# Ventilation (intake) questions with partial overhangs



## jmiller (Nov 19, 2010)

If ridge vent is installed with no intake it can create negative pressure in the attic that pulls conditioned air from the house (and makes for frosty gable windows in winter). 

The first step might be checking the seal between the conditioned space and the attic. Are your bath fans vented out the roof, or dumped into the soffit? Does the hatch you access the attic from have tight fitting insulation? Do you have recessed lighting? Those are all an easy path for the ridge vent to pull air through.

Next step would be adding the continuous soffit vents and fascia vents where there's no soffit, which IMO would be worthwhile and DIYable.


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## Windows on Wash (Aug 30, 2011)

jmiller is correct in that exhaust venting without supply air is a bad thing = negative pressure and air loss.

Ultimately a bad thing for efficiency but not so bad if it is keeping the roof structure dry.

Fascia flow is an option but there are probably a couple of things you can do without buying that stuff (it is expensive FYI).

Remove the vented soffits and make sure you remove the plywood or cut large holes in it.

Make sure you have the proper vent chutes to avoid the wind stripping the r-value from the insulation.

If you want to vent the non-overhang sections, I would remove the gutters, make spacers out of some sort of azek or other rot proof wood, and you can cut holes through the fascia board in between the rafter and install circular soffit vents. Shimming out the gutter will keep it from hanging across the vents and closing them off. 

They come pre-screened in most cases and you will just need to make sure the interior is not blocked by insulation.


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## josall (May 7, 2011)

You will need 1 sq.ft of NFA or attic ventilation for each 150 sq.ft. of attic space. Split equally between the soffit and the ridge. Depending on the brand of your ridge vent you will have about 18 sq.in. of ventilation per lineal ft. Ex: 30' ridge x 18 sq.in of Net Free Area = 540 sq.in. of ventilation or 3.75 sq.ft.

If you have 1,000 sq.ft of atic space you will need 6.6 sq.ft. of NFA of ventilation.
3.3 at ridge
3.3 at soffit

If you know the brand of your soffit you can find out what the NFA of ventilation is to calculate how much plywood you will need to cut out in the soffit.


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## jmiller (Nov 19, 2010)

Windows on Wash said:


> jmiller is correct in that exhaust venting without supply air is a bad thing = negative pressure and air loss.
> 
> Ultimately a bad thing for efficiency _but not so bad if it is keeping the roof structure dry._


The old box vents probably kept the space more dry than an over-vented ridge, which could be the only reason the decking still appears to be in good shape. 



> Fascia flow is an option but there are probably a couple of things you can do without buying that stuff (it is expensive FYI).


I always figure the labor on intake repairs far outweighs the material cost, so ultimately he'll be saving no matter what if he does it himself. Luckily, the eaves with no overhang aren't very long, and the gutter can be re-used. 

I like your idea too, but would hesitate suggesting it on customers house without ever having seen it in the field. Interesting though.


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## Windows on Wash (Aug 30, 2011)

jmiller said:


> I like your idea too, but would hesitate suggesting it on customers house without ever having seen it in the field. Interesting though.


We have used it previously with good success. Customer had some custom trim and other things and wanted to be as surgical as possible. Every other rafter bay and some 4" pipe to hook it up, you should have felt the amount of air it was pulling once we opened it up.


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## shazapple (Jun 30, 2011)

Those circular vents don't really flow much air. The 4" diameter vent has 2.43 sq. inches of NFA, which means you would need 4 of them per foot to balance your ridge vent. You are better off going with a continuous soffit http://roofing.owenscorning.com/homeowner/accessories/ventilation/8-foot-continuous-soffit.aspx


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## Windows on Wash (Aug 30, 2011)

shazapple said:


> Those circular vents don't really flow much air. The 4" diameter vent has 2.43 sq. inches of NFA, which means you would need 4 of them per foot to balance your ridge vent. You are better off going with a continuous soffit http://roofing.owenscorning.com/homeowner/accessories/ventilation/8-foot-continuous-soffit.aspx


Where to you come up with 2.43 square inches? Are you assuming that the 4" vent pictured is only +80% obstructed?

The original poster does not have an overhang in those locations and near complete removal of the fascia board is probably not an option.

The purpose of the circular vents was in those locations without overhangs and an unobtrusive way to get some intake air at those locations.

Perhaps those vents weren't the best example as they are a bit obstructed. Here is a better example. In a 4" capacity, I would estimate them to be less than 40% obstructed which would provide roughly 7.5 square inches of ventilation per vent. 










