an attic.


Absolutely no venting whatsoever gabel, soffit or ridge.


There amidst the old poured insulation and remenants of knob and tube wiring was nothing but dark charred wood from heat build up.


That and some sweet old victorian vine embrossed gold leaf trim pieces of interior molding which I was given.


Must have been like an oven in the summer.


Must have had atleast one hole for ventilation tho'. That bat had to have gotten in there from somewhere. 


 

 

(post #111474, reply #19 of 51)

Hmmm.  We had same.  1914 house, no venting anywhere.  But when we explored it, we determined that it was probably smoke from a poorly maintained coal furnace drawing up the balloon framing and out when that roof was covered with cedar shakes.  Rafters were original, never had been replaced. (Still had the builder's numbers on 'em...they match the numbers on the back of the molding pieces we found in the rafters of the garage.)


I was originally alarmed enough during the inspection to look into it because I wondered if there had been a fire in the house we hadn't been told about.


Either that, or the five raccoons living up there were smokers :)



HouseBlogs.net...DIY Geeks Rejoice

(post #111474, reply #22 of 51)

They weren't smokers. They were building bonfires on really cold nights.


The convection currents will try to go out the highest point or line (exhaust), but if there isn't enough air flow coming in at the low places (supply) due to lack of vent area, there will be a net heat gain in that space. It's just back pressure. If the gable vent stays, that will be the main supply and will keep air from coming in through the soffit vents because there won't be as much negative pressure above them, caused by the air rising out through the ridge vent. If the ridge can flow more air than the soffit vents, it won't flow as well as needed. You want the soffit venting to be able to pass more air than the ridge, so that whatever the ridge wants to release by convection, the soffit vents can supply.

"I cut this piece four times and it's still too short."

(post #111474, reply #23 of 51)

Mike,


I recently purchased a home (Cape-style) that has a ridge vent, and gable vents at each end of the roof, and also soffit vents but only on one side of the house. I was puzzled by the soffit vents only on one side. When I look at the roof trusses it seems that they were placed on the house biased to only one side giving an overhang for the soffit vents. Should I block up the gable vents in this case too? Or since I only have soffit vents on one side should I leave the gable vents there? It gets really hot up on the second floor in the summer and I recently installed central air whose ducting runs thru the kneewall space. Thanks in advance for any reply.

(post #111474, reply #24 of 51)

pizza.. more important than the vent queston is sealing the living space from the attic space.. once you have all of the leaks sealed into the attic, you can increase your insulation levels..


 this will do more to keep your 2d floor cool in the summer than trying to optimize your vents.


and .. where the A/C ducting runs thru the kneewall, if you can get in there and bury the duct work in insulation,  this will make your A/C run more efficiently..


 naturally.. i'm assuming your ductwork was tested for leaks  ( smoke test or pressure test )...


before you increase your insulation around the duct.. you should make sure any leaks have been sealed


as to the vents .... the  best thing would be to add soffit vents to the side that doesn't have them.. but good  luck with that .. i'd concentrate on the sealing and insulation


Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #111474, reply #25 of 51)

What kind of venting should there be in a small cape cod style house with a slate roof in Northern New Jersey?

I just read the Slate Roofer's Bible and learned a lot about my slate roof, and that answered my question about why there is no ridge vent, but it did not talk about what kind of venting it does need.

I looked in my attic, and the only vents I see are louvered gable vents at each end. One was almost blocked with a huge bird nest. I got that removed and had wire screening nailed over the inside so the birds don't come back in. Will the screening block too much air flow?

The attic is unheated and unfinished with no floor and there's an old attic fan up there which is not connected to anything so I don't know if it works.

I also think the insulation is installed wrong. It looks like there was some original insulation of some kind (maybe rock-wool?) then someone added a layer of the pink fiberglass stuff over the top, but the vapor barrier is on the top. I don't think that's the way it's supposed to be.

I'm now wondering if there are a lot of air leaks because I do get some ice dams forming on the edges of the slate roof. I have also seen frost on the underside of the roof and it gets pretty hot in the summer. Do I need a vapor barrier?

I just called an insulation company and asked for advice. I thought the best thing to do would be to take all the old insulation out, seal up the air leaks and start over with new insulation. But he said he does not remove the old insulation, he just blows the cellulose stuff on top of the old stuff and he thought that would take care of any leaks. That doesn't sound right to me. It would probably be a real hassle to get the old stuff out since the only access is through a 20" x 30" hatch in my upstairs hallway.

A handyman said for $600 he would remove the old insulation and turn the pink stuff upside down so the vapor barrier is on the bottom. From what I'm reading though, I don't think that would do the trick.

What should I expect from a professional insulation contractor? Will they find the air leaks and seal them or just add another layer of insulation?

(post #111474, reply #26 of 51)

cynthia.. does your state have an energy office ?


 if they do , they will test your house for leaks.. you can do a blower door test and smoke candles.. this will tell you just where the leaks in your house are..


 you don't have to remove the insulation to seal the leaks.. once you have the leaks sealed the ventilation  needs will become moot.. and your gable end vents will continue to function as they have in the past..


if you don't have warm air leaking out of your heated space, you won't have ice dams either..bet your house is about  75 to 100 years old , right ?


and if your roof / attic is hot in the summer / and cold in the winter... who cares?


certainly not your slate.. once you have the attic sealed.. you can slash the vapor barrier on the fiberglass batts  ( or not .. you could ignore them )  and you can have an insulataion contractor blow a cellulose cp right over everything.. leave the rock wool there.. leave the fiberglass.. blow a cap..


the only thing you have to watch out for is fine snow blowing in thru your gable end vents


PS: you actually could have a ridge vent with a slate roof.. but it would be useless without balancing soffit vents.. and then you'd have to block the gable end vents..


ignore all that and concentrate on controlling moisture in your crawl space / basement, sealing the heated areas from the attic, testing your combustion heaters for CO and backdraft


garsh... where is fredL  when you need him  ?  andy says he moved to Florida..


Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #111474, reply #27 of 51)

Mike,

Thanks for your suggestion about the state energy office. I finally found a number and called them but they only do tests for low income people and I don't qualify. I asked them if there was a way I could pay for it, but no.

So, then I started calling the insullation contractors. Most of them had never heard of a blower-door test. One said he didn't want to answer a bunch of questions, but if I figured out what I wanted done, I should call him. Yeah, right! It took about six or seven calls before I found someone who would come out and do an evaluation.

One guy actually came out and looked in the attic and all around the house. He discovered what I think is the problem. There's a small unheated (and uninsulated) storage space in the kneewall behind the closet. This space is right where the biggest ice dams have been forming, right over my front door. There has probably been a lot of heat escaping up through this space.

He is going to seal up the leaks, take the vapor barrier off the top of the insulation in the attic and blow in a layer of cellulose on top. Then he will blow insulation into the floor and insulate the wall of of that storage area. I think that will take care of the ice dams.

It's a lot of work finding someone who will do decent work around here. With my slate roof, I had 4 contractors come over to give me estimates, but only one got a ladder and went up on the roof and actually looked around. Since this guy knew about the Slate Roofer's Bible and was listed on Jenkin's site I decided to hire him.

I ended up spending about an hour talking with him. It turned out he has a background in art, loves old houses, antiques...long walks on the beach...just kidding.

I hope these guys work out.

Thanks again.

(post #111474, reply #28 of 51)

amazing ain't it ?


guys call it a career and don't know the first thing about weatherizing houses


i like the long walks on the beach.. nothing like a  sensitive insulator.....


keep us posted on this thread about how it comes out..


 


Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore