BobHr

Mike

You state that you are able to have a 2600 SF roof sprayed with 8 inches. That is 20,800 board feet. That comes out to $0.27/board foot. I have never seen foam at that low price.

Personally I dont think we can build all of our homes and commercial buildings with spray foam as it is a petroleum product. That will put a great strain on the oil market when it heats up again. Typically we dont use oil to heat homes except in the northeast. OVerall heateing oil is a small part of oil use. Now to save oil you have created another use for it, doesnt make sense to me.

Bio based foams only have a small portion of soy oil so that is not a real alternative.

What are water pipes doing in exterior walls in new construction?

Are you aware that foam insulations only achieve an effective R value in the R24 range per a Fine Home Buildings publication. That is you can spray foam and what is assumed to be a R40 or higher thickness and that it will only preform at an R24 level. This does not seem like a good use of the resource.

If a home is built with vapor and water barriers on the outside that accomadate water getting behind exterior cladding and give the vapor or water an escape route then wetting of the insualtion will not be a problem - it will not get to that section of the wall. So I dont buy the wetting of the insulation argument.

I would also say that maybe you need to update your building practices if you need to use insualtions that let you know when you have built a leaky home.

I think as a whole the building and remodeling industry needs to learn from past building practices that lead to building failures. Now that we have the knowledge to understand what caused failure with (EFIS as an example) certain building practices and materials we can build more energy efficient buildings that are also durable. A few simple barriers would have prevented EFIS failures. Water intrusiion around windows can be prevented.

Many in the building sceince field have talked of the benefits of using foam board on the outside to block thermal bridging and to move the dew point away from building materials affected by moisture. Joe L and Joe S have reported how small details like double layers of crinkled house wraps can prevent vapor drive from wet bricks from reaching wall cavities. How foam boards can prevent thermal bridging and act as a rain screen. There are many more things that can be done.

As building scientist say the house is a system. We can build walls and roofs as systems. Using different materials in the wall to achieve the goals of energy efficiency and durability. As an example wall cavities can be filled will cellulose or fiberlass. The air barrier can be at the exterior of the sheeting. House wraps and foam boards can be extra layers of protection and insualtion. The claddings can be back ventalated to provide drying. Different systems can be used for different climates, etc.

The goals should be to make energy efficient buildings that are durable and get the maximum benefit from the materials. It doesn't mean that if 2 inches of foam is good 10 inches is better. That is a waste of oil.