How to install fiberglass insulation
unclejack
| Posted in Energy, Heating & Insulation on
I have a four-foot crawl space under my living room that has a concrete floor and cement block walls. The ventilation is not very good and the walls and floor are usually damp. Previously installed (15 years ago) insulation is damp and hanging down in shreds. I want to put new fiberglass insulation between the floor joists under the living room floor. Should I install it in the usual way with the paper vapor barrier next to the floor or should the vapor barrier be facing down toward the concrete floor. Any suggestions you might have about installing insulation in this situation will be appreciated. Thanks.
Replies
OK, I'll bite.
First, you have to fix the damps. Otherwise you will get condensation in the insulation during the summer. You DO have air conditioning, don't you?
Then, unless you have foil colored fiberglass, you do NOT have a vapor barrier. The paper stuff is there for ease of handling. It does not stop water vapor.
Now, as to the fix. Put new stuff up. Nail it by the paper edges so it does not fall down. Then put up those steel rods designed to hold insulation when put overhead. Use a lot of them.
(Actually, fiberglass insulation ain't worth nuttin hardly. Air gets by it, you can't fit it into irregular spaces, and it is a mess to work with. You might want to consider one of the foams.)
Have you actually done this?
First of all, the kraft face on fiberglass is considered a vapor barrier--although not a very good one--and around these parts you are REQUIRED by the inspector to install it towards the living space. I don't know what parts either of you are around since your profiles do not say.
Second, lightning rods as they are sometimes called are designed to bow upward into the insulation... they "spring" into place. If you staple the facing to the bottoms of your joists you will not be able to use them, they'll fall out now or sometime soon. They are designed to work with either unfaced material, or with the facing installed the other way. They compress the insulation and pull it away from the joists.
The best ways I have found to hold insulation up are twine and deer netting.
Twine is available here in a box, 4500 feet long. Install the insulation first as well as possible, press-fitting it. Starting at one end of the building staple the twine to the bottom of the joists, running across the joists. Start with a run about 6" from the ends of the joists, and then continue @ about 16" on center. A small stapler with the JT21 size staples works well. One you have webbed the underside of the joists go back thru and dress the insulation nicely so it is not bunched up.
Deer netting is very lightweight black plastic netting that's 7' wide. It can be stapled under joists also, but you want a helper and you have to be patient. It works really well but will make getting at the underside of the floor hard if you have to later. I use it sometimes to wrap FG around skylight shafts that go thru the attic or similar situations.
The dampness we can agree on--that's gotta be solved.
The dampness we can agree on--that's gotta be solved
Which makes me think that, maybe, first step is to seal up the vents in the c/s.
Then put some rigid foam up against the c/s walls, and carrying that right up an fitting it to the floor structure, hoping that the there won't be much thermal bridging at the wall/floor joint since the walls are block, per OP.
I have this feeling that this is an southern east coast, or florida, house, from the description. It's just a feeling mind you. But it fits the evidence provided. Nice, cool, concrete structure in ground contact into which humid air is allowed to circulate, which ten condenses on the nice, cool, concrete.
If I'm right, that's also why the floor was insulated previously--somebody ciphered that 80-90º outside ambient air in the c/s might just try to infiltrate through the floor into the 72º conditioned space above.
Which would be really bad to then have a pedantic BI who'd insist on the facing be to the habitable side . . . Occupational hazard of my occupation not being around (sorry Bubba)
Regarding the permeability of kraft paper--while I haven't looked up the values, it is quite high and effectively is not a vapor barrier.
Yes, I have done this, using the "lightning rods" which I despise. I have never tried your idea of the twine, but I really like it, and will use it in the future.
I don't know about your area, but kraft paper goes either way in my area. [NO CHEAP JOKES PLEASE ;>) ]
" [NO CHEAP JOKES PLEASE ;>) ]" That is an open invitaion. Which has some good ones right now.I have not installed any in years. But what I have seen does not have kraft paper, although that is what is called. It is multiple layers with an asphaltic or plastic layer. Kraft paper is just the outer surface..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
You're right, we call it "kraft-faced" or "faced" but it is indeed laminated with a thin layer of asphalt. I do not know how permeable it is, or how valuable it is either, but the inspector absolutely has to see it when he walks in your job.
John D1,
Regarding the permeance of kraft facing: kraft facing meets all building code requirements for a vapor retarder. A vapor retarder is defined by the 2000 IRC (and every code I've ever seen) as a material having a permeance rating of 1.0 or less when tested in accordance with ASTM E 96. Kraft facing has a permeance of 0.30 perm.
kraft facing meets all building code requirements for a vapor retarder
Well, the material meets the code, true enough. But in three decades of this biz, I've yet to see an installation that came more than "close." This is part and parcel of the anti-FG "reflex" many here have.
A person can run that stapler or the hammertacker down that facing along the joints, but never in a way that really seals the opening as a VB ought (assuming, of course, the VB is on the correct side anyway--a whole different thread). And, that nice, neat, straight run of whole batts with nice clean margins to tack the facing to the joists only really occurs over maybe a third of the surface in question.
