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Alec
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Alec

Anon

Attic insulation

Hello, I have a question about attic insulation.. I'm building a house in northern NJ. It's a two story colonial house. I have two options in terms of insulation - insulate the attic roof (I was considering 3' spray foam + R15 fiberglass) and not do anything on the ceiling of the 2nd floor OR insulate 2nd floor ceiling (with R36 fiberglass) and not do anything in the attic. I know that insulating the roof would be more costly, but i'm building the house for myself, I expect to be living there for the next 10-15 year so eventhough money factor is important, it's not my #1 priority at this point. Could you possibly tell me which is a better way to go in terms of energy efficiency/comfort/etc? I will have HVAC units in the attic, if that makes any difference. One of my concerns is if I leave the ceiling not insulated and do the attic, eventhough the whole house is insulated, will I be essentially heating/cooling non-living space? Thank you very much.
66860111 (banned)
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66860111 (banned)

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The insulation creates a thermal envelope between conditioned and unconditioned space. If you want the attic conditioned or plan to use it as living space say an office at some point you'd want to create the thermal envelope on the roof otherwise you'd want to create the thermal envelope in the ceiling. I'm not sure what state this is in but here code for a ceiling is R-38.

Alec
@66.9.88.x

Alec

Anon

Thanks for your reply. I don't think i would be using an attic as a "living space" in the sense of having some sort of a room up there, but I will have HVAC equipment there, as well as the ducts, and possibly some storage. However, my question is more in terms of energy efficiency and insulation quality of the whole house, will insulating the attic improve that?
66860111 (banned)
join:2014-04-28

66860111 (banned)

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said by Alec :

Thanks for your reply. I don't think i would be using an attic as a "living space" in the sense of having some sort of a room up there, but I will have HVAC equipment there, as well as the ducts, and possibly some storage. However, my question is more in terms of energy efficiency and insulation quality of the whole house, will insulating the attic improve that?

I doubt it. You would insulation the ceiling and roof the same so by doing the roof you just increase your conditioned space which means more heat and a/c costs. I have my roof insulated in my house because I want the attic as conditioned storage but insulated the ceiling of garage and left that attic as unconditioned. From my experience air sealing is a huge part. Some of the other guys here might have more insight.

shdesigns
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shdesigns to Alec

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to Alec
I have one area of my roof that was insulated (vaulted ceiling.). The shingles did not last as they overheated.

I had to remove the underlayment and add insulation dams to allow some airflow under the roof to keep it cool.

A well insulated ceiling and good ventilation is the best way to go. I added a powered gable vent on a thermostat. Once I added a better ridge vent and added more soffit vents, it never comes on anymore.

pende_tim
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join:2004-01-04
Selbyville, DE

pende_tim to Alec

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to Alec
I would consider r 38 to be a MINIMUM for a roof in Northern NJ.

Insulate the ceiling unless you are planning to finish the attic some day.

Consider doing the spray foam on the ceiling ( good to stop infiltration ) then R 38 on top of that. You should end up with about an R 50 ceiling.
66860111 (banned)
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said by pende_tim:

I would consider r 38 to be a MINIMUM for a roof in Northern NJ.

Insulate the ceiling unless you are planning to finish the attic some day.

Consider doing the spray foam on the ceiling ( good to stop infiltration ) then R 38 on top of that. You should end up with about an R 50 ceiling.

I missed the OP being in NJ. Code is R-38 there so he has no choice there.

mityfowl
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join:2000-11-06
Dallas, TX

mityfowl to Alec

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to Alec
Whatever small amount it cost extra I would install radiant barrier OSB for roof decking.

This is the type of OSB with the foil laying toward the living space, then your R-38.

morbo
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morbo to Alec

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I'd insulate the attic roof with spray foam and other to R-50 and use a metal roof.

The reason is foam, done correctly, seals like nothing else. If you have HVAC units in the attic, you want those units to be in a conditioned space to keep your heating and cooling requirements as low as possible.

