Answers to Insulation Questions #3 Answers to Insulation Questions #3
A. For the wall, add R-13 paper to the inside. If you put insulation up in the roof, you'll have to put the foam vent next to the roof, then your insulation. You're better off to just put R-19 paper down to the room in the ceiling rafters.
Q. When insulating a basement wall, should the insulation go right to the basement floor or should it stop slightly (8") above the floor?
A. Assuming you're framing it up first, take the insulation right down to the top of the treated sill plate at the bottom of the wall.
Q. I have a family room over an unheated crawlspace. There is plastic covering the floor and what appears to be R-25 insulation. The floor above is cold, even with carpeting. Few questions: 1) What R is recommended for a crawlspace? I am in Connecticut and it is four degrees right now. 2) Since the ceiling is insulated, insulating the walls is out, correct? 3) Finally, is it OK to close the vents in the winter to warm the crawlspace a bit? If so, what problems should I be checking for?
A. The ceiling is insulated, so you should not insulate the walls. Since the ceiling of the crawl space is insulated, you have to vent the crawl space to remove the moisture that manages to get pass the insulation. The floor is cold over the crawl space because of the exposure of surface areas of this room to unconditioned spaces, like the crawl space. This makes this room harder to heat and in fact requires more heat to the room due to the heat loss created by the exposure. I Suggest asking a qualified contractor about the variety of ways to increase and/or supplement heating to this room to compensate for heat load.
The reason why the inside air is drier (lower humidity level) during the winter is the heating of the air inside the house. Relative Humidity (RH%) describes the amount of humidity an air mass can hold at a certain temperature. For example, if an air mass is at 50 degrees Fahrenheit with 100 grains of moisture in it, it may have a RH% of 50%. But if I raise the temperature to 70 degrees Fahrenheit, the amount of moisture in the air does not change but the RH% goes down to 20%. The reverse is also true. By dropping the temperature of the air mass, the RH% goes up but the amount of grains of moisture remains the same. In other words, RH% describes the relationship of certain amount of moisture in something under different temperature conditions. For example, in the above example let's say Dew Point - 100% Saturation or the formation of condensation - should occur for this air mass with 100 grains of moisture at 35 degrees Fahrenheit. But let's change the amount of moisture in this air mass to 80 grains. Then at 50 degrees, the RH% is at 40%, at 70 degrees, 10RH% and the Dew Point is at 25 degrees Fahrenheit. This is why humidity is called relative. Psychometrics is the term used to describe this behavior in Physics.
The Water Shedding, Expulsion or Drying Out process of the structure relies on RH% in the process known as Equilibrium Relative Humidity (ErH%). This states that an object of lower humidity will absorb humidity from an object(s) of higher humidity levels, until the humidity levels in the objects are equal. The principle of RH% still apllies but the rule lower absorbs from higher until equal is added.
To answer your question, you have to apply the aforementioned calculation. It is more important to me that you understand the reasons why you have to leave your vents open during the winter, rather than me expecting you to accept what I say. In other words, merely stating that you should leave your vents open during the winter because I say so and I am an expert, is not only inappropriate, it doesn't mean much. Anyone can call themselves an expert.
Insulation does not stop heat flow; it slows it down. Vapor barriers slow down moisture flow that is inside the heat, but does not stop it. Think of it as a leaky faucet that drips water into a bucket. If the bucket is in a sink, the water that overflows goes down the drain. If the sink drain is blocked or closed, the basement will eventually flood. The dripping water represents the continuous flow of heat with a percentage of moisture in it. The bucket represents the crawl space. The overflow represents the condensation of the heat. The sink drain represents the vents in the crawl space. Even though the vapor barrier reduces the amount of moisture, the moisture flow is continuous. As the heat with this reduced amount of moisture in it enters the crawl space, it begins to lose or lower its temperature. And when you lower the temperature of air, you increase the RH%. At first this should pose a problem, but the continuous flow of this heat with a percentage of moisture into the crawl space, eventually 100% Saturation, Dew Point or Condensation will be achieved.
The outside air during the winter is not only cold but also possesses fewer grains of moisture per volume of air. The vents in the crawlspace allow this outside air to enter the crawl space continuously. As it enters the crawl space, it absorbs the heat. The rule "low absorbs from high" also applies to temperature. When you increase the temperature of air, you decrease its RH%. Now the colder air from outside has a considerably lower humidity level than the heat with a percentage of moisture in it that managed to get through the insulation. ErH% takes over and the rule applies. The lower humidity of the cold air from outside absorbs the humidity from the higher humidity heat that managed to get through the insulation. As with the heat flow with a percentage of moisture in it, the vents provide a continuous flow of cold air into the crawl space, thereby creating balance. This is the best way to describe nature.
Moisture barriers (plastic sheets over dirt floors in crawl spaces) also reduce the amount of moisture introduction into the crawl space but address different functions, namely, capillary action and evaporation. While all the things mentioned here attempt to prevent moisture problems in crawl spaces, they do it by controlling the amount of moisture into the crawl space. They DO NOT impede the Water Shedding, Expulsion or Drying Out process of the structure (crawl space).
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