We think we love them, they have been a part of the American dream since the days of the pilgrims. The lingering quest in homeownership how do we protect them from the elements, after that how to make them warmer years after they have been built.
In the old days the log houses used the logs as insulation and a barrier from the elements, the timbers in a log house were a good insulator because no air could pass through theses timbers, just around them, as the logs dried out naturally over time they shrank leaving gaps, while the body of these timbers have released the trapped water it now traps billons of air pockets pushing up its insulating ability also over time. In the late 1800-and early1900s people were packing their balloon-framed houses with newspaper thereby creating a low R-value in the exterior wall cavities. During WW11 to save energy they required houses to be insulated the houses using insulation that was batt of fibrous material about 1 1/2” thick placed into the stud cavities.
Today we have to tighten our budget again because of the high cost of living. One place to do this is to insulate our houses from the exterior than install new siding over the insulation, but there is a catch if done wrong it will rot your walls, what would take nature 60-80 years could be done in as little as 3-8 years. Houses built before 1950 were designed to breathe, it wasn’t until the last 10 years that we had no idea as to how much water vapor actually passed through the exterior walls of our houses. If our house has a crawl space, cement floor, basement foundation walls, that are now waterproofed on the inside (not water resistive paint) you could be absorbing anywhere from 10-150 gallons of water per 24 hour period into your homes atmosphere this water vapor wants out of your house because there is less humidity outside than there is in your home, thereby forcing its way through your exterior walls to the out side.
Now the Law states you must install a house wrap. House wraps work great in the far south, but what happens in the north is a world apart from the south. The inside temp of the house is 70° outside is 30° automatically the water vapor in the house wants out the humidity in the air outside is dryer than the air inside so it forces it’s way through the exterior walls. If your installer installed a house wrap under your siding this is what is happening the water vapor just past through the insulating and wall sheathing, the next surface is colder so now it freezes on the back side of the house warp (you have white frost between your wall sheathing and your house wrap). When the temperature warms up the frost now turns to a liquid, with tarpaper the paper sucks up the water and spreads it to help it dry out the back side of the siding. While if you installed a name brand house wrap it now pooling up behind your siding. It a liquid not a vapor so it is not allowed to pass through, but instead it starts freezing and thawing on your wall sheathing breaking it down.
Adding more insulation on the exterior of the wall if done right will save you a boatload of money. On the exterior of a building you best results are going to be from a rigid insulation board. There are at least 2 types 1st is just an insulation board and the 2nd has aluminam foil on both sides you must choose according to the siding you want to install as to what insulation board is best. For example; horizontal cedar lap siding does not like aluminum for behind it. Before installing any type of rigid insulation on to an exterior wall surface you must make a way for the water vapor to escape to the outside air.
I recommend 1 product “mortairvent” Made by Benjamin Obdyke, it’s only 1/4” thick installed over the tarpaper, than you install you insulation board next and finally your siding. It’s made of woven plastic with enough rigidity to keep 1/4 inch air gap to allow the water vapor to escape either by going down the wall to be vented at the foundation line or vented at the soffit line of the house.