I recall reading an article that looked at energy usage for homes with HVAC in condition space vs non-conditioned space, and it was significant.

pende_tim
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Selbyville, DE

pende_tim to 66860111

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The R38 is a minimum. You can go as high as your pocketbook will allow.
66860111 (banned)
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said by pende_tim:

The R38 is a minimum. You can go as high as your pocketbook will allow.

Yup. I went with R-60 in the ceiling last year.

cowboyro
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join:2000-10-11
CT

cowboyro to Alec

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to Alec
If you'll have the HVAC units then insulate both the roof and the ceiling of the 2nd floor. You'll create a semi-conditioned space which can be used for storage and won't be a significant extra load for your HVAC.

cableties
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join:2005-01-27

cableties to Alec

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to Alec
You might want to pose this question with some at FHB
»www.finehomebuilding.com/

North Jersey is Zone 5
»www.energystar.gov/?c=ho ··· on_table

Msradell
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join:2008-12-25
Louisville, KY

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Msradell to cowboyro

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to cowboyro
said by cowboyro:

If you'll have the HVAC units then insulate both the roof and the ceiling of the 2nd floor. You'll create a semi-conditioned space which can be used for storage and won't be a significant extra load for your HVAC.

You Won't Find Any Place Recommending That Approach! By doing that you create an area in the attic that has no ventilation and were still in getting extremely hot in the summer putting additional load on the HVAC equipment. You either insulate the roof and condition the attic or insulate ceiling and ventilate the attic, the 2 are mutually exclusive. I'm personally of the belief that insulating the roof is a better approach and that using spray foam is the correct way to do that because of how well it blocks infiltration. It also acts as his own vapor barrier if you use closed cell foam.

pende_tim
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Selbyville, DE

pende_tim to Alec

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One other place to consider: before you insulate the walls, when the studs are up and sheathing is applied, foam the corner area where the 2x4 meets the sheathing. (A calk will also do the job, but more labor/time intensive ). This will prevent air from entering from between the gaps in the sheathing and around the 2x4s..... and don't forget the sill plate where it meets the sub-floor decking.

This will greatly help reduce infiltration and make the home more efficient.

Alec
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Ok, makes sense. What about ventilation in your attic that's ventilated? Are you concerned about that at all? I assume you have the full insulation of the roof, so there's no venting of air, is there?
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said by Alec :

Ok, makes sense. What about ventilation in your attic that's ventilated? Are you concerned about that at all? I assume you have the full insulation of the roof, so there's no venting of air, is there?

The house was built in 1960 and never designed for ventilation. There was never any soffit vents. There's a ridge vent but that's it.

That is 2" rigid board (r-13) with unfaced r-30 between the rafters then spray foam air sealed for a total of R-43.

cowboyro
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CT

cowboyro to Msradell

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said by Msradell:

You either insulate the roof and condition the attic or insulate ceiling and ventilate the attic, the 2 are mutually exclusive.

You can very well have both with roof ventilation. It will help a lot. I actually have it, the attic never goes below 40F in winter (even with 0F outside) or above 115F in summer - the attic fan also helps. It creates a nice buffer zone that greatly reduces HVAC losses and can be used for storage.

robbin
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Leander, TX

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robbin to Alec

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Another recommendation for insulating the underside of the roof. Please make sure that you use closed cell foam. Do not just use fiberglass under the decking as it will create moisture problems. Having your HVAC unit and ducts in conditioned space will result in better efficiency.

Alec
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Alec to Msradell

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to Msradell
Msradell, that's exactly what I was concerned about -- attic ventilation. Insulating the attic seems like a better way to go to me as well, but how would it be ventilated? I do have an attic fan, but i'm not sure that would be enough. So you think that by leaving 2nd floor ceiling without insulation, the attic would be able to "breathe" a little better? At the same time, would this "increase" the area on the 2nd floor that would have to be serviced by the HVAC units?

morbo
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morbo

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said by Alec :

Insulating the attic seems like a better way to go to me as well, but how would it be ventilated? I do have an attic fan, but i'm not sure that would be enough.

I would think with this method you would get rid of any attic fan or vent.
sparks
join:2001-07-08
Little Rock, AR

sparks to Alec

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to Alec
so you are saying if you insulate the roof don't insulate the floor or can you do both?
If price is a consideration insulating the attic floor is a lot cheaper then doing the ceiling, when done correctly.
Has anyone ever come up with a price comparison of this?
The idea of having heat/air units in the attic would be a big bonus for ceiling insulation.

