Venting a shed roof with 2/12 slope

atulc · 08-23-2006, 11:55 AM

Hello,
I have a low-slope (2/12) shed roof over a single-story addition on the back of my 2-story house. The builder was forced to keep the slope low because of the 2nd floor windows. At the low end, the roof drains into a gutter. There is no soffit for ventilation. At the high end, the roof meets a wall. There is absolutely no ventilation in the roof. To make problems worse, there is no insulation in the ceiling/roof. In the winters, with 6+ inches of snow on the roof (I live in NY), the heat from the room escapes through the roof and causes an ice dam.

For the last two winters, I have been using a roof rake to remove snow from this roof to prevent ice dams. How can I permanently fix this problem.

I am planning to add insulation above the ceiling sheetrock. (I will have to do this from within the room by removing the sheetrock.) But I doubt that this will fix the problem alone. Should I vent the shed roof?

I am replacing the shingles over the entire house. I plan to install inhaler vents (http://everflovent.com/inhaler.htm) and ridge vents (http://www.airvent.com/homeowner/pro...ngleVent.shtml) on the main roof which has about 6/12 slope. Currently there are just gable vents in the main attic. I will close off the gable vents. I was thinking of putting inhaler vents and flash filter vents (http://www.airvent.com/homeowner/products/ridgeVents-specialtyFilter.shtml) on the shed roof. But these are not recommended for slopes less than 3/12. What are my options for the shed roof?

Thanks in advance for your help,
atulc

AaronB · 08-23-2006, 07:32 PM

Insulate the dooky out of the ceiling, install a low slope roofing system, forget the vents, and voila! Youre good to go.

I like spray foam insulation myself.

atulc · 08-24-2006, 09:07 PM

Thanks Aaron.

By the low slope roofing system, do you mean something like the GAF Liberty 3-layer membrane roll roofing? (see http://www.gaf.com/Content/GAF/RES1/...S_Liberty.html
)

When you insulate a low-slope shed roof with spray foam, do you just fill the space between the joists on the roof below, or do you fill the entire empty space in the roof all the way up to the rafters?

AaronB · 08-25-2006, 12:01 AM

You could just do the ceiling cavities if theyre large enough.

I do not trust Self Adhered (SA) modified bitumen systems. 2/12 may be alright as long as there are no obstructions.

atulc · 08-25-2006, 12:29 AM

Quote:

Originally Posted by AaronB

You could just do the ceiling cavities if theyre large enough.

I do not trust Self Adhered (SA) modified bitumen systems. 2/12 may be alright as long as there are no obstructions.

If modified bitumen is not good, then what other kind of low-slope roofing do you recommend? Remember, ice dam formation at the eave is a frequent problem on this roof. I have to always use a roof rake to clear the roof after every snowstorm.

Thanks

AaronB · 08-25-2006, 08:28 AM

Well, modified bitumen isnt bad in itself, but moreso the SA type. Modififed bitumen torch applied is an excellent product, but must be installed by a licensed trained professional.

EPDM (rubber) is another option. Success of any of these systems really lies with the installer and his details.