My house in Northern Virginia has a hip roof, two attic exhaust fans and about 3 inches of intermittently dispersed loose insulation from 1960. It’s getting hot and I’m thinking I need to add some more insulation.
The attic is all open, though there are some lamp cans that are not insulation contact approved that the contractor built some metal surrounds for, but are not covered. Since it is wide open (about 1500 sq ft), I’m considering buying some batt fiberglass insulation from home depot and laying it up there myself. Any thoughts about this or if I should get blown insulation? And what type?
Replies
Batt insulation is a great do-it-yourself project.. just rremember to not (repeat, NOT!) cover the vents.. both at the roof and in the soffits. provide an air path for cool air to flow thru the attic from the soffits to the peak..
while you don't need to keep warm air in as desperatly as we northerners do, you could keep some cool air in and the greater the R value the longer the cool air will stay around..
I'm not a fan of blown in insulation. sooner or later it settles and sort of compacts itself and you wind up with less than you think you have..
wear a dust mask so you don't get itchy lungs... In spite of the heat, cover yourself up well.. do it in the cool of the morning..
Thanks.
tm... if you're into wasting money.. go for it..
or rent a blower and blow in some cellulose... of course it settles... it's settled density is 2 lb/cf
figure it in to the equation.. we design our work for 24" of cellulose.... which settles to about 20 "... about R70.. our average attics are above R60..
in VA.. i'd be looking for an R30 minimum.. but i'd probably still go for a lot of insulation.. it cuts down on your cooling load alsoMike Smith Rhode Island : Design / Build / Repair / Restore
I'am happy to hear of someone else going for the "extra" insulation Mike. For around here most of the builders will go the minimum, ie R-30,in Lids. Usually, when I ask "why not more", they get this blank stare in their eyes. For me, in the few new homes that I do, the more insulation I get, the better I feel. I suppose some would/will say, it's a waste of money, or it's actualy a poor design decision to insulate so heavily, so be it. Oh how I enjoy this board. Jim J
Mike,
Thanks for your reply.
Am I to read that putting in batt insulation would be a waste of money? Or doing it myself?
Thanks also for your suggested r-values.
Ted Mundy
doing it yourself is usually good.... using fiberglass batts is usually bad.. slightly ahead of not doing anythingMike Smith Rhode Island : Design / Build / Repair / Restore
Mike, you and I will have to disagree on the value of batts over blown in.. Batts of spun fiber glass can get you up to R-30 for no more cost then the batts themselves. If that isn't high enough just add another layer..
Blown in on the other hand is prone to settle which loses insulation value..
In addition it requires the rental of a blower and the ability to operate it.. normal is one person operating the blower and feeding the insulation into it while another directs the hose to where it's needed..
The coordination required for the safe and efficent operation seldom comes from the first time you use one.. In addition lugging that hose around is serious work if you don't know the little techniques required.
On the other hand, you can lug batts of fiberglass up at whatever pace you feel up to and then spread them around..
Frenchy, cellulose is required to be labeled so that the R-value for a given thickness actually is the R-value for what that blown thickness settles to. The R-30 you blow in today will be R-30 twenty years from now.
Andy Engel, The Former Accidental Moderator
Nobody has mentioned vapor barriers. If you install insulation batts that have a vapor barrier attached (kraft paper or foil) on top of existing insulation you could trap moisture in the existing insulation. If your existing insulation has no vapor barrier attached, I recommend shoving the old insulation aside and installing batts with a vapor barrier against the ceiling. Then put the old, loose insulation on top of the batts. If your existing insulation has a vapor barrier, then I recommend installing unfaced batts or loose, blow-in insulation on top of the old insulation. You want a vapor barrier of some kind between the ceiling and the insulation.
The vapor barrier in a climate like virginia is problematic. It needs to be on the inside during the winter and on the outside during the summer, particularly if the house is air-conditioned.
