Insulation ? - Contractor Talk - Professional Construction and Remodeling Forum

sponge racing · 08-31-2009, 04:00 PM

Hey guys maybe someone can help, im insulating the upstairs of my new house. The ceilings are 8 feet on the left and right side, then slopes up to 10 feet for a 10 foot height going across the rooms. Ive installed baffels to the roof plywood goin from the soffit up to the ridge vent. Now goin to insulate the roof rafters. My ? is would it be ok to also insulate the attic floor. The attic height is only about 22in at the peak, very small attic.. Attic is probably for storage only.. Using fiberglass batt inuslation for all. Thanks guys..

mics_54 · 08-31-2009, 04:50 PM

Sounds like a cluster. You basically have a hot roof and want to add insulation at the ceiling but the baffels only vent between the rafters all the way to the ridge. This makes the small attic space above the ceiling unvented and not warm but not cold and no vent ....in New York...in the winter...dew point...moisture...mold. Wheres your VB? And to make it worse you'll install an attic access hole in the useless 22" tall attic space for storage?

sponge racing · 08-31-2009, 05:54 PM

Definetly a cluster. Since the ceilings at the sides of the house are sloped and should be insulated id figure might as well go all the way up to the peak with the insulation. Then maybe insulated the attic floor also? The only vapor barrier installed is the paper on the insulation and guess thats useless do to no sheetrock goin up against the rafters to help seal it.

mics_54 · 08-31-2009, 06:10 PM

I'll draw you a picture. be right back

mics_54 · 08-31-2009, 06:36 PM

Use batts at the green areas, rigid foal sheet between the rafters at the red areas (2"-4" depending on rafter size) leaving space above for airflow. The foam sheet forms the baffles. Install a 6 mil poly VP at the walls and ceilings. Forget about attic storage. continuous vents at eaves and ridge or gable vents of the appropriate size. R21 in the walls...R38 in the ceiling.

sponge racing · 08-31-2009, 07:22 PM

Thanks for the info. My walls are already insulated with r-19 and they are 2x6 walls. Now my rafters are 2x8 and collar ties are 2x6 every 16 in. The baffles I had already stapled up to the plywood in every bay on the roof. Thanks for the picture. You dont suggest insulating all the roof and all the attic floor? Rigid foal sheet is that just styrofoam with the foil face on 1 side? Also definetly need the attic storage plywood is already down up there?

mics_54 · 08-31-2009, 08:38 PM

2x8 rafter with baffles and glass will be r19 max.

baffles all the way to the ridge will not vent the attic.

insulation on the ceiling will keep the attic space closer to the dew point.

an attic crawl hole will let warmer moist air into the attic.

insulfoam like Rtech 2" foam has more r value per inch than glass.

I predict ice dams in the winter.

I predict mildew at the ceiling perimeter.

I predict mildew in the attic space.

But the icicles will be pretty...send pictures!

sponge racing · 08-31-2009, 09:13 PM

Aight the icicles probably would look pretty during the holidays.lol Since the plywood is already up in the attic any right way to insulate it? Do you mean take the baffles down in the attic space and only leave them at the slopes sides, then use 4 in foam on top of the baffles on the slopes then batts in the ceiling only? Thanks for your help

mics_54 · 08-31-2009, 09:38 PM

Or...you can leave the baffles all the way to the ridge and get as much insulfoam inbetween the rafters and sealed at the joints with tape
If you get four full inches of foam in there you'll have about an R28 on the roof. 6 inches would be an R38-40. Foam is expensive so see what you can buy it for. I usually rip the foam (carefully) of a table saw to get a nice tight fit between the rafters.

Then you can use your attic storage... only vapor barrier the walls and not worry about ice dams and icicles falling on your head.

All you need is an inch or so above the insulation to allow air to flow and keep it from condensating.

sponge racing · 08-31-2009, 10:05 PM

Really appreiate your help here. Doin it that way would be a fortune and alotta work. Thinking I might go with your first suggestion and just take the attic plywood up. ? on the baffles do I keep them to the top of the ridge or just use them on the sloped sides? Keeping them on the sloped sides then putting the 6 inches of foam on top of them and tapeing the seams??. Then a 6 mill plastic all over everything I insulated stapleing it up? No need for the plastic to go to the ridge right? Thank you again

mics_54 · 08-31-2009, 10:11 PM

You got it! you dont need the baffles but at least remove them down to where the rafters are near the ceiling...leave them about 16 inches into the attic space so they keep the batts from blocking airflow

sponge racing · 08-31-2009, 10:18 PM

Thanks again.. There is a ridge vent installed already at the peak dont think I mentioned that. Last question installing the 6 mill vapor barrier on top of the batts through out the whole house would be ok.? first floor walls and basement also? Guessing that would help heating and cooling costs in a huge way?? by sealing it up..

mics_54 · 09-01-2009, 12:47 PM

The VB goes on the inside surface of the walls and ceilings separating the warm side from the cold side on exterior wall/ceilings.
Dude..I'm beginning to wonder about you.

sponge racing · 09-01-2009, 04:16 PM

Thanks yes the barrier goes there guess I just worded it wrong. Thanks