I’m getting ready to re-roof my 1950’s ranch. I’ll be removing all the old ceder shakes, laying down plywood over the skip sheeting and installing about 26 squares of composition roof (includes a two car garage). I currently have four 14″x5-1/2″ eve vents, two 14″x14″ gable vents, and a powered attic vent (not sure what size). My question is should I install a ridge vent or not?
Thanks all
Tim
Listeners write in about a fondness for palm nailers, German translations, and insulating behind masonry.
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial NowGet instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
Shure..why not? Gonna be up there anyway and it costsabout the same.
Vent wars or not on here, I'd do it just to CYA on the manu specs.
Spheramid Enterprises Architectural Woodworks
There is no cure for stupid. R. White.
I'd add the ridge vent and ditch the power vent. No sense paying for electricity to do what gravity will do on its own.
glad we see it the same..
Soooo..how's tha young knight preparing for the wedded bliss?
Spheramid Enterprises Architectural Woodworks
There is no cure for stupid. R. White.
tide for gnilleps..
Edited 6/2/2006 2:26 pm ET by Sphere
"how's that young knight preparing for the wedded bliss?"
Well, he's looking real hard for a job. That should make any prospective FIL happy. (-:
He has his own email address. Maybe we should just have them swap emails and see what happens?
Eternal vigilance is the price of liberty used to mean that we watched the government, not the other way around
She is enamored with a guy in Pa ( grumble, grumble) that is 14...the kid plays a mean guitar...more later.
Spheramid Enterprises Architectural Woodworks
There is no cure for stupid. R. White.
Carl plays the guitar too.I can provide pics....Oh yeah - He can play the french horn, too. You know what they say about french horn players?They're good kissers. But they sure do hold ya funny.
Bumpersticker: Next time you wave at me, use more than one finger please.
Ditto other post to install the ridge vents. Ridge vents seem to me to be the mopst efficient as they are in the top of the attic convection flow and provide a continious element for exhausting hot air.
Ditto on losing the power vent, but I think you need more eave venting and I'd close off the gable vents. Air will tend to short circuit in the gable vents and out the ridge and not pull from the eaves.
Can I get that Little Debbie snack cracker out from under the heel of your pointy boot?..
http://grantlogan.net/
You don't have enough soffit/eave vents. There should be same amt in at soffit as out at ridge/top.
What you are doing is using the power vent to suckk air in at the gable vents and blow it out the power vent. Air should be going out the gable vets
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Thanks
I went to the Cor-A-Vent website and they recommend having an equal or more soffit vent than ridge vent and no gable vents. I'll have to do some calculations to figure out how much more soffit vents I'll need. My current soffit vents are just a screen where the "freeze" blocks have been knocked out. Is this the proper method or should I drill holes in the blocks?
I'm curious why it is not a good idea to suck air though the gable vents with the power vent? The gable vents are slightly above center on the 4' tall gable ends. The power vent is centered between the gable vents and seems to pull a lot of air though the attic.
Thank again
Tim
>>I'm curious why it is not a good idea to suck air though the gable vents with the power vent? The gable vents are slightly above center on the 4' tall gable ends <<
Because you end up with the lower half of the attic as a dead air space. And, as the other's said, your 4 eve vents are not adequate, nor do they provide uniform ventilation.
"I'm curious why it is not a good idea to suck air though the gable vents with the power vent? "The whol3e idea is to change the air in the attic. Just moving air across the top while the air near the bottom - where most problems show themselves - stagnnates, doesn't do much good
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Find out what works best in your area.
As a general rule, in my area, ridge vents with linear soffit vents work best, especially where the soil tends to clay and moisture in subgrade spaces is likely/higher.
The venting needs lessen some as the soil changes to a more readily 'drainable' sand, with lower amounts of moisture in the basement/crawl.
I suspect that "over-venting" can lead to pressure zone problems in some cases, esp. if the attic isn't well sealed from the living spaces, but I cannot support that view with concrete evidence.
Experienced roofers or home inspectors should be able to give you guidance for your area.
Fighting Ignorance since 1967
It's taking way longer than we thought
As a general rule, in my area, ridge vents with linear soffit vents work best, especially where the soil tends to clay and moisture in subgrade spaces is likely/higher.
