Insulating rooms over the garage

Q.  I have two bedrooms over an unheated two-car garage with finished ceiling and 2-inch foil-backed insulation (house built in 1968). I would like to add more insulation since the rooms are cold, but have been told that insulation cannot be blown in over the existing insulation because the blown-in material will “stick” and not fill the void. Others have said that should not be a problem and to go ahead with the job. Who is right?

A.  The rooms above are cold because the joist cavities of the garage ceiling are most likely empty. Insulating the garage ceiling with 2-inch thick rigid insulation did nothing for the rooms above; it only insulated the garage.

There should be no reason why you can’t have cellulose blown into the joist cavities. Select an experienced insulation contractor who will blow in the cellulose carefully to ensure that the entire cavities are filled and make the necessary patch up repairs once the job is done.

Ice dams on roof of heated garage

Q.    I have a problem with ice damming on my garage roof. I use a heater during the winter in the garage. The snow melts and ends up in the gutters, and at night freezes and ice forms in the gutters.

The roof in the garage is not insulated. Any suggestions other than shoveling the roof when it snows, to getting on a ladder and trying to remove it manually? Install heating cables? Insulate the attic? Thank you.

A.    If you are putting your cars in the garage, be aware that heating the garage activates the salt that accumulates on them during the winter, and it encourages rust formation — so it’s best to keep garages unheated. However, if you use the garage as, say, a shop, then you should treat it as a lived-in space and insulate the roof. Insulating the walls exposed to the outside as well would save you a lot of energy.

I would not recommend getting on the roof to shovel the snow or using a roof rake from the ground for the purpose; besides the personal risk of injury, it is not good for the shingles. Heat cables have some use but would not solve your problem.

Insulating bedroom floor over unheated garage

Q.    My bedroom is located over an unheated garage. The unfinished garage ceiling is insulated with two layers of rolled bat insulation. The paper vapor barrier is facing the garage, not the bedroom floor.

I would like to seal off the garage ceiling with foam boards to stop any cold air from coming in through the bedroom floor and to provide some additional insulation. My understanding is that the vapor barrier should be next to, or on the side of, the heated room. Does this hold true for my bedroom/garage situation? Must I reinstall the insulation with the vapor barrier next to the bedroom floor before I put up the foam board?

A.    Ideally, yes but we know that paper vapor retarders are not very effective. Moreover, the addition of at least 1-inch thick rigid insulation will warm the joist cavities and reduce the chance of condensation within them. It will also reduce any heat loss through the floor joists.

And if your sub-floor is plywood, that in itself is an effective vapor retarder. However, pull down some of the fiberglass insulation in a few widely scattered spots, particularly next to the outside walls, and check for any signs of moisture or mold development. If you find any of these, you should seriously consider pulling the insulation down wherever these conditions are visible, allow the areas to dry and put the insulation back (if it is dry) with the paper vapor retarder facing the bedroom floor.

Be sure that the entire joist cavities are filled with fiberglass insulation to prevent heat loss and cold air from infiltrating between the top of the insulation and the subfloor. You are unlikely to find that the entire area has been affected.

Also be sure that you use extruded polystyrene rigid insulation (XPS — blue, pink, grey or green). Remember that rigid insulation on the garage ceiling will have to be covered with fire-code drywall, properly taped.

Determining source of leak in garage roof

Q.    Today we noticed some water dripping down the inside back wall of the garage during a steady light rain. I went in the garage attic and noticed at the seam of the sheathing (½” plywood) four feet from the end of the roof, it was wet. It appeared to be running down the inside of the roof, hitting the wall and then dripping down (conveniently into an empty bucket we use for bird food).

I went up on the roof during the rain and didn’t notice anything anywhere near that location. There is a valley  a couple of feet away (to the side, not above). The wood on which the dripping occurred did not appear stained so this may have been the first time it leaked. How do I figure out where the leak is coming from and how do I get it fixed? The trusses are 2 feet on center. I am somewhat handy and might be able to take care of things myself with guidance.

