[jsjones01]

I just bought an old house that has thin insulation between the 2x6 joists in the crawlspace. Can I just install new batts over the old or do I have to start over? Since the old has kraft paper against the subfloor above, do I use batts with no kraft paper? Is there such an animal? Thanks!

[hkstroud]

Yes there is unfaced batt insulation. If the paper, which serves as a moisture barrier is in good shape you can install additional unfaced insulation.

[jsjones01]

Yes there is unfaced batt insulation. If the paper, which serves as a moisture barrier is in good shape you can install additional unfaced insulation.

The guy at Home Depot told me I needed to cover my insulation in the crawlspace with plastic for a moisture barrier, even though I have visqueen covering the dirt under the house in the crawlspace. Is this correct?

[rtw_travel]

I'm trying to picture what you have:
a) house on 2*6 with thin insulation and kraft paper on the warm side of the insulation
b) a crawlspace under house, with plastic covering the dirt floor (i.e. you walk on the plastic when you are in the crawlspace, and the thin insulation is above you?)

If I have understood you correctly, then Home Depot is wrong and Harold is right. Just use uncovered insulation.

If I have not understood you correctly then here are some vapour barrier rules:
a) vapour barrier goes on the warm side of the insulation only
b) there can only be one layer of vapour barrier in any insulation.
FYI: in my area of Canada, the building code states we actually don't need a vapour barrier from a non-heated room to a heated floor above it: insulation only.

[jsjones01]

I'm trying to picture what you have:
a) house on 2*6 with thin insulation and kraft paper on the warm side of the insulation
b) a crawlspace under house, with plastic covering the dirt floor (i.e. you walk on the plastic when you are in teh crawlspace, and the thin insulation is above you?)

If I have understood you correctly, then Home Depot is wrong and Harold is right. Just use uncovered insulation.

If I have not understood you correctly then here are some vapour barrier rules:
a) vapour barrier goes on the warm side of the insulation only
b) there can only be one layer of vapour barrier in any insulation.
FYI: in my area of Canada, the building code states we actually don't need a vapour barrier from a non-heated room to a heated floor above it: insulation only.

Yes, you understood correctly. I didn't think the HD guy was correct, but thought I'd check. I'm in Pacific NW. I'll use unfaced batt insulation. Thanks!

[ballengerb1]

You may want to look into rigid foam insulation panels that can be nailed to your floor joists. Batts and roles are very good be can be difficult to install over head and getting them to not sage can also be a challenge. Rigid Foam Insulation Materials

[jsjones01]

Thank you for the link. Can I install the rigid foam over the existing thin batts or do I have to remove the old insulation to install new thicker rigid foam? How is the rigid foam attached?

[ballengerb1]

It can be nailed with nails that have a plastic washer attached to them. Don't look in the insulation aisle, they are with the regular nails. I'd leave the old stuff in place, the rigid stuff will help to hold it in place.

[jsjones01]

Thank you very much for your help. Can I do the same thing in the attic? Or would batts be better there. In the attic I have some fluffy stuff, not in batts that fills up the joist cavity. I also have sections of old roof visible in the attic, but not from the outside of the house as a new roof was added above the old roof when additions were made to the house. The original cabin was built in 1943. The areas where this old roof is visible from the attic has no insulation on it at all, and there is none in the new roof joists above . Should there be? What is the best way to insulate this portion of the house? It's a weird little house but its charming. Thanks!

[hkstroud]

If by roof joist you mean roof rafters, you should not put insulation there if you have insulation between the ceiling joist. What you have now is loose cellulose insulation in between the ceiling joist. This can be purchased in bags and spread out usually using a broom. Best way is probably have a insulation company come blow in additional insulation. They can get in places too small you to get into.

[ballengerb1]

Yep, I'd go with blown in due to the configuration of your attic. Many home centers rent you a blower if you but the insulation from them, messy job but a no brainer.

[mismaster]

What if you have unfaced thin layer currently in the crawl? I live in WA but have a very dry crawl, but the floors are very cold since only R-11 unfaced is there now. Can I install on top of that or take off the unfaced, but faced on top, then the old stuff underneath?

[hkstroud]

The moisture barrier is to prevent the warm air from inside you house from mixing with the colder air outside. This is done to prevent condensation which would occur if the two air masses mix. The moisture barrier always goes on the warm side. You can install additional unfaced insulation over (actually under) the existing insulation. If you use an insulation with a moisture barrier you should remove the existing and put the moisture barrier up against the floor. You can reuse the existing insulation as long as it does not have a moisture barrier. The extra work of reusing the existing insulation is probably not worth the cost difference of the two different thickness of the new insulation however.

