Can I add 2″ rigid insulation at exterior of the building and keep existing windows?
modea92
| Posted in Green Building Techniques on
I am working on the renovation of an existing commercial building. We would like to add 2″ of rigid insulation and a drainage plane to the building, but we plan on keeping some of the existing awning windows that are in good condition. Can I furr out around the existing windows? Or do I need to relocate the existing windows to the new exterior plane of the wall? I am concerned about the weak point for water infiltration at the window sills. I am using xps foam, blocking as required, and p.t. strapping. We are installing new fiber cement siding and new trim around the windows. Thanks for your help.
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Replies
Maura,
It is not necessary to move or replace the windows, although most building owners investing in a major exterior retrofit involving new rigid foam and siding will probably decide that an investment in new, energy-efficient windows is worthwhile.
The trick is to get the flashing details right. The new exterior sills must, of course, be durable and waterproof; 20-ounce copper flashing would be a good choice for sills. The exterior jamb extensions and new exterior head trim could be made from cellular PVC or a similar durable material. The important details involve transitions between dissimilar materials, especially the seam between the old window sill and the new window sill. Your installer should make liberal use of peel and stick flashing, and use redundant flashing methods. Think like a drop of water, and assume that a single layer will eventually leak.
Good luck.