Roof Overhangs -Why some home have none?
A general question. Why do so many home especially on TOH and Bob Villa etc, and i guess they are frequently New England homes, built with no overhang of the roof? I am not a home design expert. My present early 80s contemporary has a 24 inch overhang plus another 5 inches or so from the gutter. This helps greatly on water problems as in falling on doors and windows (reduces warping and cracking) , and when it hits the ground or a patio deck it splashes less on patio doors, foundation, and side of the house (wood lap siding).
Was the no overhang new england thing a style thing or some extended frugality thing? “Overhangs are evil excess’ etc etc. Are overhangs bad in snow belt? Seems with all the wood shakes (vice bricks in the South) they would need more overhang not less.
When I was a kid I lived in tropics – house had at least a 4 foot overhang – you could walk around the house in the rain and stay dry.
Replies
Shhh! Hundreds, if not thousands of carpenters are directly employed repairing the water damage caused by no-overhang construction. Too much talk on this subject could destroy an industry.
Bob Villa may not be a God
( your logo here) Turtleneck
That's a great question, wain. I grew up in New England and came West in my mid 20's. I've always been interested in buildings and that lack of overhangs on Colonial style homes is something I've thought about a lot through the years.
At first I thought it was the problem of supporting heavy roof loads, like snow, in the Northeast, but then I thought about the chalets I'd seen in Bavaria and Switzerland, with their great overhangs...
Or it might be the problem with wind getting under an overhang and lifting, but many other climates around the world get more wind than Coastal North America and as you said, overhangs are common on other styles of buildings.
Then, for a while I thought about timber framing, which predates the stick framing we use today, and maybe engineering overhangs on those big timber frames was not considered worth the work involved...
Add in to all that the immigration of trades people here from many parts of the world, and that they all brought practices with them that they might not fully understand, much the same way we do many things today we don't really understand, and it's not that hard to see why there are so many regional differences that don't seem logical.
"...our grandfathers built this way and their buildings lasted this long..." there's an underlying truth there that is hard to argue with.
It seems a larger overhang would be desirable to keep the water runoff as far away from the foundation as possible. Looks like shortsightedness from a practical point of view not to have larger overhangs. But that's never stopped anyone before. Actually in that point of view the whole idea of stickframe above ground and exposed openly to the elements could be debatable as a practical form of homebuilding also.
Character? I never had any problem with character. Why, people've been telling me I was one every since I was a kid.
Most sources I've read attribute the use of hip roofs with no overhang primarily for withstanding wind (especially effective with hip roof usage, > 100 mph winds, etc). Gable roofs (even with no overhang) are at a disadvantage in high winds.
On the lake side of the Wasatch range in Utah there are almost no buildings built with overhangs due to the frequent strong and steady winds.
One of best films I ever saw was of a Hawaii roof with overhangs lifted in one piece total off the building.
Of course, here in the Pac NW with steady rain, and only very occasional 100 mph wind gusts, the trade is usually to go with the overhang for drizzle protection.
Most uplift in high wind situations comes from the "airplane wing effect" of the wind passing over the top of the house.
Overhangs dont really contribute much to the uplift, unless they're really long.I used to work in a blanket factory, but it folded.
Overhangs are generally a good thing, especially on one story houses. Keeping rain water away from the building is not only good for the foundation, it also gives the windows and doors less water and less direct impact from water, so they leak less. Around here we have a lot of older buildings with little or no overhang because they used to build within 16" of the lot line, and the decision was to sacrifice rain protection for more square footage. Mine's like that, but being a tall two story (26 - 30 ft.) overhangs wouldn't help much.
-- J.S.
Maybe the new england practices of "no overhang" we see on TOH is a result of the stone work in England. I guess, with stone there is not much overhang at least without a big cost. But I am not a history expert.
It was always my understanding that the "Cape Cod", one of the styles typical to New England, didn't have roof overhangs so that the wind wouldn't have the overhang there as a handle to help tear the roofs off the houses.
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By working faithfully eight hours a day, you may eventually get
to be a boss and work 12 hours a day. - Robert Frost
You may be onto the root of it, Wain. Of course, I don't really know, but your thought makes sense. Early New England homes were patterned after English homes. Not only were English homes stone, thus not much needing the overhang, but the roofs were thatch. An overhand would be difficult to create with thatch. I would guess the "overhangless" practice continued as a habit and style until it was found that wood siding really benefitted from the protection an overhang might provide. Also, without modern insulation and venting knowledge, early attempts at overhangs probably produced ice damming, so they were not universally viewed as an improvement.
