GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted Hamburger/Search Icon
Musings of an Energy Nerd

Every House Needs Roof Overhangs

Adequate roof overhangs help shade windows in hot weather and reduce the amount of rain that hits your siding, windows, and doors

Roof overhangs protect siding, doors, and windows from rot and water entry. Swiss builders have understood the advantages of wide roof overhangs for hundreds of years.
Image Credit: Image #1: Static.panoramio.com

Many residential designers pay too little attention to roof overhangs. Roof overhangs have several important functions: they can protect exterior doors, windows, and siding from rain; they can shade windows when solar heat gain is undesirable; and they can help keep basements and crawl spaces dry. A house with improper overhangs can overheat in the summer, can suffer from water entry problems at windows and doors, and can have premature siding rot.

The most common design error is to make roof overhangs too stingy. It’s also possible (although much rarer) for roof overhangs to be too wide.

A typical gable roof has two kinds of roof overhangs: eave overhangs and rake overhangs. Because it’s easier to frame a wide eave overhang than a wide rake overhang, problems from stingy overhangs are more common at rakes than eaves.

Perhaps the most important function of wide roof overhangs is to help keep water off siding, windows, and doors.

[Photo credit: Tom Arstingstall, Tromler Construction]
While it’s impossible to stop all wind-driven rain from reaching your walls, wide roof overhangs make a big difference — especially if there is just one story under the overhang.

Of course, an overhang that is trying to protect two or three stories is much less effective at keeping the wall dry. (Fortunately, there are solutions to this problem — notably the inclusion of a “brow roof” above the first floor. I will discuss brow roofs in more detail later in this article.)

[Photo credit: Lynnette Hartwig, gettingbestprice.com]Walls with stingy roof overhangs get regularly soaked. These repeated wetting episodes cause a variety of problems. Although these problems are worse in high-rainfall climates than low-rainfall climates, almost all North American homes are built in regions where it makes sense to protect walls from the full force of wind-driven…

GBA Prime

This article is only available to GBA Prime Members

Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and construction details.

Start Free Trial

19 Comments

  1. David Hicks | | #1

    typo
    Martin, I think there' s a typo in this sentence: "significant percentage of exterior roofs are inexplicably unroofed.".

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to David Hicks
    David,
    Thanks. Not enough coffee yet, I guess. The typo has been corrected.

  3. User avater GBA Editor
    Patrick McCombe | | #3

    "like an orphaned lamb
    "like an orphaned lamb released near a pack of wolves..." Where did this come from? Funny though!

  4. Mark Fredericks | | #4

    PERSIST overhangs?
    Thanks Martin, another super article and some great examples of successful overhangs. I was hoping you would discuss applying roof overhangs to a PERSIST style home that is intentionally built with no overhangs to simplify the installation of control layers. Particularly I'm curious how to build well supported ladders for the rake overhangs, but it would be great to have some general comments on the challenges to building good overhangs with this type of construction.

    Side note: you wrote: "Although these principles are obvious, a significant percentage of exterior roofs are inexplicably unroofed." Did you mean to say a 'significant percentage of exterior doors are inexplicably unroofed' ?

  5. Flitch Plate | | #5

    ... could not agree more.
    Not only are wider rake and drip edges more pleasing to look at, they are much better at protecting the building and occupants when they approach and exit the house. I have 40” eaves.

    The upside is well outlined here. The downsides need to be compensated with planning or there is a lot of extra work in order to benefit from this feature:

    1. Grass does not grow so well when close to the house since rain does not reach the lawn under the eaves. Because its dry and weed prone, watering is needed if you want grass but then watering that defeats the purpose of the overhands intended to keep water away. I have 24” and 36” perimeter gravel borders over weed barrier fabric and galvanized hardware cloth to keep out critters (it’s a country home and ground hogs compulsively nest next to buildings) which means less work to keep grass there.

    2. Birds love to nest on any surface or edge they can find under a weather protected, well shaded eave. Swallows can build a nest anywhere. I use bird spikes to limit the nesting behavior. I like the birds but bird poop wrecks the siding and paint and corrodes any metal roofing, window frame and flashing below.

    http://www.birdxcanada.com/roost/bird_spikes_steel.html

    3. In western NY the carpenter bees can turn any wood surface into swiss cheess. Often owner built wide eaves, soffits, facia and overhangs are unsided, painted lumber. Carpenter bees, just like the birds, are too far from the ground to fight off and remove. So the wooden elements of overhangs need to be covered with flashing or siding materials (vinyl trim).

    http://inspectapedia.com/structure/Carpenter_Bees.php

    4. Wide overhands reduce incoming light to the building and so need careful planning to not make the mistake of blocking upper window views, airflow and natural lighting.

