I have a few questions I was thinking of this morning and was hoping for some input. I wanted to add some insulation to my roof. I now have whatever they blew in, a white fiberglass mat. I wanted to blow some more in, seal as many leaks ect… can i take some 1/2 inch poly board and lay down on top of the insul??? the kind with the relective foil , I also have some pitches from other rooms and they just have the pink stuff on there since you cant really blow anything on top of that cause of the angle, can i put the board there and seal the gaps?? would that be effective?? was thinking it would help seal out some of the heat in the summer… any info would be more then welcome. Thanks
Frank
I only use my gun whenever kindness fails…
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The rigid insulation boards would have more effect in the summer because cold air will stagnant low. In the winter the warm air from the top side of the ceiling is trying to find a way to convect up and be replaced with cold air from the attic/roof. The shiny side would help a bit in summer. At least until it gets dusty and then it is just like any other surface.
Blowing in more insulation will help summer and winter. Thermal imaging of the top of the insulation (looking for hot spots in winter) or of the ceiling (looking for cold spots in winter, hot in summer) might help you indentify which areas would benefit the most. Sears has them starting at US$59. More accurate ones run about $110 from industrial instruments supplies.
Your utility company might do a lot of this inspection, assessment and make recommendations for free.
Thanks Dave,
I would do the blown in, but I have two rooms that stick up at 45 degree angles and it would be hard to get the insulation to sit on that. I was just wondering if i could put some foam board on that part leaving the batts in place, it would seem to help tighten up the roof a little and maybe keep some of heat out as well, In Ga mostly we have to worry about summer, but it does get in the 10-20 degree range Nov-Feb, and for a new house its pretty darn cold :( I could then blow the rest of the attic, I was mostly wondering how that would do. I went around and sealed as many holes down below as I could find, took me 2 weekends and there are still more. the windows are the worst, they leak inside the rails that slide up and down. I read some other posts and one in particular by Mongo was saying kinda the same thing about the foam board and it seems like a neat idea. My utility here dosent do the thermal thing, wish they did would love to see where all the holes are. I appreciate all your help, thanks Frank
I only use my gun whenever kindness fails...
Frank,
There's either a mis-interpretation of my previous post, or I just wrote it poorly.
I'd never recommend putting rigid foam board insulation over loose insulation that's on an attic floor. That puts a VB on the wrong side (the cold side) of the envelope.
I do advocate putting RFBI on the rafter faces, to either cover batts in the rafter bays, or to cap the bay so cells can be blown in behind the RFBI, filling the bay. This brings the attic space into the building's envelope, which results in the RFBI, acting as a vb, being on the correct (interior/warm/living space) side of the wall.
Good info from some of the others here.
I'll be down your neck (ATL) of the woods the latter part of March.
yes I see what your saying now, went back and reread it... sorry... the slower ones have to read it a couple times... :)
hope you have a good time here, i will be about 8295 miles away... picking up wife and son :) yeah !!!!!!!
FrankTime to get a gun, thats what I've been thinkin, I could afford one, if I did a little less drinkin...
I am not sure I follow where you want to put the foil backed foam board. It would not be good to place it on top of the attic floor insulation, as that could cause vapor to condense on the bottom side, and drip into the loose fill below it.
If you put a radiant barrier (staple) on the rafters, aluminum side toward the attic, not toward the roof, you can stop a tremendous amount of heat in the attic. It has to be vented correctly.
As for keeping in winter heat, sealing all air leaks,around pipes, wires, light cans, pull down steps, etc. is the first step. Then I would add blown in cellulose. Be careful around the light cans. Only those rated IC can have insulation contact. Paul
Placing poly on top of the blown insulation would probably not be a good idea, from two standpoints. First, it would compress the blown insulation, reducing its R value. Second, the poly would act as a vapor barrier, trapping moisture below vs allowing it to escape.