A.    You haven’t told me how old the roof is and what type of roofing it is. I will assume that the roof is covered with asphalt or fiberglass shingles. Since you are handy, I will also assume that you would have noticed if any of the shingles had cracks or missing pieces, which can happen with fiberglass shingles that are 15 years old or more.

At this point, my guess is that the leak is occurring at the valley. If it is made of coil-stock aluminum, it is probable that it was nailed all along both its sides and that it has buckled. This is caused by temperature changes and, eventually, the thin metal develops cracks, which will admit rain.

A valley gets water from two roof planes so quite a bit of water runs down the valley, even in a gentle rain. Once the water has penetrated through the cracks, it can travel sideways following the rows of shingles until it finds a joint in the sheathing where it seeps through into the building. If that is the case, roofing cement applied over the cracks will stop the leaking for a while, but you will have to re-apply it every couple of years as the sun destroys it.

When a new roof is put on, have the roofers use heavier gauge metal with no run longer than eight feet. Each run should only be nailed at the top and held in place on its sides with clips so expansion and contraction are not impaired.

An ice and water protecting membrane applied on dry sheathing and extending a couple of feet on each side of the valley is also a wise thing to do.

Restoring a pitted garage floor

Q.    My garage floor has become pitted from road salt over the years. I’m considering using one of those epoxy coatings to fill in the pitting and smooth it out and/or first using concrete restorer to fill in the pits and then the coating. What do you think of the possible outcome (looking decent) from this approach?

A.    Why not simply using a polymer-modified product such as Thorocrete or vinyl-reinforced TOP’N BOND? They are both one-step processes for repairing damaged concrete surfaces and should be easily available in building supply stores.

Just be sure that you remove all loose particles with a strong jet of water before applying the new mix and that you follow the instructions on the containers.

Garage windows fog up and remain damp

Q.    Nearly every time it rains, the windows on our garage get fogged up and the inside feels damp. I assume that happens because of  humidity. I want to be able to store things inside this building but I am worried about mold. What can I do to prevent this fog-up in the future?

A.    It sounds as if the condensation on the garage windows is occurring because the rain lowers the outside temperature, which cools the glass, and the humidity in the garage is so high. And like most garage windows, they are probably single-glazed.

Garages are quite humid, particularly if they have a dirt floor or concrete that was poured directly on soil. Cars also bring in moisture.

This is not a good situation for storing anything that can be affected by humidity. Your garage may need ventilation in the form of gable vents or soffit and ridge vents.

Insulating the floor over garage

Q.    I live in a split-entry brick home. The garage is in the house. The back bedrooms are very cold. I have insulation between the joists with the vapor barrier up against the floor of the bedrooms. There is some heat in the garage but I don’t want it too hot because of the salt from the roads on the cars. Should the vapor barrier face the garage or should the insulation be unfaced?

A.    You did it right: the vapor retarder should always be on the winter warm side of the insulation but, in your case, the insulation should be tight against the floor above. The exception to this rule is in climates where air-conditioning is prevalent over heating — the deep South.

Keep in mind that the bedrooms (which I assume are over the garage) have an added exposure to the cold — their floor. In such cases, the insulation should completely fill the spaces between the joists. If the fiberglass batts are left exposed in your garage, they are subject to heat loss through air movement (fiberglass is a filter, after all). In that case, do whatever is needed to fill the spaces between the joists with more unfaced insulation, fasten 1-inch thick rigid insulation to the bottom of the joists and cover it with fire-rated gypsum board, making sure to tape the joints.

If there is already gypboard on the garage ceiling and the fiberglass insulation does not completely fill the spaces between the joists, your choices are to have dense-pack cellulose blown in or the gypboard removed and additional fiberglass put in. If the spaces between the joists are filled with fiberglass, consider adding 1-inch thick rigid insulation to the bottom of the joists, even if the ceiling is covered with gypboard, and cover it with another layer of fire-rated gypboard.

You don’t say what your heating system is but it may need to be better balanced. If your system is warm air, insulate any ducts in the garage space and balance the system to feed more warm air in the bedrooms. If you have a hydronic system, and the bedrooms are not on a separate zone, you may need to add radiation in each of them.