I had a project where I had freedom to do whatever it took to convert a bulldozer worthy farm house into a comfortable, efficient home and office. We wanted to stretch the budget as far as possible, so we tried to discover material sources and techniques that would allow us to add our own improvements.
I had converted the kitchen ceiling to an open ceiling at the owner's request. I'd never dealt with insulating something without an attic, so I had to do a lot of reading to learn how to insulate the underside of the roof without creating potential rot problems from moisture transfer. Too, I wanted to deal with the high amount of heat that would result from a summer sun beating down on dark composite shingles.
One of the first things of concern was the installation and reliability of a vapor barrier between high moisture areas and wall interiors. Stopping wind was, of course, a primary concern too. Finally, there was the question of how to stop heat gain in the summer and loss in the winter. This meant addressing heat transfer by both conduction and radiance.
Tyvek addressed both air movement and vapor penetration in the walls (we even went so far as to caulk joints where siding underlayment joint up against 2x's). The tar paper under the shingles and in combination with them functioned as a moisture barrier far as the roof was concerned. That left only the matter of addressing interior moisture sources and heat transfer.
As we know, steaming and other cooking projects, like showers and baths, generate a lot of humidity. As such, we needed to stop it from entering the drywall and then passing on into the insulation. Oil paint, unlike latex, does not allow moisture to pass into the walls. As such, it makes a great moisture barrier. After it's applied, you can put anything you want over it.
Insulation is usually all that is done to address heat transfer, but as I noted, I wanted to also address radiant heat transfers, which are significant in a house. We learned about a bubble wrap type of material, which had layers of reflective material on both sides. Its R value was said to be only around "4," but in combination with regular insulation the two had a greater final value than the sum of their individual values. Because of its overall insulation value, we did use it on the ceiling areas. Not having an attic to buffer the kitchen called for all the help we could get. We wanted walls to also be protected as much as possible, but the budge wouldn't tolerate the expensive bubble wrap.
I remembered that all the old fiberglass insulation came with reflective barriers. I figured "aluminum foil is aluminum foil," with exception that the Dollar Store variety may tear much easier. With these thought in mind, we set off to the local Cash-n-Carry, which is a restaurant supply store. There, we found large, wide roles of foil at a very reasonable price. One role was enough to more than cover the kitchen walls and dealt well with the sixteen inch centers. So, for about fourteen dollars, all the south facing walls now had highly reflective surfaces under the sheet rock.
Summer came not long after we finished. What a difference the new insulation and reflective barrier made. The house was always several degrees cooler than the outdoor temperature, even with the two large vaulted ceilings. Another very obvious advantage of our extra efforts (e.g., caulking wall interiors) was that there were several heavy windstorms while we were working in the house and we didn't even know it until we opened a door. It was almost eerie.
The trick with reflective surfaces is to leave a small air gap between it and other surfaces. While the foil will do a wonderful job of blocking radiant heat, it also conducts. As such, you want to avoid actual contact with inner or outer wall , or ceiling-roof surfaces to further increase its insulating characteristics.
The techniques we applied and described here could prove invaluable as times get harder and we try to stretch our nickles. However, many of those things are just not practical, for various reasons. Nonetheless, if things do get really tough, an investment in a few roles of aluminum foil could mean the difference between staying warm and being miserable, or worse.
Research shows houses transfer a remarkable amount of moisture through their walls, both from habitation and from the elements.
As to the moisture barrier which comes in contact with the insulation, much of the insulation available at the big box store doesn't have any. As such, the base coat of paint may be all the more important (after it's applied, you can use latex), if you are not going to install a vapor barrier.