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Discussion Starter #1
I was getting familiar with the attic in my new house, and looking for places to air seal and the insulation over the vaulted ceiling has raised some concerns.

There is about 3 or 4 feet at the peak of the ceiling to stand so it's not a traditional vaulted ceiling in that the drywall is almost directly on the roof rafters. I crawled all the way down to the soffits and pulled back some insulation batts. They stuffed the soffits with the batts and there appears to be no soffit vents. I can't confirm from the outside of the house yet, because they covered the soffits with the aluminum wrap and soffit covers.
the previous owner had a ridge vent installed when they replaced the roof, so I'm wondering if I should crawl down and add some soffit vents. Even though it's vaulted, it seems to me that it could be treated in the same way that a regular flat ceiling would be as far as ventilation is concerned. Thoughts? Do I need to be worried about adding vents if it wasn't constructed that way?
 

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The general approach is to have both high and low vents. This approach provides the desired air pressure created by the difference in height and (to borrow their term) washes the underside of the roof with incoming air. The primary purpose of attic ventilation is to remove unwanted moisture that diffuses or leaks through the ceiling from the interior of the house. Although ventilation can reduce the heat in the attic in the summer that issue is best controlled by lots of insulation.

Confirm whether there is or was soffit venting and if none, if you can add some it would be best.

Sounds like scissor trusses where you have some space but still a sloped attic floor. Nice, but a pain to work in.

We can help you run through the recommended amount of insulation for your home if you would like.

And welcome to the forum.

Bud
 

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Discussion Starter #3
Thanks Bud. Yes the trusses do look scissor-like so I would imagine you're right. Do I need to vent every rafter bay and if not, is it ok to leave the insulation they jammed down in there? I will add attic baffles for the bays I add vents for sure.

Speaking to the attic baffles, there is no way to get that close to the soffit from the attic. I see that I can add them from the outside, but that will require removing the vinyl soffit covers, cutting an access hole in the bottom of the soffit and then reinstalling the the wood, adding a vent and replacing the vinyl cover. sound about right?

the rest of the house has regular 8' ceilings with blown in white fiber glass, but it doesn't seem too thick.

Here is a crude picture of the situation:

http://imgur.com/a/MZv6S
 

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Yes, you should open every bay to allow air flow from the soffit to the top. That assumes your soffit area provides a common space that connects all rafter ends.
Google "installing attic ventilation with scissor trusses pictures", I like pictures and Google answers. Basically it is much better than me guessing what you are seeing.

If it is difficult or impossible to slide a pre-made baffle down there, consider making your own. Google "GBA site built ventilation baffles for roofs " and select the like with that name. If I post the link it requires you to sign up, but this way they seem to let us read for free.

The insulation should help hold the lower section up against the roof, with spacers attached and the upper section you tack it in place anyway you can.

As for the vents themselves, total net free vent area is your objective. If it can be continuous great, but not necessary if the soffits are all connected.

Bud
 

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Discussion Starter #5
Thanks Bud. I've got one more question for now if you can assist. the ''gable'' side of the vaulted ceiling in the attic just has some loose batt insulation stapled to it but there are lots of gaps and it doesn't look like it's too effective. Are there best practices in this situation to properly insulate? I was thinking foam board or something might work well. Thanks.
 

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Typically a gable end wall will face a cold attic on the inside and mother nature on the outside. In that case no insulation to the outside is needed. Only place that needs it would be the top of the exterior wall, usually buried along with the attic floor.

If the other side of that vaulted gable is conditioned space then that wall needs very good insulation. Let me know.

Bud
 

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Looks like heated space on the other side. If 2x6 wall then fill with insulation of your choice and be neat as small gaps greatly reduce the potential insulation results. If 2x4 then covering with a layer of rigid would be better than just 3.5" of insulation.

If it were mine I would use Roxul, very dense and easy to cut and fit where needed. Then I would add a 1" layer of foil faced rigid insulation over it. Tape all seams and be sire the results are air tight.

If just fiber insulation then you still need to cover it, either drywall or at a minimum house wrap. But I prefer a rigid covering.A flexible covering can still billow in and out pumping air through the insulation.

Bud
 

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Discussion Starter #9
Wow, I just looked it up on the Roxul website. Seems like it might be better than the fiberglass batts I have over the vaulted ceiling, too!

It is 2x4 construction. Seems pretty easy, just fill the cavities with Roxul, then cut the foam board to fit, and tape the seams? there is a plethora of air leaks i need to fix as well so while i'm up there it seems like that would be the best.

There are tons of different types of insulation out there it seems. How does Roxul compare to others? Is it better than say, fiberglass batts?
 

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One of the failings of regular fiberglass insulation is its low density and susceptibility to air movement. Roxul is much denser and suitable for a wide variety of applications. When you cut it, leave it a bit oversized so it is a press fit when installed. I think their 14.5" cavity insulation is actually 15". Cuts easily with a long bread knife.

I'm currently installing some 1" Dow Tuff-R in my basement (orange box store) and although it doesn't have the rating of the Thermax it does have a very substantial foil covering on the primary side. A bit thinner on the other side.

Rigid foam board has the concern of needing a thermal barrier, but in an attic your local authority would have to decide what you need to meet those requirements. Thermax should and if asked I suspect my local AHJ (authority having jurisdiction) would approve the Tuff-R. If not I will glue a layer of drywall over it, some day.

I switched to Roxul when it first came out and there were no other mineral wool products. In my area it is still the only one but I believe there are now others. Fiberglass comes from a variety of mfgs and they have a high density. other than cost i can't see a reason to go back to fg.

Bud
 
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