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andy buff Posted: Dec 05, 2010 09:03 PM	lake house mason i;m bidding a house right on the water. right now we have a foot of snow. the contracor wants open cell foam to the roof deck and in the crawl space to underside of floor they have infloor heat with the metal plates holding it up,they want to spray directly to the heat pans.I feel they should staple up foil/bubble wrap leave an air space and foam in with 1.5-2 inches closed cell.? would .5lb work to the roof deck being 2 ft from waters edge or is best to closed cell and no worries...thanks
mason Posted: Dec 06, 2010 07:58 AM	If the roofline is properly flashed, either open or closed cell foam can be used there. In the case of the open cell, be sure to add a vapor retarder over the foam to reduce water vapor from the inside of the house diffusing to the underside of the roof deck. Many folks recommend closed cell in crawls spaces due to its water resistance in case of flood waters(in areas designated by FEMA as severe flood prone areas, closed cell foam is one of the few insulating materials accepted) and its lower perm rating. Crawl spaces tend to be more humid than other areas of your house, so additional protection against moisture vapor transmission is usually a desirable thing. But you could use the open cell foam if additional vapor retarder elements are added to reduce the potential for water vapor transfer into the flooring. But regardless of which foam you use, be sure to encapsulte the floor joists along with the underside of the flooring. This will minimize the potential for achieving a dew point temperature on the wood joists. As for the infloor heating, there should be a space above the foam so that the radiant heat can work properly.
steven argus Posted: Dec 06, 2010 12:39 PM	"But you could use the open cell foam if additional vapor retarder elements are added to reduce the potential for water vapor transfer into the flooring" Where would you put the vapor retarder? In the North East, we need it on the "warm in winter" side. If you spray the vapor retarder after the foam, the vapor retarder is on the wrong side. Correct me if I'm wrong Skinny, you are most concerned with the lake being so close, right?
mason Posted: Dec 06, 2010 01:39 PM	Guiness, in the case of using open cell in the crawl space, you would try to stop water vapor from entering the crawl space and try to remove any that is in the space. I would put the vapor retarder on the outside of the foundation, on the floor (if it is dirt). But, you forgot that the crawl space is typically the source of the high humidity and the rule is that you can place a vapor retarder separating the permeable insulation from the higher humidity. Water vapor will flow from high humidity to lower humidity. Most often that would be from warm to colder areas but not neccesarily if you have much higher humidity on one side and much less on another. Swimming pools are another example. My personal preferencw would be to use the closed cell foam in the crawl space in the lake area. Easier to protect against condensation and water damage. But you could use a more permeable insulation if you take care of the high humidity situation.
steven argus Posted: Dec 06, 2010 02:03 PM	So 6 mil poly on the floor and up the walls? Does this apply to both heating and cooling seasons? I understand vapor difusion in an indoor swiming pool situation, but I'm still confused with crawlspaces because the crawlspace in this situation is unconditioned space. Winter time: heat and higher humidity inside, cold and lower humidity outside. Heat to cold and high humidity to low humidity. Summer time: The situation is reversed if there is A/C. Not a big deal if the windows are used. So in this situation, would 6 mil poly cause more problems? Should the crawlspace be vented?
andy buff Posted: Dec 06, 2010 07:33 PM	guiness cheers long freakin cold one today. yah the crawl space is vented or grated because of flood plain water can get out.so its cold.
mason Posted: Dec 06, 2010 09:06 PM	Sometimes I try to be too diplomatic and confuse the issue;. Closed cell foam would work best in this situation. Use the poly on the dirt floor, seal the underside of the floor including the joists. For good reading on crawl spaces and basements, go to buildingscience.com, Check out their articles on crawl spaces and basementss.
quentin Posted: Dec 06, 2010 09:24 PM	I follow the KISS rule on this. Anything below grade I stick to closed cell due to the risks of moisture. That also means they can't come back and bite you later because it failed due to their kids playing with a waterhose or that 10 year rain record issue.
steven argus Posted: Dec 07, 2010 11:07 AM	If there is dirt on the other side of the wall, use closed cell.

