Latest Discussions : HVAC

06:39AM | 10/25/01

Member Since: 10/24/01
10 lifetime posts

Improving insulation/ventilation in finished attic

Tags: HVAC

I recently moved into a 1922 2-1/2 story colonial in Baltimore, MD (hot, humid summers and fairly cold winters). The previous owner did a poor job of insulating when he finished the attic this past year; he stuffed R-19 faced fiberglass between the 2x6 rafters directly against the roof sheathing and covered it with drywall (the FG facing is correctly placed to the inside). There is no venting at all in the attic - the roof is a "hip roof" (?) with no gable ends and has a large dormer on each side. This summer, temperatures in the attic were stifling, even with the A/C running full bore, and I am concerned about moisture problems in the winter. The problem is the room design is very complex and I do not want to take down the existing drywall as this would be a monstrous undertaking, and we use the room frequently. I have consulted many sources for advice, including two local insulation contrators. The first contrator visited my house and said I basically could do nothing, and that he didn't think I would have a problem with roof rot. The second recommended pumping PolyMaster plastic foam to completely fill all the void cavities between the existing fiberglass insulation and the roof sheathing, including over the eaves and to the roof peak, basically closing off all air gaps between the the roof and the finished room. The thinking is that the foam will both prevent moisture from reaching the roof in the winter and will prevent superheated air from being trapped against the roof in the summer. The cost would be $1800, which seems very expensive, and I have not seen this practice suggested anywhere else. Does anyone have any recommendations on:

1. Will foaming in against the roof solve the problem (cost not withstanding), that is protect against winter moisture and summer heat build up?
2. Are there any other possible solutions? My top choices have been to either leave it alone and take my chances, or to try to cut a hole in the drywall between each rafter and try to shove something (PVC, etc) between the FG and the roof to add an air gap, then install continuous soffit and ridge venting. This would greatly compress my existing insulation and minimize its effectiveness.
3. Could I paint the ceiling with a type of paint that would prevent moist air from penetrating the drywall/FG and reaching the roof in the winter? Although the insulation is faced, from what I can see the previous owner did a poor job and left some gaps.

Sorry if I was long winded, but I have researched long and hard on this issue to no avail. Please help!!!

Jay J

09:04AM | 10/25/01

Member Since: 10/26/00
782 lifetime posts

Hi wible1,

You seem to have a good handle on what's going on. But for the benefit of others, I'm going to offer more background on what's going on. (You will pick up whatever you can ...)

Well, I'm going to be the bearer of more bad news. What's happening up there is the roof is getting heated (especially in the Summer) and the heat is radiating into your living space right THROUGH the sheathing, insulation, AND drywall. This is really bad especially in summer where your A/C is running all the time. You'll probably NEVER cool that room. And in Winter, you have the same effect except less so but you will have moisture up there as it cools.

Before there's any recommendation to the 'problem', let me explain what should have been done when the attic was finished off. Whoever finished off the attic should have installed Soffit Vents and Soffit Chutes and a Ridge Vent. The Soffit Vents are installed at the eaves which allow fresh air to rise up and along the UNDERSIDE of the roof's sheathing via the Soffit Chutes (to cool the roof), and to channel the hot air to the outside via the Ridge Vent. When this doesn't occur (as in your case), adding more insulation isn't going to help. In short, the roof needs to be kept 'cool' in order to prevent any heat from building up.

If you want to know what a Hip Roof is, see Shingling a Hip Roof (assuming this WEB page loads up.)

For more info, see OwensCorning.com and there are pictures and product links too. (They call their 'chutes' - Rafter Vents ...)

Now what should you do??? That's a good question! If you need a new roof, consider installing the lightest colored shingles you (... well, your wife) can tolerate. This will help a little to keep the heat off of the roof. Beyond that, I'd consider installing the Chutes even if you have to cut out parts of the ceiling. BUT, before you do, I'd learn as MUCH as possible about what needs to be done to have a successful 'retrofit'. (Get the proper sized and type vents and chutes. Yes, they even make Soffit Vents if you don't have eaves on your home!) If you need more info or guidance, post back.

My best to ya and hope this helps.

Jay J -Moderator

PS: Hopefully I've made it known, indirectly, that you don't want to use PVC as a 'chute' ...

