hot roof,,,able to leave existing insulation in attic ??
I have a fifties ranch with a 4/12 pitch roof 28 feet wide. There is 3 1/2 inches fo fiberglass batting covered by almost two feet of blown in celulose. No venting in the soffit, gable or roof. No vaper barrior. After reading about all the ways that this is improved what I still don’t know is can I do a hot roof and leave this in place without causing condensation problems? The idea of having a conditioned space to add some duct work is a great way to add air conditioning. I would like to add four inches of foam to the roof and two inches to the walls. I’m planning on adding a metal roof on top of the foam. Would it work better to add some spray foam to the top of the drywall with the celuose on top of it? I Ilive in zone seven, winter can be brutal here,many days each year below zero. Anyone have any ideas that might work????
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If you live in zone 7 with a 50s ranch you already have "a condensation problem". You just may not know it.
oh I do know it, have repaired sheetrock ceilings in half the house, All the seams in the ceiling have some level of damage. So far I haven't found any rotted wood other than in the bathroom.and under windows. I've already added egress windows in the bedrooms and removed the low temp wiring from the light fixtures. My concern is that if I seal the roof what happens in the attic. Do not want to cause more problems.
Well, you can work through the numbers and see whether the temp and dewpoint profiles ever cross. There used to be a pretty good web site for doing the numbers for you, but it went away about a year ago, and I haven't found another.
is there any place you know of for me to find what the formula's are to do the numbers.
Or the title of a resource so I can get in the loop. This is my first energy retrofit,it will not be my last. I want to do it right,, why do the guides want the loose fill insulation next to the underside of the roof? Anyone out there have any ideas how to move it up there without tearing the roof off? 4/12 pitch roof leaves little room to work under. Really don't want to waste all the material that's already installed.
Living in a cold place.
You have condensation in the roof because you are making water vapor in your home, and your walls and ceilings are leaking air and water vapor into the roof.
You can easily stop the water vapor passing through the ceilings and walls by – blocking all the holes and cracks and painting the ceilings and walls with either gloss or latex paint.
You have other problems: The passing wind is creating a low pressure area above your roof and downwind of your home. The air inside your home is slipping out to fill this low pressure area, and colder air is being pulled in to replace it. You need to find all these holes and block them.
Water vapor is caused/made by you! You make it by breathing and sweating, you breathe out and sweat about 800 ml each, every 24 hours, then you wash and cook, this adds even more water vapor to your home. In your location, you badly need a dehumidifier to remove most of this water vapor from the air inside your home. At the same time, you must block all those holes, and make sure you have an air tight porch covering each door to the outside, otherwise, you will be trying to dry out the whole of our country, trying to win an impossible fight, and spending a lot of un necessary money.
The cold coil inside the dehumidifier converts the water vapor inside your home into pure water, but at the same time, the water vapor outside your home will also be attracted, and it will enter your home via any opening as it tries to replace the condensed water vapor.
foam and dew points
If anyone has similar questions or wants to look up formulas and explanations at the green building advisor site.lots of useful information about useing foam and the real world results. especially the information from alaska and the standards being used there.