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Attic insulation


Ellis5201's Avatar
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12-13-02, 01:34 PM   #1  
Ellis5201
Attic insulation

All,

I will begin my newest project of putting new insullation in my attic. I am interested in flooring a large portion of it when I am done. Is it bad to compress the insulation between the plywood and the ceiling at all? If it is what would you suggest doing. I can always install loose fill where the floor is going to be and rolled everywhere else.

Thanks,

Jason Ellis


Last edited by twelvepole; 12-14-02 at 01:39 PM.
 
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12-13-02, 04:24 PM   #2  
Attic insulation

If this is an unfinished, unheated attic, it is not recommended that you insulate the under side of the roof. Insulation goes between heated and unheated spaces to keep heat in the areas where you need it.

Check with your local building inspector before you begin your project. Depending upon truss system and local codes, your project may or may not be viable because trusses will not be able to support a load.

Go to www.doityourself.com/insulate on this website to learn more about insulation, its installation, and to calculate the amount of insulation you need for your ZIP.

You can also do a search on this forum by clicking the blue search button in the top right corner of the screen. Type in the keyword box to learn more about attic conversion, a frequent topic on this forum.

 
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12-14-02, 09:17 AM   #3  
Norm Abram
Ellis,

compressing insulation does reduce its R value, but as long as you get the appropriate size to fit your joists, you won't really be compressing it.
R-19 will fit 2x6 joists with minimal compression.
Now R-19 isn't very good, but its probably the highest R you'll achieve without using rigid foam.

good luck...

 
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12-19-02, 06:58 PM   #4  
rbisys
Greetings,

You must leave an airspace between the insulation and sheathing, 2". It is a very good idea to install a ridge and soffitt vent system too. cor-a-vent.com

I'm guessing that you have a 1 1/2 story. If so, then a big problem is the excessive heat transfer thru the rafters directly to the drywall. If you use FG then you are using a product that is only about 10% efficient. This means it will be hot-hot-hot in the summer and hard to heat during the winter.

I have developed a very efficient system using two layers of 4 mil radiant barrier (RB) insulation. It is about 95% efficient and will will not condensate moisture or grow mold.

It is easy to install. If you want more info, let me know.

Thank you for considering my opinion.

 
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02-20-04, 07:35 AM   #5  
usb2004
I have a question on installing radiant barrier insulation. I'm currently using astro foil in my attic, but have a few questions:

Is it ok to lay the rb down on the ceiling floor between the joists?
The problem here is I have a vaulted ceiling in my living room with a narrow area above it. I can't reach down to tack it up on the rafters near the roofline, so I figure the next best thing is to cut it to width and shove it down between the joists. I plan to also seal this area off with more rb so the ambient heat won't leak into the rest of the attic. I'll then place more rb to the underside of roof,tacking it to each eave. What do you think of my ideas?

thanks
usb 2004

 
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02-20-04, 06:28 PM   #6  
wildfire6460
I always suggest raising the floored area up with 2x4's so that the insulation doesn't get compressed.

 
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02-21-04, 10:59 AM   #7  
First usb2004 if you look at Rbisys name he is banned from here . He is trying to sell you on his R/B . If you go to any of the Gov www you will find that they say after 1 year it goes down at just 5 years R/B dont work . There is a ply board with it on the underside for the roof sheeting out now. BUT they dont know what it will do to the shingles yet. A power vent fan in the attic pays back the best ED

 
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02-22-04, 09:45 AM   #8  
conexos
Attic Insulation

I have purchased R-30 fiberglass insulation, and planned to replace the old insulation in our 1937 house here in north Florida (Gainesville). Should I remove the paper vapor barrier (which seems to be recommended for Florida)? Would there be any harm in this climate to facing it down over existing insulation? How about facing it up?

 
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02-22-04, 10:50 AM   #9  
Conexos You dont say just what you have there for insulation now . If you have some why take it out???? Now if what you have has a paper down to the room ceiling or not . You do not want any more insulation to go on top of it that has any paper on it at all top or bottom. There is a roll for the attic with no paper on it use this. Put the rolls across the ceiling joist the other way than what is up there now ED

 
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02-22-04, 12:32 PM   #10  
conexos
Thanks for the reply.

What I have now is a mixed bag. I don't know how old it is, but it appears to be old fiberglass with a black paper (kind of like roof sheeting?) backing. However, the backing is on top, not underneath--which appears to reflect the practice of not putting a vapor barrier toward the heated/cooled space in Florida (?).

We just bought in August, and we can see that there has been rodent droppings over the years (no current infestation), and in part I thought removing the existing stuff would rid us of the dust and crud.

Also, there are places where the old insulation is very raggedy--the rafters are only 5 1/2 inches, and the old insulation at best is only about 1/2 to 3/4 of that thickness.

How much concern should I have with vapor barrier in this situation? What should I do with the paper that is on my new insulation, if I layer it over the old insulation as you suggest?

And what should I do to identify air intrusions before laying out the insulation?

Thanks!

 
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02-22-04, 12:45 PM   #11  
Its what you want to do and how. So paper on top this has to be turned over paper down to the room side or the celing for sure. So take it out or turn it over. New insulation you say has paper on it. So take old out all of it. Put new in paper side down for sure. This way you can come back later and blow insulation over it. Now you need to check the vents in the attic for sure need them in the over hang and at the ridge of the roof there is a foam rafter box like home depot and lowes have them go in the rafters at the edge of the roof so tha air from the vents gets in over the insulation. Put them in first then the new insulation. been down here 19 years now and you put the paper side down here and way up north ED

 
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02-23-04, 12:31 PM   #12  
conexos
Okay, now I have removed a section of the old insulation. I note that there is no apparent ventilation under the eves at the edge of the roof. The rafters are seated right atop the block walls. From the outside, there are no soffit vents under the eves.

