rubble foundation

Terdale · 11-20-13, 08:17 AM

We have a rubble foundation that needs attention, cleaning and insulation. a wire brush will remove most of the loose material and scling. The question is what is the best way to insulate . The cost to foam is approx. $ 3,000 vrs the cost to insulate with a breathing material on the wall. either way we need studs and drywall. I think that we should leave the wall accessable for air flow to get rid of any moisture, so I am questioning the foam. Any thoughts?

Terry

wewantutopia · 11-20-13, 09:46 AM

I'd say the BEST way to insulate a basement is with rigid foam insulation on the EXTERIOR of the wall bringing the thermal mass of the foundation into the envelope...

Terdale · 11-20-13, 01:34 PM

We can not install insulation from the exterior, so we must do from inside . My question is 'if we spray foam insulation on the interior rubble wall, will that not trap moisture from the exterior?' Would it not be better to let the moisture through the wall and down to the slab where it could be controlled by a fan. There is not a great deal of moisture!

Terry

MN Renovator · 11-20-13, 09:10 PM

There is information about basement insulating on buildingscience.com. The information suggests that concrete/rubble doesn't need ventilation and that sealing it off prevents moisture and radon from entering the conditioned area. Any moisture being trapped in the conrete/rubble supposedly is not an issue because they are not affected by moisture. Materials such as wood and drywall(and your whole house and comfort frankly) are affected by the moisture and should be protected from it.

Ryland · 11-21-13, 09:37 AM

Spray foam will remove condensation points, but yes, like you said, it will not breath to the inside, it will however breath to the outside, so as long as you have good drainage and no moisture problems already you should be fine.

If you are really worried about it, you could install a vent system under the foam and have a suction fan that pulls any moist air out and expels it from the house, this could be as simple as every few feet having a small perforated pipe next to the stone wall, connected to an exhaust fan and have that either on a humidistat that is in a cavity cut in to the foam so it's next to the stone, or on a timer to let it run an hour per day, I would opt for a humidistat.

My house has sand stone walls, with crawl space, we put plastic on the floor of the crawl space, a drain tile under that and a vent fan, the plastic then ran up the sand stone walls far enough to be foam sealed in to place.

Mikesolar · 11-27-13, 06:04 PM

i would be very careful that there is not a lot of hydraulic pressure from the outside. I have seen spray foam on the inside become pushed off the wall in places when there is a lot of exterior pressure. I think that, if at all possible, it could be sealed from the outside it would be the best option.

11-20-13, 08:17 AM	#1
Terdale Renovation Consultant Join Date: Nov 2013 Location: Ottawa Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts	rubble foundation We have a rubble foundation that needs attention, cleaning and insulation. a wire brush will remove most of the loose material and scling. The question is what is the best way to insulate . The cost to foam is approx. $ 3,000 vrs the cost to insulate with a breathing material on the wall. either way we need studs and drywall. I think that we should leave the wall accessable for air flow to get rid of any moisture, so I am questioning the foam. Any thoughts? Terry

11-20-13, 01:34 PM	#3
Terdale Renovation Consultant Join Date: Nov 2013 Location: Ottawa Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts	rubble foundation We can not install insulation from the exterior, so we must do from inside . My question is 'if we spray foam insulation on the interior rubble wall, will that not trap moisture from the exterior?' Would it not be better to let the moisture through the wall and down to the slab where it could be controlled by a fan. There is not a great deal of moisture! Terry

11-20-13, 09:46 AM	#2
wewantutopia Lurking Renovator Join Date: Apr 2013 Location: Woodstock, IL Posts: 22 Thanks: 1 Thanked 1 Time in 1 Post	I'd say the BEST way to insulate a basement is with rigid foam insulation on the EXTERIOR of the wall bringing the thermal mass of the foundation into the envelope...

11-20-13, 09:10 PM	#4
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	There is information about basement insulating on buildingscience.com. The information suggests that concrete/rubble doesn't need ventilation and that sealing it off prevents moisture and radon from entering the conditioned area. Any moisture being trapped in the conrete/rubble supposedly is not an issue because they are not affected by moisture. Materials such as wood and drywall(and your whole house and comfort frankly) are affected by the moisture and should be protected from it.

11-21-13, 09:37 AM	#5
Ryland Master EcoRenovator Join Date: Mar 2009 Location: Western Wisconsin. Posts: 913 Thanks: 127 Thanked 82 Times in 71 Posts	Spray foam will remove condensation points, but yes, like you said, it will not breath to the inside, it will however breath to the outside, so as long as you have good drainage and no moisture problems already you should be fine. If you are really worried about it, you could install a vent system under the foam and have a suction fan that pulls any moist air out and expels it from the house, this could be as simple as every few feet having a small perforated pipe next to the stone wall, connected to an exhaust fan and have that either on a humidistat that is in a cavity cut in to the foam so it's next to the stone, or on a timer to let it run an hour per day, I would opt for a humidistat. My house has sand stone walls, with crawl space, we put plastic on the floor of the crawl space, a drain tile under that and a vent fan, the plastic then ran up the sand stone walls far enough to be foam sealed in to place.

11-27-13, 06:04 PM	#6
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	i would be very careful that there is not a lot of hydraulic pressure from the outside. I have seen spray foam on the inside become pushed off the wall in places when there is a lot of exterior pressure. I think that, if at all possible, it could be sealed from the outside it would be the best option.