Evaluating the options for crawlspace insulation

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Old 02-24-08, 08:07 AM
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Evaluating the options for crawlspace insulation

The best advice I've read so far is to expect a variety of opinions on this topic. I'm bracing myself.

Issue: I have a 50-year-old house and this winter the hardwood floors were COLD as can be.

My house:
-800 sqft
-Crawlspace (enough room to crawl anywhere) is roughly a 23*38 rectangle
-Heatpump/Gas hybrid heating, 1.5 ton AC (1.5 ton is just big enough for my house)
-The heating/blower system is located in the crawlspace in the very middle fo the house
-All horizontal plumbing runs are visible in crawlspace
-No insulation between floor joists
-from the crawlspace, the visible subfloor are diagonally-run 1*6 boards. I don't know if there's additional sheeting between those boards and the finish flooring. Most of the house has the original hardwood still in place (and thankfully it's in great shape!).
-plenty of foundation vents
-there have been moisture problems down there (the base of foundation walls always seem moist, but I don't know if this is normal or a problem)

Questions: (I have a lot, so if you're willing to reply, you might want to read them all first before responding)


1. I have read 'some' about making the crawlspace part of the heated/cooled envelope of the house. I believe I understand the concept but it introduces a few questions:

A. If I suspect that water can seep into the crawlspace area, does this have the be 100% remedied before considering doing the envelope thing?
or
B. If there is a minor moisture issue - that is, no standing water but the foundation walls also seem moist - can that be overcome by the envelope method?

C. If my cooling system is barely big enough to cool my house, is it feasible for me to consider conditioning the crawlspace?

D. If you condition the crawlspace, doesn't the air inside your house start to smell like your crawlspace?

E. I intend to keep this house as a rental for a while. In the future, I will have to replace the blower/furnace unit that's under the house. I suspect they will remove it, even if they put in a gas pack instead. When they take this thing out, it's probably going to do some damage to the floor plastic and possible the opening to the crawlspace. Are these envelope systems like a balloon such that, if you put one small hole in it, it quickly fails or else looses a large amount of efficiency?

2. Paying someone to do the envelope method right might be too $ for me. SO - I have read some about just making sure your plastic on top of the dirt is in good condition and perhaps insulating the foundation walls.

F. If I have foundation vents (crucial since I have a moisture issue) is there any point to insulating the walls?? Do you only insulate the walls if the area is closed (aka no vents?)

G. When I lay the plastic down, how does the moisture escape? Does it just come out around the perimeter of the plastic?

3. Ok, so perhaps none of the above are feasible until/unless I get the foundation issues in place. So let's talk about just putting insulation between the floor joists.

H. I have flexibe ductwork running all over the crawlspace, and as I mentioned above all of the vertical runs of my plumbing are down there, too. It just doesn't seem reasonable to put insulation bats in such a 'busy' space. Am I right to think this way?

I. Is there a spray insulation that might be used in this situation? If so, is it so permanent that, if I have to replace plumbing, I'll ruin it?


Sorry for the all questinos.
 
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Old 02-24-08, 12:42 PM
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Fasten your seatbelt, here goes. If you already have foundation vents, they are there for a purpose, to rid the crawlspace of moisture. Laying a 6 mil vapor barrier on the dirt of the crawlspace will keep condensation from getting to your wood, which is good. Moving the air is important, so having the foundation vents open in the summer moves the hotter moister air from under the house to the atmosphere where it is dissipated. Don't make the crawlspace a part of your heated/cooled system. Insulate the floor area between the joists with probably R30 kraft faced batts with the kraft vapor barrier facing up, and suspend the batts using the spanner wires made for that purpose. You will close the vents in the winter to keep your pipes from freezing and for holding some of the warmer air created by the heated items. The moisture under the vapor barrier on the dirt, generally will find its way back down, but, as you suggest some may eek its way around the edges, but not enough to worry about. You already know there are several schools on this, so Airman, you're up!!!
 
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Old 02-24-08, 03:39 PM
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Just did mine

I agree there are alot of schools on this, But I just finished mine. I have alot of info and am not a good typer.
call me if you wish.
303-246-7685
 
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Old 02-27-08, 09:08 AM
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Chandler, in your response you mentioned:

Originally Posted by chandler View Post
...Insulate the floor area between the joists with probably R30 kraft faced batts with the kraft vapor barrier facing up, and suspend the batts using the spanner wires made for that purpose...
One of my original questions was:

"I have flexibe ductwork running all over the crawlspace, and...all of the vertical runs of my plumbing are down there, too. It just doesn't seem reasonable to put insulation bats in such a 'busy' space. Am I right to think this way?"

What's your take on that? Does the kraft barrier need to be against the subfloor or can it truly be suspended (leaving an air pocket between the vapor barrier and the subfloor). I've heard the saying that a poor seam in insulation is like a bad zipper on a winter parka, so I can't imagine the chore of custom-cutting each bat and ensuring good fits around all of the obstacles.

Hammer, I'll be calling you soon...

Thanks,

Chris
 
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Old 02-27-08, 01:26 PM
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You're right about the space, but you will want to get insulation above the ductwork, if it is below the joisting. The ductwork itself, if it is running in between a joist can act as an insulator as long as you keep air from infiltrating around it by lightly stuffing the edges with pieces of the fiberglas insulation. Otherwise, in the areas where you can insulate, use the batt installation rods and keep it as close to the subfloor as possible without over crushing it. Crushed insulation is worthless as the insulation properties come with its loftiness. The side fill will keep air from becoming a problem if the kraft happens to fall slightly, which it will anyway.
 
 

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