Latest Discussions : HVAC

LDoyle

02:37PM | 06/05/01
Member Since: 06/03/01
324 lifetime posts
I'm looking for a product that will replace the clear plastic vapor barrier that is installed between the insulation & drywall but is also a thermal/radiant barrier. Has anyone got any leads? Thamks

Lawrence

06:24PM | 07/27/01
Member Since: 11/14/00
333 lifetime posts
I'm not sure if you are still looking for a response, but I fear you might be making a big mistake from the context of your question.

The plastic is there as a VAPOR barrier, not a thermal barrier. It protects your insulation from warm, moist inside air getting into your insulation and condensing into water when the temperature changes inside your insulation (the purpose of insulation: to provide a temperature barrier from the outside). That condensation can, in turn, rot out your insulation. The vapor barrier keeps the humidity inside of that barrier. Even though the temperature might pass through it, the denser moisture-vapor will not. 6 mil plastic sheeting is the most common, simplest, and inexpensive way to do so.

As such, DO NOT REMOVE THE VAPOR BARRIER. If you replace the plastic sheeting, make sure that the replacement is specifically RATED and LABELED to serve as a vapor barrier.

LDoyle

02:10AM | 07/28/01
Member Since: 06/03/01
324 lifetime posts
Thanks for the response. Am looking to new construction next year & was wondering if a radiant barrier as well as a vapor barrier is useful for living areas? Never have seen much in discussions. Thanks.

Lawrence

05:21PM | 08/25/01
Member Since: 11/14/00
333 lifetime posts
"Radiant barriers" are usually wrapped around the outside of the framing before the siding is put on. The old school method was to use builder's felt; new school is to use that white, poly-stuff building wrap.

Your insulation should do the bulk of the radiant barrier work, though. This outer barrier merely provides draft protection, similar to the way a gore-tex shell provides wind protection from cold. Gore-tex shells usually suffice as a coat unless it gets below freezing even though the shells really do not provide much insulation at all. They suffice because they restrict direct transfer of cold and warm air. They do so by not allowing the cold air to blow through the barrier. Same thing on a house wrap. It prevents the cold air from blowing inside the insulation layer, thus making the insulation do its job of providing a true thermal barrier.

As far as I can tell, there would be no advantage to adding a second thermal barrier inside the insulation. It should be on the outside, not the inside.

Babies50@comcast.net

10:10AM | 05/04/14
Member Since: 05/04/14
1 lifetime posts
I am considering installing Radiant Barrier Foil in my home to help cool it more efficiently and take strain off my A/C unit. The plan was to tack this foil on the roof deck a few inches from the peak and few inches from the insulation deck allowing air to pass through the bird boards and the attic insulation surface deck and out the peak to escape through the side gable vent. I have read that this stuff can be 30% affective in a SW home but looses 46% effectiveness over a 5 year period. The other question raised can the reflected ultra violet rays increase heat to the shingles and roof ply damaging them or wearing them out quicker? Last, does it prevent easier heating in the winter due to the reflected rays. Overall, is this a good investment compared to cleaning and sealing ducts? Or using radiant barrier paint when I paint the house? TP


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