We don't even count the overhang in considering volumn etc here, Frenchy
Many European styles are not only stone but also they have interior or hidden eaves troughs. The lack of overhang in the old country may well have contributed to the fact New Englanders also avoid overhang.( why did Europeans not have overhangs though)
But there's more.
Most all of the old places (200 years or so) that I worked on have trees for rafters that were notched to set on the wall plate and trimmed on the top side in place to a string line. I don't see that as being very easy with an overhang.
But I also have to ask myself over the years why not shed that water farther away from the foundation so it doesn't hurt it or leak into the cellar - but remember that they used gutters to collect rainwater for personal use in a cistern. They weren't about to waste good rainwater on the ground!
There's still more...
Back in the days of no insulation, it wasn't a bad idea to have the sun hitting as much surface area as possible on your house, if you lived in a cold climate. Ancient architecture always placed opennings facin the east, not only for sun worshipping cults but also because after a cold night, it was a warm feeling to let some sun shine in. Notice that it is in the tropics and Australia ro the desert Southwest, that large overhangs are more common feature. You want to avoid having direct sun striking your house surface there so you create shade on the walls in various ways, overhangs, pergolas, arbors, trellises. These features we often look at as decorations had utilitarian purposes in older times. We have mostly forgotten their origins.
I had an old archy explain to me some of these things and even to the point of explaining some corbel designs are intended to divert water flow using surface tension in a copy of a design that goes back to ancient altars and blood sacrifice where the horns of the altar diverted the blood flow into basins.
I agree with what Boss had to say about wind lift being strongest at the ridge, as it passes over. I was once airborne there on a lake job. And most of the wind damage I have repaired to shingles has been within two or three feet of the ridge.
There's my two cents worth.
.
Excellence is its own reward!
Being paranoid, maybe its a cost thing on new homes. Considering the typical 2500 ft2 single story ranch, whats the cost savings to do it without an overhang?
Labor and materials + savings in paint labor and material?
Typical?
figure labor and added material somewhere in the neighborhood of a grand.. depends on too many things.
You're right about a lot of variables. I was thinking closer to between two and three grand for a two foot overhang all the way around..
Excellence is its own reward!
We have set backs from property lines and it starts at the roof . If there is doubt about getting a house on a lot legally , .... 2 feet becomes 16 inches, 1 foot, or none.
Hip roof design and no over hang provide the best 'tornado defense'. Tornados do some weird things that are not easily explained. Ive seen roofs taken completely off because of carports. But I dont think anyone can prove it because it might leave a house next door undamaged.
Two major reasons ; Cost . When you are trying to" get in " an effective price range, its an alternative to cut . Let us assume that we are qualified for 50,000, 75,000, 100,000. Those are the percieved price breaks by the buyers here in my area. [that one was for you Pif] Price a house at 76,000 and take a chance on loss of sale . This has been proved with groceries . But most importanly it has been backed up by the sales of homes. 74,900 should be the asking price. Then we want the inside to have WOW, but have a certain sex appeal on the out side. Lanscaping is most effective . Bye overhang ,..... possibly.
Logic and style. Many houses facing the west need a four foot over hang while two is minimum in this country. Its very hot here and we dont want the sun . Cooling is harder here than heating . The style of the house often determines the overhang from the picture it was found .
Tim Mooney
Edited 1/13/2003 10:59:30 PM ET by Tim Mooney
Tim - What part of the country are you referring to? Here, in San Diego, California, a 20% down payment is $70,000.
HAHAHA! I should have figured that would get a response , as it always has on here . That's the main reason why prices are no good to mention on here as we see a lot of posts asking how much. Piffin set me straight a long time ago on regional differences and that was a personal note to him above meant to poke him gently as he remembers I'm quite sure.
However the prices were used to show that pricing must stay with in "fixed amounts common to an area. Perceived value in a persons mind in a regional area.
I live in one of the cheapest areas in the US to build , jobs also pay less than most anywhere. I just read teacher pay in the paper and we are LOW on the list in the US.
Rural Arkansas , population 7558, but that was boosted by our Southeastern natives. Before that we were at 5000. Not close to any major city. But on the other hand we don't have any major cities. Sell out when you retire and live your retirement here , but you might other wise starve making a living.
Tim Mooney
Groing up in Mass, I remember being told that the reason houses on the cape didn't have overhangs as due to wind.
Blocking solar wasn't a consideration...and rain splash was handled with graduated reveals on the clap siding.
