Invisivent & Insects; any experience/opinions?

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Old 02-13-15, 10:58 AM
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Question Invisivent & Insects; any experience/opinions?

Hello,

I'm using the Certainteed T 3 1/3 soffit material and, as I'm putting it up, I'm becoming more and more concerned about insects--particularly yellow jackets and wasps since I'm allergic to bee stings.
The Certainteed literature says that screening material can be installed behind the soffit material. I have two concerns with that though;
  1. Adding screening material will reduce the air flow. That's particularly a concern for areas where I don't have balanced soffits (i.e., there is an Eastern soffit, but the roofline dives into another roofline, so there is no opposing Western soffit).
  2. Even with screening material behind the soffit material, bees would have plenty of room to setup housekeeping in the vented valleys of the soffit material. Heck, they manage to get into vinyl windows through the weep holes.

Do you have any experience with the Invisvent soffits? Any opinions, suggestions, or advice.

Thanks in advance.
 
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Old 02-13-15, 01:02 PM
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Hi Styrdy,
sorry, no direct experience with that produce, but I do have extensive experience with balancing venting. In addition, I recently installed my new front vinyl soffit vents and elected to screen the entire area above them. With vinyl soffits the bugs just walk around the ends if they don't fit through the holes.

You wrote "there is an Eastern soffit, but the roofline dives into another roofline, so there is no opposing Western soffit". In many cases the guidelines for balancing venting are not entirely correct and when you have multiple height soffits/vents it can become necessary to diverge considerably from traditional thinking. In my particular case, adding my screening did reduce my lowest vent area (NFA), but that was good.

Do you have high vents in combination with those soffits?

Bud
 
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Old 02-13-15, 01:56 PM
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Thanks @Bud9051.
On an addition that has an East-side soffit only, there is a single box vent.
For the original structure, there is a section that only has a West-side soffit only. That section has a ridge vent.
If a sketch would be helpful, I could put something together later today.
 
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Old 02-13-15, 02:55 PM
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Sketch would help, include elevations and NFA if you can estimate them.

Bud
 
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Old 02-13-15, 09:50 PM
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adding a sketch

Bud, Hopefully the sketch will help you visualize what I'm working with.
Soffits only exist on the lengths of the house. There are no soffits on the gable ends. The soffits are 23".

To simplify, if I treat the original (longest) portion of the house as a rectangle, it is 1356 sq. ft.
The addition is 121 sq. ft.
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Old 02-14-15, 03:33 AM
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It's no wonder there is so much confusion in the construction industry and especially in the newer energy related sciences. Since it is 4:40 am and I'll be awake for a few hours I'll make some corrections.

http://sidinginnovations.com/Products/vinyl-siding-brochures/Certainteed/Triple3.pdf

Page 4: "Triple 3-1/3" InvisiVent Helps Meet Code Requirements"
"Current building codes for attic ventilation require a minimum of one square foot of net free area for every 300 square feet of attic floor space provided that either the ventilation is in balance with 50% intake vents and 50% exhaust vents, OR a vapor retarder is being used." That should not say either and should say AND not OR although a vapor barrier should not be required in all climate zones.

"For today’s more energy efficient, airtight homes, the 1/150 ratio is recommended with evenly balanced intake and exhaust vents." I believe this should state 1/300, as a more energy efficient homes will have the necessary air sealing and insulation to allow for the reduced amount of ventilation.

"Since most ridge vents produce 18" of net-free area of exhaust per linear foot of attic floor" The 18" should be 18 sq in, and the "per linear foot of attic floor" should drop the "of attic floor" to avoid confusion. Attic floors have length and width and not all are rectangles and not all have a full length ridge. Ridge vents are optimistically rated as 18 inē NFA (net-free-area) per linear foot, some do not achieve that as any bug screening should reduce that number.

"Only Triple 3-1/3" InvisiVent provides more than 10" of intake ventilation." Again, this should be 10 inē, not to be confused with their next reference to a 10" overhang.

People in this business should know better than this, even if they copied it from some poorly written code somewhere.

