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Old 07-20-2019, 08:27 PM   #1
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Adding insulation to attic


After having some high heating bills in winter and an AC that on really hot days can't always keep up its apparent I need to add some attic insulation sooner rather than later. During a home energy inspection it was noted there were some air gaps and insulation was 50 years old and only about 4-5 inches deep. I was going to rent a machine and add about 9 inches of blow in when an experienced AC tech said you can just lay bats over the blow in for less work, mess and cost. Is that true or should I do blow in? Thanks!
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Old 07-20-2019, 08:56 PM   #2
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Adding insulation will likely have a minimal impact if that's all you plan to to. You will get more benefit from air sealing the attic floor, and it is easiest to accomplish as step one. Once air sealing is complete, then add another layer to get up to the recommended R value for your area.
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Old 07-21-2019, 04:10 AM   #3
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Re: Adding insulation to attic


Air sealing efforts (as Steve suggested) can vary from sealing everything to just addressing the major leak areas which account for the majority of leakage. Here is a link on air sealing throughout the house. Always best to do as much air sealing as you can before you bury the attic in insulation.

But, to be honest, reducing your energy costs is a package of improvements and if that energy inspection was worth while it would have detailed the options and how much improvement each could contribute.

Tell us more about your home and we can help with the guidance.

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Old 07-21-2019, 07:34 AM   #4
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Re: Adding insulation to attic


Where do you live ? What type of attic ventilation do you have ? How old is the house ? Do you consider your house to be drafty in the winter when wind is howling ? How good are your windows and doors ? A good energy audit would have given you a report card on these items and more . And as already stated a grade would have been assigned to each fault area giving a payback vs. cost outlay . I am not a fan of blown in insulation it's just a personal thing with me . Very messy , hard to apply evenly even for a pro .

I like fiberglass rolled insulation with the first layer going in between the joists/parallel . Then the 2nd layer running the opposite direction . This would be done AFTER sealing the ceiling leaks/gaps . Fiberglass gives you the ability to roll it out of the way if needed , maybe you are inspecting for wires as an example . Blown in you have to shovel it out of the way . If the fiberglass gets wet you can roll it up , take it outside and let it dry in the sun and reuse within reason of course .
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Old 07-21-2019, 08:38 AM   #5
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Re: Adding insulation to attic


Firstly, I just want to agree that air sealing is important to do first. I know that, but I was really just asking in regards to the method of installing insulation on top of what I have and if putting in rolls on top of old blow in would work or be advisable.

The home inspection was very thorough. His first things to address were any air leaks between the first floor and the attic and adding more insulation. Our windows are fairly new, there are no drafts to speak of, etc. The other area we would need to address at some point is proper sealing between the basement top plate and the first floor. But thats a harder DYI so I haven't figured out how to address that yet.

Also, when inspected, he was quite thorough and didn't seem to be too concerned about the air leaks. As in, there was nothing major. It was mostly around lights, wall top plates, things like that. Hopefully this additional info helps.
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Old 07-21-2019, 09:02 AM   #6
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Re: Adding insulation to attic


The additional information does help.

Sorry for the lecture but you must realize we don't know the level of knowledge of our posters and we can't see what you see. In this case we don't even know where you are. It often takes some back and forth for the details to be filled in. J

Yes you can roll out batt insulation over blown in insulation but best if the joist cavities are filled to the top before going perpendicular with the batts, that eliminates the voids that would otherwise exist on each side of the joists. With insulation, neatness counts.

In his report did he include any numbers from his air leakage test, we refer to it as a blower door test? That number eliminates the guess work and if he combined an infrared inspection with the blower door you would have pictures of where the worst air leakage exists.

The link I provided has a description and pictures of many of the problem areas, always nice to find and seal a few of the BIG ones. I have had home owners in shock when I show them the tornado of air going from basement to attic. Not saying you have one, but nice to know where to check.

And yes, the rim joist area (foundation to house) is an important area to seal and insulate.

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Old 07-21-2019, 11:13 AM   #7
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Re: Adding insulation to attic


Quote:
Originally Posted by bluegrassliving View Post
I was going to rent a machine and add about 9 inches of blow in when an experienced AC tech said you can just lay bats over the blow in for less work, mess and cost. Is that true or should I do blow in?

Does a bundle of bats fit through the hatch? Less mess so long as you can open the bundle in the attic. Call me weird, but I like the nice neat rows of bats. Less cost, doubt it, but you would have to price it out.
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Old 07-21-2019, 01:39 PM   #8
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Re: Adding insulation to attic


A bundle of bats should fit through the garage hatch, it's pretty decent size. Does it matter if I use rolls vs precut pieces in a bundle?
@Bud 0951 - good call on making sure the blow in is up to the top of the joists at least. I haven't been up in the attic for a while as it's been really hot. But it cools down tomorrow so maybe I'll finally venture up there again to inspect things a bit further.

I don't believe he did a blower door test. It was mostly thermal imaging stuff. While his report was thorough I didn't see a lot of it as it was sent to the gas company. I'll have to email him and see if I can't get that. To be fair, he was incentivized to not tell me everything I should do because he was one of the utliity company's approved contractors for doing the insulation and air sealing work. That's what his company does in general but he also does these inspections for the gas companies. He was pretty straight forward and we talked about a lot of things but he didn't go into great detail where the air leaks were aside from the general knowledge ones like around can lights, bathroom fans, ductwork that runs between floors, things like that. So I do plan on using your link when I get up there to spot air leaks and I play on using expanding foam to fill those before adding any insulation.

