how to insulate under horiz. vinyl siding?

We have an area on the floor that was cold under our feet in winter, and it happens to be just over a basement entrance. The 4'x6' region above the basement entrance has vinyl siding under it (the siding is horizontal, covering the underside of the first floor in the overhang just outside the basement door).
How do I insulate it? Inserting a sheet of the pink styrofoam stuff would require taking all the siding strips off. Is this easy, or there an easier way?
Of course, maybe the problem is air infiltration...
Many thanks for any suggestions. I am not an expert on vinyl siding; I do have a tool for locking/unlocking but I've never actually used it.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Consider insulation inside the joist bays, under the floor and against the rim board. Just use some unfaced fiberglass and stuff it in. Don't need to pack it. You may also want to consider insulating the entire joist bay under the floor. in that case you can use faced insulation with the paper facing the insulated space. There are support wires made for holding it in place. If you have pipes or wires to exterior in this space you can use that foam in a can stuff to seal the penetrations up first. You shouldn't need to remove the siding.
For more information see http://www.owenscorning.com/around/insulation/project/floors.asp and http://www.owenscorning.com/around/insulation/insulationhome.asp

it
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Caveat: I am not sure this is practical:
See if you can find a company that can squirt utherene foam in thru some small holes. Done right this will take care of air infiltration as well as insulating.
--
Rich Greenberg N6LRT Marietta, GA, USA richgr atsign panix.com + 1 770 321 6507
Eastern time zone. I speak for myself & my dogs only. VM'er since CP-67
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.