Insulation options for a basement ceiling

[DL]

I am in the process of finishing our basement where I used fiberglass batts between the perimeter studs, but given the number of wires, pipes, lights and duct work between the ceiling joists, I am not sure the fiberglass batts will be the best option as it will be too hard to get effective covereage. I have been told that if you don't have consistent coverage with the insuation or the insluation it compacted to much, you lose much of the effectiveness (r-value).

I saw the tail end of a home improvement show the other day where it looked as though they had stapled a clear plastic barrier to the bottom of the joists and were blowing in some type of insulation. I think this would be a very effective way of getting around all of the duct work, wires, pipes, etc, but I would be concerned about the insulation around and on the recessed ceiling lights I installed. The lights I installed are all insulation rated, but the lights still get hot.

Additionally, given that my workshop and media rooms are in the basement, I would like some level of sound barrier between floors and the different rooms.

I was wondering what others have done as for insulation between the basement ceiling joists for temperature control as well as sound barrier.

Your comments are appreciated.

David

[Greg O]

Insulation does a poor job off stopping sounds from traveling. Your best bet would be to use resilient channels to mount the sheetrock to the ceiling.

[Doug Boulter]

"DL" wrote on 17 May 2005:

1) If the basement is finished space and is going to be heated, insulating for temperature between floors is a waste of time and money except at the rim joists. 2) Compacting insulation does reduce the R-value, but not by much. For example, stuffing R-19 (6")into a 4" wall cavity reduces the R- value to 15-16 IIRC. 3) For sound insulation, it depends on what type of sounds you're trying to eliminate? The sound of footsteps on the floor above? Heavy carpet and pad, and the resiliant channels that Greg O mentions. Voices or music? Regular batt insulation (or better, the type of batt designed to attenuate sound) will be fine. You slice it to fit around the pipes and wires. Heavy carpet and pad above will help too. Also, be sure to stuff with insulation the holes in which any pipes or wires go to the floor above.

[Calvin Henry-Cotnam]

Here is an excellent article on sound isolation:

[DL]

Greg,

Thanks for the article, very informative.

I am primarily trying to minimize (not eliminate) the sound from my woodworking tools (tablesaw, router, planer, etc) from travelling through the house. Honestly not sure it is worth a significant level of effort / $$ since I don't run any tool all that long.

Secondarily, the family media room will have a surround sound system, so I could see some benefit there, but after a quick review of some sound absorbtion articles in my google seaches, I expect that I would most likely be wasting my time and money since it is not a contained room. The room has a hallway leading to the other areas of the basement (which isn't really a problem) and the stairs going to the main level, where I feel I would lose the benefit of any sound absorbtion efforts.

I guess I was just expected that adding some insulation between the joists would dampen the sound somewhat, but since the sound travels throught the sheetrock and the joist beams, I can see that the insulation would be if little help.

Thanks for the response and information.

David

[DL]

Calvin,

Thanks for the article.

David

[DL]

I guess I don't understand this. What is the difference in the ceiling of a basement and the ceiling in the upper most level of a home? Are you saying that since the floors above are controlled by a the HVAC system as well, I am not going to get any benefit from putting a layer between the floors, only where the joists are exposed to the outside (rim joists) would it be beneficial to do this.

Good to know. I have some spaces where the insulation is behind wires and was wondering if I should cut the kraft paper and put the wires in the middle of the insulation.

As I replied to Greg O, the main reason is to dampen noise from my woodworking tools and our medial room traveling to the upper levels of the house. Not sure resiliant channels will be worth the effort and $$ to do since I only use most tools for a short period of time. I was hoping that adding some insulation between the joists would help dampen the noise, fully understanding that it wouldn't eliminate it.

We have hardwood floors over the entire main level of our home except an office that has commecial vinyl tile, all of which are directly adhered to the subfloor plywood which are nailed to the joists.

Sounds like for voice or music, you feel that batt insulation designed to attenuate sound would be of some benefit. While I am willing to do this, based on the labor and precision of cutting around all the pipes, wires, vents, and lights, I would be concerned that the effectiveness would be limited due to not being able to get the insulation in all of the areas of the joists. This is why I liked the idea of the blown-in insulation. I seemed to be the best way to get a much more consistent level of insulation installed in the joists.

I do plan to use the expanding foam insulation around all pipe and wires that go to other parts of the house.

Thanks for the response,

David

[BocesLib]

David; What I used was to the space/mass method. On the outside walls in my basement I used a standard fiberglass (listed to help with accoustics too) On the ceiling I used a 4" batts as well. Why the heck 4" batts? because it provides a space void for sound to be trapped into (same principle is listed the article that people sent). Is it completely sound proofing the basement? Nope. But does it help?? Sure! I am not building a sound proof studio down there, just dont want to easily hear people talking nor the TV going.

I initially put this in a bathroom I made down there. You really dont hear that much going on in that bathroom. Even when the shower is on. Just using insulation did help and didnt even come close to blowing my budget.

Tom

[DL]

Tom,

What you did was my original plan, but after running alot of wiring and duct work, along with all the recessed lights, I guess that I became concerned about how many "holes / spaces" around the duct work and lights there might be that would allow sound to penetrate. After seeing the show on the blown-in insulation, I figured that it would be a good way to get around all the stuff between the joists, but I forgot about wanting to keep some dead space above the insulation.

Thanks,

David

[Chris Lewis]

According to DL :

Perhaps the simplest approach (batt or blowin) is to use rock wool, _not_ fiberglass. Rockwool blocks sound much better than fiberglass.

_Wires_? No, don't do that. Or are you just talking about floor penetrations?

