Downsides to a shed roof? (a.k.a. monopitch / skillion / lean-to roof)
John Ranson| Posted inEnergy Efficiency and Durabilityon
Are there any energy efficiency and or durability issues from using a shed roof on a house?
–John
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Replies
John,
Q. "Are there any energy efficiency and or durability issues from using a shed roof on a house?"
A. No. To my eye, however, there are major aesthetic issues. I think that a gable roof or a hipped roof is more elegant and beautiful than a shed roof. But there is no disputing issues of taste.
From a design perspective, you want the long axis of your house to align east to west. That means you have two ways to pitch your shed roof. If it is pitched from north to south, your roof will be ready for the installation of a PV array. This is the preferred approach.
Before PV modules became cheap, passive solar designers often recommended that a shed roof be pitched the other way, from south to north, so that there would be a higher wall on the south side for more windows. These days, however, the advantages of a roof allowing for PV installation make the older approach obsolete.
Monopitch roofs are the easiest to insulate, see detail. When it come to aesthetics, its all a matter of opinion. The attached pics shows a roof style that has become "IN" in the North Texas area. I'm sure this style would not go well in other areas of the country.
Both of these houses are custom Zero Energy homes, one finished and the other under construction..
Armando,
It's not clear to me where the air space is for air flow on the insulation detail you provided?
Or is this an un-vented roof? I assume not since the soffits are vented.
Is the detail the same on the high side? If so, any concerns with driving rains entering the vented soffit which is sloping upwards on the high side?
Thanks.
Installed and sealed properly, SIPS (Structural Insulated Panels) of 12" or more thickness make a good single pitch/shed roof. Minimal thermal bridging. Great to finish simply with screw-down metal roofing. Goes on easy and finishes fast, with modest skills. Careful, though, the metal can be SLIPPERY WHEN WET! Snow sheds easily! Awesome sound-rumble, rumble. Scary the first time you hear it, but amusing after....
Chris Harper,
Armando's detail appears to show an unvented roof assembly. Some builders like to install ventilated soffit material, even when there is no ventilation channel in the roof assembly. The ventilated soffit material is basically decorative, and the openings are harmless.
For more information on different ways to create an insulated unvented sloped roof assembly, see these two articles:
How to Build an Insulated Cathedral Ceiling
How to Install Rigid Foam On Top of Roof Sheathing
克里斯-马丁说过,这显示了一个细节unvented attic assembly. The 36" overhangs are ventilated, since we live in humid zone, plus if it ever gets wet, it has a chance to dry.