# Insulating an attic



## Runners (Nov 6, 2003)

I like vapor barriers on the inside of the house - up north, it was pretty much standard in construction. The insulation stayed dryer they said.

How it is down south, I don't know - but, I got a house with no visible vapor barrier in the attic... and boy, does that dark roof make it HOT when the sun is out!

I want to super insulate, starting with the attic (maybe a couple of solar fans too). We have fiberglass batts, about 6-8" thick, just laying in there. The ceiling is drywall, glued and screwed in place, so removal to install a barrier is out. I've even considered strips of reflective mylar between the trusses, but that might focus the humidity into the trusses...?

Any suggestions short of selling the house? I'll take up the batts if necessary to put down something additional.... *I'd like to stop the solar gain in the summer months (global warming, heh..), and keep the heat & humidity in during the winter.*


----------



## littlebitfarm (Mar 21, 2005)

Could you paint the ceiling inside with a vapor barrier paint?

Kathie


----------



## ericjeeper (Feb 25, 2006)

just on the walls. I have between 15-18 inches of cellulose in my attic.


----------



## crafty2002 (Aug 23, 2006)

6 " is R-30. If you have that in the entire ceiling area, you don't need to worry about the insulation.
The idea of installing solar fans is a good idea. Once installed you have no energy cost and they will drop the temp. in the attic which not only saves on AC bills, but also lets your roofing material last a lot longer. 
If I did any thing, I would install more of the fans and make sure you have a free flow of air into the attic for the fans to get the hot air out.


----------



## SolarGary (Sep 8, 2005)

Hi,

I think that 6 inches of fiberglass is more like R 20, which (to me) is not enough -- especially because its fiberglass. 

Fiberglass allows small air currents to form within the bats that can reduce the effective R value under cold conditions to half of the nominal R value.
This is the Oak Ridge National Labs test that shows this:
http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/92/920510.html

I think if it was my house I would just blow in more cellulose over the existing FG bats. The cellulose does not have the air currents problem -- it will add R value and make the FG more effective as well. Most of the home centers will loan you a blower if you buy a few bags of cellulose from them.

The Building Sciences web site has a lot of information on whats required in the way of a vapor barrier in various climates and constructions. I'd take a look there and see if you really need anymore vapor barrier than you have.

Think about sealing up all the electrical and plumbing penetrations and light fixtures with the foam in can stuff before you add any insulation.
And, apply duct mastic and then insulation to any heating ducts that go through the attic. Much easier to do this before you blow in new loose fill insulation. 

I've noticed that some of the good places (like southface.org) are recommending against forced ventilation in attics. The objection is that 1) it does not do a lot, and 2) that it can slightly lower the pressure in the attic which tends to draw air from the living space into the attic, which is an energy loss. There position is that if you have good passive attic ventilation you should not need the forced ventilation.

Gary


----------



## wy_white_wolf (Oct 14, 2004)

For the vapor barrier how about adding it to the inside of the drywalled ceiling and installing another layer of drywall below it?


----------



## suburbanite (Jul 27, 2006)

I have nothing of value to contribute except that I first read the title as 'insulting an attic'.

:doh:


----------



## Ross (May 9, 2002)

I'd remove the batts this summer and install the plastic vapour barrier over top of the joists and then reinstall the batts. Then add another R20 on top of that. Don't forget your attic needs good ventilation.


----------



## MeanDean (Apr 16, 2002)

I've got insulation between the 2nd floor and the attic BUT I also have a Radiant Barrier installed as well - which keeps quite a bit of heat from the roof and roof tiles out of the attic.

For us, we found the the tempurature in the attic leveled out rather nicely, though your mileage may vary.


----------



## arbutus (Jun 8, 2006)

Anyone have any experience with polyurethane foam applied directly to the underside of the roof decking?


----------



## SolarGary (Sep 8, 2005)

Hi,

"Anyone have any experience with polyurethane foam applied directly to the underside of the roof decking?"

Part of my house was done this way.

I was not there when the insulation was put in (during construction), so I can't speak to how the installation went.

This area is a cathedral ceiling, and the foam fills the full depth of the ceiling rafters. With bat type insulation, you would probably have to leave a ventilation space between the roof deck and top of the bats, but the PU foam apparently does not allow water vapor to pass through it and is OK without the ventilation space. The roof rafters in this area are only 2X6's, so the PU foam at R6 or 7 per inch was the only way to get a high R value without going to deeper rafters -- the 5.5 inch deep rafters give about R36 with the foam.

We have had no problems with it, and I'm inclined to think its a good way to go. It should be great for infiltration. 
I understand that its no cheap. 

Gary


----------



## Explorer (Dec 2, 2003)

Wind, breeze, driven roof mounted turbine fans are popular here in the southwest for peaked roofs.


----------

