Originally Posted by sway
Sorry to barge in on thread, but I am a bit confused. It sounded like the OP was planing on putting 10-12" insulation in the joists in his attic. Isn't the SIPS system put on the outside of the roof? Are you suggesting this over the alternative? Or are you thinking a SIPS system for the outside of the house? I am getting ready to buy a house to rehab that is very old, so these suggestions really help.
Chicago can be cold and windy!
The typical American light weight home is not suited to Chicago weather as originally built.
What you need is a modern air tight insulated home, to avoid the effects of the wind.
Luckily the original home can be modified to meet modern Passive House standards.
An original new SIP's building will be made in a factory, where each side of the home will be made in one piece, a piece that is self supporting has all the window and door openings in place and is just stood up on site and joined together. Minimum joins equal minimum heat loss due to wind suction. No frame.
You are proposing to convert an existing frame building, placing the SIP's structure on the outside creates problems.
You will have problems sealing the sides to the roof and base. You also have the problem that you will be heating the frame and the spaces inside the frame, when you are intending to save the maximum amount of heat and heating/cooling cost.
By placing the SIP's structure or similar, on the inside of the rooms, you end up with rectangular boxes, that are easy to join together easy to seal and you only heat the comfort zone that you live in, no heating of frame or spaces between the frame.
You also maintain the exterior appearance of your home.
If you are buying in a high Radon gas zone, you really need a home that is sealed against rising Radon gas.