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Adding attic ventilation?


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Disclaimer: I am not an inspector, so if that's against the rules, mods please feel free to delete this without reading further.

Basic question: My attic is inadequately vented, and nobody seems to agree on the best way to remedy this. What is the best type/size/frequency/position of vent to add?

Too many background details: My husband and I just bought our first house in April. It's a 1989 Cape-style (appropriately, since we're on Cape Cod). My dad, who's been inspecting in Michigan for a quarter century now, did our inspection but warned us that his expertise is centered in a different region with a different climate so some of his advice may be inaccurate.

One of the findings in his report was that our attic, separated into lower and upper sections, is only ventilated by gable end vents in either end of the upper section. The lower section has no openings, and the space between the two, which he said should be mostly filled with insulation but left partly empty to allow air circulation, is filled with fiberglass top to bottom. There's evidence of mold in the lower attic, which may be from having no exposure to fresh air but may also be from leaks in the previous roof, which evidence suggests was allowed to deteriorate much longer than it should have before being replaced - our current roof is only a few years old and, according to the previous owners, is the first to have replaced the original. We can't tell whether there's mold in the upper attic, because there is no access hatch.

The conclusion so far has been that the gable end vents are adequate for the upper attic because of the consistent breeze this close to the coast, but that the lower attic definitely needs help. The options presented by various quarters have included either simply adding another set of gable end vents in the ends of the lower attic, or installing soffit vents along the length of the house (which I think would also require somehow propping up the insulation between each pair of rafters to allow air to move from the soffit vents up to the gable vents, but that wasn't part of the original suggestion). To add to the pressure, one of these was suggested by my dad and one by my husband's father, and since we're each sure that our own father is the ultimate oracle about everything, there's some severe cognitive dissonance going on.

More complete question: which, if either, of these options is preferable? Is there an easier solution that we're missing?

Thanks for any advice or insight you may be able to offer. I'd be happy to provide pictures or further details if necessary.

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Hi,

Find Fred Lugano. He's a weatherization contractor that used to write a lot of articles about insulation and weatherizing houses for Journal of Light Construction and Fine Homebuilding. He used to run Lake Construction in Charlotte, VT. I believe that he's semi-retired but still available for consults.

Google the guy and you'll probably pull up a bunch of articles. Who knows? One might just be about how to properly insulate a Cape Cod style house.

If anyone will know how to properly insulate a Cape Cod house in that part of the country, Fred Will.

ONE TEAM - ONE FIGHT!!!

Mike

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Mike gave the best advice of all. Follow thru on that if you can. Otherwise:

If I could assume that by 'upper and lower sections' you're referring to the upper and lower attic spaces in a two story house, I'd suggest that you first open up that bottleneck between the two attics. The air flow might be improved by greater vertical displacement. Attic air flow doesn't subscribe very well to any simple formula. There's lots of factors involved. So it's somewhat a 'trial/error' method I'm suggesting you use at first and avoid spending big dollars until you find something that works.

If the two attics are not spaced vertically or somewhat vertically than do describe a little more what their spatial relationship is.

Marc

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Cut a hatch into the lower attic; see what's going on. It could be fine. Or not. Can't tell without looking. If there's no apparent condensation issues, it can be "wrong" but still work just fine.

We know that the building codes are wrong about a lot of stuff related to insulation and ventilation (re: Joe L., William B. Rose). Couple that with entirely different performance characteristics in building envelopes due to a multitude of variables, and it's hard to come up with hard and fast rules applicable to every situation. We all make our usual commentary about insulation and ventilation because that's what we do, but sometimes it's a lot of blather with little practical application.

Jimmie's comment about skirting problems is pretty accurate; I see Capes all the time that are "wrong", but they work fine.

Capes are one of the hardest designs to retrofit insulation into; lots of angles, lack of access, etc. Depending on how long you plan on living in the house, it may not make economic sense. I understand if you're dedicated to Green regardless of it's impact on your wallet; some folks are going to do the right thing even when it's not in their immediate best economic interest.

Cut a hatch. Take a picture. No, take lots of pictures. Post them. It's not hard to figure out what's going on with good pics.

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More info would help, but here is a start.

BTW, evidence of mold in the lower attic means this house design is not working as well as it should, no?

Soffit vents are almost always a good thing to add, and this can be done from outside.

How were you able to determine that the insulation in the lower section is pressed against the roof sheathing? If it is fiberglass batts, they will sag a bit as a rule, unless the drywall is pushed up against it from below. A gap of an inch or two will allow air to move along the underside of the sheathing. If the ceiling is vaulted, you may have to do some dismantling to install baffles.

Then you need vents across the upper side of that roof plane to let the rising air out. A roof vent installed every 4 feet or so along the ridge is usually adequate. Roof vents or continuous ridge vents will work better than gable vents.

Cut a hole in a closet ceiling so that you can access that other attic space.

If you are on the Atlantic Coast in a storm path, you should certainly go with local knowledge. What works well here may not be so good where you are.

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Cognitive dissonance.. I like that! Sounds like a simple problem.. I see a lot of bad ventilation issues from houses of that period around Boston and on the Cape..