However, if what you have is loose fiberglass (vs cellulose) then putting a layer of Tyvek on top of it will significantly increase its insulating value (especially in winter) without causing a moisture problem.
the moisture prob was what was concerning me, thanks, what about that thin radiant material, its rolled like a car window shade, it says it has a real high R Value but its only like 1/4 inch thick? I could put that on the side where the sun hits the most, the roof is a few feet, above the attic floor. I put in a powered roof vent last summer and it seems to help somewhat, though its hard to really tell. the point sits at least 10 feet or so from where you stan when you climb up. I am going to go back when it warms up a little and put some soffet rafter things in to keep the insulation away and blow some cellulose in. is there any harm in mixing the cellulose and fiberglass? some is blown, but the rooms that stick up have batts at about 45 degrees extending some 5 feet or so into the attic. Our bedroom has a trey ceiling about 3 feet into the attic and also one more bedroom trey. on top of the treys its not all that thick, maybe 6 or 8 inches or so, on the floor its 13 or 14 i would guess but its all just loose blown fiberglass, except the batts on the one room roof. Can i put some more batts there and run them at 90 degree angles or does it matter? sorry for asking so many questions, i can see you have all answered similar questions but i think my case is slightly diff. thanks Frank
I only use my gun whenever kindness fails...
we're getting ready to overlay the main attic in this project... it's got some rooms as you seem to be describing...
mainly R30 batts with lots of gaps.. lot's of non-IC can penetrations... all -in-all... a giant seive..
we'll blow a 6" cellulose cap on the whole thing
View ImageMike Smith Rhode Island : Design / Build / Repair / Restore
so the cellulose will seal the leaks?? cause the fiberglass dosent seem like it could stop much of anything... its just like cotton candy. Thanks for the pic... that does help alot...
Frank
I only use my gun whenever kindness fails...
Yep, cellulose is much better than fiberglass since it tends to seal leaks (though not as good as using a real sealant). Also, cellulose doesn't need to be covered to achieve full R value like fiberglass does.
Of course, non-IC cans should not touch either fiberglass or cellulose. I think one approach for them is to build a drywall box around them, sealing it to the ceiling. The box can be put together with tape -- no framing required.
should i get rid of the fiberglass or just put it over top of it?? thanks for the info, dont have any cans to worry about...
Frank
I only use my gun whenever kindness fails...
There's no harm in putting cellulose over fiberglass. The fiberglass will compress, of course, but will still provide some insulating value.
My 2 cents on covering the FG with cels: It will help a lot, as the cels helps to block airflow, unlike the FG. Another big advantage of cels is that it is not transparent to infrared radiation like FG is, so it will provide a radiant barrier that will help you in the warm weather. If you can afford it, and are dealing with level attic surfaces, I recommend removing all the FG and doing 100% cellulose.
Here are my reasons:
1) The cels will block convection a lot better if it hugs the ceiling directly. A FG layer touching the ceiling acts as a plenum to distribute leaks.
2) Removing the FG will allow you access to seal any macro air leaks with foam in a can, or the equivalent method of your choosing. Also a good time to check for funky wiring, non-IC cans, etc.
3) Rodents love nesting in FG, but the borates in cellulose insulation turn them away. Eliminate their home, and they will stay away. Same for insects. Capping the FG with cels will not deter them if they find a way in without having to tunnel thru the cels. Think about it... the warmest part of the attic is in the FG just above the ceiling, away from the cels overcap.
4) Finally, a full cels job will also be quieter, and help protect your life in a house fire by slowing its spread, allowing more time to escape.
I don't sell or install the stuff, but I appreciate what it does. Hope this helps.
Bugle
I did this in my attic before blowing the attic with cells. Took some scrap drywall and made some square pieces to make a box around IC light can. Cut some scrap 2-by lumber at 45* angles and screwed the drywall to the 45* pieces in the corners. Spray foam insulation at the joints and around the bottom of the can base on attic side of drywall ceiling. Foam-seal any gaps on the can itself (turn off your attic light -any light you see thru/around the can is an air leak). Make a lid either from more drywall or any rigid foamboard (or both). This seals up the box. Pile up the insulation around the box and over the top (or make an insulated lid).
Even if light cans are rated IC (insulation contact) building an airtight box around them serves some useful purposes.
One, the light cans do leak air - heated air from your rooms will go right up. What goes up must have some make-up air being drawn from somewhere, contributing to: Drafts and heating money lost; Moist air will frost on underside of roof in winter; heated air drafting to attic can cause ice daming in winter; etc etc.
Two, if you ever need to change out the can itself or it's thermal control, finding that box in the attic is easier than digging around. Plus the box keeps the loose cells from falling out the ceiling if you remove the can.
I have been told that even some IC cans will "trip" on and off when buried in cellulose with no airflow around them. The box gives them some air around them, and you can loosen the lid a little to let out that excess heat buildup. If you have airsealed the can-to-ceiling contact and the little holes of the can itself you shouldn't have much if any heatloss from room below.
Your mileage may vary.
Phil