Insulation touches underside of roof in home with no soffit or soffit venting.

I performed an assessment for a recent home buyer and the home inspector they hired when they purchased the home said the fiberglass insulation that is touching the roof where the roof slope meets the exterior wall may cause condensation issues and needs to be pulled away from the underside of the roof. The house was originally designed and constructed with no soffit, so there are no soffit vents. The top plate of the exterior wall meets the lower slope of the roof. To properly insulate the attic, I would think you would want the attic insulation covering the top plate. To ensure proper levels of insulation above the top plate, the insulation will be in contact with the lower area of roof slope. Since the attic does not have a soffit, I would think there is no issue with the fiberglass batt insulation being in contact with the underside of the sheathing? Since there is no soffit in the original design of the house the insulation does not limit the airflow ventilating the roof. The house does have gable and ridge vents for proper attic ventilation.

Is there an issue with fiberglass batts installed on the attic flat touching the underside of the lower slope of the roof if there is no soffit venting? 

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Location, location, location

In hot dry climates - not really an issue unless it gets damp (and yes this still can be an issue in places like Phoenix)

Places where it freezes - nothing beats trying to pull fiberglass that is frozen to the sheathing

Got mechanicals up there or crazy enough to put a power ventilator in there then never in contact

Should it be over the top plate - absolutely, just never in contact with the sheathing 

It would be very helpful if posters thought a bit about what other information might be very useful for replies to their post, keeping in mind that most forums are national and include many different climates. In this case, knowing the approximate age and style of house would be helpful.

Your profile indicates that this is in New York, a cold climate. If the house is at least as drafty as the average home and there is no notable moisture sources (lots of plants, wet basement or crawl space, lots of occupants, including pets, pot of water on wood stove, etc.), then it is likely to not be a problem. The RH in the winter should be low enough and there will be some air movement through the fiberglass to remove any excess moisture.

If the above is not true, then it will be tough to fix, depending on length of slopes and access to slopes from attic. adding a vent space above the fiberglass, if there it is possible, is a challenge not only because of the difficulty of sliding something over the fiberglass, but also avoiding nails for roofing (I know, because I have done it). another option is to pull the fiberglass and carefully dense-pack the slopes.

Bottom line, it depends on RH levels in winter.

Good point on other information. The house has 4 bedrooms was built in 1976 and is located in NY, 50 miles North of NY City. The house does not have a basement or crawl space and is built on a concrete slab. 

I always scratch my head on this one.  The general rule is insulation baffles to keep insulation from touching the underside of sheathing even without soffit venting.   I'm in Alaska and run into this issues all the time.  The majority of my houses are already built in the bush.  They are relatively tight, owner built and seldom have soffit venting.  Often there is severe wind loading on the building shell.  Soffit venting allows too much wind washing and can move loose insulation around in the attic.  Without an energy truss, insulation baffles decrease the amount of insulation I can have over top plate, so I have thermal bridging and risk ice damming

So I ask the dumb question, how is a typical cold attic eave assembly that different from a framed wall assembly?

We dont put baffles in walls and vent them.  I like a vented rain screen on a wall, and can do a similiar vented  roof, but I don't usually have the budget.

db

Adding a vent chute above fiberglass insulation in a roof slope is NOT creating a "cold" roof. If anything, it can accelerate the escaping of heat. The venting of roof slopes with fiberglass has not changed since the 1930s when fiberglass was first used and it was discovered that any moisture that got into a closed rafter cavity could not escape.

Heat is transferred by 3 methods- conduction, convection and radiation. Fiberglass minimizes conduction by have lots of air space. If air is allowed to move through it, such as by the stack effect or wind, heat is not only transferred by convection (the heat energy in the air escaping) but also it diminishes the effectiveness of the fiberglass to minimize heat loss by conduction.

The reason we vent a roof and not a wall is because a roof loses a lot of heat by radiation, particularly at night. A wall loses heat by radiation as well, but a chunk of that is radiated back by the surrounding environment. A clear sky at night neither reflects nor emits any infrared radiation back to the roof. Think of a car parked under shade in winter, vs. a car parked under an open sky. The latter will have frost all over it in the morning and the former will have none (or very little). When a roof cools down quickly at night from that radiational cooling, the roof deck gets very cold very quickly and the air in the rafter space condenses when it is below its dewpoint.

good description of the building science.  So now the applied science.  Insulation touching the underside of roof sheathing. Ok or not?  This is not a situation of a enclosed slope but an open cold attic.   

db

Are you are referring to a situation such as a ranch style, where insulation is touching the roof deck at the eaves, where the insulation may be as much as about 18" deep? If so, I would not be at all concerned, as long as there are gable end vents or a good ridge vent. The soffit vent is not important in that application.

I don't think it would be a problem provided there is no large source of interior moisture getting into the attic, especially in a cold climate.  With that in mind, a thorough sealing of the attic floor - including those plates at the outside edge of the eaves - would be imperative.  Best way to treat those exterior plates might be to remove the insulation and use a 2-part spray over the entire plate to make it easy.  You might use that foam to seal the entire area and build it up to add a higher quality insulation where the space gets small.  Other leaks in the attic I would seal with single part foam after moving aside the insulation.

What does it look like now, and how long has it been like that?

There is no visible issues anywhere in the attic. The insulation in the attic is from when it was installed in 1976.

The house is over 40 years old, if it is a problem there will be evidence of condensation, like mold, where the insulation contacts the roof deck. If it looks good then it is no worry. If someone were to add a humidifier to the furnace or another new source of abundant moisture, it could cause future problems but that would be the case for any house in a cold climate.

It mainly depends upon your location. It also matters that what does it look like now and how long it has been like that. You should once contact to your HVAC service provider to fix your problem. To know more on this issue or get valuable suggestions from HVAC industry experts contact to White Mechanical, Inc. a leader in providing superior HVAC services near you.

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