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Insulating A Porch With A Crawl Space


GORDON HAMMER's Avatar
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05-27-03, 08:50 AM   #1  
GORDON HAMMER
Insulating A Porch With A Crawl Space

I HAVE A CRAWL SPACE UNDER A FINISHED PORCH.
THIS SPACE IS ABOUT 4FT OFF GROUND, I HAVE YOUR ANSWER AS TO WHAT INSULATION TO USE, BUT I WANT TO KNOW IF I SHOULD USE ONE OF THOSE CAN INSULATORS AROUND ALL THE SILLS AND OPENINGS THAT ARE CAUSING A DRAFT ALL AROUND THE ROOM. THERE SOLID INSULATION UP THERE NOW WHICH I PLANE TO REMOVE AND REPLACE WITH A VAPOR BARRIER, BUT WANT TO ILIMINATE ALL THE DRAFTS, IF POSSIBLE?

I HAVE JUST READ THE ARTICLE ON ROOF ICE JAMS AND I SEE MY PROBLEM IS NO VENTILATION IN ATTIC, THE SOFFITS ARE NOT REALLY PART OF THE ATTIC SO IO DON`T SEE THEM AS ONE OF THE PROBLEMS, BUT WILL VENTILATE ANYHOW. MY ATTIC IS FULLY INSULATED, FLOOR & CEILING. I DON`T HAVE ANY VENTS FOR AIR ANYWHERE. SHOULD I HAVE VENTS PUT AT BOTH PEEKS AND ALSO IN ROOF? I WANT TO MAKE SURE I UNDERSTAND WHAT I READ. MAYBE I SHOULDN`T HAVE ANY INSUALTION ON THE ROOF PART AT ALL.

 
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resercon's Avatar
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05-27-03, 08:56 PM   #2  
By putting the vapor barrier up towards the floor, the vapor barrier will act as as air barrier. You should recognize an immediate difference once installed. However, the volume of the air in your home remains constant. What that means is, air cannot come into the home without that same volume of air leaving the home. So the drafts that you feel coming in at the floor above the crawl space is probably a result of air leaving the home. For example, let's say your windows in this room do not close tightly. Heated air escapes through the poorly sealed windows, this creates a void in the room. The result of this vacuum causes the drafts you experience on the floor. In other words, weather-stripping your windows will probably do more in improving the comfort in this room than the insulation under the floor. The air leakage through the windows are the source of the problem and the air infiltration (drafts) at the floor is the result of the air leakage and not vice-versa. There can be other sources of the air leakage and not just windows.

If the attic is unfinished and the underside of the roof is insulated, it is probably the cause for the ice damming. This is because insulation does not stop heat flow, it slows it down. The way it accomplishes this is by retention of heat inside the insulation. The retention of heat under your roof inside the insulation causes the snow to melt from underneath the snow. The melted snow goes down your roof to an area on the roof where it is colder, like your eaves or overhangs, and freezes. This creates the ice dam.

In the summer, this retention of heat inside the insulation prohibits the roof from dissipating heat and condensation is highly probably under these circumstances. What attic ventilation actually does is ventilate the roof. Insulation underneath roofs prohibit the vents in the attic from ventilating the roof. Besides the ice damming and condensation problems, inadequately ventilated roofs have a dramatically shorten life span and require more maintenance than adequately ventilated roofs.

 
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