Structure

Attics

Image of an uninsulated attics framing
Attics

On homes with pitched roofs, the attics are spaces between the roof and the living area ceilings of the home. In homes with high, steep-pitched roofs, the attic can be quite large with enough headroom to walk around comfortably. The roof framing in the attic is typically exposed and uninsulated which allows for direct visual inspection of the underside of the roof for leaks and moisture.

To allow air circulation, attics will have screen covered air vents around the perimeter of the roof/eaves, “eyebrow” vents on the roof plane itself, and possibly vents along the ridge of the roof.

 Electrical wiring, the mounting cans for recessed light fixtures, ducting and some plumbing lines and furnace equipment may also be located in the attic space.

Access to the attic space(s) will be through hatches in the ceilings of the home and sometimes through the garage. These hatches can be equipped with retractable, pull-down ladders making access much easier. Even with easy access, homeowners should know that the attic space is not designed or intended for storage. Access to this area is for inspection of the structure and maintenance of mechanical equipment in the attic space. If you wish to store things in the attic, a design to modify the space should be developed to do so properly.

When performing tasks in the attic, use extra caution and avoid stepping off structural members and onto the drywall. This can cause a fall of about 8-12 feet, resulting in personal injury, death and quite a bit of damage to the ceiling below.

Attic Exhaust Fans–Why they don’t work and what to do instead!

One of our HPS clients called to say that their attic was extremely hot and requested we install a larger a/c powered fan.  They decided a new fan was needed replace a solar unit they had installed several years ago, that “didn’t seem to be working”. The second-floor rooms under the attic area were hot compared to the rest of the house.

On inspection, we found a single, roof mounted, solar powered fan. It was working properly. There was no other ducting or HVAC equipment in the attic. Insulation was a 6”-8” layer of blown-in fiberglass on the top of the ceiling, plus random pieces of R-19 fiberglass batts tossed askew atop the blown-in material, but not fully covering the space.  The 2×6 roof rafters with 4” skip sheathing, and ½” plywood shear was all exposed to view. 6”x24” eave vents were installed around the perimeter every 8’ and were not blocked by the insulation. The temperature of the roof sheathing inside the attic was 147 degrees. The 45’x24’ (approx. 4500 cubic foot) attic space was very hot.

I explained to the client that the idea of attic fans to remove hot air from the attic area might seem logical. But it doesn’t work. Here’s why: thermodynamics

Imagine yourself laying in the sun on a beach in Cancun. All is good for about 5 minutes then you start to feel hot. You go and get a big fan and set it up to blow air over you. Ah, feels better for about another 5 minutes. Soon even the blowing air feels hot, so you exchange the fan for an air conditioner and let that blow cold air on you. Feels great now so you stay out in the sun till you notice that your skin is red and blistered and burned to a crisp.

What happened?  Radiant heat! It’s why you can still get a terrible sunburn even on a cold day. Radiant heat moves right through cold air without any affect.  So, what does that have to do with your house?

Image of affects of sun and cold on attics space
Thermal motion at attics

On your home, the roof is like your skin.  Radiation from the sun hits the roof surface and warms the entire mass of the roof structure (roofing, roof paper, nails, sheathing, rafters). Soon the roof structure is so hot that it will radiate heat on its own. This radiant heat passes down through the attic space and hits the material on the surface of the ceiling structure (insulation, wood joists, drywall, ducting etc.). Very quickly the entire mass of the ceiling structure is a giant heat radiator and if your ceiling is not sealed airtight and well-insulated, all this heat is going to find a way into your home.

The point of this discussion is that if you have an attic space, it is going to get hot. And attempting to cool it off by pulling air through it doesn’t work*.

Here’s what works: 1. Seal off any air leaks at the ceiling. This will also prevent excessive moisture from migrating in and out of your attic. 2. Install additional insulation to bring the total to over R-30 everywhere-even over the access hatch. Cover the tops of any wood joists by at least 3 inches. 3. Make sure the eave vents are unobstructed. 4. Install radiant barrier foil over the top of the insulation as described in this video: https://youtu.be/FJZrJLiP3Pc

For a number of reasons, attic fans are not recommended no matter how they are powered. 

  • If there are not enough soffit, gable or ridge vents, a powerful attic fan will pull the air from your home through the ceiling if it is not perfectly sealed off. 
  • Strong attic fans can actually back draft furnaces or water heaters by pulling combustion gases out of their burners and into the home.
  • Maintain good attic ventilation without fans for preventing moisture and condensation, not cooling.

Solutions for a hot attic

Unless you have ductwork or HVAC equipment in your attic, heat is not a terrible problem. You definitely must have a completely sealed ceiling and a very thick layer of insulation and radiant barriers to isolate your hot attic from your cool house. If you do have ductwork or HVAC equipment in your best attic solutions would be to: 1. Move the ducting and HVAC equipment to the interior of your home. 2. Seal leaky duct seams and adding insulation on top of your duct work. 3. Move the insulation from your attic floor to the sloped roof assembly thus creating a “conditioned” space in your attic.

Bottom line:

If you your house has a hot attic and ceiling during the summer, the solution is not a powered attic ventilator. The solution is to seal any air leaks in your ceiling and to add more insulation and a radiant barrier to the attic area of your ceiling.

*Removing or circulating attic air does not stop the radiation from transferring heat. During the day, any cooler outside air brought in will be heated up immediately by the surrounding structure. At night, the sun’s radiation source stops so any cooler air brought in from outside then, will eventually cool down the attic structure, but that will happen very slowly. As soon as the sun rises in the morning, the heating process will start again.

Maintenance

  • 1x per year: Have a qualified inspector perform a visual review of the attic space annually. For safety reasons we do not recommend homeowners enter the attic. Stepping in the wrong place can result in falling through the ceiling with the prospect of injury or death. Attic inspections should look for water stains on the underside of the roof and around plumbing penetrations, vents etc., signs of rodents, broken ducts, missing insulation, chewed wires.
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