Crawl Space Insulating Confusion

Hello, I have read many posts in the forum and have seen many different, conflicting solutions on how to insulate my crawl space. Since no one else seemed to have my exact situation, here it is:After receiving a particularly high electric bill, we have decided to insulate under the house. After realizing that FG is going to be tough with unusual joist spacing, I started looking around. Here are some of the things I've read:So i'm pretty confused on which to proceed with. Which is best for my situation? Which is easiest? And which is going to be the lowest cost? I realize that I need to check and seal any heat leaks in the ducting, but if I insulate the exterior will that help if I happen to miss any or new leaks form in the ducting?

Thanks for your help, I am a first-time homeowner so please be gentle!

 

Hi iscribble and welcome to the forum. You sure make it tough, all you want is the "best", "easiest", and "lowest cost" . I guess we all start out that way, just hope you aren't disappointed when we tell you, you can't have them all.

OK, kidding aside, when you have ducts, plumbing, and such in the crawl space, it is usually best to close it off from the outside and insulate the walls. If it has a dirt floor, then you are going to want to cover it with a heavy plastic vapor barrier. I will attach a link that goes over crawl spaces rather well. Review that and see if you have more questions.

Omit the foil under the floor idea and think about rigid foam around the perimeter. If the budget ends up controlling what you can do, I have looked at and tried a couple of low cost alternatives for seniors on a budget. Not the best, but many home owners just want an improvement.
BSI-009: New Light In Crawlspaces —

Bud

 

Thanks Bud,
I've gone over this and other material and I like the idea of adding rigid foam directly to the foundation, however I still have have a number of questions:Thank you!

 

There is a plastic barrier on the ground, however it is not sealed. Does it need to be if I seal the crawl space vents? Why?

It is best if sealed as the soil will provide a constant supply of moisture. But, a VB with 90% coverage, is still a 90% VB. As long as air isn't flowing through the openings. Air carries a lot more moisture than evaporation from the soil. However, if you are in a radon area, the VB should be sealed and mitigation installed to vent any radon. EPA Map of Radon Zones | Radon | US EPA

I found a reference to building code that says I need to provide "conditioned air" to the crawl space if I take out the ventilation. What's that all about? Would I need to add a heating vent? What about cooling (no A/C)? Would I need a vent between the crawl space and the house?

The risk with ventilation is the warm moist summer air bringing in moisture that may condense out on the cool crawl space surfaces. With your heat ducts down there you are already exchanging some air, as noted, during the heating months. For the summer, it may be beneficial to run a dehumidifier when needed. Monitor the RH to keep it below 50%.
termites?

Termites don't eat the foam, but may use it to tunnel up to the framing. Where the house rests on the concrete/block walls, there should already be a termite barrier. That can be extended from the sill plate out over the top of the rigid foam and down a bit, then some rigid glued on top of that flashing.

I saw a reference to fire-safety concerns, but couldn't find anything more than that. What are the fire safety issues with this?

Not an expert on fire issues, but the final ok has to come from your local AHJ (authority having jurisdiction). Unfortunately, the local people tend to have their own rules. In my area, some say in unoccupied spaces the rigid foam can be left uncovered. Others say they want a fire barrier. Some allow the basic foil faced polyisocyanurate, while others require 1/2" of sheetrock. Check to see what your area requires.

Finally, I found this video regarding the owens corning brand rigid foam. Is this installation process similar to what is recommended?

Similar, if drywall is to be added. If you can get by with just exposed rigid foam, then it can be glued and strapped (while the glue drys) directly to the foundation walls.

They make a paperless drywall that would be good in that location. I would seal the VB up the foundation at least 6" and then install the insulation over that, keeping the bottom up an inch or two above the floor.

Foil covered foam is a VB so should not extend too far below grade, one foot would generally be ok.

They do make a commercial foil faced foam (Dow) that would satisfy all fire codes, I just haven't dared to check the price. They also make fire rated paints, but they are more expensive than the foam.

There is another product that I have looked at, duct board, which is a rigid fiberglass used to fabricate commercial air ducts. No fire issues, abour R=4 per inch, available in one or two inch thicknesses, comparable price to foam boards, and comes in 4x10 foot lengths. Or at least the ones I tracked down. I can dig up the listing if you are interested.

Time to eat
Bud

 

If the crawl space is vented now, it probably meets your local code. To change to a closed crawl space you need to: use the whole area as a plenum or heat trunk; OR add mechanical exhaust fan; OR add conditioned supply air from the house. Also, seal the outside access and add an inside access. The foam on the walls may need a fire barrier, per code: http://www2.iccsafe.org/cs/committee...E_06_64_07.pdf As Bud said, consult your local Building Department to get the required R-30.

If any gas appliances in crawl, they need their own air supply.

As you are South of me, you may find this interesting: http://www.energy.wsu.edu/documents/...awl_Spaces.pdf

If you insulate the floor, read "Insulating a vented crawlspace" : Energy Savers: Crawl Space Insulation

I'm insulating my crawl space with existing faced glass batts, strips of foil-faced rigid foam board on the joist bottoms, and typar for an air barrier. Closing the vents in the Winter, open in the Summer. I want a warm floor: http://www.advancedenergy.org/buildi...l%20Spaces.pdf

My foam pipe insulation was 60% eaten by rodents, you may want to research the foam product applied, and take appropriate steps if necessary.

Insulation pros have a string stapler that self-feeds continuous string through the staples to hold up the batts, very fast.
Be safe, Gary

 

Thanks all,
After some deliberation, I think we are going to more conventional route by insulating the floor (rather than the crawlspace). Will seal up the floor and ducts first.

Regarding the "new light in crawl spaces" article: About how much better is Figure 7 than Figure 6? Double?
Also, figure 7 uses unfaced FG, right?
Is this product equivalent to figure 6?

If for funding reasons I go with old-school straight FG, I will have to support it with twine or furring strips, etc. How important is it to get the insulation backing all the way up against the floor?

Gary- Where did you find foil faced rigid foam? Lowes and HD don't seem to sell it... at least not as far as I can find online.

 

"Gary- Where did you find foil faced rigid foam? Lowes and HD don't seem to sell it... at least not as far as I can find online. " -----------Foam board: Insulated Sheathing

Be safe, Gary

 

Darn, I don't see foil-faced at that link. I took at look at my local Lowes' rigid foam over the weekend and no foil-faced.

I am currently leaning toward using Reflectix to insulate the floor. Their website suggests 9.5" of air space would be R-17 (in addition to radiant). In my case, it would be 7.5" ...any idea how much that hurts the R-value? How much would some fiberglass (maybe R-13?) sitting on top of the Reflectix help?

Also, is the heat lost out of the floor by radiant heat significant?

I don't need any exact answers, just "a lot" or "not much" etc.

THANKS!