Did they use 'drip-edge flashing vents' as low-intake vents?

They tend to get clogged up with organic debris from the trees and not work over time (and get blocked by snow in winter and get totally blocked)..

There is a nice guy up here in the Boston area that may be the answer for you.. he's helped a lot of my clients.. www.ventmasterinc.com

You don't need an international team of experts.. ! :)

The cross-flow thing can work both ways.. not always a good thing. 'depends'..

Low-intake/high outlet systems tend to work fine in my experience ..

The Cape is misty often and what with all the conifer trees... you get a lot of problems...

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The Cape is a funny place climatically and they get away with skirting nearly all convention there without consequence.

Jimmy, what makes you think she's in Provincetown?

I am amazed by how many inspectors here either missed the fact the house is a Cape Cod style, or don't know what that means. It's a 1 1/2 story house with the second floor tucked under a steep roof. The lower attic is the space behind the knee walls and the upper attic is the space above the collar ties.

If it were mine, I'd insulate the roof deck and condition those lower attic spaces. Odds are they are being used as closets, built in dressers, and storage anyway making effective air sealing impossible.

There are dozens of options for insulation that range in price from 'a nice dinner out' to 'an entry level commuter car'.

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I am amazed by how many inspectors here either missed the fact the house is a Cape Cod style, or don't know what that means. It's a 1 1/2 story house with the second floor tucked under a steep roof. The lower attic is the space behind the knee walls and the upper attic is the space above the collar ties.

If it were mine, I'd insulate the roof deck and condition those lower attic spaces. Odds are they are being used as closets, built in dressers, and storage anyway making effective air sealing impossible.

There are dozens of options for insulation that range in price from 'a nice dinner out' to 'an entry level commuter car'.

That's something I run into fairly often. Acadian-style, one-story homes with DYI developed attics have an identical layout as Capes, but with the gable facing the street instead of the eaves. With soffit venting, opening the bottleneck between the two attics (or returning the attic to it's original condition) was my prescription but your suggestion is a good one too.

Marc

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There are dozens of options for insulation that range in price from 'a nice dinner out' to 'an entry level commuter car'.

That's why the first thing I'd do is cut a hatch.

If it was an "old" one, i.e., built with dimensional lumber, it's probably fine.

Since it was built in '89, at the time when pretty much everything was getting built wrong, I have reservations.

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I am amazed by how many inspectors here either missed the fact the house is a Cape Cod style, or don't know what that means. It's a 1 1/2 story house with the second floor tucked under a steep roof.

Are we talking about a full cape, a half cape, or a three quarter cape, like my house?

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There are dozens of options for insulation that range in price from 'a nice dinner out' to 'an entry level commuter car'.

Since it was built in '89, at the time when pretty much everything was getting built wrong, I have reservations.

The recent re-roof would have been an excellent time to open it up, see what science projects were there, and install SPF under the new sheathing. Since they missed that opportunity, I'd be leaning toward an injection foam like Applegate or Retrofoam. Yeah it's open cell but given the age there will be at least 2x10 rafters and that's plenty o' foam to avoid moisture issues.

Yes, she needs to get into the attic to see what's going on. It sounds like there is access behind the knee walls since someone saw mold in there, but whatever area doesn't have a hatch needs one.

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Thank you all for your responses! I'll definitely look up the names people have recommended and talk over the suggestions with my team of advisors (read: husband and all the relatives we have who've ever done their own home repair).

Adding a hatch to the upper attic was already on our winter to-do list, but if seeing what's going on up there is important to deciding how to vent the lower attic before it becomes ice damming season, I'll bump it up to top priority.

For anyone still pursuing further conclusions, I managed to get some pictures today before the daylight totally disappeared.

The front of the house, with annotations:

IMG_20121022_175749edit.jpg

Other pics of the exterior: gable ends and back of house.

Several views looking up into that all-important cavity between ceiling and roof:

http://img.photobucket.com/albums/v92/A ... 181120.jpg"]IMG_20121022_181120resize.jpg[/url]

[2] [3]

Inner surface as the roof slopes down to the eaves. Not the best color representation, but in person I could see that the sheathing was clearly discolored. I didn't see the mold I remembered being told about, so maybe my inspector's suggestion to spray a Borax solution in there and let it air out was more of a precaution based on the evidence of past water intrusion.

(There are a few more pictures in the Photobucket album that I think, but am not certain, aren't very useful.

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The options presented by various quarters have included either simply adding another set of gable end vents in the ends of the lower attic, or installing soffit vents along the length of the house

Maybe this will help. I've got gable vents on the upper section, too. I also have cup vents in the soffits between the rafters and there are vents on the exterior walls at either end of the house for the space behind the knee walls. No problems

Adding a hatch to the upper attic was already on our winter to-do list, but if seeing what's going on up there is important to deciding how to vent the lower attic before it becomes ice damming season, I'll bump it up to top priority.

This section has cup vents at the soffit and a ridge vent at the top. It works here. No ice damming, ever. I'd try that, and don't get excited if installing baffles is more of a headache than it's worth. It's a small area and should be fine without them. I'm personally not sold on the importance of needing them in the first place.

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