[brad37]

Hi all,
My wife and I are remodeling the 2nd floor of our home and I'm looking for some advice as far as insulating the space. The house itself is in NJ and was built in the early 60's I think. Its a Cape Cod with Cinder Block walls. The house is 29x22 with no soffits and 2 small gable vents. We are having a roofer put in a ridge and edge vents to promote air flow, and I will be installing rafter baffles. The rafters are 2x8 24 inches apart. The space has been gutted down to the studs so access is not an issue. We are going to box the room in with knee walls and a flat ceiling leaving a small air space above the ceiling about 20 inches or so. We would like to the storage spaces behind the knee walls to be in the insulated space, which from my reading means I should just insulate all the way down the roof. SO... what I'm trying to figure out is what insulation materials should I use , I see many people using a combination of materials. The depth of the rafter is 7 inches , so after leaving a 1 inch air gap across the 24 inch span I have 6 inches of space to pack insulation. I see alot of people using the rigid boards and gluing them together, or using the with batt insulation. And others adding a radiant barrier. I'm lost as far as how to proceed , any help would be greatly appreciated .
Thank you

 

[TheCamper]

The traditional method of insulating is to place a R-19 fiberglass insualtion between the 2 X 8 rafters ensuring an air space between the insulation and the sheathing is kept (the baffles you referred to). I suggest a vapor barrier be installed. If you can spare a few inches off the interior space you could pack down the rafters and install an R-30, that would increase your energy efficiency. You might also want to speak with an insualtion contractor and see about other methods of insulation that they could do, e.g. Icynene.

 

[joecaption]

Make sure to go back and add your location to you profile not just mention it in your post.
You not going to have enough room for the amount of insulation needed in your area with just 2 X 8 rafters and baffles.
http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table

 

[windowguy]

this is easy. if you dig around for other threads you will see a diagram of how to insulate a cape cod..

you DO NOT insulate the roof rafters.. you insulate the walls and ceiling of the living space only. its overkill to insulate the entire ceiling cavity. leave the storage area unconditioned space.

so you would just use batts on the floor (to insulate the 1st floor ceiling) then batts on the knee wall, then batts up to the small roof space (allowing for the air gap to the peak).

Easy.

 

[Ed911]

And...here's some additional information that you might want to mull over...so you don't find the same shoddy work that I did. If your going to use a ridge and edge vents, I was told that you need to close off the gable vents. The last roofer on our home didn't...when the previous owner had the roof replaced and a ridge vent installed.

Here's something that I found that speaks to the issue.

___________________

The following is offered in response to your request for an interpretation of the provisions of Section 1503.5 of the 2003 International Building Code (IBC) portion of the 2005 State Building Code.

Question:
When re-roofing a building that has existing gable end louvers for attic ventilation, can one add ridge vents without adding soffit vents and disabling the gable end louvers?

Answer:
No. Section 1503.5 of the IBC states, in part, that roof intake and exhaust vents shall be installed in accordance with the manufacturer’s installation instructions. A review of a variety of manufacturer’s installation instructions as well as several ICC evaluation reports for ridge vents indicates that in all cases reviewed the ridge vents are intended to be installed in conjunction with eave, cornice or soffit vents. The combination of low intake vents at the eave, cornice or soffit, and high exhaust vents at the ridge promotes uniform ventilation of the entire attic space based on cooler air entering at the low vents and warmer air exhausting at the high vents. Gable end louvers, while not as efficient as a combination low and high system, likewise promote uniform ventilation where intake and exhaust occur at different ends of the attic depending on wind direction. When one mixes gable end louvers with ridge vents, however, the venting system is short circuited when air enters through the gable end louver and exits through the ridge vent in close proximity to the gable wall with the louver in it. Thus, the air at the lower portions of the attic and in the middle of the attic midway between the gable end louvers becomes stagnant and may result in a build up of excessive heat or moisture.

NOTE: Although this interpretation is based on the requirements of the IBC it is likewise applicable to attic ventilation in building construction governed by the 2003 International Residential Code portion of the 2005 State Building Code.


Hope this helps...

Any comments...pro or con.

Ed

 

[carpdad]

The baffles and ridge venting will not do anything since you don't have a soffit vent. Enough air has to come in from the soffit, take the moisture and exit through the ridge, but in your case, without the soffit, facia has to be reframed for intake air and somewhere to put the gutter.

Soffit venting also minimize ice damming, which is caused by heat from first floor and snow trapped by the gutter.

I would first seal every joint you can see along the wall plate, rafter tail and facia with a spray foam. Practice not wasting the foam. Try to fill every way that air can travel from outside and from inside. Second, fill the floor bay, at least into where the knee wall would be, with cellulose. Pack it in. Insulate the wall with fiberglass. Last, I would use cellulose for ceiling and pack it at least 12". See the depth that will give you r-40 or better. I would not use fiberglass in ceiling because it will lose a lot of R value from air moving across it vent to vent.

Cellulose is very good with stopping the air movement, but damage is greater if it gets wet. Choose deep/steep gable vent covers against wind driven rain, and maintain the roofing and roof flashing.