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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

Posted on Jul 11 2014 by Martin Holladay, GBA Advisor

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 gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss. 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.

Keeping water off of walls

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 rain.

[Photo credit: Olek Lejbzon & Co. / oleklejbzon.com]

Protecting siding. A house without roof overhangs leaves siding unprotected and vulnerable, like an orphaned lamb released near a pack of wolves. Unprotected walls suffer high rates of water entry, premature failure of any paint or stain, and premature siding failure.

[Photo credit: Martin Holladay]

Protecting windows and doors. Windows and doors can be protected either by roof overhangs, by recessing windows and doors in thick walls, or by including head casing and head flashing that are designed to be significantly proud of the siding plane. If you look at older buildings, you’ll often notice that the casing on window heads and door heads is substantial, and is often capped by a protruding ledger. These features help deflect rain.

[Photo credit: Five Star]

There are two reasons that all exterior doors need to be protected by a roof: to prevent jamb rot, and to keep visitors dry until the homeowners answer the doorbell. Although these principles are obvious, a significant percentage of exterior doors are inexplicably unroofed.

[Photo credit: John F IV / Flickr]

Getting rain to drip away from the foundation

Another function of wide eave overhangs is to ensure that roof water doesn’t drip near the foundation. Keeping the eaves-drip away from the house helps keep your crawl space or basement dry. (For more information on this topic, see Fixing a Wet Basement.)

[Photo credit: Martin Holladay]

Reducing splashback

Keeping the eaves-drip away from the house also limits the damage caused by splashback. Splashback is a common cause of siding rot.

Shading your windows

Roof overhangs can help shade your windows. In cold weather, any shade on your windows is probably unfortunate; in hot weather, shade is almost always welcome. Since shade is sometimes good and sometimes bad, window shading strategies are usually a balancing act.

Climate matters. If you live in Fairbanks, Alaska, you will probably welcome solar heat gain through your windows on almost any day of the year. However, if you live in Phoenix, Arizona, you may prefer all of your windows to be shaded in every season.

North windows. In the northern hemisphere, north windows don’t get much sun — so roof overhangs don’t really affect north windows.

[Image credit: © 2014 Home Power Inc. - http://www.homepower.com. Reprinted with permission. ]

South windows. Roof overhang length matters more on the south side of a house than it does on any other orientation. If you intend to follow traditional passive solar design principles — and it usually makes sense to do so — you will probably size the roof overhang so that south-facing windows are fully shaded at noon on June 21st (when the sun is high in the sky) and receive full sun at noon on December 21st (when the sun is relatively low in the sky).

While this describes the design goal, the result is not ideal. For one thing, in July and August the sun traces a lower path through the sky than it does in late June, so more sun may enter the house during the late summer than is desired, even though the weather is still hot.

Moreover, the sun’s path through the sky on March 21 (when weather may still be cool) is identical to its path through the sky on September 21 (when the weather may still be hot). Any attempt to balance solar heat gain through a building’s windows with outdoor temperatures faces an insurmountable obstacle: the planetary flywheel effect. This effect introduces a delay between peak insolationAmalgamation of the words “incoming solar radiation” that means the total amount of solar energy that strikes a given surface in a given time. It is commonly expressed in kilowatt-hours per square meter per day. and high outdoor temperatures.

A related problem: in all seasons, the sun is lower in the sky at 10:00 a.m. and 2:00 p.m. than it is at noon. So even if south windows are fully shaded at noon, they might receive unwanted sun at 2:00 p.m.

In spite of the fact that it’s impossible to achieve perfect shading of windows, it’s still worth following traditional passive solar principles when designing roof overhangs. A useful online tool to help designers with this task is Overhang Design. (The free software program is provided by a Seattle company called Sustainable By Design.)

If you are trying to achieve a good balance between solar heat gain and shading, you can tweak your south overhang to achieve the results you prefer. In a hot climate, you might want to lengthen your roof overhang somewhat, to favor shading during the shoulder seasons; and if you live in a cold climate, you might want to shorten your roof overhang.

