Proper attic ventilation

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Gilly826

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Hello, newbie here!

I recently bought a house, and upon home inspection mold was discovered in the attic. We went through the proper steps and had the mold remediated. Now we are looking to properly vent the attic to prevent this from happening again going forward. The roof has a ridge vent as well as soffits, but apparently the previous home owners roofing company did not make them functional.. They are just there "for show." Anyways, we have been advised the easiest method of ventilation will be using gable vents, along with a fan controlled via thermostat.

I have a gable picked out that has automatic closing/opening louvers for the fan (as required per fans instructions), but my main question is how many/what size vents should I have on the opposing gable!?! If it helps the attic is roughly 900sq ft, with about a 4' peak in the middle that slopes down on both ends.

TIA
 

Snoonyb

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The soffit vents should have nothing to do with the roofer, so before you install a mechanical venting system that has louvers that close, make sure that your eve or soffit vents work and that you have the proper attic dampening installed, which with the ridge vent should be appropriate.
 

oldognewtrick

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The soffit vents should have nothing to do with the roofer, so before you install a mechanical venting system that has louvers that close, make sure that your eve or soffit vents work and that you have the proper attic dampening installed, which with the ridge vent should be appropriate.
Well, yes and no. A roofer should identify if there is functional intake venting at the soffit. If vents are not there or are compromised by insulation or framing there are options to retrofit intake venting. All shingle mfg require a proper venting system to not void shingle warranty.
 

Gilly826

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I wasnt sure exactly where to post this, and since its an attic/venting question I chose the roofing section... Neither the soffits/ridge vent are functional, and given the situation we have going on here the easiest method of proper venting is gable vents/fans. This is what the mold company advised. The fan I'm getting is definitely overpowered for the application, but its very energy efficient and I would rather have morn flow than not enough.. Im just unsure of how many/how big the "supply" vents should be in order to properly air out/cool the attic via the "exhaust/gable fan"
 

jeffmattero76

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I understand that a soffit vent can be "non- functional" if they are blocked by insulation or other barrier.

However, I don't understand how a Ridge vent can be "non-functional". Can someone explain that?
 

Gilly826

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If I remember correctly, the home inspector/mold company stated the soffit/ridge vents were both "in place," but they had solid plywood/beams or other obstacles in the way that would prevent, or make it not worth while trying to make the vents functional. Which is why we were advised to go the gable vent/fan route.
 

oldognewtrick

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Ventilation on a roof works very similar to an internal combustion engine. You have to have intake and exhaust. If either are compromised, it's rendered useless. Simply putting in a gable vent will not improve your current situation without some ability to introduce cooler outside air. Air will flow up, very little will move left to right.

I know budgets are always a concern, but, I hate to see people throw good money after bad just to be put in a different position. My suggestion, have a qualified roofing contractor install a functioning ridge and soffit vent.
 

Gilly826

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I totally get where your coming from, but right now cash is tight and I need to do something given we are in the middle of summer (todays 100+ degrees here in MA, with the worst humidity) A fan and gable vent are only gonna cost me $3-400. But, what Im getting at is what you were speaking of: ventilation and exhaust. My attic, at it's tallest point allows you crowch on the joists at best, and like I said maybe 900 sq ft.. My exhaust is going to be an overpowered fan with the louvered gable.. What I need to know is what is the best method of providing sufficient gable intake (on the opposite side of the house) for that exhaust. I understand it won't be perfect, but its something I need to deal with ASAP.. And to be honest, I feel its such a small attic that with the proper intake/exhaust it can be perfectly functional. Not trying to come off as a "know-it-all" or anything of the like, so please dont take it that way.

Here's the thing, installing "intake" gables are fairly cheap, and I'm a handy guy with good help.. What I dont know is how much intake is enough, where's the best place to install the gables, and if too much intake is bad for the exhaust (which I assume it would be).. Given my situation, I'd appreciate if you can help me find a happy/sufficient medium. Again, thank you!
 

Snoonyb

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Attic venting is "generally" 1/150, so at 900sq.ft., 6sq.ft. of venting should be sufficient, so a couple of 16"X24" gable vents should do.

Correcting the "non-functional" ridge vents will be far less cost, for you to accomplish.

You say, "house/mold" inspector, so if you had the dwelling inspected, why wasn't this corrected before escrow closed?
 

Gilly826

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The mold was remediated before we moved in, but the seller did not agree to providing proper venting.. When we heard about the gable/fan setup that was recommended we werent to concerned, having plumbers, electricians and carpenters in the family.. It seemed to be "simple enough." What I/We didnt know, were the questions I have presented to you all. Thank you for giving me an idea of what needs to be done..

That being said, what is involved in making a ridge vent functional? The soffits look to be a real PITA to ever make them truly functional.. You can see the "ridge vent" visually from the outside, but there is nothing done inside the attic that allows it to breathe. If we were to get the ridge vent functional, I assume we would still need gable vents/fans if the soffits aren't functional?

Sorry for the long post, but I used to be an insulator. And from the way the "soffits" are set up.. Its damn near impossible to properly cut the plywood and install the plastic/foam attic joist vents (losing my train of thought here) that allow air to circulate up into the attic above the layer of cellulose insulation that will be covering the attic floor. Where the "soffits" are the space is just too tight, it really should have been done when the previous owner had the roof fixed years ago.
 

Snoonyb

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To remedy the ridge vent they need to be removed, the sheathing cut and removed and the ridge vent reinstalled.

True the insulation dampers should have been installed at the last roof repair, because now it's a real job.

As previously mentioned the venting works best when the air flow is low to high.

At this stage your choices are repairing the ridge vent and dealing with the static air, or add a couple of timed fans in the attic. The other is the fan driven gable end vents.
 

68bucks

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If you put in a fan way oversized for the vent capacity you'll pull conditioned air from in the house.
 

raymond-

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I'm your average joe-blow homeowner with little expertise, but just tossing in an observation
with regard to attic/roof venting. it should be viewed as a system so you take into consideration
each vent's design and LOCATION and size. the person evaluating these should be looking at
the direction and air flow to ensure maximum efficiency.....something that may get lost over
the keyboards and without drawings. there is art/chitecture and aerodynamics involved
 

Gilly826

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Thanks for the replies everyone. I just went ahead and ordered a fan and a few gable vents. Im also going to look into the ridge venting this weekend. The fan I purchased has variable speeds, so I can adjust it if it is pulling too much air.. And I got a couple gables that equate to about 7sq ft of intake ventilation. If the attic were bigger there would be more options on placement of the gables, going to hopefully have them installed this week.

Thanks everyone
 

oldognewtrick

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PLEASE, DO NOT MIX DIFFERENT TYPES OF EXHAUST VENTS! Use one or the other, not both.
 

Gilly826

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Luckily I bought 2 of the same vents, same size and everything. I hadnt thought of it before hand, but I see your point!
 

oldognewtrick

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Ridge vent is a passive system, a powered gable vent is an active system. When the fan is pulling air out of the attic, any ridge vent will become an intake vent. This short cycles the venting. Air will take the path of least resistance. It can lead to water intrusion into the attic.
 

Gilly826

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Ohh, I thought you were talking about using different brand of vents/etc.. Thanks for clarifying. Ok, it looks like I wont be going the ridge vent method then. I had thought about a ridge vent sucking in air with a gable fan, but not moisture etc.. Makes sense! Again, thank you!
 
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