Insulation Advice.....Please Help


Old 11-27-08, 07:06 AM
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Join Date: Sep 2001
Location: Philadelphia, PA
Posts: 56
Insulation Advice.....Please Help

I have a two story house on a crawl space at the Jersey shore. The crawl space has 6 openings covered with screens only. Crawl floor is bare cement. Block foundation. Joists in crawl have rolled insulation in between w/o vapor barrier. Attic has rolled insulation w/vapor barrier. House is very drafty. Windows and doors are new and tight. Lower level is at least 10-15 degrees cooler (checked with my digital thermometer) than upstairs. If seems like cold air easily infiltrates the lower level through the crawl. My first ideas were to block the crawl openings with rigid insulation and even attach rigid insulation to the walls of the crawl or even to the bottoms of the joists. Any recommendations from the experts?

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Old 11-27-08, 12:02 PM
Join Date: Nov 2001
Location: USA
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The first thing to consider is that the volume of air within a confine remains constant. If you blow air into a balloon, the balloon gets bigger and if you let air out of the balloon it gets smaller. Since the house cannot get bigger or smaller the volume of air you sense entering the house on the first floor is equal to the volume of air that must be leaving the house. The rule HIGH (pressure/temperature/humidity) to LOW (pressure/temperature/humidity) influences how air leaves and enters the house. Furthermore due to the natural buoyancy of heat, heat stratification is more pronounced when air leakage/infiltration is high. All of the aforementioned, your description and the large temperature difference between floors indicates air leakage on the ceiling of the second floor resulting in air infiltration on the first floor.

For example, let's assume the louver for a whole house fan is located on the ceiling in the hallway of the second floor. These louvers are not air tight and allows air to escape into the attic. Because of the natural buoyancy of warm air, the warmest air in the house escapes into the attic. This characteristic will move warm air from the first floor to the second creating negative pressure on the first floor. This vacuum on the first floor draws air from the crawl space until the pressure is equalized.

In this particular example the solution is quite simple but the results are dramatic. By taping a piece of plastic over the louver you eliminate the air leakage on the second floor and infiltration on the first floor. The temperature difference will drop between 3 to 5 degrees and your heating costs should drop between 20 to 30%. In most cases the source of the air leakage is not so straight forward and there is usually more than one source. The link below is a New Jersey program where the people involved have either been supervised, trained or influence by me.

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Old 12-15-08, 07:14 AM
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Simply put-the attic & crawlspace are typically the two easiest to insulate and will have the most profound impact on your heating and cooling bills. When I say easy, I mean the least disturbing to prepare for.

Regardless of the product or the budget, improving the insulation in the crawl space and the attic WILL absolutely reduce your monthly expenses. Insulation alone without some attention to sealing off the entering and escaping air will do little more than slow the air movement. Consider an air seal as well but involve, or at least get the opinion of, an HVAC specialist as it may affect your HVAC system if you seal off the air flow too tightly.

Good luck.
Old 12-15-08, 08:51 AM
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Join Date: Sep 2001
Location: Philadelphia, PA
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Good ideas

Thanks for both of your posts. Got me thinking in the right way. What I found was that several of the light fixtures in the ceiling under the attic were not sealed too well allowing heat a quick way out of the house. One door seemed tight until the house gets wind on that side and it leaks badly. Fixed both of that stuff.

Attic insulation looks ok. If I wanted to improve, what could I do up there?

Crawl is a big concern. Insulation looks shoddy at best. I think I need to seal that area to reduce air movement from the cold crawl space into the living area above. What would be the best way to do so? Insulate the crawl walls and add more insulation to the floor joists? Maybe even install vapor barrier under joists from side to side to minimize direct air movement from crawl area to living area? Crawl is three blocks high so not the easiest job

Old 12-15-08, 10:29 AM
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Join Date: Sep 2001
Location: Philadelphia, PA
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Good points. House is actually on the Jersey shore so flooding is not out of the question. If I were apply the 20 mil as described, I'd have to remove it completely in case of a flood b/c water would be trapped underneath. Maybe an alternative would be to reinsulate the floor joists and apply the 20 mil and foam to the floor joists and halfway down the block to create the airtight seal that way?

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