I prefer overhangs. In general, about 18" is the standard, along wth a nice return. Where I've seen it make the biggest functional difference is the life of the paiint/stain on the siding and exterior trim.
The reason most builders here in CT don't do overhangs? Cost. And that's from the mouths of the architects and builders. I figure the cost of a standard overhang at $70 a linear foot of roof edge per 12" of overhang. If the house had a 24" overhang and the total perimeter of a simple gable roof measured 200 feet (50 feet long gutter times two, 25' up the rake times four), the estimated cost of the overhang woud be 2 feet times $70 times 200 feet = $2800.
Just a wag, but it has worked.
Here's to eliminating pork chops.
We get some pretty hefty winds here on the PNW coast, particularly at the headlands. A lot of the wind damage occurs on the LEE side of the roof due to the vacuum created as the wind roars over the ridge.
One home I worked on about 3 years ago had a refrigerator sitting behind the house. Big storm blew in, 120 mph winds on that exposed hilltop, sucked that refrigerator away from the house and they later found it several hundred yards away, down in the woods on the back side of the ridge.Jules Quaver for President 2004
It could also be a zoning/ordinance thing.. Around here overhangs are considered structural and count towards the squarefoot you can build to.. For example We are restircted to no more than 15% of the land may be structural. Two foot over hangs would leave a lot of homes with no closets/ fewer bedrooms etc..
Let me start by saying that I am a fan of roof overhangs. I believe that the protection from sun and rain outweigh the negatives.
The reason that many New England homes are/were designed with minimal or no overhang and no gutters is that they contribute to ice damming.
Snow melt over the conditioned space of the house re-freezes at the overhang. Eventually the water can no longer flow down and backs up under the roofing. A heavy rain under these conditions can be disastrous.
Although less of a problem with todays "super insulated", "tight" homes, ice damming still occurs, even here in Southern New England in extremely cold, wet winters.
Eric Testani
Since the issue of roof overhangs and uplift came up, I decided to run a little test on our roof truss design program.
I started with a 32' common truss at 6/12. We do millions of them for houses in the St. Louis area. I ran an 80 MPH wind based on the latest specs we have for wind (ASCE 7-98, for you technical types)
These are the results I got:
No overhang - 62# max uplift
1' overhang - 91# net uplift (A 50% increase)
2' overhang - 117# net uplift (Almost double the zero overhang numbmer)
4' overhang - 172# net uplift (don't do many of these - Just ran this one to see how much diference it would make)
As much as I hate to admit it, adding overhang made more difference than I thought it would.
Please note that this is the first time I've admitted I was wrong here on BreakTime. Please write this date on your calanders.
And DON'T get used to it.A hangover is the wrath of grapes.
say the 117 ft uplift
is that per running inch of overhang, or per running foot , or what type unit?
Trying to get an idea what the uplift would be and also what the normal "holddown" strength of a soffit/roof edge is?
The 117# is the net uplift reaction on a truss that's 2' O.C.
In other words, you'd have to tie down each end of each truss to resist 117# of uplift.Corduroy pillows are making headlines.
Boss,
Thanks for running the numbers. Theoretical question (I know, I know...<g>)...do those hold down numbers (117#) at each connection point take into consideration the dead weight of the typical roof structure itself?
Theoretical example, of the uniform load, non-gust figuring, non-real world nature(<g>)...which as we al kknoow is no where perfect in the real world:
If I have 20 trusses, I have 40 connection points on the exterior walls. If the roof structure itself (trusses, sheathing, shingles) weighs 5000 pounds, I have a dead load of 125 pounds at each connection point. Theoretically (I know, I know...<g>), this roof could withstand that 117# of uplift as the wind lift would have to offset the weight of the roof before any net liftiing moment came into play at the connection points.
So, to restate...is the 117# number a gross number or is it a net lift, already offsetting a theoritical dead weight of a typical roof?
Thanks...
I suspect net means net
Anyone have a copy of Hooked on Fonics I can borrow?<g> I must have raced through the thread so fast that I forgot to read it.
The software allows you to specify how much of the typical dead load you want to apply during the wind uplift cases. We use 10PSF on the top chord and 10 PSF on the bottom chord for typical design loads. And we generally use half of that (5 PSF) as the ACTUAL dead for the wind runs.
So the numbers I gave you have already taked the weight of the roof structure into account.Atheism is a non-prophet organization.
Kahm-sa-hahm-ni-da!
(Thanks)
Boss,
One other question...is there a fixed pitch where the liftiing moment max's out and then starts too decline?
