Archive for the ‘attic’ category

Leaks Coming From the Attic

November 18th, 2013

Question:

I have frost in the attic of my five-year old, two-story house. I noticed a small leak coming out of the can light in the bathroom. Do I have enough insulation in my attic? I have 2″ x 4″ ceiling rafters, with ~16 inches of blown-in white insulation. I also have a ridge-vent running along the peak. Could heat be exiting through the attic door, exhaust vents, or can light, then melting the frost?

–Kevin

Answer:

Most folks who study moisture and home systems would identify your issue as an air-leak problem into the attic. Warm, moist air from the heated space is escaping into the attic, and moisture from that air is condensing on the cold roof deck. This may show as ice in very cold weather, and water in warmer weather. The problem is not insulation.

 

I025 - Air Leaks - Top of Wall

You need to search for air leaks at can lights, plumbing, electrical penetrations, chimneys, trap doors, etc. Seal up the air leaks, and the problem will be solved. Sounds easy? It’s not. You need an experienced contractor, who knows how to locate and seal the leaks. However, stopping theair leaks will save lots of energy.

I suspect you saw the leak at the can light because the light heat was melting the frost. The plastic vapor barrier is also open at the can light. If you want more information on attic insulation and air sealing, read my article Insulate Your Attic – But Don’t Stop There!

–Mr. Fix-It

Frost on One Side of Garage

February 17th, 2013

QUESTION:

We have a new home. With the cold, windy weather, we have noticed frost on the screw heads in the drywall garage ceiling edge. This issue is on the north side; none of the other walls have this problem. The garage is unheated, and the walls/ceiling are insulated. There is also a vapor barrier over the insulation. My husband says cold air is coming through the outside soffit, and there is no way to insulate this. There is also an electrical switch with frost on the screw heads on that wall. What can we do? Should we be concerned?

SHARON

ANSWER:

I014 - Air Bypass at Insulation - OverhangThe problem is caused because the screw heads are colder than the dew point temperature in the garage. In fact, the screw heads are below freezing so the moisture condenses and freezes. You have two solutions – raise the temperature of the screws or reduce the relative humidity in the garage.

Assuming you don’t want to raise the temperature in the garage, you can try to raise the temperature of the screws. I think your husband is correct – cold air is leaking into this wall area, either at penetrations, gaps, or through the roof venting. The cold air blows in and cools the wall.

For the attic venting, you should check above the soffit vents and make sure there are air chutes that direct the ventilation air over the insulation. If it blows into the side of the insulation, it will chill the wall. At times the best solution is to seal the air chute from the top of the wall to the roof deck with spray foam insulation. You want the air flowing over the insulation.

You should also look for any exterior gaps that may need sealing – perhaps around light fixtures, at the lower edge of the siding and around windows and doors. Any penetration in the wall and house wrap is suspect.

You could heat the garage; that would solve the problem, but I don’t suggest that. Lowering the relative humidity in the garage is virtually impossible, however you could sweep out snow and ice that may drop off your car.

MR. FIX-IT

Excessive Moisture in the Attic

January 21st, 2010

In September I added blown cellulose to my attic. I then covered the cellulose with plywood in order to have a usable space for storage. I have a walk-up stairway that does not seal very tightly. When I went in the attic to bring Christmas decorations down, I noticed it was damp. I installed a humidistat, and it read 90% humidity. I have a ridge-vent, and I installed sofit vents before blowing in the insulation, so I am not sure where the humidity is coming from, or why it is staying in there.

Dave

Answer:

Your problem is warm air leaking into the (now) cold attic. In the past, air leaks existed but the attic was warm because of the lack of insulation. When the air is warm it holds a lot of moisture, so the “relative” humidity was low and there was no moisture problem.

The solution is to air-seal between the attic and the heated space below. Seal around the chimney and all penetrations, including the access door. If you stop the air leaks you will solve the problem and save lots of energy.

Check out my article:

Insulate Your Attic – But Don’t Stop There!