In placing the new insulation, should I go right to the edge of the roof? I don't see any reason to use the foam block vent covers since there are no soffit vents. Should I caulk anywhere I see any possible air intrusions prior to placing the new insulation down? (Of course, paper down as you suggested..)

 
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02-23-04, 01:06 PM   #13  
If you can see out into the overhang you should put vent in it. So air can come in from them and go up and out the top one . Do you mean that there is no over hang on the home????? ED

 
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02-23-04, 02:15 PM   #14  
conexos
There is overhang, but it is not enclosed. Below I have tried to represent it graphically. There is the tiniest amount of light visible in some places along where the "<" appears. Should I be caulking these places to block the opening? Or should I rather be using the blocks you recommend to ensure that these tiny points of venilation (no matter how small) not be blocked by insulation?



above -
roof -
-
- Inside attic
- <-------------------------
- -
- -
- - Inside house
-

 
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02-23-04, 04:33 PM   #15  
I would not seal them. In fact there are small what is called button vents that you can drill a hole and put them in this block and put the rafter foam in so the air can get from them up into the attic and out. think of the attic as a big flue. Or just a tent to keep the rain and" snow"???? off the insulation in the home. The cooler there the less AC it takes ED

 
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02-25-04, 07:43 AM   #16  
usb2004
Hi Ed

Another question on the rb. Did you say that the rb is not effective as a shield to heat? I live in Hawaii where temps are in the 80s - 100s year round. I also live in a townehouse where you can't alter anything on the exterior of the building. this includes exhast holes for an attic vent. I do have 2" soffit holes
around 3 sides of my unit (one level end unit).
So I don't have too many alternatives.

The salesperson said that the astro foil reflects 97% of the radiant heat back towards the roof and composite shingles. She said venting is not necessary. Just seal off everything and the heat readiates back out.

I've sealed off about half of the attic. Ventilation would be nice, but I have only the soffit holes--240cfm of ventilation.

I've thought about a whole house fan, but again not enough air flow exhast out to make it feasable.

Any suggestions?

thanks,
usb2004

 
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02-25-04, 10:59 AM   #17  
usb2004

Have not seen anything on the R/B glued to the roof sheeting as yet. They dont know what it will do to the shingles on top of it. The .gov www say that R/B goes down hill and dont pay .Even with R/B up there I have seen 160o in the attic. So it all comes back to VENTS for the attic. Power vent fans on the roof . almost like a 1/2 ton of ac almost free.

Sq ft of attic X 0.7 = Cfm of fan

old way was 1 sq ft vent for every 150 sq ft of attic
also like 1sq " per 1 sq ft of attic almost the same

1/2 in and a 1/2 out

New way 1 sq ft vent for 300sq ft of attic . Thats like if you have a R30 or 40 up there. You could go down and find out what code calls for on vents there.

Lived down in the caribbean for 6 years. Didnt have AC down there. Didnt insulate but the whole attic was open just like a big tent over the home Used fans some . Where are the sea breeze when you need them.How about one big fan blowing out in one window and let the air in where you want to.

ED

 
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02-26-04, 08:22 AM   #18  
usb2004
window fans

Hi Ed,

thanks for the reply to my posts.

Could you use a whole house fan in place of a window fan to suck in the cooler outside air for the entire house? Seems to me window fans have much lower suction or blowing power, so you'd need a higher velocity fan for cooling the entire house.

awaiting your reply,
usb 2004

 
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02-26-04, 09:40 AM   #19  
conexos
Regarding the use of radiant heat shielding, I note that the gov. info site (probably the same one referenced above) also discusses two other ways to retrofit in the attic:

1) Placement on the attic floor, above the insulation

2) Placement on the attic ceiling gables

In either case, the radiat barriet should face toward the roof. I am considering doing the latter after I upgrade attic insulation.

Do I understand there is a degradation of the effectiveness on the r/b overtime? I was thinkin of using the light insulation sheets with radiant barrier on them, and see if I can assess the change in temp in my attic.

 
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02-26-04, 10:00 AM   #20  
usb2004
ventilation in the attic

I only have 2" soffit holes in between each eave...I don't think it's enough to vent out the attic with a whole house fan. I can't cut any holes in my townhouse (ass. rules).

A suggestion: I have an inside bath that has no windows, only a bath exhast fan that shoots out air through a 13" (circumfrence)
aluminum tube through the attic up through the roof. My idea is to cut the tube and install a pvc pipe with a "Y" joint, then connect a duct flex hose to the outlet and into a box where a exhast fan would blow heated attic air out the roof. The air would be going in an upward direction, so would not contra flow back into the bath. Also, the exhast fan would be thermomatically controlled.

Any inputs on my idea?

usb 2004

 
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02-26-04, 10:43 AM   #21  
Usb give it a try why not -------------thats why I dont like Condos

Conexos--- See you say florida. I like to look at all new homes here and see if anything new is going on . To stay up to date in building. Still mess with homes up north. Now no one here is useing that R/B at all . I dont have that gov www. at hand .But if you went down into it .It said that it dont do what it should from the first year and at 5 years it was done for .The main thing that kills R/B up there is that it gets a light dust on it. It also said that more insulation paid off. I know for sure a roof vent fan pays and a tile roof dont help at all down here ED

 
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