East and west windows. Sunlight hits east and west windows when the sun is low in the sky, and it’s hard to control this nearly horizontal sunlight.

The larger the area of east-facing and west-facing windows, the more likely that these windows will cause overheating during the summer. As a first step, east-facing and west-facing windows should usually be fitted with low-solar-gain glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill., especially in hot climates. (In colder climates, where summer mornings are often cool, a little heat gain through east-facing windows may be welcome, so high-solar-gain glazing may make sense for east windows in some climates).

[Photo credit: Rose and Joe Schlatter]

Overheating matters more in late afternoon than in the early morning, so west-facing windows are the most challenging — especially in a hot climate. In a very hot climate, west-facing windows should be minimized or eliminated entirely.

It’s hard for roof overhangs to be wide enough to shade west-facing windows, especially when the west side of the house is one of the gable ends. If you want to shade your west-facing windows, the best approach is to include a deep porch on the west side of your house.

Roof design strategies

Having listed some of the reasons why roof overhangs are important, we can now address roof design strategies.

[Photo credit: TransylvaniaDreaming.eu]

Strategies for protecting doors. There are at least four strategies for protecting doors: making the overhang of the main roof wide enough to protect the door; integrating a gable or cricket with the main roof to protect the door; creating a recessed entry; and attaching a “roofette” to the wall above the door. (“Roofette” is my personal nickname for a small gable or shed roof that protects an exterior door.)

After a few years, the lower sections of the jambs of unprotected exterior doors begin to rot. Many carpenters and handyman make a good living repairing these rotten door jambs.

[Photo credit: ActiveRain.trulia.com]

If you don't want to protect your exterior doors with a roof overhang, at least make sure that the doors are recessed from the exterior plane of the wall.

[Photo credit: Martin Holladay]

“Brow” roofs. The roof overhangs on two-story homes are at least 17 feet above the lowest courses of siding, so they often do a poor job of protecting walls from rain. That’s why two-story homes often need a roof for every floor.

The usual solution is a so-called “brow” roof — a narrow shed or hipped roof attached to the wall at the level of the first-floor ceiling. If a brow roof is sized to shade south-facing windows in late June, it can meet passive-solar design principles while helping to protect the wall from rain.

Gable-end overhangs. Gable-end overhangs — that is, rake overhangs — extend to the peak of the roof. Since the peak is a long way from the base of the wall, these overhangs are less effective than eave overhangs.

[Photo credit: Casual Country Log Homes]

One solution is the prow roof overhang. While this type of gable-end overhang does a better job of protecting the walls than most rake details, some people don't appreciate the prow roof aesthetic.

[Photo credit: Martin Holladay]

A safer strategy is simply making a conventional rake overhang wider than usual.

[Photo credit: FloridaDisaster.org]

Sometimes it makes sense to frame wide rake overhangs with ladder-style outriggers. If the gable end is two stories tall, a wide rake overhang can be supplemented with a brow roof between the first and second floor.

[Photo credit: Tom Auger / Rever & Drage]

Modern design

In the middle of the 20th century, architects who embraced modern design principles often promoted buildings with flat roofs and no roof overhangs. Unfortunately, this severe aesthetic has not yet died.

[Photo credit: Ciiwa.com]

It's worth noting, however, that it's possible to embrace the modern aesthetic in a way that retains generous roof overhangs.

Can roof overhangs be too wide?

While it’s far more common for roof overhangs to be too stingy than too wide, some designers have gone too far and ended up with roof overhangs that are oversized.

For example, homes with porches on two or three sides can be dark and gloomy. Especially in cold climates, it’s good to let some sun come in through your windows.

Finally, remember that wide roof overhangs need to be properly engineered to resist wind uplift. In most cases, so-called hurricane clips (steel clips that attach rafters or trusses to top plates) are better than toenailed birds’ mouths. When in doubt, talk to an engineer.

Martin Holladay’s previous blog: “South-Facing Skylights: Threat or Menace?”

Click here to follow Martin Holladay on Twitter.


