Expert: Dave Johnson - 9/28/2008

Question
Hi, I have a stick built home that has 1/2 inch foam insulation under vinyl siding that is loose.  I am planning on replacing the vinyl siding either with the old vinyl, tightening it up when I do or using the newer siding with the insulation attached to it.  I have also thought about adding some sheet styrofoam insulation, sealing the seams and adding tyvak house wrap when I do the vinyl replacement.  Is it worth the money for the insulated vinyl siding, is it okay to add styrofoam siding to the existing aluminum coated styrofoam insulation under the new vinyl installation?  The walls are 2x4 and are insulated with 3 1/2 fiberglass insulation and 1/2 inch aluminum coated styrofoam.  It is a north wall and with natural gas prdicted to go up this winter 25%, it seems like a prudent time to seal this area up better?  thanks

Answer
Hi Bob,
Yes, any insulating you can do in these ridiculous economic times is a good idea!!
If you're doing just the one wall, there is no problem with adding foil faced foam to the building before siding. however, use only one vapor barrier, otherwise you can trap condensation between a second barrier.
A vapor barrier is any non-breathable membrane, i.e. foil/plastic/typar etc.
Personally, I would use the existing siding (if in good enough shape)
and re-do the existing foil faced foam tightening the seams with duct tape or other. If you add any more insulation don't use any more barriers.
Best of luck,

Dave