"Trying to warm the unfinished basement"
Column #869 10/22/11
On The Level
Q. Our house was built in the early 1980s and our basement remains unfinished. However we do have ducts down there for heat and air. Needless to say it's still cold in the winter. Our basement ceiling is insulated-- paper side to the floor upstairs and plastic sheeting stapled to the joists. Unfortunately, mice and snakes have come in over time and have made a mess of the insulation and plastic. We are in the process of removing the plastic and some of the insulation. I found at least one hole where a gas line comes in that I will be filling with spray foam.
The million dollar question-- because I've read too many conflicting articles-- is whether we redo the ceiling insulation - paper side up or install a 2" foam board insulation on the walls, glued. By the way some years ago we painted the walls with a waterproofing finish. We do not plan to finish the basement but some day someone else might. We don't want to spend the money on framing, we just want to keep the basement pipes safe as well as help the next floor stay warm. Your thoughts would be greatly appreciated.
A. Given the age of your house Iím going to guess the foundation walls are block. You may have a gas furnace to which the gas line goes or you may have a heat pump. If you have a heat pump the basement is regarded as non-conditioned space and must be isolated from the conditioned space via insulation and weatherstripped door. Even with a gas furnace the basement being considered non-conditioned still has insulation requirements, whether between the joists or on the basement walls.
I don't like the notion of stapling plastic sheeting to the underside of the joist with insulation above. That presents a condensation plane which can under certain circumstances set up wet conditions that can wreak havoc over time with rot and mold. Usually insulation between joists-- with the paper set to the warm side or no paper at all-- is held in place with wire spring like holders set every eighteen inches to two feet. This allows air to get to the unconditioned side of the insulation letting it breathe should anything cause moisture to form-- which happens most commonly during hot, humid weather.
Youíd be wise to get rid of that plastic and while youíre at it wear a very good respirator and get it into a garbage bag and out of the house. The droppings of the critters who were living up there are still harmful and disturbing them and breathing it into your lungs can make you sick. While you are taking this stuff down place a 24 inch cheap box fan into the areaway door or in the open egress window facing it out turn it on high while youíre working and leave it on for about 30 minutes after youíre done. Open the door to the house and any other windows down there so the fan can pull air from outside of the basement. Thatís a trick I learned doing demo work inside finished houses for dust control and it really works.
As for the placing spray foam around any penetrations to the exterior youíve found such as that gas line-- pack steel wool around it first and use foam or caulk to stop air movement. Steel wool will stop critter movement.
If it were my job to do I would stay with the ceiling insulation but done properly-- it isolates your living space and will keep the floor worm. The added benefit is when the basement ultimately gets finished it will act as a nice sound barrier between the floor and the living spaces now on both sides. Any parent with a basement rec room and a teenager would appreciate the benefit.
As for the notion of glueing foam boards to the concrete foundation wall be aware that foam is flammable and it must be covered with either drywall or paneling. I frequently go into basements where foam boards have been attached to the outside foundation walls and on many foam products there is a stamped warning on the board that tells the installer that it must be covered to be safe
I donít blame you for not wanting to bear the cost of framing walls out. You can get large floor to ceiling foil-faced insulation sheets that can go against the outside walls and help get that space warmer prior to finishing it off. Iíd hire that out because it takes more than one person to put it up and power-actuated (shot) tools to attach it to the walls. It really wonít cost that much and youíll thank yourself in the long run.
Keep the mail coming. If you've got a question, tip, or comment let me know. Write "On The Level," c/o The Capital, P.O. Box 3407, Annapolis, MD 21403 or e-mail me at firstname.lastname@example.org or email@example.com.