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rich-pittsburgh
03-16-2007, 06:37 PM
I am putting on a second floor addtion to my house and we are at the point that we are getting ready to insulate. I already bought the fiberglass batts, but my wife and I just attended a local home show and saw a company that does spray on insulation. insulright is the name of the company. They are coming out in a few days to give us a quote to do the walls and the attic below the roof - they say that it doesn't really raise the temperature of the roof signifgantly and from what I have read they are correct and that it really keeps the temp down in the attic. With having installed the HVAC in the attic, keeping this area somewhat controlled environment sounds like a good idea. I am sure that this stuff insulates far better than fiberglass, but a few questions that I have are:
a. Does this seal the house up to much - I know you want some fresh air coming in.
b. does it cause any problems to the electric wiring over time?
c. How do inspectors view this stuff?
d. Is there any other potential problems with it?

Thanks to all who have answered my other questions - you have been most helpful.

Rich

jimbo
03-16-2007, 07:02 PM
The attic MUST be ventilated....WELL ventilated. Insulation must not block soffit vents. It would not hurt wiring, but must not cover electrical light fixture unless you know for sure that they are IC rated.

If you are putting insulation on the underside of the rafters, and you are in snow country, that is a bad idea unless you ventilate between the roof and the insualtion.

geniescience
03-16-2007, 07:48 PM
....
a. Does this seal the house up to much - I know you want some fresh air coming in.
b. does it cause any problems to the electric wiring over time?
c. How do inspectors view this stuff?
d. Is there any other potential problems with it? It works well and will replace loose fiberglass batts within a matter of years not decades, in my opinion. Notice that batts are never used in "real" buildings? I mean big concrete or steel ones, commercial and industrial. Batts insulate well in a lab test where there is no air movment, no wind, no barometric pressure. They act as very porous filters in the real world, in fact they ARE filters when you buy the very same material as a furnace filter. Batts also do not insulate well when moist humid or wet. Attics do get moist, because water vapor (an invisible gas unless higly concentrated) rises fast in air. This is why you need to dehumidify attics, or ensure that enough outside air gets in to dilute the moist air inside.

After you insulate with foam, you will have both a good insulator and an airtight cover sealing nuisance air leakages and heat losses. Your HVAC or air handling system handles humidity buildup. How you manage humitidy in your attic is not something that one can advise on from a distance, one has to be there and diagnose the situation in real time.

In a house built with traditional 2x4 methods, you will not have sealed the house up too much. There are services that can measure the number of air exchanges per hour in a house, if you want to measure this. Remember you have all those bathroom vent ducts, and the dryer vent, and the kitchen range vent, and all those leaky doors and windows. Add to this all the leaks that you cannot see but sometimes feel when a cold winter wind storm pushes air through electrical outlet holes and all the other openings (for lights, switches stairs, etc) that you don't put your hand next to.

david

leejosepho
03-16-2007, 07:56 PM
A former friend and landlord of mine used to have his own insulation business and now sells for another company, and about three years ago he sent a crew out to foam the underside of a dormer I was making into a small bedroom in one of his own places where my wife and I used to live. The material they sprayed that day was ultimately only about an inch thick on the underside of the sheathing and between the rafters ...


a. Does this seal the house up to much


No, it only "seals" the bottom side of the roof sheathing.


b. does it cause any problems to the electric wiring over time?

No, there is no wiring there.


c. How do inspectors view this stuff?

If there is no ambient source, probably with a flashlight! ;)


d. Is there any other potential problems with it?

Not if my squeaky-tight former friend puts it in his own rentals.

("Former" is because he got really nasty when after renting from him for over ten years on an unfulfilled promise to at least consider selling to us, my wife and I finally found a way to get a loan for our own house.)

alternety
04-08-2007, 09:42 AM
Foaming the bottom of the roof actually works better with snow. Keeping a cold deck pretty much cures ice dams. It certainly keeps the attic cooler in the summer.

I foamed the attic floor and sort of wish I had done the roof deck. Much simpler to control air tightness without having to get under all the stuff in the attic (mechanicals, funny framing, lights. I spent hours in a sauna bath attic and ruined a pair of eyeglasses (urethane speckles) doing some spraying to fix what the foamer was/not doing. I think it is tight. When I close a door, my window glass moves.

This makes the attic conditioned space. I did however add fluffy stuff to get the full R value. That would have been a more complicated issue if I had foamed the roof.

This attic should not be vented to the outside but should have air circulating from the house.

FloridaOrange
04-09-2007, 01:30 PM
In Florida the attic, if the air handler is mounted there, must be "conditioned". Basically means the attic usually gets foam sealed at the underside of the roof deck. Small leakage from the unit qualifies as conditioning the space. It's common practice with new construction.