So the best course of action for houses in mixed climates (where there is an extensive heating season as well as extensive cooling season) is often no vapor barrier.
What is critical is a good air barrier. To that end you need to fill up those stinkin' nooks and crannies and air seal around those cans...but that's another topic altogether.
I suggest Lstiburek's book "Builder's Guide for Mixed Climates" to get a grap of the issues involved.
Steve
Edited 7/6/2003 3:07:55 PM ET by STEVENZERBY
Thanks for your reply.
And now that you mention it, how does one seal cans?
My wife wanted a special type of can that is not IC rated and the installer built sort of a circular corral with no top on them. I'm guessing it is not okay to lay batts over top without putting some sort of lid on first. I have another reason to want to seal them, we had the cans installed last fall after the a/c days and now this year, we are getting a lot of smokey chimney flu smells that I didn't notice last year and I am wondering if it isn't due to the attic exhaust fans pulling air up through the cans, pulling the air down the chimney. Net net, another reason to seal them up. Any thoughts would be greatly appreciated
Ted Mundy
Ted,
There has been discussion here in the past about how best to seal non-IC cans, and the consensus seems to always roll around to it not being a real safe thing to do. If I were going to try it, I would build a rather large (16" square?) drywall box over them.
As to the attic fan, does the smell go away if you turn off the fan?
I'm with the cellulose school. Better radiant blocker than glass.
If you can deepen your rafters and/or skin them over on the bottom side with thermax, tape the joints, and blow the rafter cavities full of cellulose at 3 1/2 lbs/cubic foot, you'll get your air seal and you won't have to worry about the leaky cans because they will be inside the thermal envelope.
Steve
Check prices often insulation contractor can install blown attic insulation for close to the price you can buy the batts,blow also gets better coverage no gaps and less hollows. Many contractors are buying blown insulation in quantities that allow prices as much as 40-50 percent less per bag than you buying it and getting the free blower rental at depot. (when I was selling the products 6 years ago I had customers using 2-3 45' trailers a week about 2500 bags a week, their price was about 4.75 a bag compared to about 8 at depot. blown insulation should be blown to the the settled density, check the chart and be sure the number of bags are installed. Never rely on the inches, this was a great money maker for "creative insulator" fluff the blow get the inches and save as much as half the material. This is how blown got a bad name.
On my houses I like to use a mixed system, any areas that will be travel often for repairs (new wires, etc) I install fiberglass batts than have the bulk blown, normally down the center of the attic where you will walk or crawl. do the batts and attic prep your self then have insulation contractor blow. Contractor discount on batts is not good enough to off set labor cost.
"It's getting hot and I'm thinking I need to add some more insulation."
That right there is the key.
The sun is heating your shingles. Your shingles are conducting heat through to the uderside of your roof sheathing. The underside of your roof sheathing is acting like a massive radiant panel, heating the attic space annd the attic floor (the ceiling oof your living space). That in turn is adding unwanted heat loads to your house.
Adding FG btts will do little to nothing too solve youur problem. FG iis transparent to radiant heat.
Adding cellulose will prevent the heat load from being transimitted through to the living space in your house. Your attic will still be hot, but the heat will not be transimitted through to the living space beneath the attic.
Sure, blown-in insulation settles. That's why you blow in more than neccessary so it settles to the desired thickness.
You can do it yourself or hire it out.
"FG iis transparent to radiant heat."
Could you explain?
For the most part...
You've got to love a reply that begins with a disclaimer.<g>
For the most part, FG is transparent to radiant energy. Radiant passes through FG. It really doesn't hinder it, as it does with conductive or convective methods of heat transfer.
Cellulose will absorb radiant energy. As it absorbs the radiant energy, the upper exposed thickness of the cells will increase in temp, then the cells will hinder the heat transfer as it tries to pass through the cells via conduction. As long as you have an adequate thickness of cellulose on the attic floor, it'll do a much better job preventing attic heat from passing into the living space below.