Bud
 
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Old 02-14-15, 03:53 AM
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Now, to your house. I think it says the main house attic is not connected to the addition attic. If so that is good. If connected I will expand on the concerns that raises.

Gable ends would rarely benefit from soffit vents as that is often a closed space that is not above conditioned area, but it doesn't hurt.

Being a smaller area, a single box vent combined with the proposed soffit vents material will be fine, regardless of the ratios. Again, I can expand if needed.

For the main house, I see a gable vent illustrated (not a problem) and a full ridge vent and you will be adding full length soffit vents on both sides. That should be fine. The primary concerns would be air sealing and insulation levels and depending upon climate, possible the existence of a vapor barrier.

Where the main roof dives down to another roof line, that would concern me more for snow and water issues. With a well ventilated attic I don't think that small area will be an issue.

The 50/50 guidelines for attic venting are not a rock solid necessity. I've seen it stated that a 25/75 ratio would limit the air flow to the 25% NFA as a maximum. In the real world, the pressure will increase across that 25% and decrease across the 75% until the intake matches the exhaust. Yes, the 25/75 will provide somewhat less air flow, but far more than what is implied by saying it will be limited to the 25%.\

Let me know what I missed.
Bud
 
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Old 02-14-15, 10:09 AM
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Thanks again @Bud9051

I'm in Western New York. So it gets plenty cold here in winter (tomorrow is supposed to be around 0 degree Fahrenheit). And, it can get plenty hot in the summer (upper 90's F. are not uncommon). Probably not much different than your temps in Maine (unless you're way up North).

I see that the labeling of the sketch is somewhat difficult to read (it wasn't that way in the original). There is no airflow between the two attic crawlspaces.

I should clarify. In the sketch, the rearmost, unlabeled, structure is the unconditioned garage.
The gable vents have been sealed off, so they are no longer operational.

When they (you) refer to a vapor barrier, I assume you are talking about on the attic crawlspace floor (which I don't have). True?

So, in your opinion, you think I'll have enough ventilation even if I use screening behind the InvisiVent. True?

Thanks for taking the deeper dive Bud.
And, what the heck are you doing up at 4:30 AM?
 
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Old 02-14-15, 11:07 AM
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A typical "by the book" house in very cold country would have ceiling drywall, vapor barrier, and then the insulation on the attic floor between and above the ceiling joists. Placing rigid insulation in the top position requires rethinking as stated because it would serve to some degree as a vapor layer.

The old myth that the gable vents needing to be closed when a ridge vent is in place was based upon bad thinking. There are reasons to do so, but they are issues with snow or rain blowing in, not competition with the ridge vent.

I used staples, nylon screening (no rust), and construction adhesive to close off any sneaky holes where bugs could get in. For some reason we have hordes of lady bugs, which are good for eating other bad things, but every fall they look for hiding places and when they find one they fill it. I have run into pockets of thousands of them. And yes, I do have wasps but not allergic so just take out the nests I find.

Adding the screening should not restrict the air flow that much. If you consider the area of the holes vs and area of the screening, since each hole isn't specifically covered with a little piece of screen, those holes share a lot of screening.

Bud
 
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Old 02-15-15, 01:09 AM
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@Bud, I'm curious why you don't subscribe to the theory that gable vents rob from a ridge vent. It makes logical sense to me. Air follows the path of least resistance, so, if an outtake (from ridge vent) stream can be established more easily from the gable vent acting as the intake, it seems that's where the stream would be established.

Oh, and, although I'm not worried about them stinging, we had a huge influx of "stink bugs" this past fall. It's similar to your ladybug issue (except that ladybugs do have some redeeming qualities, whereas, the "stink bugs" remind me of the Klingons from the early episodes of Star Trek).

Thanks.
 
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Old 02-15-15, 04:55 AM
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I'm also a little curious although I've always heard that the ridge vent would draw in rain from the gable vent being the main reason.

We also have the stink bugs along with lady bugs. The lady bugs get in by the dozens but the stink bugs only get in one by one.
 
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