Example...a flat 2/12 would have little lift. An 8/12 would have more. When getting into Frenchy's world, a 27/12 starts acting more like a wall (zero lift, all shear) than a roof, so I'd guess that the lifting moment on a 27/12 would be less than the lifting moment on a flatter, more conventional roof. Less lift, but more lateral from the wind load.
Boss, way cool! what a neat bit of information! can you change the pitch how does that affect the uplift.. for example what would a 12/12 pitch do? (and while I'm at it a 27/12 or 17/12?)
Run the numbers for me and I'll vote for at least one republican in the next election!!
Edited 1/14/2003 12:28:37 PM ET by frenchy
If I get some time, I'll try some runs at different pitches. Not sure I know the answer offhand.
BTW - How will I know you REALLY voted for a republican ???Plan to be spontaneous tomorrow.
Not a problem,,
I always vote for the liberal and sometimes the liberal is a republican.. So far in every election I've given at least one (or more) republicans my vote.. 'sides, I live in a republican strong hold, you couldn't cast a vote for Mayor or council without getting at least a couple.
Had a couple of minutes to play around a bit more, and here's what I came up with for a 24' truss with 2 different pitches:
4/12 - Max uplift 83#
12/12 - Max uplift 55#
Makes me wonder - What pitch would give you the MAX uplift for a given set of criteria? I don't have the time to experiment with it.
The max HORIZONTAL reaction went from 72# at 4/12 to 308# at 12/12 however.
.
I could run some numbers on 27/12, but would have to use a MUCH smaller truss. The program doesn't work well with anything over 14' tall.Dancing cheek-to-cheek is really a form of floor play.
Very interesting, When fine homebuilding did an article on truss attachments they discovered that the typical toenail only required 208 pounds to cause it to fail.
Thanks Boss, I have never seen a chart like that before . It is helpful.
"I started with a 32' common truss at 6/12. We do millions of them for houses in the St. Louis area. I ran an 80 MPH wind based on the latest specs "
Ok, you had to start somewhere . [80 miles an hour] Arent tornados rated at 180 miles an hour ? I was thinking hurricanes run at 80. Any way it seems a low number to consider in a tornado area like where I live. Have you got any information on hip construction values , or would a truss guy be interrested in that kind of number?
Tim Mooney
I just picked 80 MPH as an arbitrary number - It's fairly common in specs for commercial projects. I've read articles that said designing for wind speeds over 110 MPH has little additional benifit, but costs a great deal more. (Don't remember where I read that, though)
You could spend weeks and weeks studying every possible condition for wind uplift. I just don't have that kind of time.
I don't think anyone has said that you should design for tornadoes. Don't even know if it's possible.
The point I started out to make was that overhangs didn't make much of a difference in wind design. But it ended up making more of a difference than I thought. I'm actua;y surprised - I figured I would get some serious crap fer that...........(-:Q: What do you call a woman who knows where her husband is every night?A: A widow.
the early new england homes had little overhangs mostly due to their construction.. they were hewn , usually oak framed, and the common rafters had no birds mouth.. just a seat cut , fully seated on the plate , probably a 6x8..
anyways.. the overhang detail had more to do with building in the manner they wre trained, the english idiom..
any extension of the eaves required additional trim wood.. which was just not in the cards for the frugal new englanders...Mike Smith Rhode Island : Design / Build / Repair / Restore
I can say that no overhang for uplift is never a consideration here , plus there is no break in insurance . I checked that already.
Tim Mooney
> Ok, you had to start somewhere . [80 miles an hour]
A DC-3/C-47 will fly quite nicely at 80 MPH, so it's possible to get significant lift at that speed.
-- J.S.
What effect would adding "hurricane" ties to every rafter or truss/top plate jucture have? Would that make wider overhangs more practical in high wind areas, or would the whole house just blow away?
Jen
Whatever works!
I certainly want Boss to answer his own thoughts . I want to give my two cents to your question.
I live in tornado alley in Arkansas. Ive worked 4 tornados personally , and Ive seen several more here I didnt work because I was preoccupied. I dont speak with hurricane experience.
The damage done by tornados is really magical. Too many times there is no reason accountable for the kind of damage they cause . I have seen tornados demolish to the foundation one house and leave the ones around it with some missing shingles. I worked several houses in an addition that had shingles missing. One house in the addition had its entire roof system in tact sitting on the back lawn. It separated the trusses plus drywall ceiling intact. The roofing on that lawn roof had about the same amount of shingles missing. All houses on that street but a couple on the end were build by the same crew. 16 inch overhang on every house.
