I agree with someone above: this is a double edged sword. A lot of folks are starting to use lighter, reflective materials in order to handle other forms of radiating heat and insulation (you'll see this more in older construction vice newer). Issue is a lot of these materials rely on metallic foils (much akin to those space blankets we all started seeing back in the mid-80s), and people just don't have a good idea as to how these foils interact with radio waves.
I would say in either case (new or old construction), do your due diligence to do an adequate Wi-Fi survey (I'd recommend using ALL the 802.11 standards (a, b, g, AND n)) as well as determining if the residence is either wired or capable to be wired with Cat5e/Cat6. Personally, I'd go the wired route, as it's more secure and you can combine cabling with coax, phone, HDMI, etc. to multiple points in a room, allowing for maximum flexibility. Sure, costs a little extra, but in the end, it's definitely worth it.