PPS: You can always take your chances ...

PPPS: God Bless America!

wible1

01:04PM | 10/25/01

Member Since: 10/24/01
10 lifetime posts

Jay J,
Thanks for the reply. You're explanation was a good one. Someone suggested to me that filling the cavities between the roof and drywall with foam would help alleviate the heat buildup because the foam would block out any air and would allow for a greater heat gradient, essentially dissipating the heat gain, and that the real cause of heat buildup is superheated air that gets trapped under the roof in the absence of proper ventilation. Do you buy that? I have considered supplementing my A/C with a window unit in the attic to help with the cooling. By the way, the shingles are fairly light and were replaced a couple years ago before I moved in. As you can tell, I am really hoping to find a solution that does not involve removing the drywall, simply because I hate working with drywall (not to mention I don't have a lot of spare time right now). Would you even consider the foam solution?

Jay J

06:05AM | 10/26/01

Member Since: 10/26/00
782 lifetime posts

Hi wible1,

You know, it's hard for me to say what you should do. I'm the kind of guy that, regardless of how 'disruptive' the job might be, I like to do it right the first time, and be done w/it. (Then again, I'm not in your shoes ...)

No, I don't buy the theory that plugging the holes, or whatever, will do what's being touted. Your heat is a radiant heat problem. A radiant heat problem is one that's similiar to heating an empty pot on the stove. The pot has no holes, yet it gives off heat on the INSIDE if you were to stick your hand in in it and touch the bottom. See what I mean? The hot bottom has nothing to do with the 'air' that's in the pot, even though it is 'warm' too (as you reach through it to touch the bottom.)

You know, you could leave things alone to see what happens, for at least all 4 seasons. As for adding a window unit, I'd forget that. Instead, I'd consider installing a ceiling vent with a fan to allow the warm air to get out of the room. By cooling all that warm air, remember: Warm air holds a LOT of moisture, and by cooling it, you'll get dampness on a lot of surfaces (which will lead to mold/mildew.) IMO, bad idea.

So as you see, it's real easy for me to say what you should do. It's a shame the previousl owner did a poor job. The only way you MIGHT have known this is if you actually noticed that there weren't any soffit vents and a ridge vent. Did you have the home inspected??? Did the Inspector catch this??? Were there any 'signs' of mold/mildew when he went up into the attic?

Jay J -Moderator

PS: God Bless America!

BV022092

08:23PM | 04/09/20

Jay J, You're just the guy I need to speak to! I love the fact that you "likes to do the job right the first time" and that's exactly how I feel about it. I actually don't care how disruptive I have to get to make things right. There is a reason things need to be done a certain way. If you do them incorrectly, you get nothing but headaches and future unnecessary expense, in my opinion.
That said, I have a 1920 American foursquare home. The attic is not finished, but it is a beautiful space! I love the way it feels! The roof shingles need to be replaced within the next 5 years. I would like to replace the outside (down to the wood) with a base layer of roof ice & water shield, followed by metal roofing tiles.
It's important for me to do this project right the first time. I will be doing the job myself.
So, if I understand correctly, the soffit vents, chutes, and ridge vent on the outside? Is it part of the roofing materials?
Inside the attic I have bare rafters with solid wood boards beneath the shingles. Can I insulate between those rafters and close up the wall? If I do ice & water shield followed by metal shingle tiles ... that has venting built in, right? ... do I close off the attic vent hole with the spinning roof vent on it?
Thanks, in advance, Kimber

BV022474

08:51PM | 05/19/20

Your ridge vent is on the underside of your roof where the exterior wall meets the roof, from there air will flow through the vents along the ridgeline of the interior attic space, keeping airflow to the underside of your roof (attic space) this airflow is assisted by installing baffles that are stapled in the 16” on center bays, normally just in the eves but can extend to the ridge if need be. The air then follows the roof line up and out of the ridge vent to completely ventilate the space.

This being said, adding foam, a vapor barrier, and closing off your eves and ridge vent you are now creating a sealed space between your roof and the shingles. Before doing this make sure wood has a moisture content of less than 18%. This recreates you’re building envelope and provides a true livable attic, which now must be conditioned.

BV022474

08:53PM | 05/19/20

Sorry not ridge vent, soffit vent.