    5. Wide eaves and gable end turbulence affects the microclimate and increases the possibility of capturing and holding pollutants and airborne particulate. It adds a design element to the building and how they affect stacks, chimney performance, etc.

    http://www.scotland.gov.uk/Resource/Doc/217736/0090838.pdf

  6. User avater GBA Editor
    Martin Holladay | | #6

    Response to Mark Fredericks
    Mark,
    There are at least two GBA articles that discuss "applied overhangs" (roof overhangs which are framed after the peel-and-stick membrane is installed on the exterior side of the wall and roof sheathing of a PERSIST building).

    Check out Image #3 on this page: Getting Insulation Out of Your Walls and Ceilings.

    Also check out Image #1 and Image #2 on this page: Airtight Wall and Roof Sheathing.

  7. Aj Builder, Upstate NY Zone 6a | | #7

    Flitch man, your knowledge
    Flitch man, your knowledge base and comments most always add an element of surprise and interest.

    But.... how do you deal with the forty days of continuous sideways snow from lake effect out your way? We here on the East side of the Southern ADKs are living a sheltered life compared to you in Buffalo.

    Wait, I think your post answers the my question, you zoom around the world to Scotland and beyond seeking worldly knowledge and more...
    ;)
    aj

  8. Jin Kazama | | #8

    this is definitly on the list ...
    Every building openings should be protected from rain.

    At my location, ( ~ 45-46latt ) designing for 45degree from window top from sout-e to south-w orientation is usually simple and blocks ~50% of direct SHG while in cooling season
    without blocking any of the required SHG during the heating season.
    As your drawing demonstrate, it is possible to design as such for every climate and lattitude.

    A more effective method requires adjustable sunshade.

    Might i add that east to sout-w windows should be overshaded by PV panels ?
    the price is right where it needs to be, and with the mini-rectifiers from enphase and such,
    it is very easy to provide individual shading and rain deflection for most windows.

    Unfortunately, all we see around here are short roof ends .

    Way too many design decisions are based on profits and aesthetics nowadays.

  9. Jin Kazama | | #9

    W D
    There are many different possibilities to treat solar on windows depending on climate and orientation.
    But , from a user point of view, the best compromises leave the horizontal view untouched or almost untouched.

    It is very easy to shade a window with a direct blocking obstacle, but unless the view through the window is seriously uninspiring ( aka side wall of your 20ft far neighbor :p ) , unobstructed sight and indirect light input should be a priority.

    I have an adjustable aluminum " plane wing " sunshade type on the south/west side of my house,
    which is attached to the wall with a pivot a few inches above the windows of this floor.
    I just moved it down so that is blocks all sunlight until ~ 4-5pm ( low west ) from getting directly inside, and the temperature difference is enormous .
    But it does not block more than ~ 15% of the view ( top portion where it hangs on its lowest position ) .
    Very effective on blocking the right portion of light but not very cost-effective though ( should've been PV panels, but back then they were still very $$$ ) and a little on the complex side ( pivot, stainless cables, weight and a 4K lbs winch bolted on the side of the roof parapet )
    I am even wondering if i should replace it with "less adjustable " PV panels in the near future.

  10. Flitch Plate | | #10

    360 degree prevailing winds

    AJ ... for sure you hit the Rochester - Buffalo corridor weather nail on the head. This year’s storms have inundated my half round 6” gutters. Today I just finished doubling my downspout capacity and adding another catch basin. Every side is a weather side: winter, spring, summer and fall. Can’t for the life of me figure out where to place the snow fences. It blows as much from the NE, E, SW, and W as it does from the NW. And as you say, it blows sideways.

  11. User avater GBA Editor
    Martin Holladay | | #11

    Comments by Lloyd Alter of Treehugger
    After reading this article, Lloyd Alter (an editor at Treehugger.com) was sitting near his open window -- a window that lacks roof protection. Water was entering the window and getting Lloyd wet.

    Contemplating this depressing situation, Lloyd wrote a blog: Every house needs roof overhangs, except when they shouldn't or can't.

