Crawl Space Insulation

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  #1  
Old 11-15-03, 10:06 AM
RedLevelMike
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Question Crawl Space Insulation

Just bought 200 year old home, need to insulate under the floors. Is there any easy application or spray-on product that a homeowner can apply? Also need an easy way to insualte the water pipes.
 
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  #2  
Old 11-15-03, 10:37 AM
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Probably the easiest way to insulate under the floor is to use batts and the push in support wires.

I used a foam tubular product that is split along the side to insulate my pipes. It went on easily enough. The split edge has protective tape that is removed so the adhesive can hold it in place.

Hope this helps.
 
  #3  
Old 11-16-03, 01:54 PM
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Exclamation crawl way

Over the years I have not found any kind or any way to put insulation in the joist over a crawlway. The insulation should go on the out side walls and just in the joist space there on the sill plate all around the home. With a 6 mil poly down on the ground. This way the water pipes should be ok if not just some heating cable on them is all you need for a short time. One is call Safe-T-Wrap. ED
 
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Old 11-18-03, 10:44 AM
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Ed, are saying to just insulate the walls and rim band? Why wouldn't you put R-19 or better between the floor joists?
 
  #5  
Old 11-18-03, 11:43 AM
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Lightbulb crawl way

It just dont work that way. I have taken so many out did that way. First from the home warm moist air will go down in to it. then the moisture there in the ground will get up in it. I have taken out like what Chfite said with the wires. I have seen them try chicken mesh, 1/2" 1/2" mesh just wire and on and on and it all got wet in there. We have for years did it this way and the gov. said to do it this way and it works. 6 mil poly on the ground 2 ft over lap tape all seams up the wall 2'. 2" or more polystyrene on the walls up to the joist. R 19 in all joist on the sill plate around the home. If you have duct there for heat and cool we cut small registers in for some heat and cool down there. this way the whole crawlway works like a big heat sink and you have warm floors. ED
 
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Old 11-20-03, 10:27 AM
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The more research I do, the more I find that insulating the walls and sill with plastic on the dirt is the preferred way. Some major information sources still promote insulation between floor joists, though. That adds to the confusion.

It seems to be cheaper to insulate the walls and sill and add polyethylene to the dirt than it would be to do the floors. In my case, I have about 500 sf of wall, but 2000 sf of floor. The math becomes compelling.

The filter for my HVAC is under the house. You know for sure that it is not all that well sealed. Sealing the crawl space and insulating it would probably be the same as putting a register and return air in the crawl space due to the presence of the filter mount.

Still have this project before me.
 
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Old 11-20-03, 10:47 AM
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Exclamation crawl way

We do put register for heat , cool and a return when the duct work is in the crawl way As I said it makes it a big heat sink and helps as a dehumidifier ED
 
  #8  
Old 11-20-03, 03:27 PM
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Got Lucky

Hmm, maybe I did okay anyway. The basement and unvented crawlspace of my 30-yr-old house smelled bad when I moved in, the culprit clearly being the crawlspace. Tests showed that we also needed a sub-slab radon pump, in the basement only. I asked the radon contractor to also cover the crawlspace dirt with a membrane, however, sealed 2' up the concrete walls, and to run a pipe from underneath the membrane to the radon system. I figured that would pump moisture away 24/7.

Then I put R19 between the floor joists with the vapor barrier up towards the house. The crawlspace and insulation are still dry and sweet-smelling 3-1/2 years later, so this seems to be working.

I have, however, received an education in this thread. Perhaps I can ask some additional questions:

1) Are you talking about unvented crawlspaces only? For vented crawlways like those on the west coast, blowing heat down should be like throwing money into the wind. Do you block the vents?

2) A return-air grill in the crawlspace will suck mold, dust, etc. into the living space. How about leaving a small leak to the outside and no return grill? Then when heat is blown down there "clean"makeup air comes in from somewhere topside (like a leaky front door).