Author

Comments

andy buff

Posted: Dec 05, 2010 09:03 PM

lake house

mason
i;m bidding a house right on the water. right now we have a foot of snow. the contracor wants open cell foam to the roof deck and in the crawl space to underside of floor they have infloor heat with the metal plates holding it up,they want to spray directly to the heat pans.I feel they should staple up foil/bubble wrap leave an air space and foam in with 1.5-2 inches closed cell.? would .5lb work to the roof deck being 2 ft from waters edge or is best to closed cell and no worries...thanks

mason

Posted: Dec 06, 2010 07:58 AM

If the roofline is properly flashed, either open or closed cell foam can be used there. In the case of the open cell, be sure to add a vapor retarder over the foam to reduce water vapor from the inside of the house diffusing to the underside of the roof deck.

Many folks recommend closed cell in crawls spaces due to its water resistance in case of flood waters(in areas designated by FEMA as severe flood prone areas, closed cell foam is one of the few insulating materials accepted) and its lower perm rating. Crawl spaces tend to be more humid than other areas of your house, so additional protection against moisture vapor transmission is usually a desirable thing.

But you could use the open cell foam if additional vapor retarder elements are added to reduce the potential for water vapor transfer into the flooring.

But regardless of which foam you use, be sure to encapsulte the floor joists along with the underside of the flooring. This will minimize the potential for achieving a dew point temperature on the wood joists.

As for the infloor heating, there should be a space above the foam so that the radiant heat can work properly.

steven argus

Posted: Dec 06, 2010 12:39 PM

"But you could use the open cell foam if additional vapor retarder elements are added to reduce the potential for water vapor transfer into the flooring"

Where would you put the vapor retarder? In the North East, we need it on the "warm in winter" side. If you spray the vapor retarder after the foam, the vapor retarder is on the wrong side.

Correct me if I'm wrong Skinny, you are most concerned with the lake being so close, right?

mason

Posted: Dec 06, 2010 01:39 PM

Guiness, in the case of using open cell in the crawl space, you would try to stop water vapor from entering the crawl space and try to remove any that is in the space. I would put the vapor retarder on the outside of the foundation, on the floor (if it is dirt). But, you forgot that the crawl space is typically the source of the high humidity and the rule is that you can place a vapor retarder separating the permeable insulation from the higher humidity. Water vapor will flow from high humidity to lower humidity. Most often that would be from warm to colder areas but not neccesarily if you have much higher humidity on one side and much less on another.

Swimming pools are another example.

My personal preferencw would be to use the closed cell foam in the crawl space in the lake area. Easier to protect against condensation and water damage. But you could use a more permeable insulation if you take care of the high humidity situation.

steven argus

Posted: Dec 06, 2010 02:03 PM

So 6 mil poly on the floor and up the walls? Does this apply to both heating and cooling seasons? I understand vapor difusion in an indoor swiming pool situation, but I'm still confused with crawlspaces because the crawlspace in this situation is unconditioned space.

Winter time: heat and higher humidity inside, cold and lower humidity outside. Heat to cold and high humidity to low humidity.

Summer time: The situation is reversed if there is A/C. Not a big deal if the windows are used.

So in this situation, would 6 mil poly cause more problems? Should the crawlspace be vented?

andy buff

Posted: Dec 06, 2010 07:33 PM

guiness cheers long freakin cold one today. yah the crawl space is vented or grated because of flood plain water can get out.so its cold.

mason

Posted: Dec 06, 2010 09:06 PM

Sometimes I try to be too diplomatic and confuse the issue;. Closed cell foam would work best in this situation. Use the poly on the dirt floor, seal the underside of the floor including the joists. For good reading on crawl spaces and basements, go to buildingscience.com, Check out their articles on crawl spaces and basementss.

quentin

Posted: Dec 06, 2010 09:24 PM

I follow the KISS rule on this. Anything below grade I stick to closed cell due to the risks of moisture. That also means they can't come back and bite you later because it failed due to their kids playing with a waterhose or that 10 year rain record issue.

steven argus

Posted: Dec 07, 2010 11:07 AM

If there is dirt on the other side of the wall, use closed cell.

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