The venting needs lessen some as the soil changes to a more readily 'drainable' sand, with lower amounts of moisture in the basement/crawl.
We shouldn't even be talking about roof venting in relation to soil moisture. Deal with each separately. They were linked when we didn't understand buildings as well. In the basement crawl spaces, use moisture barriers / better drainage / good surface drainage /sump pits & pumps to keep the moisture levels down.
If house moisture levels are too high, vent what needs to be vented properly to the exterior.
To prevent moisture (and paid for house heat) from getting to the attic, airseal, airseal, airseal. Then the venting you already have will probably be enough. Don't fix what ain't broke. Fix the other things that never got considered in the first place!!!
Attic venting is overrated. It was never even studied until the last 20 years or so. As the results of these studies come out, most people refuse to believe them!
With unvented attic space as you propose, is there any provision for air circulation in that area or not?
Our attic spaces are not that tight that there's no air leakage in or out. We don't try to make those areas as tight as the heated shell of the house. For properly prepared regular attics with high insulation levels (R40-50), my feeling is if you used solid panel soffit (which is fairly loose anyways due to F trim or other methods of support/installation) and air shutes every 2-3 rafter/trusses, you would have enough air movement for all situations, if needed.
>>We shouldn't even be talking about roof venting in relation to soil moisture. Deal with each separately. They were linked when we didn't understand buildings as well. In the basement crawl spaces, use moisture barriers / better drainage / good surface drainage /sump pits & pumps to keep the moisture levels down.When (if) we can(could) keep the crawl space at the same moisture level as the house, you're right.Until then, we do need to consider them together.And, except in very new construction, I have yet to find a crawl space in my area that doesn't have some elevated moisture levels.And, after going through thousands of crawls and attics, it is my impression (although I cannot prove it) in the real world an "overvented" attic actually pulls more moisture out of the soil by creating a higher pressure differential. (A "dry crawl space - i.e., the soil is very dry - sometimes is one with major moisture migration upwards issues.)>>If house moisture levels are too high, vent what needs to be vented properly to the exterior.Depends on where and what the exterior conditions are like.Damp crawl space which is cooler than the outdoors in humid weather?Venting isn't the best solution, in my area.Conditioning is needed.
Fighting Ignorance since 1967
It's taking way longer than we thought
And, except in very new construction, I have yet to find a crawl space in my area that doesn't have some elevated moisture levels.
Are these spaces that have had remedial work of any type?
And, after going through thousands of crawls and attics, it is my impression (although I cannot prove it) in the real world an "overvented" attic actually pulls more moisture out of the soil by creating a higher pressure differential. (A "dry crawl space - i.e., the soil is very dry - sometimes is one with major moisture migration upwards issues.)
These houses would have high to very high heating bills and the air would be very dry in the colder parts of the winter due to high ACH. Normally except in deserts, is the soil very dry. This soil is very dry due to the amount of air flow through the space and possibly from parasitic heat losses from heating equipment/pipes/ducts that may be in the space helping evaporate soil surface moisture. Can't forget that the soil under the dry stuff is connected to an infinite humidifier called the water table always wicking water upwards.
>>If house moisture levels are too high, vent what needs to be vented properly to the exterior
I meant the interior living areas of the house- baths, kitchen, dryer.
Damp crawl space which is cooler than the outdoors in humid weather? Venting isn't the best solution, in my area. Conditioning is needed.
There is a school of thought now saying that covering the soil with a moisture barrier and sealing these spaces from exterior moist, humid air infiltration is the best way to deal with them. Buidling Science Corp, Sheltair Scientific, Home Energy magazine, Energy Design Update, CMHC, St Gobain (French owner of Certainteed) have all reported on this technique as in most cases better than venting.
>>Are these spaces that have had remedial work of any type?I see all sorts of crawl spaces.As a home inspector, I look at whatever folks are buying and my territory covers an area with pretty high clay content soil to pretty sandy soil.>>There is a school of thought now saying ....In my area, conditioned crawls unquestionable perform best>>Can't forget that the soil under the dry stuff is connected to an infinite humidifier called the water table always wicking water upwards.Exactly, which is why I believe a crawl with very dry soil is, counter-intuitively, a house which has some problems, along the lines / possibilities you mentioned.