[DL]

Interesting, I will have to check into rock wool.

Most are floor penetrations, but I do have some some lines that go between the garage and basement where I have added some dedicated circuits for a compressor and welder. I guess I could use the electrical clay to seal around the wires. I will need to do the same for some of the outside outlets as well.

Why the don't do that?

[Calvin Henry-Cotnam]

For thermal insulation, you only get benefits when there is a difference in temperature, and temperature control, on either side of the insulation.

Two rooms heated by the same system, especially if controlled by the same thermostat, will not produce a benefit by having thermal insulation between them.

The insulation will help damp a lot of the noise, particularly higher frequencies, but sound can be transmitted well through the framing and the insulation will do nothing to stop that sound. Lower frequencies are particularly susceptable to be transmitted this way.

Resiliant channel will help to reduce what is transmitted to the framing.

All the more reason to use the relilient channel -- hardwood, and to a lesser extent vinyl, makes a great sounding board to launch the sound transmitted through the floor (from the framing, since the insulation will dampen the air-born sound) into the room above.

At least carpeting will have some effect of reducing what noise comes through. Ever driven a car with its carpeting removed?

[Chris Lewis]

According to DL :

See

for one brand.

[Just a happy user of the stuff.]

Because the interior walls of a house are leaky enough that sealing interior wire penetrations is absolutely useless. I'm not sure why you'd want to do it anyway.

Go ahead if you wish, but don't use foam. You'll regret it.

Exterior boxes should already be weather sealed (ie: vapor barrier wrap), and exterior penetrations (ie: "DUX seal") for the mains.

The only time I use foam for sealing electrical holes is when sealing the _outside_ of conduit penetrations. The foam does not touch the wire.

[BocesLib]

The blown in stuff is interesting, but my question is there really a need to make this a sound studio? Naa, just want to dampen thing down. I do know that the blown in stuff does settle after awhile. When its blown in I really wouldn't want it to completely surround the lights. FIRE (using recessed lights too) I went over to Lowes (HD doesnt carry it) encapsulated r13 insulation. The stuff works real nice and doesnt make me itch too much at all. I'm going to run it around the framework and ceiling.

I also do have duct work down there. I might put some compressed insulation in between the ducts and future ceiling. Again sound studio? Not. Dampen a thing or two?? Sure. I noticed at lowes they also have some styrofoam insulation that looks like it might do the job.

My bathroom is really quiet using the technique that I mentioned. No complains and if I eat really bad food I can go down there and let it rip without the whole house getting an earfull. (heck I like my privacy when I need to go) LOL

Tom

[Doug Boulter]

Calvin answered most of your questions. Here are some answers to the rest.

"DL" wrote on 17 May 2005:

If this is an exterior wall, the kraft paper is your vapor barrier and shouldn't be cut. Cut from the other side. Or if you do cut the kraft paper, tape it closed again. If it's an interior wall, you don't need a vapor barrier. If you're using batt insulation for sound control between floors, you don't need a vapor barrier, so you can stuff the batts in above and below the wires. I think you're making this harder than it is.

Batts will work fine for this.

Boomy base will travel through the floors. See Calvin's explanation. Batts will help more with the mid-range and treble. I'd consider either doubled drywall or resiliant channels or both for the media room.

Or regular batts which will only be slightly less effective.

This isn't nearly as hard as you're making it sound.

The only problem with air spaces you should have would be around non-IC recessed lights, and you can't allow blown-in insulation to contact them either.

And I think you'll find blown-in to be an order of magnitude more difficult than batts, or will be very expensive to pay to have done in a ceiling.

[DL]

Sorry for the late response as life has been busy.

The exterior penetrations are for electrical mains, phone connections, cable internet, and satellite connections. I plan to use the DUX seal for this.

My thought was to use the foam around PVC pipe penetrations from the basement to the main level, but it sounds like it is not worth the effort. I will probably use it for the plumbing that goes into the garage from the basement as well.

I assume that there is a problem with using the expanding foam on the romex electrical cable? Based on your comment, I won't do it, but I would like to understand why. Does the foam eat the sheathing of the romex?

I ran the wires to the garage through plastic conduit into a PVC junction box so no seal is needed there.

Thanks for your comments.

David

[DL]

Sorry for the late response as life has been busy...

Thanks for the recommendations and these are good points that I will consider them when doing the install.

David

[DL]

Tom,

Sorry for the late reply as life has been busy...

I think you have the right idea and looking closer at what it will take, I think won't be all that hard to do.

What did you do around the recessed lights with the batts? Mine recessed lights are insulation rated, but they still get very warm, so I wonder how close the insulation should be to them.

Thanks again,

David

[DL]

Doug,

Sorry for the late reply as life has keep me busy...

After reading your post and looking at the situation more closely, I agree that I am making a mouontain out of a mole hill. The installation of the inuslation in the ceiling should go a lot faster than on the walls as most of the wires are above where the insulation will go. Addittionally, I have run studs at the bottom of the joists to get around most of the water pipes so that will leave an 1-1/2" space between the sheetrock and the insulation, then 6" of dead space to the subfloor after the 4" insulation. Should do a decent job of dampening the noise as Tom stated.

Since my recessed lights are insulation rated, how close can (should) the batts get to the cans even if they are insualation rated? I probably makes sense for me to talk to the county inspection office for their comments as they are going to approve / dis-approve what I do.

Thanks again,

David

[BocesLib]

I used the encapsulated insulation all over. Around the recessed lights I put the insulation around 6" from the light. The 4" insulation doesnt completely seal off the joist area anyway, so heat generated by the light (mine are IC rated too) has some way of releasing.

Tom