Opinions on insulating a finished attic in Ohio

[tk421]

hey guys, friend of mine is starting a project pretty soon and asked me to give him a hand. They have a Cape cod style house with the typical finished attic space (knee walls, sloped ceiling, flat ceiling on top). It had previously been "finished" and the walls and ceiling are a cardboard-type tile, which has been torn down. There was no insulation on the knee walls or either parts of the ceiling.

Looks a lot like this:

http://dspinspections.com/images/AtticVenting3.gif

Heres the catch though: There are no soffit vents. The attic is sealed with the exception of gable vents one each end, just like in the picture. The roof is new (but no ridge vent) so adding overhangs with soffit vents is not an option.

He would like to insulate and drywall both rooms so they can be used as bedrooms and i want to make sure we get this as right as possible.

His knee walls are 2x4, but his roof rafters are 2x6. Are we able to do 3.5" Deep insulation on the knee walls and on the ceiling parts without a problem? i know it wont be vented, but the insulation will be 2 inches from the underside of the roof deck.

Thoughts/opinions? Thanks!

 

[srmofo]

You HAVE to have ventilation. There is no way around it. He will have countless problems if he doesnt take the steps to ventilate it now. Ice dams, condensation problems which can lead to mold problems, and the rooms will be hard to control the climate in

 

[tjpavlov]

Srmofo is right unless you sprayfoam it. That route would be expensive but may be your best bet. Check out finehomebuilding.com to learn about non vented attics.

 

[tk421]

I understand what youre saying, but the house is 60 years old and has never had any ventilation. Theyve been there about 6 years and have not had any of those problems (its gutted right now, no evidence or condensation or mold in the roof) and have never had an ice dam issue.

Would they be better off not insulating it at all and just drywalling it? Sprayfoam is not an option, theyll never spring for it, because they will be putting the house up for sale after the bedrooms are done.

 

[Architorture]

i would recommend insulating in a similar fashion as the left side of the image you posted. have the insulation follow the finished living space leaving a small uninsulated attic space where the roof and floor/ceiling construction meet.

even though you have 2x4 knee walls, you can still use 6" batts with the face paper stapled to the 2x4.

in the sloped portions first install foam insulation baffles to the underside of the roof decking to create an air space, then install the batt insulation attached to the sloped roof structure. only run the baffles high enough so they will exit above the small horizontal portion of insulation that will be above the flat portion of the ceiling.

do this will allow for air to circulate around the uninsulated space and exit through the existing gable vents.

the setup can be greatly improved by installing a few vents in the soffit. what is the soffit currently made of? since we have left the small triangle of uninsulated space at the base of the roof all around you can add venting at a few points instead of needing to have venting available for each 16" or 24" roof structure cavity

 

[tk421]

arch, there is no soffit or soffit vents. the end of the rafters sits directly on the top of the exterior wall and its closed off with no overhang. That "fascia" for lack of a better word is where the gutters are attached.

 

[Architorture]

no overhang...that is a pickle.

is there a portion of fascia available on the gable end? essentially creating a soffit vent on the "side" of the soffit? so when looking at the triangle that creates the gable you would have a vent point at each point in the triangle (soffit, gable, soffit)...just a thought.

 

[tk421]

Id have to double check but I do NOT believe there is. I know, its a helluva thing.

There are two rooms upstairs and it turns out one was insulated and the other was not. Very strange!

 

[Architorture]

even without the soffit venting i wouldn't be too concerned about condensation as long as the interior space is sealed up well as that is your most likely source of vapor during the winter...in the summer the uninsulated space will be hot and dry....and in both cases the gable venting will allow for the movement of air.

chances are in an older home there are already some points where air is circulated between the roof and wall construction...