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Image Credits:

  1. Image #1: Static.panoramio.com
  2. Image #2: Allstate Exteriors / Roofinestimatorprowebsites.com
  3. Image #3: www.lovebeinganonny.com
  4. Images #4 and #6: Kenthillwebblog.blogspot.com
  5. Image #5: Syracuse Home Remodling / Allcraft
  6. Image #7: G. Mills / www.frontiernet.net/~gmills/garage.htm
  7. Image #8: Square Jer / Jerry H.
  8. Image #9: BungalowRestore.blogspot.com
  9. Image #10: Coconut Pete
  10. Image #11: www.KarenBenvinRansom.HoulihanLawrence.com
  11. Image #12: Paul Duncan
  12. Image #13: Media.merchantcircle.com
  13. Image #14: Blog.siffordsojournal.com
  14. Image #15: Building Science Corporation / http://www.buildingscience.com/documents/insights/bsi-063-over-roofing
  15. Image #16: Inspirtationalvillage.files.wordpress.com
  16. Image #17: Build LLC
1.
Fri, 07/11/2014 - 09:08

typo
by David Hicks

Helpful? 0

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


2.
Fri, 07/11/2014 - 09:11

Edited Fri, 07/11/2014 - 09:12.

Response to David Hicks
by Martin Holladay, GBA Advisor

Helpful? 0

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


3.
Fri, 07/11/2014 - 09:26

"like an orphaned lamb
by Patrick McCombe

Helpful? 0

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


4.
Fri, 07/11/2014 - 09:54

PERSIST overhangs?
by Mark Fredericks

Helpful? 0

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.
Fri, 07/11/2014 - 10:32

... could not agree more.
by flitch plate

Helpful? 0

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.
Fri, 07/11/2014 - 13:23

Response to Mark Fredericks
by Martin Holladay, GBA Advisor

Helpful? 1

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.
Fri, 07/11/2014 - 13:29

Edited Fri, 07/11/2014 - 13:31.

Flitch man, your knowledge
by aj builder, Upstate NY Zone 6a

Helpful? -1

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.
Fri, 07/11/2014 - 16:07

Edited Fri, 07/11/2014 - 16:11.

this is definitly on the list ...
by Jin Kazama

Helpful? 0

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.
Sat, 07/12/2014 - 15:20

Overhangs, window shading, and electricity savings
by w d

Helpful? 0

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 3-4 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.


10.
Sat, 07/12/2014 - 22:15

W D
by Jin Kazama

Helpful? 0

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.

sunshadeopc.jpg IMG00079-20101104-1443.jpg


11.
Sun, 07/13/2014 - 17:39

360 degree prevailing winds
by flitch plate

Helpful? 0

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.


12.
Wed, 07/16/2014 - 11:26

Edited Wed, 07/16/2014 - 11:27.

Comments by Lloyd Alter of Treehugger
by Martin Holladay, GBA Advisor

Helpful? 1

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.


13.
Wed, 07/16/2014 - 19:08

FIRE !!!
by John Mattson

Helpful? 0

http://www.fema.gov/media-library-data/20130726-1652-20490-2869/fema_p_7...
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.


14.
Thu, 07/17/2014 - 01:41

Active shading?
by Derek Roff

Helpful? 0

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?


15.
Thu, 07/17/2014 - 08:45

Response to Derek Roff
by Martin Holladay, GBA Advisor

Helpful? 0

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.


16.
Thu, 07/17/2014 - 14:18

external roller shutters
by Jin Kazama

Helpful? 0

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.


17.
Sun, 08/03/2014 - 01:58

Beware of wildfire and emission plumes
by Wilma Leung

Helpful? 0

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


18.
Mon, 08/11/2014 - 11:36

Toronto Eavestrough replacement
by umair habib

Helpful? 0

Thanks for sharing this article, its been a really interesting read. I haven't' ever dealt much with Toronto Eavestrough replacement before. I always thought it would be a simple enough thing to fix and deal with. I'm really excited about giving it a try and seeing how well it goes, thanks again for sharing!
Toronto Eavestrough replacement


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