When designing the roof of your home, an important point to factor in is the insulation as well as air circulation. During the hot summer months, your roof will be the first line of defense against the sun’s radiation. And in the cold winter months, your roof will act as the barrier keeping the heat from escaping upwards. (Heat flows upwards.)
Walls and floors are equally as important, but in this article we’ll be focusing on the roof and how you can design it so it will do its job in the most efficient way, taking all things into consideration.
There are many roof designs and styles from which you can choose, and as far as aesthetics go, the sky is the limit and there is no right or wrong. However, if you want your roof to play its part with maximum efficiency, you’ll make sure you follow 2 crucial points.
Proper Air Circulation
It doesn’t matter how good your insulation is, if you don’t allow for proper air circulation, your insulation simply won’t be as efficient. The reason for this is that the sun’s radiation will initially heat up the roofing panels, which then transfers through to the subroof underneath.
And if your insulation is installed directly beneath the subroof, that heat will be allowed to conduct into the insulation. By adding a gap between the subroof and insulation, you provide a cavity through which hot air can circulate and escape via convection.
This of course won’t eliminate the effect of heat making its way into the insulation, but it will greatly reduce the amount. It’s also important to install vents (soffit vent, ridge vent, or gable wall vent for attics) through which the hot and/or humid air can escape outside, otherwise heat and moisture can build up causing decay as well as reducing the effectiveness of the insulation.
Broadly speaking there are 2 ways that roof insulation can be installed: Above, between or directly under the rafters; and above the ceiling of the top floor of the house. The former is used when the interior space of the house stretches all the way up close to the roof, while the latter is used when there is an attic.
Insulation should be installed as snug as possible and secured in some way to prevent shifting. Staples are used for rock-wool or types that come with plastic housing, while specialized hardware or washer screws often must be used for rigid styrofoam insulation.
If your rafters have enough height to where you can install styrofoam insulation between them and still get adequate air circulation between it and the roof, you can simply nail boards to the underside of the rafters and slide the styrofoam sheets in from above.
If not, you can use screws with wide circular washers and secure the insulation across the underside of the rafters, as opposed to between them. If space isn’t a problem, this is the recommended method, as this option provides a larger air pocket as well as insulates the rafter itself. Of course, the best method would be to lay the insulation directly above the interior ceiling, as this provides a large buffer area where air can circulate (see images above).
Styrofoam insulation panels are rigid enough to where plywood can be fastened directly over them and not compress significantly. Still, screws or nails used should have small heads so they don’t place excessive pressure against the styrofoam panels, and plywood joints should be staggered from the styrofoam joints.
From here sheetrock or other finished surface material can be fastened to the plywood for your interior ceiling. How your ceiling looks from below can be altered by building framework accordingly, but should be done prior to installing insulation, as it will get in the way.