[ballengerb1]

mismaster, it is always a good idea to start your own post even if your situation is similar to an old post. Harold's info and advice is correct and you never want to get into a situation with two separate vapor barriers. I'd recommend taking out the old stuff and start with new, faced insulation that will expand to completely fill your floor joist area, likely 2x10.

[rtw_travel]

I mentioned it earlier... but where I live, there does not need to be a vapour barrier between an unheated basement area and a heated room above it. Plain R28 insulation will do.

Check with your local building department to find out what is required in your area.

[wecanoe18]

It can be nailed with nails that have a plastic washer attached to them. Don't look in the insulation aisle, they are with the regular nails. I'd leave the old stuff in place, the rigid stuff will help to hold it in place.

Greetings, I am facing similar problem in PNW. Had thought about adding foam board or reflective on bottom of floor joists to cover exisitng r19 glass between floor joists to stop air movement; but then got to wondering about condensation. Unless what is added under the existing insulation is adequately permeable, then condensation from water vapor in the home has a strong potential to occur. Would that not rule out foam board? Ain't nothing quite like a strong mildew smell, except dead rats. Now looking into vapor permeable reflective barrier to stop air movement in the glass (we get serious winter wind here and it whistles through the crawl space), else just add furring and more glass under the floor joists. Yuk. I hate working with that stuff...
Hope this is useful. Thx wecanoe18

[jsjones01]

Thanks for everyone's help. I have decided I'm going to take out all the old insulation, most of which is falling down because the retaining wires have rusted and broken. When I try to repair with new wire, the glass just isn't poofy any more, so I feel the R-value has decreased and its probably mildewed. Does faced insulation come in 24" widths? I have a whole section of floor joists that are 24"o.c. Also, I live close to the water and have heard that varmits abound. Can I put something like smalll meshed chicken wire on the bottom of the joists to prevent nesting in my new insulation? Any recommendations? Thanks!

[wecanoe18]

Thanks for everyone's help. I have decided I'm going to take out all the old insulation, most of which is falling down because the retaining wires have rusted and broken. When I try to repair with new wire, the glass just isn't poofy any more, so I feel the R-value has decreased and its probably mildewed. Does faced insulation come in 24" widths? I have a whole section of floor joists that are 24"o.c. Also, I live close to the water and have heard that varmits abound. Can I put something like smalll meshed chicken wire on the bottom of the joists to prevent nesting in my new insulation? Any recommendations? Thanks!

First my qualifications; I know a little about building and have back ground in forestry which includes stone age physics, biology, toxicology (yep, a little) and chemistry. Here goes; heat flows via radiation, air movement (convection and advection) and conduction. Fiberglass primarily works by slowing air movement. R value is linear with thickness. Thus thicker (suitably fluffy) is better than thin, torn or compressed or wet (water is good heat transfer medium). Glass is essentially inert to biological organisms though mildew can live on dust or other organic matter (rodent poop, etc) in the glass if moist enough. Mildew is nearly impossible to kill. If mildewed, getting the old glass out sounds like a good fix. Widths various; 24 and 23.5 seem common either unfaced or faced with Kraft paper or foil. Check the manufacturers web sites (JM, Certainteed, Corning, etc.) To keep critters out, code here calls for 1/8 mesh galvanized hardware cloth (if I recall correctly) for crawl space vents. That keeps nasties like yellow jackets out as well as rodents and raccoons. Mice, and likely small rats, can get through chicken wire and as I recall, it is not galvanized. Rusts quickly. Rats can gnaw through sheet rock easily, some plastics like those insulating electrical wires are rodent appetizers (I discovered the hard way) and maybe chicken wire can be breached (that full story not germane here). Sounds like rus is an issue. Fglass can be supported by laths, 1x2s, plastic baling twine, etc. Speaking of critters, my neighbor up the hill (forced air heating) had a room that was ice cold in the winter. Heating bills were stratospheric. Found a broken duct and racoon family basking therein. They quickly got evicted and crawl space sealed. Install a good solid vapor barrier between your floor and the new glass that meets local code. Maybe use one of the radiant barrier products as vp and to block radiation from the floor downward with the glass. Or use them alone in a couple of layers. The advertising says they perform well when in "suitable" layers by creating dead air space (caveat emptor). TFor sure they have to be a whole bunch less nasty to install than glass, though some new glass products seem sealed in pouches which could make them less nasty (until cut). That's about all I know. Hope this all is useful. Good luck. And ALWAYS wear the right ppe. wecanoe18

[jsjones01]

"Install a good solid vapor barrier between your floor and the new glass that meets local code. Maybe use one of the radiant barrier products as vp and to block radiation from the floor downward with the glass. Or use them alone in a couple of layers."

OK, what does this really mean? What is a radiant barrier product? Sorry to be so dense, but I don't get it :-)) Thanks!