Roof Ventilation Authority

[JoeMA]

About to replace the asphalt shingles on my mid-1980s house/garage. I want to consult with a professional to assess the current ventilation system and determine whether there is an opportunity to make it more efficient (hip and valley roof with soffit vents, a couple roof mounted powered vents but no ridge or hip venting). I am also considering replacing the asphalt shingles with a standing seam steel roof.

Opinions from roofers are all over the place in regards to the most efficient ventilation--I don't think they are the best source of advice on this.

Who should I consult with that will be most knowledgeable on this? Engineer, architect, one of those home energy companies?

 

[wasfuzz]

I would think a "reputable" insulation contractor could help you out. You will need to assess if soffit vents will work without installing vent channels in the attic. Ideally you want to place vents as low as possible for intake and vent has high as possible for exhaust, you are trying to create a venturi effect to move the warm air out.

 

[doublearon98]

Like said intake at bottom and exhaust at top. Ridge vents are great (highest point in the roof)

Sent from my SM-G930V using Tapatalk

 

[wrenchguy]

as long as powervents work and u got enough eave venting u should be ok. i don't care 2 much 4 ridge venting... i believe they don't provide enough rain protection in storms. imho. good luck with ur project.

 

[doublearon98]

as long as powervents work and u got enough eave venting u should be ok. i don't care 2 much 4 ridge venting... i believe they don't provide enough rain protection in storms. imho. good luck with ur project.

If its built right it does. Just sayin [emoji848]

Sent from my SM-G930V using Tapatalk

 

[bdbecker]

If you're willing to do the math, its not as difficult as you might think to figure out how much ventilation you need to install. If anything, learning about it and going through the exercise will help you know what to expect when a contractor shows up to make recommendations. If they recommend something wildly different than what you came up with, you can at least have an educated conversation with them to figure out the source of the discrepancy. There are a few calculators out there to help you along with the process, this is the one I used when I had to figure this out for my garage:

https://www.gaf.com/en-us/for-professionals/tools/ventilation-calculator

The two main things to remember are to...

1) Make sure you install at least the minimum recommended amount of exhaust for your attic area.

2) Make sure you have at least the same amount of intake area as exhaust (if not a little extra). From what I've read, its better to have more intake than exhaust, especially if you are using a ridge vent so it does not **** weather (snow, rain) into your attic.

 

[dave_dj1]

I'll just add that if you do go with standing seam metal roofing you won't get a ridge vent (at least not that I'm aware of) and you will need your power vents or at a minimum some bay vents or static vents.
https://www.wholehousefan.com/different-type-of-roof-vents/

 

[Ole Slewfoot]

Here ridge vents are pretty much mandatory on shingles. they have the advantage of actually pulling from the peak...make sure you get that out of whatever system you install.

 

[Lelandwelds]

If you install standing seam, why not a hot roof? Spray foam under roof deck.

 

[glentre]

My experience with roofing contractors is that they know very little about proper roof ventilation and will just "do what they have always done", whether correct or not. I agree with bdbecker above about educating yourself and doing the math. There is plenty of info on the net on how to do this and it's not rocket science. I believe your local and state building codes will have acceptable parameters on roof ventilation so you might want to check the codes before going ahead with anything.

Also, you will want to make sure your ceiling insulation is protected with baffles on their **** ends where they meet the soffit. If not, moist air rising through the soffit vents and moving up to the peak will wet and erode the insulation. You are wise to not trust roofing contractors and to make sure your structure is ventilated properly.

Glen

 

[JoeMA]

Thanks for the input. It appears that the effectiveness of powered ventilators is controversial and shouldn't be combined with ridge/hip vents. One roofer wanted to keep the powered vents and open up every ridge and hip.

Its a fairly large (90 squares) and complex roof (some areas have attic space and others have the ceiling vaulted to the roof). I plan on being in the house for a long time and only want to do the roof once.

There are several engineering firms and architects near me so I'll start by talking with a few of them and seeing where they lead me.

 

[dave_dj1]

If you have vaulted ceilings and are going to be there a long time, go with the standing seam metal, you won't regret it long term.

 

[rijndael]

My experience with roofing contractors is that they know very little about proper roof ventilation and will just "do what they have always done", whether correct or not.

That's my experience as well.

 

[matt_i]

I see a lot of 12:12 super tall hip roofs, in a high-end real estate area that seem like they end in 8 feet of ridge. But I can see that its really hard to equalize areas: soffit vs. ridge.

The calculations are pretty simple but it takes some homework. You have to figure out what is installed at the soffit. The cross-sectional area is typically published. Same for the ridge vent per linear foot of ridge. Ideally these figures are equal.

GAF Cobra "Snow Country" ridge vent is what is typically put in around here. It seems to be pretty well-developed as far as snow and water intrusion. The "Snow Country" differs from the standard in that it comes with a set of 3" ring shank nails to aid in installing it. The non-snow-country has no nails; you supply your own.

