An "insulating" proposition

[Z33]

So I wanted to run an insulation scenario by you guys and get some thoughts if you dont mind.

Wall of text warning:

The background: I have a 2200 square foot split level home in Atlanta which I'm sure you guys know is hot as hell. We bought the house three years ago and replaced all the single pane windows and doubled the total tonnage of the HVAC while splitting the units from one grossly undersized unit to two 2 ton units for a total of 4 tons capacity

This did wonders for making the house more comfortable got rid of a TON of duct work in the basement that we have since finished and halved our summer electric bill to usually about 80-90 in the summer and 40-50 the winter.

Currently I have about an R-35 of fairly new blown in cellulose insulation that was put in at some point before we purchased the house. The problem is that with adding the new HVAC in the attic above the bedrooms much of this was moved around and compacted down to get the airhandler in the attic and the ducts run. I can tell a significant difference in this area verses the other bedrooms that were undisturbed.

Now for the question: I am considering three scenarios to help keep the upstairs cool and resolved the missing/compacted insulation issue.


The first would be to have some one come in and suck all the existing insulation out and have 2 inches of closed cell(?) foam sprayed in the open bays and then topped with blown in cellulose to take me to an R-50 or so. I am hoping this would also seal around the attic fan and the HVAC registers where they pass through the ceiling. This option would keep the total depth down quite a bit and still allow easy access to the air handler to change filters and service the unit.

The second option is to just blow another 10 inches (R-50ish total) of cellulose not worry about the air sealing and try to find a way to keep the insulation off the platform that the air-handler sits on. This would be the quickest and cheapest option as I would do this my self.

The third is to have the bays filled with closed cell foam and forget about it. No mess of tracking cellulose all over the house every time I change filters. The space is air sealed and tightened up and just doesn't have to be messed with anymore.


We plan to say in the house for the next 4-5 years at least. I will be putting a roof on it next year and at that time I will be converting it from soffit vents, exhaust fans, and turbines to ridge vents.


If it were your house what would you do?

 

[EatenByLimestone]

I'd air seal from below then blow fiberglass on top of your cellulose.

The reason for the fiberglass is it has so little cleanup and doesn't cover everything with dust like cellulose.

 

[semipro]

In general, ventilated attics are a bad place for air handlers and duct work.
Have you considered going to an un-ventilated attic and insulating the underside of the roof rather than the ceiling. Spray or board foam would work. This may be more than you're willing to do for the 5 years you'll be there.
If that's not an option you could install a radiant barrier on the underside of the roof and then add the insulation to the attic floor as you're thinking already. In the areas where you can't get enough loose fill thickness, installing some foam board in addition to, or instead of, should work.

If you stick with the ventilated attic make sure its ventilated properly and that ventilation near the eves is not obstructed by blown in or batt insulation. In general a continuous soffit vent combined with continuous ridge vent on a shed-style roof is best.

One more comment: although increasing your cooling capacity may seem like a good idea this can actually backfire. If the system runs in short cycles you will not get proper dehumidification and comfort will suffer. As you improve your insulation this effect may become more an issue. A properly sized AC system should run almost continuously during the hottest part of the hottest days.

 

[woodgeek]

Hire someone to do pro airsealing (which is for the framing openings, which are likely huge), a blower door test, and then prob skip the extra insulation

When was the place built?

If you need 4 tons with an insulated attic, the place is prob a sieve.

 

[blades]

Cellulose does not lose r factor when compacted- as was mentioned ya got holes that are causing migration. Now if you got ducting in attic- is it insulated ducting?

 

[Cynnergy]

If you are replacing the roof next year, you can also make an unventilated attic ("hot roof") by placing foam board above the sheathing.

 

[Z33]

I'd air seal from below then blow fiberglass on top of your cellulose.

The reason for the fiberglass is it has so little cleanup and doesn't cover everything with dust like cellulose.

The fiber glass isnt really an option in my mind. The existing cellulose is far too uneven ranging from about 5 inches thick where we have had people in the attic doing work to 2 feet deep in the areas where there have been no traffic. In addition you would trample down the exisitng insulation as you laid down the new batts

In general, ventilated attics are a bad place for air handlers and duct work.
Have you considered going to an un-ventilated attic and insulating the underside of the roof rather than the ceiling. Spray or board foam would work. This may be more than you're willing to do for the 5 years you'll be there.
If that's not an option you could install a radiant barrier on the underside of the roof and then add the insulation to the attic floor as you're thinking already. In the areas where you can't get enough loose fill thickness, installing some foam board in addition to, or instead of, should work.

