insulation choice?

[martyinlincoln]

Still trying to decide on the best insulation for my house. Some background to help in the process...
Small paid off home,1000 square foot, with very cheap utilties. No plan on moving untill they wheel me off to the nursing home or mortician in 30 years. All ceiling penetrations have been sealed but there's still infiltration issues. New roof with ridge vent and soffit vent around entire house. Pitch is 4/12 with 3' overhangs so the max insulation over exterior walls is 2.5-3" without blocking roof ventilation. Existing insulation is 6" of 55 year old rock wool everywhere except the tight spots over the exterior walls. No vapor barrier. One gabel end and one hip end. Supply duct is in attic wrapped in 2" fiberglass with no vapor barrier. Design temps are 2 and 95, very humid in summer, heating hours are double cooling hours. Can be heavy snow loads on the roof,2x4 construction.

Best application for this house would be?
A) Spray foam underside of roof deck eliminating venting
B) Remove rock wool and foam the ceiling
C) Add a layer of batt over the rock wool
D) other- please explain

[skippedover]

Still trying to decide on the best insulation for my house. Some background to help in the process...
Small paid off home,1000 square foot, with very cheap utilties. No plan on moving untill they wheel me off to the nursing home or mortician in 30 years. All ceiling penetrations have been sealed but there's still infiltration issues. New roof with ridge vent and soffit vent around entire house. Pitch is 4/12 with 3' overhangs so the max insulation over exterior walls is 2.5-3" without blocking roof ventilation. Existing insulation is 6" of 55 year old rock wool everywhere except the tight spots over the exterior walls. No vapor barrier. One gabel end and one hip end. Supply duct is in attic wrapped in 2" fiberglass with no vapor barrier. Design temps are 2 and 95, very humid in summer, heating hours are double cooling hours. Can be heavy snow loads on the roof, 2x4 construction. I'll assume the 2x4 construction refers to the walls, not the roof joists with a heavy slowload??

Best application for this house would be?
A) Spray foam underside of roof deck eliminating venting I'm not a fan of unvented attics. JMO. Once the air exfiltrates from the treated envelope, let it go, as you've lost it.
B) Remove rock wool and foam the ceiling You need a moisture barrier. I'd removed the rock wool, install a moisture barrier, then foam. I now dense foam is supposed to be a moisture barrier but somewhere in the thickness of that foam, the temperature reaches dew point and moisture that's penetrated the dense foam can condense, lowering the R-value. Again, I'm conservative. I like to see a solid moisture barrier, solidly sealed envelope and then insulation. Dense foam will seal and insulate.
C) Add a layer of batt over the rock wool This is a waste of time and money if there is air movement. Loose rock wool and/or bats are useless against air movement, except to filter the air.
D) other- please explain

[martyinlincoln]

Thanks. Was leaning toward "B" from the start but then read some of the threads suggesting "A" on other homes. They were in warm weather zones though so I though the snow load info could be important . Joists are 2x4 but lots of support webbing which combined with a short roof makes attic work a real treat. Didn't know a vapor barrier was still needed with high density foam so will make sure it's installed.

[ga-hvac-tech]

My vote would be the foam under the roof. I have done HVAC on 'foamed' houses (both foam around the entire envelope and foam under the roof with bats in the walls). There is not denying the advantage to not having the attic an oven or refrigerator.

Foaming a roof does raise other issues, a quality foam contractor can explain them and work out solutions.

[adamwhatley]

If you go with foam under the roof you well need to seal off ridge vent & softfits for it to work right. I am not a fan of ventless attic to may variables plus your home was designed to be vented. What size hvac system do you have? Adding foam is going to decrease the load on your home even adding add fiberglass or cellulose well do as well. You don't want to have to big a system once insulation work is done!!! Just some thing to think about. Just wondering with good electric bills why add foam verus standard blowen insulation? I am sure you want to spend the less amount of money to get quick payback.

[tinmarine]

I have to agree with skippedover. That dewpoint is a ***** and if it condenses on or in the wood your going to have problems. If you were in the extreme south I would go with it. Another thing you have to concern yourself with if your going to foam is the fact that if you develop a leak, it's going to saturate and hold that moisture in that foam and hold it on the wood, just rotting it away. You see alot of that in barns with the sprayed insulation. The only thing that holds the structure together is the foam itself.