Do I need to put insulation on the plank of boards that run the length of the roof? These serve as a way to access everything in the attic like bathroom fans, soffits, etc. So I would assume you would want to keep this narrow walkway free of insulation. Thanks!
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Old 07-24-2019, 07:39 AM   #9
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Re: Adding insulation to attic


You can leave the walkway free. Just means losing some insulation value but you may not want to actually raise it. I'd work with the batts. Easier to install (no big machines needed), no dust and easier to replace if necessary. I'd buy whatever is cheaper, batts or rolls. If rolls, cut them to easy to handle sizes. More cuts means more chances of leaks but you need to think about what you can handle, a human cost. Also, you probably will need unfaced fiberglass, that is, without the paper layer. If paper layer, you need to cut slits in the paper, without cutting too much of the insulaton, so it can breathe.
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Old 07-24-2019, 08:03 AM   #10
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Re: Adding insulation to attic


Consider Roxul or another brand of mineral wool, very dense and tucks together nicely. Personally I would go right over the walkway as your added insulation should be as deep as possible.

Unfortunately you got short changes on the energy inspection as it was way short of a full energy audit. Doing an infrared inspection without a blower door or other exhaust fan running doesn't catch a lot of the leaks. Plus outside temperature needs to be considered.
You can rent an infrared camera and use a large window fan to enhance the leakage and we can guide you if you go that direction. The blower door test would have given us a measure on how much leakage exists before sealing.

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Old 07-24-2019, 08:55 AM   #11
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Re: Adding insulation to attic


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Consider Roxul or another brand of mineral wool, very dense and tucks together nicely.
That's what I did. Two layers of R22 Roxul over existing blown in fiberglass. First layer perpendicular to the joists, and then top layer parallel to the joists. As mentioned, very dense and gotta think it helps restrict any airflow. If I have to, I can throw a larger board over it to distribute my load, and walk/crawl over it. Never going to recoup the cost though.
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Old 07-24-2019, 04:22 PM   #12
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Re: Adding insulation to attic


blown in is much better than batt - no voids.

air sealing is far more important than insulating. insulating attics that have a lot of air leakage from the house and insufficient ventilation can actually cause mold growth by reducing surface temperatures. the moisture that leaks in from the house start condensing.

Adding attic insulation is over-rated.

The law of diminishing returns applies.

If you already have even R15, savings will be very modest.

It's far more important to air seal, insulate uninsulated basements, exterior walls. it can get very expensive to properly retrofit a house.
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Old 07-24-2019, 08:00 PM   #13
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Re: Adding insulation to attic


Insulation is also about comfort. Without it or not enough, ceiling area under the attic will be hot and cold seasonally. It's not been long since I bought current house so I still don't know how much attic floor (ceiling for rooms underneath) insulation I have. I can't imagine I have more than 2x6 attic floor and I assume I have about old r11 there. I can feel the heat through the sheetrock.

I don't have any concrete numbers but r15 would be inadequate, I think. Air seal if you can. BTW, if 4-5 inch you have is cellulose, it is pretty good air sealer. But helps to seal if you have light fixture boxes or around bath fan boxes, chimney chase, plumbing/vent pipe holes and electric wire holes. Then add r30 batts over them. Helps, esp with summer heat, if you have power fans in the attic. We insulate to save fuel costs over the life of the house. Even if I finish my life in this house I won't recoup the money I put into it, but that is not the only factor in working on a house. Selling the house, too. Although you may not get the money back, there is a benefit of making the house attractive and not wasting time (another cost) waiting for somebody who doesn't care about insulation.
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Old 07-24-2019, 09:23 PM   #14
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Re: Adding insulation to attic


For cellulose to be a good air sealer, it must be dense packed in walls. Loose fill in an attic won't reduce air leakage much.

Quote:
I don't have any concrete numbers but r15 would be inadequate, I think
R15 is low especially if the attic gets hot in the summer. But given the choice I would rather have an R15 attic with insulated basement walls than nothing in the basement and R50 attic.

Adding insulation is always beneficial but the law of diminishing returns applies.* The energy savings are modest when there's already something there. It's still worth doing after air sealing is complete.

Insulating uninsulated basements and air sealing saves a lot more than topping off attics.


*The amount of additional insulation material you need to reduce heat loss in absolute terms (not by percentage, by bTU/hr lost) goes up exponentially the more you add.

Heat loss = (Surface area x temperature differential)/effective r-value.

Going from R5 to R10 saves 50%, adding only an extra R5 worth of material.

Going from R5 to R20 saves 75%. Need three times as much material to gain an extra 25% savings.



But just topping off an attic will not resolve heat loss problems in many cases. The money is often better spent elsewhere first.
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Old 07-24-2019, 10:54 PM   #15
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Re: Adding insulation to attic


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Originally Posted by user_12345a View Post

Adding attic insulation is over-rated.

The law of diminishing returns applies.

If you already have even R15, savings will be very modest.

I have to respectfully disagree with the above. When I bought my house back in 1980 (new construction) there was a minimum amount of blown in insulation in the attics. I'm guessing maybe R15 in some areas and R11 in others. It was not distributed evenly and there were some voids as well. I bought the house in September and the first winter was nothing but high gas bills due to so much heat loss. After a snowfall the snow would quickly melt leaving dry shingles a day or so later depending on the amount of snow. Had an ice dam over the front door.

The following year I decided to try to reduce the heating bills for the next winter and installed R19 rolls. I guessed that I had about R35 once I was done. My heating bill dropped almost in half the following year.

Fast forward another few years and I added another layer of R30 fiberglass rolls so I now have about R60. No more melting snow, ice dams, and crazy high heating bills.

I do understand the importance of air sealing and wish I knew of this when I first bought the house but I'm not going back up in the attic anymore.

Last edited by Dave Sal; 07-24-2019 at 10:57 PM.
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