To try to answer your question ; you would never know . It might take some shingles from it and it might take it to the ground in a scattered pile of tooth picks. You may not even see the house as it went up in the whirl and came down like scattering litter from a spreader truck.
They found a flat bottom boat 12 miles from the owners yard . The new owners tried to registrer it because there was nothing wrong with it . The numbers on the boat showed the owner , and they were called.
Weird stuff,
Tim Mooney
Tim Mooney
Hi Everyone,
I'm working on a 2 story addition now with some pretty good overhangs.
To me the bottom line on why you don't see them much is cost and the pain of building, trimming and painting them.
These are relatively simple with T&G wainscoting over the lookouts and 5/4 fascia. But hey the materials add up to easily 1200.00 plus extra roofing, painting and the labor involved. Also involves a lot of extra planning upfront for design and structure.
I think they make great sense and are attractive as well.
If I could get my digital camera linked up to my new mac I'd post an image.
Tom
Your 2 cents are always welcome...that is something right out of the Twilight Zone...one house completely gone and the one next to it with hardly a scratch...that scares me more than earthquakes.
For the last few years we've had small tornadoes here and there in LA county...I saw a funnel cloud in Oxnard once...looked like a long grey finger hanging there, didn't touch down though.
If we could afford it, I'd like to tear the roof off of our house and put in trusses to get a nice, clean roof line and a good overhang...keep rain off the stucco and windows.
Jen 8}
Edited 1/15/2003 12:01:27 AM ET by Jencar
We had a waterspout come in off the ocean and hit my parents' house in San Pedro. It stripped the flat roof down to the plywood for about 4-5 squares along one side, and 12 feet from where the roof was gone, eucalyptus leaves and pods on the roof were undisturbed. It was as if a giant end mill had taken a 1/2" cut off the house.
-- J.S.
San Pedro? The one in So Cal? If so,that water spout is a little too close to home for me. Global warming is knocking on the door...
your roof story beat Tims...sorry Tim (but at least it wasn't your parents house that was relieved of it's roof)
Jen 8)
> San Pedro? The one in So Cal?
Yes, just a little way up the coast from Western Ave.
Global warming is fun. The phenomenon is real, but there are huge mistakes being made about what causes it. The surprise is that it has happened before. The earth's climate on the long scale of tens of thousands of years is not stable, and what we're accustomed to is not the only "natural" condition. Alas, there has been no legitimate science in the area since it all became politicised.
-- J.S.
Usually major climate changes stretch over lifetimes, so they're not as detectable. The melting of glaciers and the ice caps has accelerated visibly over the last 50 years, so as you say, this may be attributed to the planets normal cycle of temperature change, or not. Who knows? But that's no reason for us to devolve environmental protection strategies, as our current administration is trying to do.
When I can see the mountains during the summer around here, I know my family is not breathing as much crud, at least the visible kind.
Also don't you think it was extremeley weird for the temperature here (in the Valley) to hit almost 90 degrees today?
Jen 8}
> Usually major climate changes stretch over lifetimes, so they're not as detectable.
Major climate changes are pretty rare, so we don't have a lot of direct experience as to how long they take. We know more about the last few ice ages than most other conditons that differ from the experience of our own brief lives, mainly because they moved more stuff around and left more evidence. But there is also good evidence for at least two periods of sort of the opposite of an ice age, a global warming. Looking at dendrochronology (tree rings) in North America, cores from the second Greenland Ice Sheet Project (GISP2), and lake sediments in -- I forget whether it was Africa or Asia -- two of these hot spells line up with the Intermediary Periods which separated the Old, Middle, and New Kingdoms in Egypt. Somewhere I have a couple papers written by Barbara Bell in the early 1970's on the idea that this kind of natural global climate change may have caused these two periods of crop failure and chaos in what is still our longest lasting civilization. The transitions do seem to have been reasonably brief, 50 - 75 years IIRC, and the hot spells lasted a century or two.
With known hot events starting around 2200 BC and 1200 BC, and perhaps a new one starting now, it looks like the planet may have three modes, and it may flip between them randomly over the long term: ice age, global warming, and what we've come to think of as "normal". But if two of them are perfectly normal and natural, why not all three?
> But that's no reason for us to devolve environmental protection strategies, as our current administration is trying to do.
Indeed not, nor is there good reason to blame our technology for causing what may well be a natural phenomenon, and discard it just when we need it most. The right approach may be a Manhattan Project for HVAC, and to grow our food in Canada and Siberia for a century or so.