I have seen the vented hip caps but never installed them. It seems like it would be a good solution for those roofs I mentioned above.

I have had powered vents on my personal houses over the years as I've moved. They seem simple enough but also seem like they aren't very robust, and thus changing a motor out, 12' up from the floor of the attic isn't my idea of fun anymore. The passive solutions require zero energy and no maintenance.

Edit: some good info may come from one of the places which supply roofing and siding products in your area, that's not a box store. The inside sales people there will have a good idea about features vs. price point, what is a high-volume product in the local area, and have literature which can help with the design of the areas.

 

[ard]

You might look for someone that is aligned with some of the more modern 'green building' techniques- cant avoid being ventilation experts....

 

[jkeyser14]

I'll just add that if you do go with standing seam metal roofing you won't get a ridge vent (at least not that I'm aware of) and you will need your power vents or at a minimum some bay vents or static vents.
https://www.wholehousefan.com/different-type-of-roof-vents/

Not true, you can do ridge vents with standing seam roofs. They did it on my last garage.

I would go 100% standing seam IF you can afford it. It will outlast you and be leak free.

 

[850xpeps]

I will be doing standing seam snaplok on my house I’m building now. With a vented ridge.

 

[rburke65]

I had ridge vents installed on all ridges on my hip roof. You can feel the heat being expelled. And this spring I added larger soffit vents and more of them.

 

[Smokeem]

On attic venting code requires 1 Sq Ft of venting for every 300 Sq Ft of roof area within 3’ of the peak with soffit venting. On the soffit venting you should have a baffle in your attic against the roof deck between very 3-4 trusses. Personally I don’t think you could have to many vents unless you live in a very cold climate. Get up in your attic in late afternoon in the middle of the summer and see how hot it is. Even in the dead of winter here in Idaho the attic can be pretty warm.

 

[James-W]

as long as powervents work and u got enough eave venting u should be ok. i don't care 2 much 4 ridge venting... i believe they don't provide enough rain protection in storms. imho. good luck with ur project.

We have ridge venting on the house and on the garage. So far we have not had any leakage and it has been many years now. But, I imagine you are right, if the ridge vent wasn't installed correctly there could leakage.

 

[dave_dj1]

Not true, you can do ridge vents with standing seam roofs. They did it on my last garage.

I would go 100% standing seam IF you can afford it. It will outlast you and be leak free.

I said "not that I'm aware"
Please post some close up pics, I have never seen it.

 

[yeldogt]

Well -- I'm going to go the other way and first ask you what are you venting ? and why? The same should always be asked when looking at a crawl space.

What you need to look for is an energy expert ... also, most of what people call standing seam is not "true" standing seam and requires whatever the roofing manufacturer specifies for proper installation.

Venting a roof and venting an attic are two different things. Old school DLSS roof is sealed -- be it copper/tin/zinc.

Most houses with typical venting are energy hogs -- the roof opening (vents) create pathways for conditioned air to exit the building and create negitive pressure inside the building. Power vents are even worse -- they pull air from inside the attic (negative pressure) sucking both heat and AC out of the living space under it ..and you are paying for the electric.

Closed building structures are around for a long time 40+ years and have been proven to work -- NJ's energy program mandates it for getting the full rebate.

Again -- read up and look to get an energy audit from an expert -- blower door test.

I have eben sealing up my buildings since the late 80's -- no vents. Read up on shingle manufactures most have dropped the venting requirement. Studies show that in most climates the temp different not the roof is about 20 degrees ... and that a properly working vent (most are not)

A proper Roof vent requires double sheathing -- few do that. remember roof venting and attic venting are not the same.

My new project has a slate and zinc roof -- spray foamed deck. My house in NJ was sealed a few years ago under the clean energy program .. amazing results.

Even in snow country the idea of venting is slowing wining -- even though it's been around for a long time.

Read up on metal roofs and understand the difference -- some are 100 year others 50. Screw downs IMO are for utility building -- not finished structures.

 

[JoeMA]

What you need to look for is an energy expert ... also, most of what people call standing seam is not "true" standing seam and requires whatever the roofing manufacturer specifies for proper installation.

My impression of the energy audit consultants that I've looked up near me is that they are akin to home inspectors--are trained to go through a checklist of items but have no real expertise other than their guideline recommendations. I'm north of Philly, do you have recommendations? I was planning to bring the architectural drawings to an engineer or architect.

What do you mean about, "not a true standing seam?"
Are you referring to exposed vs concealed fasteners or slotted holes in the panels vs deck mounted clips? Was looking into 26 or 24 gauge galvalume steel from Fabral or ATAS.

 

[M_George]

What temperature would be considered to hot for an attic?

 

[850xpeps]

My own impression would be the attic should be the same temperature as the air outside. When ventilation is adequate.

