Furring out rafters

Kjl3694 · 06-29-2012, 08:56 PM

We are finishing our attic, making it a living space. The rafters are 2x4's, 24 on center. In order to get a high enough R value and have ventilation space behind the insulation we need to furr out the rafters. We are planning on using 2x4's to get to an R20. We were advised to attatch them with construction adhesive and screws. Can anyone point me to or give me a better description of exactly how to do this?

Bonzai · 06-29-2012, 09:15 PM

http://www.ehow.com/how_12193418_bui...nsulation.html

joecaption · 06-29-2012, 10:34 PM

I'm confused how would there be room for foam baffles for ventalation, (about 1-1/2") and R19 insulation which is about 6" thick fit in a 5" space?

Kjl3694 · 06-30-2012, 07:46 AM

Quote:

Originally Posted by joecaption

I'm confused how would there be room for foam baffles for ventalation, (about 1-1/2") and R19 insulation which is about 6" thick fit in a 5" space?

The house is over 100 years old, the rafters are true 2x4's. Adding 31/2" to the existing 4" rafter will give me enough room for 51/2" high density roll R20 and give me 2" for ventilation.

The linked article talked about using furring strips. I'm looking to use 2x4's i'm having a hard time imagining I'm supposed to drive a nail through that and into the rafter? We may also go to 2x6's so that we can get to R30. How much differance would we notice by upping to that R value?

hand drive · 07-01-2012, 10:57 AM

a 2x6 would be better regarding insulation value for sure. You will have fire block issues at the bottom of the fur strip because it will extend/plane the ceiling level down into the open wall cavity area. The regular wall top plate design in a wall system is what I'm referring to. You will need to add the correct wall blocking in the wall at the new ceiling height, just emulate the top plate design. I would add/nail 9" 2x4 blocks onto the side of existing rafters and then use the 2x4 blocks to nail the fur strips to along with a good nail connection up at the roof ridge and down at the wall. consider adding a flat section at the top of the ceiling to serve as collar ties to help hold everything together as well.