> Also don't you think it was extremeley weird for the temperature here (in the Valley) to hit almost 90 degrees today?
Unusual, but not a record. It takes a lot more comparison of current and historical data to say whether anything statistically significant is going on. Such comparisons last time I looked were yielding a definite maybe.
-- J.S.
I like the idea of temperature cycles a lot more than the notion that we are provoking the phenomenon. It's not as scary that way. Give it a hundred years or so, it'll swing back to normal...
An article in the Times this week was intriguing...The Northwest Passage is Thawing...
For 500 years, explorers nudged their ships through these Arctic waters, vainly seeking a shortcut to the riches of the East. This deadly maze of sea ice still holds the traces of those who failed. Whole expeditions, hundreds of men and entire ships are missing to this day.
In the summer of 2000, Canadian Mountie Ken Burton gingerly nosed a 66 ft aluminum patrol boat into the heart of the Northwest Passage. There were no ice bergs, no sheets of pancake ice. Burton cruised past emerald lagoons and sandy beaches. "We should not, by any measure, have been able to drive an aluminum boat through the Arctic", said Burton, still astonished, "It was surreal"
The once deadly route has been re-christened "Panama Canal North" by shippers eager to shave nearly 5,000 miles off the trip from Europe to Asia.
Pretty significant illustration that something major is going on with our climate.
Read a book that suggested that the present location of the Arctic was due to a "Pole Shift", that until then the North Pole was in the vicinity of Canada/N America. It speculated that Greenland and Iceland once had ####more temperate climate, and that the present N Pole is hiding the continent of Atlantis...the original birthplace of Civilization. Looks like we may find out after all the ice melts...30 years or so?
Jen 8)
Ice Ages Happen
> I like the idea of temperature cycles a lot more than the notion that we are provoking the phenomenon. It's not as scary that way.
Or maybe scarier. If we didn't eff it up, maybe we can't fix it. Maybe it's a mistake to try. But on the other hand, if the Egyptians survived it twice before at least we know it's probably survivable. Ours could be bigger since it's 3000 years since the last one, and theirs were only 1000 years apart. It seems to be random rather than cyclic.
> The Northwest Passage is Thawing... Pretty significant illustration that something major is going on with our climate.
Yes, that's interesting.
> Read a book that suggested that the present location of the Arctic was due to a "Pole Shift"
Yes, there have been lots of pole shifts, magnetic North and South getting swapped. As the tectonic plates drift apart, the Atlantic ocean widens at the mid-Atlantic ridge. Lava comes up there and hardens, and leaves in the newly hardened rock some magnetic stuff that's aligned with the earth's polarity at the time. Numerous alternating bands on both sides of the ridge show this. But the time frame is much longer for that, IIRC something like 20k - 100k years. There's also the 26,000+ year cycle of precession and nutation of the axis, basically on the long view of things, the planet wobbles like a toy top. That's what makes the North star a temporary thing....
And to think this all got started with roof overhangs.... ;-)
-- J.S.
Roof overhangs, yep, I like 'em...
So maybe the Earth is in the process of initiating another pole shift, and our friends in Maine, Ohio, and Michigan own real estate at the Future (in 50,000 years) North Pole? That's my last silly question....
Thanks for your learned interpretation....8)
The magnetic poles differ from the rotational axis by a little, but never by that much. The charts that sailors use for navigation specify the magnetic deviation you have to add or subtract from your compass reading. The deviation is given as of the year the chart was published, and the change per year is also given. This is getting into very vague memory, but I think the magnetic poles stay within a few hundreds to maybe just over a thousand miles of the geographic poles.
Then once in a long while, the magnetic field shuts down completely and reappears the other way around, with South magetism where North was and vice versa. That's a pretty significant thing for life on earth, because the magnetic field pushes a lot of radiation from the sun away from us and to the poles. That's what causes the auroras. We'd see them everywhere during a magnetic shutdown.
The axis of rotation stays the same, and it's what we use for our system of latitude and longitude. The wobbling like a top is that axis moving around a little relative to the rest of the universe.
I like overhangs, too. ;-)
-- J.S.
"your roof story beat Tims...sorry Tim "
If one cant find the strategy in winning then he must turn to the exellence of defeat to enjoy lays potato chips throughout the game. For as they say;
Its not if you win or lose , its how you watch the game ! Gotta have class ! hahahaha
Tim Mooney
I was just kiddin, because your story beat any other weather story I've ever heard, his was just a bit different than yours (and in my neighborhood, yikes!) ;)
Jen
I was playing on that new commercial on tv is all. I guess you havent seen it.