But, that's just my experience; others will differ.Occupational hazard of my occupation not being around (sorry Bubba)
Capn Mac,
It appears that you are confusing the function of a vapor retarder with the function of an air barrier. Kraft facing is a lousy air barrier; however, drywall can be an excellent air barrier, if it is properly detailed according to the Airtight Drywall Approach. Builders using ADA do not have to worry about whether or not their vapor barrier also performs as an air barrier.
Kraft facing works fine as a vapor retarder; this is easily demonstrated in a laboratory. Vapor retarders only need to slow vapor diffusion; they don't need to stop air movement. Stopping air movement is the function of an air barrier.
Kraft facing works fine as a vapor retarder; this is easily demonstrated in a laboratory.
Oh, your point is well taken.
It's just those memories of being in the "slither space" under many local houses, where FG batts had been tacked in, oh, maybe 15-18" O.C., with 1/4 & 1/2" "bellows" in the KP between staples rippling down the lines of the floor joists. And, that just doesn't quite "jibe" with being vapor retardant to me.
If we add in the local climate, where 5-60% humidity values are not uncommon; or diurnal temperatures that will pass through the dew point sometimes twice a day . . .
Well, then, that's about the worst case scenario for any "success" with FG.
Now, since OP posed the question that way, I'm being a bit pedantic about the use of faced FG batts in exposed floor structure, rather than in a vertical, enclosed-in-a-stud wall situation. Which can be an apples and asparagas sort of comparison, I'll admit. I'll also admit to having seen one too many times batts in ceilings retrofitted equally poorly--so, I have a very definite bias towards FG batts' usefullness.Occupational hazard of my occupation not being around (sorry Bubba)
I've installed faced FG and done a very nice job of it. It takes time and patience and some skill, and since it's a material that everyone hates, most people just slap it in. I have switched to having a sub do blown-in except on the smallest jobs.
I've installed faced FG and done a very nice job of it.
I've obviously never seen one of your jobs, then <G> . . . Occupational hazard of my occupation not being around (sorry Bubba)
Yeah, and I'm never doing it again so you're not gonna either!
Yeah, and I'm never doing it again so you're not gonna either!
Like I'm likely to ever be able anytime soon to be able to slither into 14-15" slither-spaces . . . <g>Occupational hazard of my occupation not being around (sorry Bubba)
We attach you to a come-along and haul you in, so you can put up your fair share of insulation.
so you can put up your fair share of insulation
Nope.
Not Happening.
Not No Way 'Tall.
Ripped out more'n my fair share already, me and the spodders, snakes, poss'ms, an' all the the ickier critters too . . .
Occupational hazard of my occupation not being around (sorry Bubba)
Edited 2/23/2007 4:51 pm by CapnMac
The windshield in my car is solid and lets absolutely no air in either. Why do I feel such a draft when I drive?
Oh the 4 windows open will do that! Kind of like the sides, top, and bottom of each bay with the kraft paper!!!Stu
Stu,
It sounds like you misunderstand me. I don't really understand your windshield analogy ("Why do I feel such a draft when I drive? Oh, the 4 windows open will do that!"). I never said that the kraft facing on a fiberglass batt can be depended on as an air barrier. I merely said that the kraft facing is an effective vapor retarder. It stops diffusion, not air movement.
I'm saying the air that carries the moisture moves right around the sides. Even if the paper were a sheet of glass the gap around the edges makes it next to useless over time.
The ability to control diffusion, though overrated, is not useless. Moisture moves by diffusion as well as convection. It seems you are very concerned about creating an air barrier. That's good. Just don't call it a "vapor barrier" or a "vapor retarder." Call it an air barrier.
my suggestion is that you don't even think about insulating until you solve the moisture problem.
how about telling us where you are located climate wise, and what your ground water conditions are. Any clues about why this space is damp.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
One source of moisture was the clothes dryer which vented into the crawl space for 15 years. That has been corrected. Another was a broken hot water pipe which recently sprayed water into the area for five days before it was discovered. Also the house is located near the ocean on the Outer Banks of N.C. where the humidity in the summer is stupefying. Thanks for your suggestion. Jack
There is a pink (I think) fg insul that is sold in a poly ethylene tube. It is sold as a non-irritating cleaner alternative. Although it is more $ I would gladly pay the diff when I am laying in the crawl. Barmo
How about getting better ventalation to the crawlspace, maybe a couple of foundation vents, drape the walls and cover the floor with 6 mil poly, and install unfaced f/g insulation?
Harry
In many parts of the country, SPECIALLY WHERE HE IS, vents will bring more moisture INTO the crawlspace..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I'd be guessing your slab in the crawl space has no poly under it, solve the moisture problem with previous suggestion...poly on floor, styro on walls and seal it up.
As to the FG , use unfaced and cover with Tyvek, 9' roll works well... has worked well for me in the North East, even with dirt crawl spaces....
Geoff