I would estimate that the footprint of the home is less than 800 square feet necessitating 5.3 square feet of attic ventilation. If he just did the soffits in those circular vents, he would need a bunch of them (roughly 50) but he has a soffit overhang on roughly 60% of the roof. These vents are likely unnecessary for the total ventilation requirement but will give him some added convective movement of air in those areas without intake air.


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## jmiller (Nov 19, 2010)

The tough Q: how does one provide intake ventilation where the porch roof covers the eave.


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## Windows on Wash (Aug 30, 2011)

jmiller said:


> The tough Q: how does one provide intake ventilation where the porch roof covers the eave.


Drop the porch soffit, access previous overhand, make sure soffits are completely open (no need to install soffit as you can just cut it opening and cover it up with some metal window screen) re-install new porch soffit (hidden vent is fine for beaded board look or non vented will not really obstruct that much air flow).

If the framing covers everything up, you can just cut a hole in the roof at the cross gable and put in some vented soffit on the porch.

If the storm door is closed, it is most likely not an air tight enclosure and the convection in the attic should drive the make up air into the vents.


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## jmiller (Nov 19, 2010)

Thanks, BUT, I'll pretend I didn't think of it.


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## shazapple (Jun 30, 2011)

Windows on Wash said:


> Where to you come up with 2.43 square inches? Are you assuming that the 4" vent pictured is only +80% obstructed?


It is from the manufacturers website
http://roofing.owenscorning.com/homeowner/accessories/ventilation/round-mini-soffit.aspx

The other one you showed is 4 square inches of NFA
http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053


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## Windows on Wash (Aug 30, 2011)

Thanks for that link.

I am not sure how they come up with that number. I guess I was figuring on the vent portion be 4" with a flange that extends beyond that. 

4" @ 60% clear, yielding about 2.4 inches x 3.14 = 7.5 sq/inches. 

Go figure though. Must be much more obstructed than that.

If the homeowner wants, take a 4" hole saw and just put some window screen over the hole. It won't be 4" clear but it will give you more than 4 sq/inches.


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## cbrc5eric (Mar 15, 2010)

jmiller said:


> If ridge vent is installed with no intake it can create negative pressure in the attic that pulls conditioned air from the house (and makes for frosty gable windows in winter).
> 
> The first step might be checking the seal between the conditioned space and the attic. Are your bath fans vented out the roof, or dumped into the soffit? Does the hatch you access the attic from have tight fitting insulation? Do you have recessed lighting? Those are all an easy path for the ridge vent to pull air through.
> 
> Next step would be adding the continuous soffit vents and fascia vents where there's no soffit, which IMO would be worthwhile and DIYable.


Yup! I've done the first extensively, crawled around the attic, sealed up electrical and vent stack penetrations. No recessed lights, and I've sealed everything as best as I could. One big offender was right over the stairs, it was completely open! Check out the dirt in the insulation:






















Windows on Wash said:


> jmiller is correct in that exhaust venting without supply air is a bad thing = negative pressure and air loss.
> 
> Ultimately a bad thing for efficiency but not so bad if it is keeping the roof structure dry.
> 
> ...


I installed the attic baffles on all the baffle bays. 16" OC construction, there was 50 of them. It was a pain crawling around the attic!

Yup, I'm replacing the soffit anyway to change the color, so while I'm in there I'll cut out what's necessary. 

Still considering all options for the non-overhang part... I'll only need about 35 feet total as the house isn't that big. I saw there's FasciaVent from GAF too which comes in a roll, but so far Fascia Flow looks most appealing for my application.




josall said:


> You will need 1 sq.ft of NFA or attic ventilation for each 150 sq.ft. of attic space. Split equally between the soffit and the ridge. Depending on the brand of your ridge vent you will have about 18 sq.in. of ventilation per lineal ft. Ex: 30' ridge x 18 sq.in of Net Free Area = 540 sq.in. of ventilation or 3.75 sq.ft.
> 
> If you have 1,000 sq.ft of atic space you will need 6.6 sq.ft. of NFA of ventilation.
> 3.3 at ridge
> ...


It is about 1000 sq ft. I just plan on getting the aluminum stuff from Home Depot, I saw it the other day but since it came in 12 ft sections it wouldn't fit in my vehicle :lol: I'll have to go back with my trailer. 




jmiller said:


> The old box vents probably kept the space more dry than an over-vented ridge, which could be the only reason the decking still appears to be in good shape.
> 
> 
> I always figure the labor on intake repairs far outweighs the material cost, so ultimately he'll be saving no matter what if he does it himself. Luckily, the eaves with no overhang aren't very long, and the gutter can be re-used.
> ...