3) You mention a heat sink, and dirt isn't a bad one. Any estimates of additional cost of heating/cooling the crawlspace? Would you be a lot more energy efficient by covering the whole membrane surface with batts?

Thanks for the info.
 
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Old 11-20-03, 04:22 PM
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unvented crawlspaces only
You would seal and insulate the walls and condition air only in an unvented crawlspace. It just makes sense. With mine, I will have to seal it.

A return-air grill in the crawlspace will suck mold, dust, etc. into the living space
If there were any, it would be sucked into the filter. After the construction is complete there won't be any airborne material. It will all settle in a short while. Notice that your HVAC system does not stir up dust in your house, yet there is dust aplenty as in most houses.

heat sink
Think about the constant temperature of the earth. It seems that if there were anything to gain, it would be from the temperature of the earth. It the earth were insulated from the crawl space, all that would be left would be the air. Air is not much of a heat reservoir.

Anyway, Ed will probably have more enlightening observations.

Hope this helps.
 
  #10  
Old 11-21-03, 10:35 AM
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Thumbs up crawl way

Think you covered about all of it there chfite.

You could go to www.taunton.com/finehomebuilding

They cover the RADON gas for you in the crawl way.

Have had fuel costs go down after a rework this way


I like what they do but dont like the insulation up there in the joist. .We dont put insulation in the joist just use the whole crawl as a heat sink. This will give you a warm floor and a happy wife. ED

No vents but check code there could cover them up in side we do
 

Last edited by Ed Imeduc; 11-21-03 at 04:44 PM.
  #11  
Old 11-24-03, 11:13 AM
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heat sink
Think about the constant temperature of the earth. It seems that if there were anything to gain, it would be from the temperature of the earth. It the earth were insulated from the crawl space, all that would be left would be the air. Air is not much of a heat reservoir.

That's exactly my point. The heat reservoir is not useable, it's too cold. That is, the heat you blow into the crawlspace will get sucked away into the ground. If you insulate your house you save money. If you decide to heat the crawlspace, you should save money by insulating it too.

Here's my reasoning:
The earth has a constant temp of about 40F at a depth of about 4-6 feet. You want your crawlspace close to room temp to help keep the house warm (assume a daily average of 65F).

To get an idea, treat the dirt as an insulator between the 65F crawlspace and the 40F reservoir. Soil is somewhere around R-1 per foot of thickness, take it as R-6. Heat loss for a 1000 square ft area is

Q=(Tc-Tg)*A/R

= 25F * 1000 ft^2/R6 = 5kBTU/hr

If you heat with gas that's 36 therms/month (over $30/month) sunk into the ground.

That's a crude calc just to show that insulating over the crawlspace floor membrane makes "cents"! My question is, does it make "sense" otherwise?
 
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Old 11-24-03, 12:51 PM
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Exclamation crawl way

I have always been told the ground is 52o. Put a heat pump highside in the lake under the ice would get 52o water temp for the coil. That was with the power company checking on it about 4 ft down. I do know our jobs have cost less to heat than others. Each to his own ED
 
  #13  
Old 11-24-03, 02:51 PM
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That's a crude calc just to show that insulating over the crawlspace floor membrane makes "cents"! My question is, does it make "sense" otherwise?
I agree with your math. Nevertheless, my research shows that the prevailing recommendation is to insulate the walls of the crawlspace and put plastic on the dirt.

My take on it all has to do with heated air rising. The attic insulation is most effective in preventing heat loss, next is the wall insulation preventing loss laterally, then the crawlspace as a buffer. Perhaps the notion that I proffered about a heat sink or reservoir is incorrect. It may be better to think of it as a buffer preventing heat loss through the floor.

Anyway, I don't have any arguement here. This is all interesting and sometimes a bit confusing. I am trying to stay on top of it.

Discussing all the points from differing perspectives lets us all know that sometimes it is not so simple as it seems.
 
  #14  
Old 11-24-03, 05:31 PM
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I agree, chfite. I get ideas but it's great to hear the voices of practice and experience. I'm learning a lot!

Thanks all.
 
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