new windows/insulation

[gordh19]

i am planning on installing new windows and siding on my older home. while the siding is off i would like to install some styrofoam insulation, 1-1/2" preferably. should i put 2X4 on the perimeter of the windows or is nailing through the styrofoam secure enough?
anybody with experience on this?

thanks

[pushkins]

What is the reason for the 1 1/2" Styrofoam on the exterior, is it for insulation only ?, I ask this because styrofoam offers little R value (R4 - R8 / inch depending on product), as your siding the house anyway this would be a good opportunity to blow in insulation through holes drilled (and later plugged) into the exterior before siding).
Regardless the simple answer to your question is no, you should not nail the new windows through the styrofoam it will not secure the window anywhere near close to satisfactory, you will not be able to seal off drafts so this would far negate the effects of adding the 1 1/2" to start with, another issue you will have is that you will then also have to build out the interior of the window 1 1/2" to meet the drywall on the inside.
Have you thought about how your going to secure the new siding through 1 1/2" styrofoam, you would need a min. nail length of 2 1/4"- 2 1/2".

If you still want to head down this path the best option would be to add 1 1/2" (2x4's) furring strips vertically every 16" and frame out each window and door opening with them, in between cut your styrofoam to fit snuggly, this would give you a strong window attachment point (and doors) and allow you to attach your new siding on 16" nailing,

[gordh19]

i live in morthern canada, and it is quite common for styrofoam insulation to be added to the outsid eof a house, sometimes it has a foil covering on both sides. i have seen it done with and without the furring strips but have never noticed what was done around windows.
i have looked into windows and have found a brand that allows you to cut the inner jamb to whatever width is needed(this is an older home so may not be the same all around the window