Pher9999
join:2011-07-06
Saucier, MS

Pher9999 to Alec

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If you are insulating the roof. if you have a soffet and a ridge vent, then install these, on the underside of the roof before insulation.
»www.homedepot.com/p/ADO- ··· c1vZbmgs
This will let air flow from the soffets up to the ridge and out. it will help keep the deck dryer. You can spray foam over it if needed. it helps against ice dams as the cool air is flowing throug it and not into the roof.

Msradell
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Louisville, KY

Msradell to sparks

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said by sparks:

The idea of having heat/air units in the attic would be a big bonus for ceiling insulation.

Actually having HVAC units in the attic is one of the big reasons to insulate the roof instead of the ceiling insulation! Insulate the ceiling your HVAC units are then in the unconditioned space of the attic so they are less efficient in any leakage or infiltration of air is extremely detrimental to system efficiency.

justme
@69.118.94.x

justme to sparks

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to sparks
If this is a this OR that, ceiling hands down, and way more than r-38, r-50 at least.

Why would you ever want to heat that whole attic in the winter is beyond me, and trust me a TON of heat is going to go up there. Location I lived at had a unheated 2ed and 3ed floor. Middle of winter, new york, be 50F up there. Floors had carpet as well... ALL from heat lose from the lower floor that was heated. You are now going to do that to your attic if you do not insulate the ceiling.

If it was my place, and again this is going off a one OR the other.

I would buy foam board, cut to fit, silicon in the foam board on the ceiling making an air tight (or as close as you can) seal to the wood. I would THEN spray foam over that foam board. I am not 100% convinced that in 30-50 years that spray foam is not going to shrink a little and kill your air tight seal, so by putting the foam board and silicon, you are covered. Then as I said, I would do at least r-50, if not more... spray foam, fiberglass... whatever depends on how much room you have left up there to get your R50 or more.

It is getting NO cheaper to heat a building, the money spent now keeping the heat IN I would think could only pay off in the long run.

The attic, I'd leave it alone and let it just vent, I'd insulate the hvac equipment ducts.

Now if you can swing both. I'd still put a good amount of ceiling insulation, and foam board it. Again why do you want to HEAT that attic all winter if you won't be using it?

Also how much heat in the summer do you think that attic being insulated is going to keep out?

I'd much rather have air flow and a barrier between the attic and the house than nothing (or less).

That's just me.

enon
@50.153.112.x

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said by shdesigns:

I have one area of my roof that was insulated (vaulted ceiling.). The shingles did not last as they overheated.

I'm really surprised how many people here are recommending the roof be insulated. I experienced the same thing as you. The last house I bought, the previous homeowner finished the small attic and put a new roof on in the months before selling it to me. Shortly after I took ownership, the shingles begagn shrinking and the surface took on a wavy pattern. The gutter was constantly full of granules that were falling off the shingles. I searched the city permit database and found the contractor that put the roof on. I called him to come out and take a look. He said this is classic overheating damage because the roof was insulated and there was nothing he could do short of recommending I remove the insulation. He said he told the homeowner this was going to happen.

Even 6 years into owning the house, I had to constantly clean the gutters because of the granules. I no longer own that home but I suspect it's still a problem.

Pher9999
join:2011-07-06
Saucier, MS

Pher9999

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If they put the vent channels in between the roof and the insulation with a ridge vent,it can take care of this issue.

shdesigns
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shdesigns

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said by Pher9999:

If they put the vent channels in between the roof and the insulation with a ridge vent,it can take care of this issue.

That is what i did. I removed the lower sheeting, slid the channels up and placed more before replacing sheeting. Then slid the rest down from the attic. Made a huge difference.

There was so much wrong with the roof: no drip edge, no tarpaper, sheeting stapled down with half missing the rafters and improper flashing.

Along with the shingles, the sheeting was sagging. I also ran a saw between the sheeting to let it expand/contract due to humidity changes. No more sagging/bowing when it gets real humid.