Re-insulating ventilating crawlspace. Would you remove the old insulation first?

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EbS-P

Minister of Fire
Jan 19, 2019
6,171
SE North Carolina
The whole house duct placement has paused for the weekend with an almost completely clear crawlspace. Now would be the time for me to insulate re-insulate the crawlspace. It will be a ventilated crawlspace.

Would you remove the old insulation or would you just staple new up over top of the old the old insulation? There’s not a whole lot left maybe an inch or two of. fiberglass.

Faced or unfaced?

If faced, faced side up to the floor (this is how hot should be I gather). Or faced side to the crawl space. Does it matter if I leave the the current insulation in place??

I might have time to get it all done before Monday morning. It will be about 20 rolls.

Thanks
Evan
 
How's about closed cell spray foam? Probably not enough time for a contractor to respond?

How's about fiberglass and then sheets of foam board nailed to the joist bottoms and seal up the butt joints?

At any rate, I would remove the old stuff. Don't know if it has absorbed moisture/bugs/pests or not.
 
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I don’t see this as a perfect/solution. I was quoted $13k to encapsulate it. It’s been ok since 1968. Nothing scary growing. Contractors will be back Monday morning. So it off the shelf at the big box stores tomorrow or nothing.
 
I personally would remove the old if I was putting in new, but if the old is fine, then I don’t see the prob w leaving it. The paper facing goes towards the floor (paper towards people).
 
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I’d tear out all the old insulation.

I’d put foam boards up over the walls.
 
An insulation vacuum will make the job as close to enjoyable as it can be.
Is the old foil faced paper. If it’s falling even a bit I’ll pull it out. If it’s still up after 50+ years I’ll leave it. There just isn’t much fiberglass left hanging to the paper anymore.

Foam boards on the walls was the plan and then seal and encapsulate. But I don’t have time to get it done right. And probably not the skill. There are piers every 10 feet on the external wall that don’t touch the brick but I can’t get insulation behind. Just a real pain.
 
I did my own crawlspace myself. It’s not difficult work, it’s just a pain in the butt trying to move around down there. It would have been much easier with a partner.
 
How close are the piers to the wall? If it’s really tight, can you push mortar into the gap and then just go around it?

Do the encapsulation afterwards. It may not be ideal, but you’ll still get improvement.
 
How close are the piers to the wall? If it’s really tight, can you push mortar into the gap and then just go around it?

Do the encapsulation afterwards. It may not be ideal, but you’ll still get improvement.
Tight enough I can’t get foam board behind. Any plastic will have to go around the piers on 3 sides then back to the wall.

If I go the encapsulation route as a DIY I will strongly consider spray foam. But the vents will need sealing and the current grills replaced with blanks. I think about 600 board ft of foam would do the job.
 
If you can’t get foam board behind it, mortar it off, then wrap the membrane around the whole thing.
 
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Take the old out; it's likely compacted by now.

I'd buy a few cans of spray foam for any big gaps. At least cuts down on the chimney effect in your home. Then new R19, paper always towards the conditioned space.
 
And that means getting those curved metal sticks to keep the insulation up (because you can't staple the paper from the crawlspace as it'll be against the floor).
 
Most ventilated crawls in my area have at least a few feet between the plastic covered dirt and the insulated floor. Plenty of room to slide around on your back.

My 1963 house had zero floor insulation. FG Insulation from the 60s is really thin and really itchy. I would tear it all out to avoid the double vapor barrier problem if it’s failing anywhere.

The pro installers did my floor in a half a day and used a plastic string to hold it up. No metal wires, Lots of string.
 
Just to clarify what I've used:

string would work as well, of course.
 
Well I just pulled out most of the old insulation. To be honest there won’t be much double vapor barrier effect for what I left.

I went with r13. It’s not like it gets that cold here. Plan is still to encapsulate at some point in the future. I just couldn’t pass up this opportunity with a wide open crawl to spent $500 and a Sunday to replace what was there.

So my floor joists are 2”x7.5” dimensional on 16” centers. Those insulation hangers might work. And honestly I probably will add just enough staples to keep it in place for right now I’m not even sure I have time to get it all cut and stuffed in place tomorrow.


All in all I can say I don’t have a mold problem. I did have a shower leaking but that shower is gone now. And for some reason there is a dead 12-2 wire exiting with the sewer line. Beer thirty here.
 
I'm not sure how you'll staple, given that the paper will face the floor and you, laying on your back, will face the glass fiber.,.?
 
I'm not sure how you'll staple, given that the paper will face the floor and you, laying on your back, will face the glass fiber.,.?
Probably shoved the bat to the side and slid the staple gun up beside the joist to staple into the subfloor. That, plus friction, should hold up the thin r13.

Minimum code up here is R30 or R34, I forget. R13 is cheap and the long rolls make it go fast. Better than nothing!
 
I preferred not to shove the fiber to the side (and leave the paper in place to be stapled) because it creates places with lower r value.

I think R19 fits between standard floor joists.
 
I preferred not to shove the fiber to the side (and leave the paper in place to be stapled) because it creates places with lower r value.

I think R19 fits between standard floor joists.
r-19 comes in a variety of widths. Joists can be 12" (unusual); 16"; 24" typical widths along with some oddball widths thrown in just to mess us up.

the 19 refers to the thickness (depth) of the insulation, not the width of the space it'll fit.

19 is used for 6" cavities. 6" joists are just not too common any longer.

But, I'm betting you know this already.
 
r-19 comes in a variety of widths. Joists can be 12" (unusual); 16"; 24" typical widths along with some oddball widths thrown in just to mess us up.

the 19 refers to the thickness (depth) of the insulation, not the width of the space it'll fit.

19 is used for 6" cavities. 6" joists are just not too common any longer.

But, I'm betting you know this already.
Yes. I spent about 150 hours to air seal and insulate my attics.

My point is that shoving the fibers sideways while keeping the paper in place (remember this is a crawlspace so the paper is against the floor and the fiber towards the crawlspace) to staple it deteriorates the insulation value, and might even tear off the fibers from the paper.
 
Yes. I spent about 150 hours to air seal and insulate my attics.

My point is that shoving the fibers sideways while keeping the paper in place (remember this is a crawlspace so the paper is against the floor and the fiber towards the crawlspace) to staple it deteriorates the insulation value, and might even tear off the fibers from the paper.
It will be 2-3x better than it was even with the staples.

The correct solution is to encapsulate and insulate the walls. I just can’t get that done yet. And to be honest since I don’t get any summer benefits from this insulation the payback time is quite large. 500$ is probably 2 years worth of heating costs. I guessing I will see at most 10-15% reduction in heating costs. Napkin math says 13 year ROI. Crawl space is not my biggest Heat loss. And since I heat with wood. It’s probably longer.

Coming up with an energy humidity control system for a ventilated crawl space one that doesn’t bring outside air in if the outside temp is below some value. That’s another thread.
 
Every insulation job I’ve done has paid off in comfort. ROI is super important, but so is comfort as I get older. My cabin floor is 3/4” of tongue and groove. I can’t insulate it due to flooding concerns and animals. When it’s-22 out and the wind is blowing my feet are cold. I’d love a single layer of R-1 bubble wrap down there, lol.
 
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Job is done. 19 rolls at 32 feet installed.

100% removal of old insulation. The wire straps were a great suggestion @stoveliker. Just for the the speed it was worth 60$. And cheaper than the 100$ battery stapler I didn’t use but might just keep.

Beer—thirty again.

Best forum on the internet!!!
 
Now maybe air seal things by attaching some foam insulation board to the bottom of the floor joists and sealing the seams. It will help with thermal bridging too.
 
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