Weatherization/Roofs

Roofs

Roofing tips

Miscellaneous advice on choosing shingles and roofing material:

• If you choose to install a roof with asphalt shingles, be sure to buy fiberglass asphalt shingles. They are stronger and more durable than regular asphalt shingles.
• If you install a metal roof, you must install some kind of lightning protection, and you will need to remove or isolate all other metal protrusions to prevent the dissimilar metals from corroding each other. If damage occurs, you can solder a piece of metal to a steel roof, whereas, with an aluminum roof, you have to use mesh and roofing cement.
• The advantage of tile roofs is that they stay cool in hot weather. They are not appropriate in cold climates, because they are not designed to handle snow and ice well.
• If your roof has a low slope, you should install a rubberized ice-shield membrane almost all the way to the ridge of the roof.

Advantages of wood shakes and shingles:

• Shed water well.
• Insulate from heat and cold more effectively than asphalt shingles.

Disadvantages:

• Flammable.
• Susceptible to the effects of trapped moisture (mold, rot, insects) when items fall on the roof (sticks, leaves).
• Not appropriate on a low-slope roof.

Before installing a new roof, check the roof sheathing for rot, both on the exterior surface (the decking) and the interior surface (in the attic). Don’t just replace rotten sheathing. Also find out why the sheathing rotted in the first place. Do not install a new roof until you have solved all moisture problems.

To protect the fascia boards from rot:

• Always install a metal drip edge.
• Overlap the eaves with a few inches of roofing material.

Use roofing cement to seal around nail holes and damaged spots in the roof.

Flashing

Flashing is a sheet or molded form, made of copper, aluminum, or plastic, that seals the parts of a roof where chimneys, vents, skylights, and other things penetrate or break up the roof surface. Repair holes in flashing with roofing cement. There are many different types of flashing:

• Install step flashing where the roof meets a wall. The correct way to install step flashing: Shingle, flashing, shingle, flashing, shingle, flashing, and so on, until you have wrapped around the top edge of whatever you are trying to direct water away from.
• Install “formed flashing” over ventilation pipes in the roof. These consist of molded plastic with a rubber collar that seals around the pipe.
• The best solution for the valleys of a roof is copper W-flashing.
• Flashing a chimney and the roof next to the chimney is somewhat complicated, involving base flashing, step flashing, and counterflashing (which seals other flashing). You insert counterflashing into a mortar joint in the chimney and secure it with mortar. The procedure for properly flashing a chimney is difficult to describe; refer to a roofing manual or roofing website.
• You can also create a “cricket” (a built-up ridge constructed with lumber and shingles) on the uphill side of the chimney) to deflect water and snow away from the chimney.

Skylights

Skylights can warm the house, by allowing more sunlight to come in, and can cool the house, if they are the type that you can open. Solar tubes are similar to skylights, in that they allow more sunlight to come in, but they do so differently, by collecting the light in a tube and sending it to a diffuser. Make sure flashing is installed properly around skylights and solar tubes. If you install a skylight, only install a high-quality one with an integral frame. Plastic bubble skylights tend to leak because the seam between the roof and the bubble expands and contracts over time. Pre-framed skylights are built to accommodate this expansion and contraction without leaking.

Houses in cold climates should have a narrow overhang to allow in more sunlight. Houses in warm and wet climates, on the other hand, should have a wide overhang.

Roof drain plane

If you have a relatively steep roof with few valleys, you should install a drain plane. A drain plane is a gap that you create between the roof sheathing or rigid panel roof insulation and the exterior roof surface. Functions of a drain plane on a roof:

• Allows any stray water or condensation to drain out from underneath the exterior roof surface.
• Provides ventilation to allow the back of the exterior roof surface to dry (especially important with wood shakes and shingles).
• Extends the life of the roof by keeping it cool and dry.
• Allows moisture forcing its way out from the interior of the house to evaporate quickly.

Roof insulation

If they do not already exist, you should add rigid closed-cell foam panels between the roof sheathing and exterior roof surface. You may need to modify skylights to match the new thickness of the insulation and roof.

Advantages of adding rigid closed-cell foam between roof sheathing and exterior roof surface:

• Thermally insulates attic ceiling. If you install foil-faced rigid foam panels, you will also block radiative heat transfer. If you install enough rigid panels, you may not need to put any insulation between the rafters.
• Resists air infiltration (and therefore, convective heat transfer) between interior and outdoors.
• Prevents condensation from forming in the rafters by keeping the temperature and humidity between the rafters similar to that in the rest of the attic.

In the attic, you should install expanding closed-cell spray foam against the interior side of the sheathing, and between the rafters, before installing (fire-rated) drywall. (If fiberglass batts exist, remove them.) Advantages of closed-cell spray foam between the rafters:

• They keep the temperature and humidity between the rafters similar to that in the rest of the attic.
• You don't need a separate vapor barrier. Closed-cell spray foam is virtually impermeable to moisture, and acts as its own vapor barrier, preventing moisture from condensing on the sheathing or rafters. You no longer have to concern yourself with moist air leaking into the attic and condensing on the sheathing and rafters.

Once you insulate the attic with rigid panels on the exterior of the sheathing, spray foam on the interior of the sheathing, and some type of insulation in the walls, you can treat your attic as part of the conditioned space of the house. In other words, you can allow the attic to warm up in the winter, and you can more easily keep the attic cool in the summer. You will most likely not be heating your attic directly -- the attic will draw heat escaping from the floors below. You no longer have to struggle to keep the attic cold and well-ventilated in the winter at the same time that you are turning the furnace up to keep your living space warm. You can insulate the floor of the attic, but since the attic is part of the conditioned space, it is not necessary.