We have thought about this and its an option. The reason I am not so sure about it is that its a large attic space that I don't really want to heat and cool. Just a guess but it would probably double the cubic footage of the space we are heating and cooling. In addition it would probably have to be done after the roof as there is no plywood on the deck, its all 1X material running the length of the roof. spraying insulation would stick to the bottom of the shingles and tar paper making them difficult to remove.

If you stick with the ventilated attic make sure its ventilated properly and that ventilation near the eves is not obstructed by blown in or batt insulation. In general a continuous soffit vent combined with continuous ridge vent on a shed-style roof is best.

The vents in the eve are about 5 foot above the highest point of insulation so no problems here. In addition we have about two dozen sofitt vents as well as 3 gable vents for about 1600 sqft of attic space which I would guess is sufficient

One more comment: although increasing your cooling capacity may seem like a good idea this can actually backfire. If the system runs in short cycles you will not get proper dehumidification and comfort will suffer. As you improve your insulation this effect may become more an issue. A properly sized AC system should run almost continuously during the hottest part of the hottest days.

I am good with HVAC. The "rule of thumb" around here is 1 ton for every 500 sqft. The three ton system we had before ran all day from about 9 am to 9pm Just to maintain 78 ( you could forget anything lower) degrees on any day above 90 which we have a ton of. We have good de-humidification with the current system and it doesn't short cycle. We are happy with the two new systems and feel like they are a good fit for the home.

Hire someone to do pro airsealing (which is for the framing openings, which are likely huge), a blower door test, and then prob skip the extra insulation

When was the place built?

If you need 4 tons with an insulated attic, the place is prob a sieve.

We have an insulation company that comes highly recommended here. I will definitely be giving them call I just wanted to bounce some ideas around before I drag them out here.

House was built in 65'its 90% brick with brick/insulation board/r-19 in the walls. Its no sieve but like anything built in the era of cheap energy it could always use some tightening up. I am really not sure why everyone thinks 4 tons is too much capacity. We regularly hit 100 degrees here in the summer with 80-90 percent humidity, it give the a/c a real work out.

Cellulose does not lose r factor when compacted- as was mentioned ya got holes that are causing migration. Now if you got ducting in attic- is it insulated ducting?

I had to go look this up... I swear I read some where that as its compacted it looses r-value. Hummmm, more reading for me.

As for the duct-work it is 6 inch insulated to an r-6 I think.

If you are replacing the roof next year, you can also make an unventilated attic ("hot roof") by placing foam board above the sheathing.

It this foam that the shingles and tar paper can be nailed directly over? Dont think I am familiar with this technique.

 

[maple1]

The fiber glass isnt really an option in my mind. The existing cellulose is far too uneven ranging from about 5 inches thick where we have had people in the attic doing work to 2 feet deep in the areas where there have been no traffic. In addition you would trample down the exisitng insulation as you laid down the new batts

He was speaking of blown-in glass, not batts.

 

[Z33]

The fiber glass isnt really an option in my mind. The existing cellulose is far too uneven ranging from about 5 inches thick where we have had people in the attic doing work to 2 feet deep in the areas where there have been no traffic. In addition you would trample down the exisitng insulation as you laid down the new batts

He was speaking of blown-in glass, not batts.

Crap! I see that now! Another bad case of fingers moving faster than brain.

 

[woodgeek]

It gets hot here too. When its 100°F and 80%RH here, my 2250 sq ft house runs my 4 ton HP on a 50% cycle. That is, 2 tons can keep up at those conditions. It was built in '60 with R-13 walls.

The difference is it has been pro airsealed. Blower door test comes in at CFM50 = 1650, and most of that is NOT in the attic.

There are likely many leakage points you haven't considered, mostly hidden in the framing. like top and bottom plates. ANY house built in '65 without blower door results should be considered a sieve. The 500 sqft/ton rule is for older, un-airsealed construction.

In hot weather, reverse stack effect is sucking that super-heated air in your attic directly into your upper story (directly through your insulation). If you had an airsealed attic and a foot or more of cellulose, the heat leaking into your upper story would be basically squat. If your upper story gets hot in the summer, that is diagnostic that you have large air leakage openings. MY house as purchased had >10 sq ft of opening between the house and attic, typical 60s construction.

Your houses's PO made a mistake that was common before 2005-2010. Hot upper story...add insulation without airsealing. Doesn't really work at all, and makes the airsealing a PITA afterward. But you can pay to make it right. But dumping more insulation on top....will just double down on the error.

-------------------------------------------------

Maybe math will convince you....say the attic is 700 sq ft and 70°F hotter than the interior. The heat flow by conduction is 700*70/R-value. Lets say your R-value is 25. Works out to ~2000 BTU/h (and no latent load due to humidity), or 1/6th of a ton of cooling. IF your only heat source from the attic was conduction.