[genduct]

How about a second opinion?
Have you had any sweating duct problems to date? seems if you had you would have said something.
The others advice is sound and a little pricey with the full foam treatment. Maybe some foam at the eaves would help the low rise space and do need to maintain the eave venting. Your ceiling as I understand has been sealed so there is your air barrier.
The rest of your infiltration has got to be the walls, windows etc.
You didn't say anything about your Bstm, crawl ?

I think blowing in some added fiberglass would be quick, easy and economical. Perhaps change out your duct with 2" duct board that is sealed-insulated would help any infiltration that is due to the unit leakage (a big deal)

The whole vapor barrier question depends on your experience to date

[tinmarine]

How about a second opinion?
Have you had any sweating duct problems to date? seems if you had you would have said something.
The others advice is sound and a little pricey with the full foam treatment. Maybe some foam at the eaves would help the low rise space and do need to maintain the eave venting. Your ceiling as I understand has been sealed so there is your air barrier.
The rest of your infiltration has got to be the walls, windows etc.
You didn't say anything about your Bstm, crawl ?

I think blowing in some added fiberglass would be quick, easy and economical. Perhaps change out your duct with 2" duct board that is sealed-insulated would help any infiltration that is due to the unit leakage (a big deal)

The whole vapor barrier question depends on your experience to date

Don't take this the wrong way, but the guy is asking opinions on insulating his house and you suggest ripping his duct out and replace it with fuzzduct? Must every post be about ductboard?

[martyinlincoln]

Slab on grade, no basement or crawl space to seal. While in the attic foaming penetrations I did notice the duct sweats enough to dampen the fiberglass wrap. The plan is to tear off the old fiberglass wrap, mastic the joints and rewrap with foil faced duct insulation once it gets more comfortable up there to work. Also will double check for more wire penetration at the same time since it was mighty hot up there to be goofing around for long. Came out looking like a fuzzy teddy bear from sweat and crawling through rock wool.
The old drafty single pane windows have been replaced with double pane, except the big picture window. Walls need a lot of work. Only R3 rock wool batts there now with no air or vapor barrier. Going to strip off the siding next summer an inject slow rise foam between blackjack sheathing and batts. Then wrapping with tyvek before reinstalling siding. That should take care of all the wall infiltration issues.
HVAC equiptment is two stage Lennox xp19-024 HP and a two stage g61-045. First stage did 100% of the cooling,74 set point, even when it hit 100 outside. Second stage HP heats the house untill it's 9 degrees out then first stage furnace handles the load from there, even down to -20 last winter. The only time second stage gas has even fired was on initail start up testing.

I realize there may never be a ROI on sealing the envelope and added insulation on this little house since cooling and heating cost average less then $50 a month now. The end goal is strictly increasing comfort by stopping drafts and controling humidity in summer and winter. Saving a few bucks a month would be a bonus but a very small one.

[genduct]

Hey Marine, no offense taken.
The reason for the new duct suggestion is if it is leaking (probably) then the building science tells us the infiltration is especially bad. Agreed?

Also chance are the existing duct is installed relatively low and the added insulation will bury it. Talk about sweating ducts, if they are not seating now then with it buried in more insulation and no vapor barrier, chances are even greater the duct surface will hit dewpoint. Agreed? You don't want to move/ reinstall an old duct system do you?

So if the ceiling is the air barrier then the added insulation with a new sealed insulated duct system installed above the blow in makes the most sense to me. I know board is leak class 6 and sealed sheet metal according to Man J & D is 48 so sheet metal is 8 times more leakage than board.
I fully understand that there are those who haven't seen it done right and think only hacks use it. Not my expierence

Sound reasonable?
Regards, Mike ( Army Artillery, the FO)

[genduct]

Marty, I didn't look at yours before I answered the Marine.
WOW slab on grade in NE. No perimeter insulation? How about since you're stripping the exterior. blow dense pack fiber glass in the cavities instead of foam? You are going to need the vapor barrier inside (TYVEK is an air barrier not a vapor barrier) and you are going to want your home to "breath" ( i.e. not capture the vapor in the wall) How about some blue board for the edge slab losses as well.

You'll need to check that with an insulation expert in your area, but I think with your major winter you are like our New England climate.
I think if you do this right you will get a return

[genduct]

YO Jim

I did notice the duct sweats enough to dampen the fiberglass wrap

Looks like I may have guessed right.

[genduct]

PS Marty, don't use cellulose! google cellulose and old wires and see what damage the borates ( fireproofing) stuff does with it's corrosive and caustic treatment to old wire insulation