Fighting Ignorance since 1967
It's taking way longer than we thought
How about this?:
Instead of putting the plywood directly on top of the skip, he could fasten on 2x2 as a nailer over the rafters and over the old skip. This will give a large continous air channel from the edge to ridge. Putting bulding paper down before the nailers went on would enable you to insulate from underneith - you could rock the underside of the rafters and insulate the cavity with cellulose. This makes your attic a conditioned space and reduces your heating/cooling load.
A little extra material can open up alot of options here.
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
From a JLC Q&A article, May/1992, selected passages:
The Science of Venting:
by
Bill Rose, Univeristy of Illinois
From intro: Although all codes require venting and most experts recommend it, surprisingly little is known how venting actually works and whether it is needed in all cases.
What does balanced mean? ....when the term "balanced" comes up , I think most of us picture air coming in through the soffits and exiting through the ridge in about the same amounts, following the arrows we see in venting diagrams. In real attics, the airflow rarely follows the arrows.
Our research shows that wind, not thermal buoyancy, is the driving force for air exchange between the attic and outdoors. (Thermal buoyancy may play a role in air movement from the indoor air space to the attic, especially in tall buildings, but its role in diluting attic air with outside air is negligible.) ........ Unless a ridge vent is designed just right, the air can blow in one side and out the other, not helping with ventilation. The amount of suction a ridge vent develops depends upon its aerodynamic properties.
For this reason, I consider the soffit vents to be the critical component of air exchange in any system. In fact, if a roof had to have only one vent device, I would opt for soffit vents. They perform as well as either intake or exhaust ports and since the holes point downward, they have one line of protection against snow intrusion. (My comments: I have a couple of stories about snow blowing up through soffit vents/vaulted ceiling air chutes about 12' to end up in the flat attic insulation!!)
On airflow rates of ridges vents: Occasionally, manufacturer's state the flow rate of soffit or ridge vents measured at 0.5 inch WG pressure difference. However, our experience and that of of researcher Tom Forest of the U. of Alberta, is that pressure differences between the attic and the outdoors rarely exceed 0.04 inch, which is at least 10 times lower than the rate used to test the vents. (my comments: Ever feel you've been lied to by a vendor before?)
How do you protect against blowing snow and rain? The ideal location for soffit vents is as outboard as possible on the eave (closest to the fascia). ....... Some areas of a roof are simply subject to strong positive pressures and vents should not be located there. Under such pressures, precipitation will enter- whatever the design of the opening.......A good rule of thumb is to install vents in areas not subject to snow drift. (my comment: Got pictures of snow in my attic from the past 2 winters....don't know how to post pictures yet)
Edited 6/3/2006 7:58 pm ET by experienced
Thanks for the info.FWIW: >>pressure differences between the attic and the outdoors rarely exceed 0.04 inch, Assuming he is talking about inch water column (- he said "inch WG[?] pressure difference) 0.04 is about the amount of air "pressure" it takes to blow out a match at about 5-6" That is, not much.
Fighting Ignorance since 1967
It's taking way longer than we thought
Assuming he is talking about inch water column (- he said "inch WG[?] pressure difference) 0.04 is about the amount of air "pressure" it takes to blow out a match at about 5-6" That is, not much.
Yeah! was inches water. (We sometimes use "water guage" up here; I must have slipped that in.) ).04 "- That is the negative draft requirement for most older (50's to early-mid 80's) oil furnaces and boilers that were naturally drafted up chimneys.
>>Yeah! was inches water. (We sometimes use "water guage" up here; I must have slipped that in.) ).04 "- That is the negative draft requirement for most older (50's to early-mid 80's) oil furnaces and boilers that were naturally drafted up chimneys.Do you have some written authority on that?I've been, ah, 'discussing' draft with an old line furnace guy here, using the National Comfort Institute guideline of .01 - .02 for atmospheric draft gas fired furnaces and water heaters, but I don't have access to the ANSI specs. (They charge a bundle to even look!)The old fart insisted that holding a match in front of a drafthood, blowing it out by blowing towards the hood, and having the smoke (surprise!) go into the drafthood established sufficient draft, even where my draft gauge showed no measurable draft.
Fighting Ignorance since 1967
It's taking way longer than we thought
Usually the manufacturers specify the draft needed for proper operation of their powered heating appliances.