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A typical brick wall is full of thousands of holes! If you stand an watch a brickie laying bricks you will quickly see why. A single leaf wall will often have water passing through it, if it is in an exposed windy location - this is why cavity walls were invented.

The other side of the story is, warm air holds more moisture than cold air. Homes and other places that are heated on a part time basis, are subject to condensation when the heating is turned down or off. Often windows or other surfaces are running in water due to people turning off their...

Going back to your original post, wet insulation. Insulation is wet because it is cold and below dew point. There is probably either a hole nearby in the crawl space wall, letting warm wet air in, or a hole in the floor where your home is pulling the air into the crawl space. I would be...

You probably know that wood is hygroscopic, and that it absorbs water from the air, this is the reason it fills with water vapor and sometimes reaches the point where mold forms and wood rot starts. Mold spores cover the Earth from pole to pole, but you don't see mold growing on everything...

Basements are interesting things, are you insulating to help keep the room above warm? Or do you intend to live there? Or for some other purpose?

Virginia is a humid place, as such a vented crawl space is not a good idea. The problem is, that warm wet air always heads for a cold surface to condense. A crawl space is likely to be below "dew point" on a number of days every year, this can result in mold and wood rot. There are ways...

People create water vapor by washing, cooking, breathing - for a start. Water vapor is pulled into the roof by the passing wind and sometimes because warm air rises. When the inside of the roof is below dew point, condensation forms on roof. Solution. Use an exhaust fan in the kitchen and...

Fascinating subject, it should be taught at school. So many people have trouble understanding. One thing that troubles me about the insulation industry and builders is, that a Polar bear has a two inch thick fur coat, yet with a body temperature of 37C it can play quite happily in temperatures...

You only mention the furnace, is there any other form of heating down there? A room can feel cold, because you are too warm or because there is no heating or the heat is escaping. How much heat are you putting into the rooms (same space) above? Are they warm? Are you putting the same amount of...

The first Law of Thermodynamics is: heat always moves from hot to cold. I assume that you really want to keep the heat inside your living space? Presumably the crawl space is cold and not used for living? So the heat moves from your living space, into the floor by radiation and...

I built my first conservatory with floor to ceiling glass patio doors, glass all round on three sides. I had under floor heating, in three zones, doubled up along the glass walls, to make sure we were warm in winter. It worked very well at night and at all times except when the sun shone. I made...

A single sheet of glass has the same insulation properties as a single leaf brick wall. Having written that: A brick wall, as built is full of holes, thousands of them, and is not easy to live with. But, it does supply shade and is a lot more comfortable to live with on a sunny day. A sheet...

There is no point in insulating crawl space walls, or in adding heat. The crawl space is not heated and it is outside the home comfort zone, therefore, whatever happens there will not effect the home temperature or humidity once the house floor is sealed and insulated. Bringing warm air...

+++++++++++++++++++++++++++++++++++++++++++++ Molecules of air are much bigger than those of water vapor. Lots of things are air tight, but not water vapor tight. It is probably true to say that, at this time there is no such thing as a water vapor proof crawl space, or home for that...

The temperature and humidity inside a crawl space stays fairly steady. The temperature and humidity outside goes up and down as days and nights pass. What you have is warm wet air entering the crawl space and the water vapor condensing on the colder plastic sheet. This does no harm, the water...

Keep in mind that heat always moves to cold. You are heating the room, the heat disappears into the ceiling, then the walls and finally the floor. Wherever you place your heating, most heat is emitted in straight lines and then moves by convection. Think of a Thermos flask the contents are...

It rather depends on where you live. In the very coldest places 10 inches of polystyrene, more than that and you cannot measure any improvement.

Many people over the years, in many places, have found that shingles do not keep out the rising snow melt on their roofs. While this is certainly not a problem in Alabama? Kindly advise why you thing a two inch gap is desirable?

Alabama is warm with high humidity. I imagine you want to keep the heat out? Keep in mind that the heat of the sun is mainly transferred by conduction. You will want the rafters and the roof isolated from the air inside. Leaving a two inch gap between the roof and the insulation, in most...