Tim Mooney
Nope, but I did have some KC Masterpiece Lays before we had spicy chicken (frozen) pizza for dinner...yum yum..
Don't watch much TV...when those telemarketers call my husband tells them we live in a cave, and don't have electricity or a phone!???
Jen ;)
"What effect would adding "hurricane" ties to every rafter or truss/top plate jucture have?"
Depends on how well they're installed.
Most tie-downs I've seen just hold the truss down to the inside of the top plate, like this one:
View Image
This does little, as the top plate is typically just nailed straight down into the next top plate. So the top plate can come off easily with the trusses.
For the ties to work best, they should be tied to the whole wall - Maybe tied to a stud, such as with this type of hanger:
View Image
That will (probably) prevent the roof from being picked up off the structure, such as in the example Tim mentioned. But the walls need to be held down somehow. Typically they're just nailed down through the sub-floor, which had little strength in withdrawl.
Personally, I think the foundation anchor bolts should be run up through the wall bottom plate, and the nuts and washers should be on top of the bottom plate. Then the wall studs should be tied to the bottom plate with something like this:
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That way the roof system is tied directly to the foundation and the house is much less likely to take off for Kansas.
That's the "Boss Hog" version of how things should be done. Banning the bra was a big flop.
If I ever build a house it will be with even wider overhangs than I have now.
I live in the Southeast hurricane belt, but I think the water avoiding aspects of a good overhang are worth it. I see main entrance doors totally exposed, nicely varnished when new and a few years later look terrible - paint popping, door panels coming apart. Same for water falling on the top of windows and on the windows and their sills themselves. Some of the sills on the few exposed windows on my home slightly sloped in toward the house, a unique feature - I solved it by grinding an angle on the exposed edge of the sill.
I have many tall and narrow "casement" type windows that stay totally dry in a heavy rain as they are under an overhang.
Plus insurance will replace a roof in a hard blow but not pay for wood rot and behind stucco rot.
My area was a DIRECT hit of hurricane hugo - 125 mph winds which blew down 27 tall trees in my yard some of which fell throught the 2nd floor into the first floor but the roof did not lift. either nailed well or lucky.
I once heard Andres Duany, the "Neotraditional" architect-guru, tell this story on himself. A rich client commissioned him to build a million-plus house on a Caribbean island. The island vernacular was hip-roof, no overhang. His analysis said that sun glare and heavy rains called for large overhangs, which he designed. After the first hurricane, his client was roofless, and the relatively poor islanders with their old half-#### self-built houses still all had their roofs, just as they had for many hurricanes before that. He designed the replacement roof with a hip and no overhangs. His lesson: ignore local traditions at your peril.
An alternative lesson would be: If you're going to build a roof with eaves in the Caribbean, pick a design that will withstand hurricane force winds.
I agree - lots of tropics homes have big overhangs due to the near constant rain.
Speaking of Kansas, I noticed just this week that a bunch of duplexes... Errr Townhomes, being built near here have a new way of tying the wood to the concrete.
When the foundations were poured they put in a long strap with a couple of rows of offset holes. They look like some of the Simpson strap ties.
Like this.. Except Simpson doesn't show these as being for that use.
Anyone ever see such an animal?
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Those are Simpson STHD's, Ken. We use them all the time out here in the Pacific Northwest. They're imbeds we pour into the wall. Basically, anytime you have less than a full 4 foot panel, like say a short return on the front of a garage, or say you have a door within 4 feet of a corner, you have to tie the framing to the foundation with more than anchor bolts or staps. These are the cheapest way to go about it, but we also imbed 3/4" diameter bolts, strategically placed that extend up through the joists, sub floor and bottom plate, then use HD2A's for much the same application. Big pain in the butt, is what they are.
Man, that's a long one! Don't tell me that it goes all the way from the bottom plate, up along a corner, and nails to the top plate? Naw, you wouldn't need THAT much continuity...maybe something to do with a framed fireplace? What do you tink it is for?
Jen 8)
Ken,
As explained in another reply these straps are used to connect the wall to the foundation. The reason they are used in the Great Northwest is due greatly to the fact that we have a problem in that the earth keeps moving around on us. Usually little rockers but sometimes fairly large jolts. They are required for shear wall requirements.
JasonIf it wasn't for bad luck I wouldn't have Any!
The roofing book by Tauton press has a wonderful article about roofing ties.
