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Larry Norton Posted: Nov 25, 2007 06:00 AM	Spray Foam for old sealed walls Mason I own a 1940's home in Philadelphia. The walls are hollow and not insulated. They are lath and plaster walls. I want to insulate the all the outside walls with the least damage. Can spray foam be installed through small holes between the 2 x 4 wall supports by drilling holes at the top of each wall and filling each cavity between the studs? Is there any information on this type of application for spray foam? Thanks Larry
mason Posted: Nov 25, 2007 10:01 AM	The problem with a cavity fill of this type is that the rising foam exerts great pressure on the plaster wall. A 2 lb foam for example can exert 2000 lbs of pressure per inch in a constrained cavity which would blow out or contort the plastered wall. However, there are specially designed SPF systems that can be used. 1. Froth foams: These systems pre-expand the foam utilizing a third stream blowing agent. This reduces the pressure and temperature. The systems are tricky and not used frequently since the EPA phase out of HCFCs. The proportioner would have a small third piston that injects the blowing agent into the B side of the proportioner just before it goes out of the machine to the hoses. The old Gusmer H 2000 and FF units had an way to connect a small pump to the proportioner. I don't think the newer units have that capability. 2. Specially designed low density SPF. Some low density SPF suppliers advertise special formulas for closed cavity fill applications. The foam would expand at a slower rate to reduce the pressure build up inside the wall cavity. In both applications, you would have a fill hole in the upper middle of the wall and a pressure relief hole at the top. Ask your supplier for their recommendations.
Luke Kujacznski Posted: Nov 25, 2007 07:22 PM	There are also one other option, that is, retrofoam or Insulsmart both of which are pre expanded foams. They will not exert any pressure on your walls. The R-value is not as high, I know Insulsmart which I install has an R-Value of 4.6 per inch. It is very hard with a existing house to reinsulate but both of these products do a very good job. Call me if you have any questions. Luke 269.217.1612

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Comments

Larry Norton

Posted: Nov 25, 2007 06:00 AM

Spray Foam for old sealed walls

Mason
I own a 1940's home in Philadelphia. The walls are hollow and not insulated. They are lath and plaster walls. I want to insulate the all the outside walls with the least damage. Can spray foam be installed through small holes between the 2 x 4 wall supports by drilling holes at the top of each wall and filling each cavity between the studs? Is there any information on this type of application for spray foam?
Thanks
Larry

mason

Posted: Nov 25, 2007 10:01 AM

The problem with a cavity fill of this type is that the rising foam exerts great pressure on the plaster wall. A 2 lb foam for example can exert 2000 lbs of pressure per inch in a constrained cavity which would blow out or contort the plastered wall.

However, there are specially designed SPF systems that can be used.

1. Froth foams: These systems pre-expand the foam utilizing a third stream blowing agent. This reduces the pressure and temperature. The systems are tricky and not used frequently since the EPA phase out of HCFCs. The proportioner would have a small third piston that injects the blowing agent into the B side of the proportioner just before it goes out of the machine to the hoses. The old Gusmer H 2000 and FF units had an way to connect a small pump to the proportioner. I don't think the newer units have that capability.

2. Specially designed low density SPF.

Some low density SPF suppliers advertise special formulas for closed cavity fill applications. The foam would expand at a slower rate to reduce the pressure build up inside the wall cavity.

In both applications, you would have a fill hole in the upper middle of the wall and a pressure relief hole at the top.

Ask your supplier for their recommendations.

Luke Kujacznski

Posted: Nov 25, 2007 07:22 PM

There are also one other option, that is, retrofoam or Insulsmart both of which are pre expanded foams. They will not exert any pressure on your walls. The R-value is not as high, I know Insulsmart which I install has an R-Value of 4.6 per inch. It is very hard with a existing house to reinsulate but both of these products do a very good job. Call me if you have any questions.

Luke
269.217.1612

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