  12. John Mattson | | #12

    FIRE !!!
    http://www.fema.gov/media-library-data/20130726-1652-20490-2869/fema_p_737_fs_6.pdf
    If you are going to build overhangs, they should certainly be of fire resistant material such as Timbersil. (I own no stock). I believe that in California codes in high-fire areas forbid overhangs. In short, unless you live in a location where you are sure there will never be a wildfire, use fire resistant materials. It will take a LOT of years for the energy savings to make up for a burned house. Not to mention the carbon footprint of incineration and re-building.

  13. Derek Roff | | #13

    Active shading?
    As Martin says, passive overhangs are always a compromise, since seasonal temperatures aren't symmetrical with sun movements. To say nothing of daily sun and temperature variations. Active shading is more common and has more well-built options in Europe, but is expensive. Mechanisms, and sometimes, homeowners, often stop working after a few years. Still, improvements arrive every year. Any chance you will create an article on recent active shading options?

  14. User avater GBA Editor
    Martin Holladay | | #14

    Response to Derek Roff
    Derek,
    Inventors have been tinkering with motorized awnings and motorized shutters for decades. As you point out, there are two big problems with these systems: the high initial cost of the equipment, and problems with durability.

    I suppose that GBA could review currently available hardware, including the best systems used in Europe. But I'm still skeptical about this entire class of hardware. I don't think that these systems are appropriate for residential applications.

    If anyone has seen a motorized shading device that combines a low price with exceptional durability, please let me know.

  15. Jin Kazama | | #15

    external roller shutters
    http://www2.heroal.de/www/de/fachkunde/heroal-systeme/rolladenrolltore

    is pretty hard to beat on quality and features from my past researches,

    They also have insulated aluminium rollers that could be used to raise up the insulation level of windows during night time.

    It is quite expensive though.

    As for late day south/west undesired SHG,
    the cheapest and most efficient solution is external reflective fabric roller shutters that are time autonomized followed by the cheaper interior solution of the same product.

    during heating season, shading east to south windows with overhangs/sunshades for high sun,
    followed with only a few hours of fabric roller shading on south/west -west windows provide more than enough protection from SHG and is pretty cheap to implement.

  16. Wilma Leung | | #16

    Beware of wildfire and emission plumes
    I agree with the benefits of an overhang, except that having a generous overhang could be a hazard under some special situations:
    - uplifts and dynamic wind load from coastal or uphill high winds
    - areas susceptible to wildfire
    - overhanging the plumes of emissions (moisture or heat), from same or neighbouring buildings

  17. W D | | #17

    Overhangs, window shading, and electricity savings
    Our house has generous overhangs on the south, west, and east sides, extending from 2' - 6'. Despite this and our shade trees, we had a fair amount of solar gain and I wanted to lighten the a/c load while preserving the sun's winter heating effect. That led to solar grates outboard of the window as an option with some pluses. The same geometry that makes an overhang or an awning work is active in a grate structure that is 80% open. Like an awning, indirect light passes the grate and enters the room. In addition, the direct sunlight strikes the grate and the visible frequencies reflect into the room. The effect is like having lighting panels on the wall instead of the ceiling. Meanwhile, the infrared portion of the direct sunlight is largely absorbed by the grate, leaving the room cool and bright. The grates are seasonal and are stored once the a/c season has passed. The mounting hardware remains in place and is unnoticed.

    The grates work. Load for the a/c is reduced at nominal cost and producing a 10 year payout in the Chicago area. Mounting takes just seconds. A view is maintained through the grate with the head-on view the least restricted. Appearance from the curb is changed. The grates are surprisingly robust despite their light weight. The wind just can't get a hold of them. Maintenance after 10+ years has been nil.

    I like overhangs. In addition, window treatments such as solar screens, functional shutters, films, solar grates, or awnings are worth considering for additional savings, with or without overhangs.

  18. Leta Bezdecheck | | #18

    Overhangs
    We have a situation where the wide soffit is so high above our door it affords little protection. Originally there was a transom window above the door but the ceiling was lowered so it can't be reinstalled. Also we have a very large window on the same southern side. Is there any low cost way (we are mom and pop business owners - i.e. not rich) to amend this odd design?

  19. User avater GBA Editor
    Martin Holladay | | #19

    Response to Leta Bezdecheck
    Leta,
    The photo does not clearly show any roof or soffit, so it's hard to judge what you have above the door.

    It should be possible to build a small roof to provide weather protection above the door in the photo. I can't comment on whether you can afford to pay for the work, however. If you would like to know what the work would cost, call up a few contractors and ask.

Log in or become a member to post a comment.

Related

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |