# Question for those who finished basement



## Abs777 (Apr 2, 2010)

I am debating on insulating the exterior walls. The basement is completely underground, so I don't know if it is worth insulating. I was going to do the ceiling with R19 and double drywall the theater room for sound barrier. 

So my question is....is it worth the money to insulate the exterior walls of the basement? Code in my area (Kentucky) is that the builder has to insulate down 48 inches, so I have celotex from the top of the foundation down below the freeze line.

Thoughts??


----------



## bpape (Sep 14, 2006)

Celotex will do very little in terms of helping acoustics. I would definitely insulate the walls with fluffy fiberglass or mineral wool to damp the wall cavities and keep them from ringing like drums. It also allows the walls to provide a small amount of bass control.

Bryan


----------



## hjones4841 (Jan 21, 2009)

Do yourself a favor and put waterproofing coating on the inside of the concrete walls, then plastic on top of that. I did that when I built my room 24 years ago and have never had water or even humidity problems. I think what I used was called DamTight. Messy to put on (almost like plaster of paris), but works very well.


----------



## tonyvdb (Sep 5, 2007)

If you have any sort of cold weather where condensation is a possibility. A vapor barrier is a must. Even in a hot climate you can have condensation issues where the hot outside air will condense on the walls if not insulated and you have A/C inside. 
You want the vapor barrier to be on the inside next to the drywall with any insulation between that and the exterior wall.


----------



## kujomujo (Apr 24, 2010)

Before I completed my theater in the basement, I treated the exterior walls with plastic and insulation... before the drywall went up.


----------



## MatrixDweller (Jul 24, 2007)

Waterproofing goes on the outside of the wall. It shouldn't go on the inside because then water might get trapped in the wall and if it freezes it will deteriorate the wall.

Insulation in the wall will stop the cavity from resonating. It will help abate some of the reflection that will come back off the concrete wall also. 

From a non acoustics standpoint: The temperature of the soil below 4-6 feet tends to say around the same temperature year round. It is typically cool (~6° to 10° Celsius) depending on the soil makeup and your latitude. This can aid in cooling your house in the summer. However if your winter season is longer or heating is more expensive than cooling then insulating below 4 feet would be beneficial. Insulating the slab (or under the subfloor) can also have the same benefits if you live in a cool climate.


----------



## bbieger (Sep 15, 2009)

the short answer..YES! It makes the room much more comfortable and will greatly help acoustics. A hollow framed wall next to a concrete foundation is nothing more than a heavy drum. 


In regards to the vapor barrier, ask around and do your research. The correct method depends on your climate. Some areas the vapor barrier should be next to the drywall. My vapor barrier is sealed to the foundation with a gap between it and the framing/insulation. 

At the very least, insulate the tops of your walls as it will reduce sound flanking to the upstairs.


----------



## MatrixDweller (Jul 24, 2007)

Vapor barrier is different than moisture barrier. Typical is that the vapor barrier goes on the warm side of the assembly. If it were on the cold/cool side then condensation would form on it. Since basement walls will be colder,if mostly below grade, than the room air. It should be attached to the studs on the room side and the drywall goes over top. All seams should be tuck taped and electrical boxes should be sealed also.


----------



## bbieger (Sep 15, 2009)

MatrixDweller said:


> Vapor barrier is different than moisture barrier. Typical is that the vapor barrier goes on the warm side of the assembly. If it were on the cold/cool side then condensation would form on it. Since basement walls will be colder,if mostly below grade, than the room air. It should be attached to the studs on the room side and the drywall goes over top. All seams should be tuck taped and electrical boxes should be sealed also.


Yes, in cold climates that is absolutely the case. But in warm climates..not so. The vapor barrier should always be placed on the high (humidity) vapor pressure side of the exterior wall. This is the exterior side for buildings in the south and the interior side for buildings in the north.

Not going to get in a debate, the point is that you should do your homework for your area and what is already in place in terms of vapor barrier on the exterior of your house (as this effects the need for internal barriers). Fiberglass batt insulation already has a vapor barrier....


----------