Best solution? Stop the gain in the rafter bays. Keep the heat out of the attic in the first place.
An aside to the original poster...before pumping two feet of cells into your attic, pull back the insulatiion that you have and use canned foam to seal every stinking little nook, cranny, crack, crevice, and hole that is currently allowing air to pass from the living space below, through the attic floor, and into the attic. Consider replacing your existing can lights with IC-rated cans. The newer cans are inexpensive, IC-rated, and for the most part, air-tight. I'd still box the new lights in to hold the insulation off of them.
In the case of someone wanting to use fiberglass, what about also using the various radiant heat barrier reflective materials or paint?
A government report on radiant barriers:
http://www.ornl.gov/roofs+walls/radiant/rb_02.html
An industry report on radiant barriers:
http://homepage.steelbuilding.com/RIMA_Hndbook3.pdf
The June issue of JLC has an article on this. "Cool Roofs for Hot Climates". It is focused on different roofing materials reflectivity, but covers some other bases also.
It is written by the people from the Florida Solar Energy Center.
You can buy the article online for $5.00
Radiant film barriers are tough to detail in residential construction.
If they are placed on the attic floor, they'll quickly lose their effectiveness as dust settles on the film.
If they are stapled to the bottom face of the roof rafters, it's almost always done after the bays have been stuffed with FG batts. The batts shed, again, dirtying up the film's foil face. Even if the bays are vacant, I have read that dust carried up the soffit-to-ridge air channel will eventually dirty the film, again, reducing its effectiveness.
I'd never try to detail a radiant film tucked up into each individual rafter bay, held off the underside of the sheathing by a couple of inches. I'd rather rip sheets of polyiso and foam them up in each bay.
Fisiks aside, from the practical point of view from the field of imperfect residential construction, I think that the best radint barrier is not a stand-alone barrier...but an insulation that also happens to act as a radiant barrier.
Cellulose, foil-faced polyisocyanate, etc. You pay for the cells, you get a barrier thrown in for free. Same with the polyiso.
FG is traditional. It has momentum. The FG industry has a huge marketing machine behind it. FG is DIY friendly. It's easily understood.
Still, in a head-to-head comparison with FG, I'd rate cellulose (dense-packed where required) as being equivalent in R-vaue, better at preventing air infiltration, better at handling water vapor, better at reducing sound transmission, and better at handling difficult, cluttered bays...filling in around junction boxes, wiring, HVAC, blocking, etc, etc.
I know radiant paints are used in commercial...mostly roofs...but I have little knowledge on their applications in residential construction.
I'm in the northeast if that matters.
OK, I'm still not sure I get it. You say FG is transparent to radiant energy (for the most part ;) ). But why? I was unable to find numbers to compare emissivity and reflectivity of rockwool and fiberglass, mainly I think because nobody has really bothered to consider radiation up to this point. Of course, FG is glass, right? If that's the case, then I gather you're saying the arrangement of the material doesn't really matter, meaning whether the glass is a solid sheet or strands comprising batts makes little difference for radiation heat transfer. Or maybe I'm missing something.
But you could negate this difference by putting a radiant barrier in the rafter bays. Then, as long as you eliminate air infiltration paths (every stinking little nook, cranny,...), the difference becomes minimal.
I guess I'm still undecided as to whether the transparency part makes sense to me, so I'm curious about the rationale behind it.
This DOE website shows that batts ARE effective at helping you keep cool:
http://www.ornl.gov/roofs+walls/radiant/rb_02.html
Any jackass can kick down a barn, but it takes a carpenter to build one.
I took the info on the site as concuding that radiant barriers, not batts alone, may reduce heat loads.
Of course it depends on the climate and some other factors but, the way I took the info, both can help. Any jackass can kick down a barn, but it takes a carpenter to build one.
The real question is: Is good insulation batt for your lungs?
Mr T
Do not try this at home!
I am an Experienced Professional!