 

[climb.on]

I just installed (last fall) 47sq ProSnap steel roof (from Menards). It's not a true standing seam, but it's better than shingles, by far. And it's half the cost of a true standing seam roof. I love it, do it if you can. Yes, it has ridge venting, very similar to an asphalt shingle ridge vent.

Here are two articles on venting. It's way over rated. Good air sealing and insulation in your ceiling are WAY more important.

Rethinking Ventilated Attics

Lstiburek’s Rules for Venting Roofs

 

[LS6 Tommy]

We just replaced our roof and went with the full GAF system including the Cobra Intake Pro and Cobra Ridge Vent. All we had before was gable vents and no ridge vent at all. The house is a Cape Code with a finished attic and insulation on the underside of the sheathing, so I was not sure if it was going to be the right thing to do. Yesterday it was almost 100° out and the bedrooms on the second floor weren't much hotter than what they used to get when it was in the 80° range out. I'm happy. The acid test will be what it's like this winter.

Tommy

 

[yeldogt]

We just replaced our roof and went with the full GAF system including the Cobra Intake Pro and Cobra Ridge Vent. All we had before was gable vents and no ridge vent at all. The house is a Cape Code with a finished attic and insulation on the underside of the sheathing, so I was not sure if it was going to be the right thing to do. Yesterday it was almost 100° out and the bedrooms on the second floor weren't much hotter than what they used to get when it was in the 80° range out. I'm happy. The acid test will be what it's like this winter.

Tommy

How did the roof change the bedrooms -- confused. You could have done the free clean energy program.

 

[yeldogt]

My impression of the energy audit consultants that I've looked up near me is that they are akin to home inspectors--are trained to go through a checklist of items but have no real expertise other than their guideline recommendations. I'm north of Philly, do you have recommendations? I was planning to bring the architectural drawings to an engineer or architect.

What do you mean about, "not a true standing seam?"
Are you referring to exposed vs concealed fasteners or slotted holes in the panels vs deck mounted clips? Was looking into 26 or 24 gauge galvalume steel from Fabral or ATAS.

I actually had the guy that did my house in NJ come and do the test on my place in PA -- he is also going to do the first blower test on my new place being built currently. He did it as a favor -- I paid him for the extra time. I have not looked for one in PA -- but they must be around because the good contractors use people to meet the certifications?

A true standing seam roof --- is panels with a double locking mechanical seam. This is the original metal roof -- each panel is double locked to the next. tin/copper/zinc being the original .. some dipped in lead. This is the roof you will see all over PA on historically accurate buildings -- the standing part of the seam ends up being thin and about 1 to 1.5 high. Because the seam is water proof -- it is not required to be tall.

You will notice all the other types of modern replication have higher thicker seams and various caps -- they were originally used in commercial settings .. but moved onto homes as they became smaller in scale.

You just have to understand what you are buying and what it's intended to do -- understand the rain capacity and snow capacity.

Going to the extreme (screw down) -- if you read the specifications closely they will indicate in strange wording that it's really not a roof. You need to have a waterproof substrate under the panels. Reason: They will leak ... they have to if you think about how they are installed.

Some (many) panels have to be ventilated others are sealed -- this all depends on the type and construction. Since many will drip it's required for them to have a way for this water to get out. A traditional standing seam roof is water proof and has no venting.

 

[Falcon67]

What temperature would be considered to hot for an attic?

LOL - underside of plain OSB decking here can get to 160F in summer. TechShield reflective I used on the shop keeps the framing around 120F or so. House stays around 120 - eve vents, 5 9" round static vents, all hip, no ridge vents. The way this roof is designed there would not be a lot of ridge to vent. I also wonder about water infiltration - rain store here can easily have 30~60 MPH wind, or worse if it's a good one. Raining straight down like it did Saturday night here is highly unusual.

 

[LS6 Tommy]

How did the roof change the bedrooms -- confused. You could have done the free clean energy program.

I don't see anything on the NJ Clean Energy Program website that's "free".

The bedrooms are in what was originally the attic, which is only insulated on the underside of the roof sheathing. They're just 2"x 4" framing with sheet rock walls and ceilings. I can't bend my leg good enough to get into the crawlspaces to really insulate the interior walls nicely and I can't access the outside of the ceilings at all, but it's never really been uncomfortable, winter or summer. The plan is to eventually do a large dormer and an extension on the back of the house, make a suite out of the first floor bedrooms with a full bath, make the existing full bath a 1/2 bath, gut, enlarge one bedroom and redo the other bedroom upstairs and possibly add a small full bath up there.

Tommy

 

[willymakeit]

See if the firms have a envolope consultant.
Most architects and engineers don’t know much about this and get their info from the consultant.
I deal with this on every project, from under slab all the way to roof

 

[wrenchguy]

My own impression would be the attic should be the same temperature as the air outside. When ventilation is adequate.

yep, this is ideal.