It depends entirely on which tie you use. Number went from 208 pounds for a toenailed rafter to approx. 3500 pounds for a 3/8ths inch lag bolt. simpson ties were in between.
Have you noticed that their books on anything (tile, drywall, framing, etc) seem to be the best on the market? The most informative, the best authors, and answer any question you could come up with about a subject.
(I'm not in the habit of saying nice things if I don't mean em, either)
Never framed a roof before except a baby one in apprentice school. It's another area of my education that's been neglected, that and tiling.
Is it getting any warmer where you guys are at?
Jen 8}
Colder,, next week promises to be the coldest so far this year..
Tomorrow when I'm up on the roof if the wind is still blowing at over 30 mph promises to freeze me solid! I wonder what the wind chill is, I'll bet it'as below 20 below right about now!
As for Tauton press, I'm convinced I've put the editors kids thru college with all of their books that I've bought...(and not some cheap state colledge either, harvard or yale)....Grin..
Edited 1/17/2003 10:17:16 PM ET by frenchy
Boss does your soffit connections back to the house improve the hold down strength of the roof?
ANDYSZ2I MAY DISAGREE WITH WHAT YOUR SAYING BUT I WILL DEFEND TO THE DEATH YOUR RIGHT TO SAY IT.
"Boss does your soffit connections back to the house improve the hold down strength of the roof?"
I doubt it would help any at all. It could, if it had a substantial attachment from the truss to the wall. But that's typically not the case.Sea captains don't like crew cuts.
Boss Hogg - Interesting study. Looks like the overhang performs much the same function on a roof as flaps do on an aerofoil. Although, I am with you on your original instincts - the numbers do seem inordinately large.
I'm curious about how you entered the overhang data. When you added the overhang for each successive calculation you made, did you add it to a successively smaller theoretical roof, so that the actual roof size remained constant in each case? (i.e. a constant-sized roof on progressively smaller houses)
This would show how much of the lift is due to specifically the overhang, or whether the majority of the increased uplift is simply resulting from an increase in roof size.
Now you've got me, (and maybe you too) in suspense. Regards - Brian.
ps. Up here in the True North strong and freezing: Small or no overhang=cheap look ; Large overhang=quality look. (except when trying to mimic a certain historical style)
Anybody used Kevlar straps?? I saw it ones a a show on TV. They had a continous connection from the trusses to the foundation. It was expensive though.
I spec'd expansion joints for a pedestrian bridge that had kevlar in it about ten years ago. The kevlar added added strength to the bonded neoprene foam. The lab pictures showed the joint return to normal after being crushed, pulled, and twisted. So, basically the joint can resist bullets or Godzilla. It was really expensive, but the Godzilla resistance won over the client....that's not a mistake, it's rustic
There's one drawback to roof overhangs that hasn't been mentioned. Fire.
Here in Colorado (the whole SW for that matter) we are sometimes at a very real and frequent risk of losing life and home from fire. Overhangs act as a "catch" of heat and often times is fire's first way in. In this area we are not facing the same regular rain (and it's damage) as you New Englanders, so rot damage is not as serious a concern.
I seem to recall an article in FHB several years ago that showed the sole surviving house in a California fire. The author wrote to some degree about this very issue. Among other things, overhang size and materials was a critical fctor.
Seth
mistake. There is no win
and there is no fail . . . there is only
make."
John Cage
Just a wild guess but isn't it because an overhang would cause an ice dam to form.
I do not live in the narwth, but I thought ice dams were caused by a warm roof - seems the overhang part would be colder??
But things are usually mo complicated than they seem
The snow on the warm part of the roof melts, runs down the slope until it hits the cold part, and freezes into an ice dam.
Actually, ice dams come from a roof w/ an uneven temperature.
Just did tons of research on them to get rid of the ones my house gets. Seems to have worked, none so far.
In my case, what caused them was lack of ventilation. When originally built pieces of fiberglass insulation were placed over the walls to keep insulation from blowing into the soffits. I got horrible ice dams on the roof above these spots.
What happens is the top of the roof would warm up from the sun and water starts to run down the roof. When it hits the area w/ the insulation the insulated roof section is still cold causing the water to freeze and form an ice dam. I added soffit vents and air chutes on the South side of the roof and my 4-5" tall ice dams are completely gone this year.
A warm roof, usually from leaking heat into the attic is more likely to form icicles. Though ice dams can also occur if there is a great deal of heat leakage. Ice dams forming when the water hits the colder soffit area.