Crawl Space Insulation - Foil Sheets on Joists

[ddurrett896]

Live is SE Virginia and house is on a vented crawl space with foil insulation stapled to the bottom of the joists.

How effective is this? It's torn down in a few places where plumbing work was done in the past and not replaced.

If it doesn't help my plan was to pull it all down when I'm under there which:
1) exposes the joists/subfloor for damage
2) gives me another 8" of headroom when I'm under there doing work

Thanks!

 

[ssdave]

Floor insulation is a funny thing when it comes to performance. The foil insulation/bubble wrap that is about a R1 or less in a ceiling, acts like a R10 or more in a floor. That is because the two mechanisms in floor heat loss are air infiltration, which well applied foil blocks, and radiation, which the foil reflects back into the living space. Foil insulation carefully applied to the bottom of the joists is more effective for most floors than stuffing the cavity full of fiberglass.

 

[K'ledgeBldr]

By your description, it sounds like the insulation is installed backwards. The foil/craft paper side is suppose to be next to the conditioned space (the subfloor).

 

[50pascals]

Does your crawlspace have a concrete floor?

 

[CombatNinja]

No way it has a concrete floor in Virginia. Warm, humid air would enter and begin to condense on that slab making it a breeding ground for God-know-what.

Keep in mind, vented crawlspaces are prone to this a bit anyway even with dirt floors but concrete down there would be a nightmare. That is why a lot of folks that attempt to 'remedy' moisture problems in their homes built this way by just putting down some DIY plastic sheeting end up causing more problems. The conventional wisdom these days is to fully insulate/encapsulate and install a dehumidifier. There's usually enough leakage in HVAC ducting to suffice for keeping it conditioned enough because the majority of these homes are built in mild climates.

 

[ddurrett896]

Does your crawlspace have a concrete floor?

No concrete flood. All HVAC is in the attic.

 

[50pascals]

No way it has a concrete floor in Virginia. Warm, humid air would enter and begin to condense on that slab making it a breeding ground for God-know-what.

Keep in mind, vented crawlspaces are prone to this a bit anyway even with dirt floors but concrete down there would be a nightmare. That is why a lot of folks that attempt to 'remedy' moisture problems in their homes built this way by just putting down some DIY plastic sheeting end up causing more problems. The conventional wisdom these days is to fully insulate/encapsulate and install a dehumidifier. There's usually enough leakage in HVAC ducting to suffice for keeping it conditioned enough because the majority of these homes are built in mild climates.

"Encapsulated Crawl Space" is exactly where I was heading. I just wanted to see what the OP was starting with.

 

[y'sguy]

I'm subscribed. I have an uninsulated crawl space under almost all of my house with a dirt floor. elevation varies, but it is definately a "crawl" space. We have had several moisture issues over past years, but all have been resolved.
I heard a ton of opinions on the way to handle thie type of space and none agree on what is best. However they are all time consuming difficlt and therefore usually expensive.

 

[paredown]

I'm also facing a similar issue--and I think that the Building Science site has the best discussion of crawl spaces and why it is best to insulate outside walls, block vents (do a radon check though and add ventilation if necessary), and make sure you have a vapor barrier in place on the dirt to limit stack effect and moisture transfer. My problem has been that is a big job to do yourself, and hard to get materials in place if you don't have a good access door.
https://www.buildingscience.com/documents/information-sheets/crawlspace-insulation

Dow makes a foam board product for doing the foundation walls called Thermax that has a class A fire rating so you can use it uncovered on the walls:
https://www.awarehousefull.com/dow-thermax-sheathing/

For the OP, I would say in VA you need to leave some way for the band/rim joist to be inspected for termites--blocks of foam cut and placed that can be removed would work...

 

[CombatNinja]

Full encapsulation seems to be the prevailing wisdom these days. That said, I have seen home built with vented crawl spaces with nothing down on the floor and they are dry as can be. Every site has its own unique soil profile, drainage and humidity characteristics. Results vary. I have just seen a lot of well-intentioned homeowners plop down some thick plastic thinking they are going to solve a moisture-related issue and they end up making it worse.

 

[lakeroadster]

Full encapsulation seems to be the prevailing wisdom these days. That said, I have seen home built with vented crawl spaces with nothing down on the floor and they are dry as can be. Every site has its own unique soil profile, drainage and humidity characteristics. Results vary. I have just seen a lot of well-intentioned homeowners plop down some thick plastic thinking they are going to solve a moisture-related issue and they end up making it worse.

I second Combat Ninja's comments. We live in a vary arid climate where it is typically cool. There are cactus growing in the yard and no air conditioning is needed.

Yet our county enforces the same set of IBC rules that apply to the most humid / wettest / hottest parts of the country.

As my favorite building inspector, Grace Slick, once said: Logic and proportion have fallen sloppy dead.

Our crawl space has R-30 insulation between the joists, a dirt floor, all the vents are closed and sealed off and I installed a radon fan. It's dry as a bone down there... year round.

So how's the drainage around your house? Does the house sit up "high and dry" and are there gutters and loooong downspouts to direct rain water away from the foundation?

 

[50pascals]

I'm also facing a similar issue--and I think that the Building Science site has the best discussion of crawl spaces and why it is best to insulate outside walls, block vents (do a radon check though and add ventilation if necessary), and make sure you have a vapor barrier in place on the dirt to limit stack effect and moisture transfer. My problem has been that is a big job to do yourself, and hard to get materials in place if you don't have a good access door.
https://www.buildingscience.com/documents/information-sheets/crawlspace-insulation

Dow makes a foam board product for doing the foundation walls called Thermax that has a class A fire rating so you can use it uncovered on the walls:
https://www.awarehousefull.com/dow-thermax-sheathing/

For the OP, I would say in VA you need to leave some way for the band/rim joist to be inspected for termites--blocks of foam cut and placed that can be removed would work...

Well, my life is complete now. A random post cited buildingscience.com!!!!

There is no bad information there. Someone above commented to the effect that "there's different opinions and no one agrees." buildingscience.com is right, every time, period.

Many experts on this garage journal forums would do themselves a favor reading their material.