Good points. I will be DIYing. :thumbsup: Fascia Flow I'll look more into, from what I read so far it comes as a pallet and they're $100+ each one? Yikes... hope I'm wrong. 



jmiller said:


> The tough Q: how does one provide intake ventilation where the porch roof covers the eave.


That's actually another one of my projects is I plan on tearing out the closed in part of the covered entry way. It's too small to be useful (can't put chairs in there) and the siding looks like such an obvious add on, where the rest of the house is brick. :laughing: I plan on leaving the peak but losing most of the area with the siding and the windows, and making it open with some columns and a new front door :yes:.

But for now, the sides of the enclosed part there are also soffit vents there. Who knows they're probably also covered with plywood...


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## cbrc5eric (Mar 15, 2010)

Windows on Wash said:


> Where to you come up with 2.43 square inches? Are you assuming that the 4" vent pictured is only +80% obstructed?
> 
> The original poster does not have an overhang in those locations and near complete removal of the fascia board is probably not an option.


I can get creative :laughing: I'm pretty handy.



> The purpose of the circular vents was in those locations without overhangs and an unobtrusive way to get some intake air at those locations.
> 
> Perhaps those vents weren't the best example as they are a bit obstructed.  Here is a better example. In a 4" capacity, I would estimate them to be less than 40% obstructed which would provide roughly 7.5 square inches of ventilation per vent.
> 
> ...


The house is actually 1000 sq ft. I gotta take some more measurements to see exactly how much area I have under the overhang areas. Perhaps I'll climb up on roof too to see what kind of ridge vent it is as well...

I'm wondering who the hell put in the ridge vent without adding the right intake vents. I'm VERY curious to see what's hiding underneath the current soffit. Just hope I don't wind up destroying the gutters pulling them loose to take out the existing soffits :lol:


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## Windows on Wash (Aug 30, 2011)

The more you get it tightened up on the attic to living space connection, the more your ventilation requirements drop.

If you are good in your air sealing details, there is no reason you can run very near the 1:300 ratio and at that point you will far exceed your requirements with the retrofit of what you have now.


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## Gary in WA (Mar 11, 2009)

Pull up those planks to try and seal the stud walls next to the lowered stairwell. (F.g. in plastic bags) The basement/crawl is probably wired/plumbed giving you a good air chase there. Be careful, we don't want you posting in "Drywall" next....

I agree, the circular vents are quite deceptive for their NFVA; http://www.lomanco.com/ProductPAGES/CirkVents.html

Did you air seal the basement/crawl space, to counter the "stack effect"? http://www.wag-aic.org/1999/WAG_99_baker.pdf

You are the very first to comment on this BEFORE I sited it, Lol; http://www.finehomebuilding.com/PDF/Free/021105092.pdf

Gary


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## cbrc5eric (Mar 15, 2010)

Windows on Wash said:


> The more you get it tightened up on the attic to living space connection, the more your ventilation requirements drop.
> 
> If you are good in your air sealing details, there is no reason you can run very near the 1:300 ratio and at that point you will far exceed your requirements with the retrofit of what you have now.


Good stuff- the frosty windows I noticed when I first moved in. I did alot of the sealing this past year, so we'll see if the effort paid off come this winter time. 



GBR in WA said:


> Pull up those planks to try and seal the stud walls next to the lowered stairwell. (F.g. in plastic bags) The basement/crawl is probably wired/plumbed giving you a good air chase there. Be careful, we don't want you posting in "Drywall" next....
> 
> I agree, the circular vents are quite deceptive for their NFVA; http://www.lomanco.com/ProductPAGES/CirkVents.html
> 
> ...


I can't get down into the cavity you see, even if I took the planks out (which were just sitting there) I can't lower myself into there as it's right above the basement stairs. What I did though, was I sealed the area as best as I could using 2 layers of 6 mil plastic sheeting and then stapled/siliconed the heck out of it. That should "hopefully" stop a good amount of the air flow.

As for drywalling, I've got pretty dang good at that . My first major project when I moved in I knocked down 2 walls to combine the foyer, dining room and living room into one 24 x 12" room. The textures of the walls and ceiling did not match so not only did I fill in the walls (and floor and ceiling) I also skim coated the entire living room! That took for-ever, esp the ceiling and was realllly messy but it came out surprisingly well esp for my first time :laughing:

I forgot to mention the bath exhaust does vent to the outside. The house had quite a few big "chimneys" before I got to it, the stairs you saw earlier, the furnace chimney was open straight into the attic as were the 2 vent stacks. I sealed them all up. Exterior walls don't have any insulation though


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