Insulating the Attic Rafters, Conflicting Advise
BMcCutcheon
| Posted in Energy, Heating & Insulation on
I was recently told by a friend at the Owens Corning Factory outside Atlanta when asked about insulating my new home that I should use Paper Sheathed Batting and place the Paper facing the Attic floor. Once all the insulation was up, to take my batting knife and make 4-5 inch cuts across the paper about every 3 feet to allow the insulation to breathe. He said that doing this will greatly cut down on the free glass floating in the air and create less of a hazard. I like the thought of the Roof Rafters being insulated to cut down on the heat buildup in the attic. I have unobstructed soffits all the way around the house and will stop the roof insulation about 3 inches from the soffit line so that air flow is not obstructed.
Your Thoughts?
Bill
Replies
There are about 50 different ways to insulate an attic. You are presumably taking the "hot roof" approach, where there is no ventillaton above the insulation, and the attic is part of the "conditioned space". But "allowing the insulation to breathe" sounds bogus -- I'd want to see that advice written down from the manufacturer, and I'd want them to explain how that doesn't compromise the R-value of the insulation.
Sun, radiation, conduction, batts.
May I mention another issue.
Having open soffits seems to be a fashion at the moment, but they do present problems and costs.
While a ventilated roof may seem a good idea, in cold areas, where homes are badly built and are full of holes, they come with a cost.
The problem is due to the wind!
A typical roof acts like an aircraft’s wing, its shape causing the passing wind to try to lift off the roof. This causes an area of low pressure to to lee of the building, this area in turn sucks the air from the building, dragging air from inside the roof and home, and in summer replacing it with hot air from outside, and in the winter with cold air.
A much better practice, is to have an air tight roof and home, where your conditioned air stays inside the home.
If you want your home to stay cool in summer, you should think along the lines of external shade from trees, and white or silver heat reflective roof and walls.
Five inches of polystyrene sheet over the roof and walls, sips panels are ideal, as they separate the hot outside from the cool inside.
I would suggest that you lay fibreglass batts in the sun on a hot day and place a temperature gauge underneath, you will be surprised how quickly the heat from the sun passes through and heats the underneath.
This applies to all types of insulation, insulation merely slows the time the heat gets through, some like polyurethane foam work better than others.
Keep in mind that insulation between the rafters, will still allow a great deal of heat to enter your roof and home, as every piece of wood that is heated by the sun, will pass that heat to the inside by conduction.
I got rid of my trees because they were clogging my sewer with roots, providing nesting areas for birds and varmints (which gained entry to my attic and chimney) and dropped limbs during storms onto my house and vehicles, as well as dropping leaves and seed pods onto my house thus clogging the gutters and making more work keeping gutters clean and making the yard nice.
Trees gone, I'm a happy man, and utilities did not increase as far as I can tell.