In practice, your air leakage could be 100-200 cfm. The heat transfer is 1.08*cfm*DTemp. That looks like 7500-15000 BTU/h, or 0.6 to 1.2 tons of AC. Plus latent loads from humidty, maybe 1-1.5 tons total.

 

[semipro]

Z33,
I suspect you may be confusing "insulation" with "air sealing" - very different things. "Insulation" basically addresses the movement of heat via conduction, no air flow involved Air sealing addresses heat movement via convection. Some thermal insulation helps with air sealing (e.g., packed cellulose, foam) also. Generally, your time/money is best spent addressing the majority of air leaks first. There is a decreasing rate of return though as you start trying to address the more elusive leaks.

The suggestion for you to get an home energy analysis with blower door test is a good one.

 

[EatenByLimestone]

I found air sealing elusive at first. You fix a leak and air infiltration moves to a different spot. But once you knock the spots out, you realize some awesome savings and increases in comfort.

 

[Cynnergy]

You can find a good primer article about conditioned v. non-conditioned attics here: http://www.greenbuildingadvisor.com/blogs/dept/musings/creating-conditioned-attic

Green Building Advisor also has lots of other useful articles too. I highly recommend their site!

 

[tom in maine]

As one who sells foam as part of my living and has a house of it, I would just add more cellulose. Cellulose is so simple to install and compacts enough in what you are describing to seal the ceiling reasonably well. Radiant heat is not going to penetrate this very much in the summertime. Radiant barriers are trumped by highly insulated ceilings.
A lot of work has been done in Florida, supporting this.
You do certainly need a highly sealed attic hatch, though.

 

[woodgeek]

Loose-fill cellulose IS air permeable, like fiberglass. Densepack is less so.

Adding more loosefill to an unairsealed attic is easy, but will not result in a noticeable difference in energy usage or comfort.

 

[tom in maine]

I would respectfully disagree. If you have 18" of cellulose, loose or otherwise in an attic, vs. 18" of FG, the cellulose is going to be less permeable and will be a more effective insulation. By its nature, cellulose has smaller fibers that pack denser as it is sprayed in place. If we were talking about 6" of material, it would be similar in performance to fiberglass and not work as well.
It will make a difference in saving energy.

 

[tom in maine]

I will say that the cellulose vs. fiberglass conversation is never ending. Here is a link with the appropriate quote from the article from someone not selling insulation:


http://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/fiberglass-versus-cellulose


Differences
Air leakage: It's true that neither insulation is an air barrier. Neither cellulose (even when dense-packed) nor fiberglass meet any technical standard for an air barrier. However, cellulose will slow air flow whereas fiberglass does not.

When dense packed into a wall cavity, cellulose prevents most air flow. Even loose-fill cellulose slows some air movement.

 

[semipro]

Radiant heat is not going to penetrate this very much in the summertime. Radiant barriers are trumped by highly insulated ceilings.

Just to clarify; my suggestion of a radiant barrier at the roof was to cool the attic primarily because the air handler and ductwork are located there.

 

[tom in maine]

I would look to have all the ductwork near the living space, with all the insulation on top of the ducting.
I realize that many AC units land in attics, which is a tough location for southern installations.

 

[laynes69]

We have an old victorian home with tall ceilings. For quite a few years the upstairs was brutal, even with attic insulation. When I realized we had massive air infiltration in the attic I chose to airseal. After airsealing, we blew in 14" of insulation and now the upstairs stays cooler than downstairs in the summertime. The ceiling is cool to the touch while the attic is very hot. The difference in both summer and winter was significant. We choose cellulose, and it was very easy to install and cost effective. Also very important is ventilation. To airseal and blow in a few inches of insulation wouldn't cost but very little and the difference would be significant.

 

[Seasoned Oak]

Every time i hear homeowners tell me "this is always the coldest room in the house" during a wall covering tearout ,i always find fibreglass insulation in the walls. I remove it all and replace it with blown in cellulose. I swear the fibreglass shrinks over time cuz theres an inch gap along the wall studs and i cant believe anyone would install it that way.

 

[semipro]

i cant believe anyone would install it that way.

They do. Much of the bad rap FG gets is due to poor installation rather than the material itself.
That said, I think its relatively harder to install FG correctly when compared to other materials...e.g., Roxul.
A rating system has been developed for insulation installs. http://www.energyvanguard.com/blog-...-Grade-the-Installation-Quality-of-Insulation
Unfortunately, historically, many installs have been "Grade III" ...and worse.

 

[semipro]

Every time i hear homeowners tell me "this is always the coldest room in the house" during a wall covering tearout ,i always find fibreglass insulation in the walls. I remove it all and replace it with blown in cellulose

No doubt some (maybe most) of this improvement was due to enhancement of the air barrier provided by packed cellulose. FG does not perform well as an air barrier, especially when poorly installed.