Proposed Porch Header will be–>2ea.2×8 w/ 1/2″ ply sandwiched inbetween,… This header will be supporting 8′ long 2×6 rafters on 16″ centers on a 3/12 pitch….
Can i span 10’3″ with this size header?
There will be no ceiling on this porch/ just the rafters & battens holding up the tin roof…
I believe the load is 20# live load & 10# dead load…
IRC 2003….North West Ga.
ps. if i purshase a IRC book @ barns&noble will it have all this info in it?
paul
When deck posts exceed what the prescriptive code tables allow, it's time to consult a structural engineer for post sizing and possible bracing.
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Replies
Greetings B,
This post, in response to your question, will bump the thread through the 'recent discussion' listing again which will increase it's viewing.
Perhaps it will catch someone's attention that can help you with advice.
Cheers
http://www.quittintime.com/
I'm from canada so I don,t know what live or dead load has to do with it I would understand if you were talking snow loads anyhoo according to the canadian wood council span book 2-2x8 with a snow load rating of 20.9 psf(pounds per squre foot)will span a max of10 ft 1 / with a snow load of 31.3 psf 8ft 8 /with a snow load of 41.8 psf 7ft 9 also the wood species is doglas fir there is lots to consider these numbers also iclude the wall in which the header is to be sheathed in my opinion I would say the header is to small I would go 2-2x10 (the 1/2 plywood doesn't do much except fur the header out for a 2x4 wall i'm assuming) and would also go with two cripple studs on each side of the opening so each side of the header had 3-inchs of bearing(10 ft opening header is 10 ft 6 good luck
Live load is any passing load, like snow, wind, people...
Dwead load is the weight of the materials that are used in building it. They sit there dead without moving ( hopefully)
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I don't have an IRC2003 so can't look it up for you. Common sense (and some experience) tells me that it will probably be OK, but if you are worried go with a triple 2x8. If you go with the triple, loose the plywood - as far as I'm concerned, it serves no purpose in this instance other than to make your built-up beam 3 1/2" wide.
I wouldn't purchase the IRC2003 from a book store unless it is specifically for Georgia or before you find out if your state modifies the code - many do - and I think Georgia does. Who wants to buy a $60 book that is mostly right? :-)
Thanks All of u...
I will probably go with 2-2X10's
another question,
...this is a wrap around porch, and i am planing on using pressure treated from top to bottom (going to order lumber friday/ $5,500.00)...
....with all the problems i here about fasteners & ACQ,.........is it a good idea to go w/ all P-T ,...rafters and all?
If so what type fasteners would you guys use?
Dont really have stainless steel in the budget...
...but hey...
dont want to rebuild this thing in a few years because of corrosion
paul
did you say your rafters will be exposed w/o ceiling joists?
I would cover the undeside of the rafters with at least 3/8" ply, but thats just me....I dont see any benefit to using pressure-treated rafters myself.
You do have a point however regarding ACQ and corrosion. Be sure that any connections made between pressure-treated and standard lumber are with stainless steel (best) or other corrosion-rated fasteners. However, that being said, it is to my understanding that accelerated corrosion occurs in the presence of water/moisture.
i.e. an exposed deck with non approved fasteners will corrode quicker than non-approved fasteners in a covered up/non-exposed situation
>> However, that being said, it is to my understanding that accelerated corrosion occurs in the presence of water/moisture.
i.e. an exposed deck with non approved fasteners will corrode quicker than non-approved fasteners in a covered up/non-exposed situation <<
That is pretty interesting. I always wondered if that was the case but never had anything to back it up... You don't have some kind of document or something that states that do you?
Im sure I can find something....but, i know I have heard others talk about it on here
Yes - we have talked about.... and common sense would say that moisture is part of the corrosion process, but no one has showed me something more concrete.
The reason I ask is this: When I have a slab on grade home framed (with PT sole plates on the first floor) I have had framers go back around the house and toe-nail with HD gal nails. I'm not certain now essential this is, but I want to build quality houses... I need some kind of data to back up the idea.
ACQ lumber is made with ammoniated copper compounds.
Common and galvanized nails are made from steel/iron.
Corrosion is a matter of chemical reactions as defined by the principles of electrochemistry....the same chemistry found in copper alkaline batteries of everyday use.
If you look on a galvanic reaction chart, or a chemical electrolysis chart for metals you will find the metals are listed from high positive electromotive force down to the greatest negative electromotive force.
The further apart the two metals on the list the greater the potential oxidation (corrosion). Copper has a -.34 volt electrode potential and Iron has a +.44 for net potential of .78 volts. The copper is the oxidizing agent and corrodes away the iron.
The corrosion occurs with the movement of electrons through a "wet" environment. Therefore the reaction will occur in materials with a moisture content of greater than 18-20%. It will progress at the fastest rate in a saturated medium where the electrons are readily flowing between the metals.
Most lumber in the exteror environmenrt fluxuates in moisture content. Exposed treated lumber in most environments remains moist to wet most of the time and corrosion should be continual at varied rates. Areas protected from rain, but exposed to the elements will exhibit slower corrosion.
Likewise cold metal components tend to condense water on their surfaces from warmer moisture laden air...thus keeping the moisture content around hardware higher than other distance areas of a wood structure, and hence an enhanced rate of corrosion.
Yes, plain nails will be readily corroded if used in an ACQ open air deck. Plain nails used in the untreated rafters to connect to the top ACQ plate will still corrode but at a slower rate dependent upon the environment you build in.
Likewise inside a house with a conditioned environment of 30% humidity the rate of corrosion would be significantly reduced, with the exception of water leaks, and condensation issues.
The galvanized coating on nails and hangers is an amalgum of zinc, tin and lead, with tin being the main component. If you calculate the electrode potential difference between tin and copper, (which are closer together on the chart) there would be a potential oxidation differential of .48 volts which is a much slower rate of corrosion.
Eventually the galvanized will be eaten away, also. The only way you can eliminate the corrosion is use stainless steel fastners.....or eliminate the ACQ.
One additional illustration for Aluminum products in contact with ACQ treated wood.
From the chart with copper at -.34 and aluminum at +1.66 we have an oxidation potential of 2.00 volts. Which is equivilent to a very efficient car battery eating away at the aluminum.
ACQ treaters explicitly state that no ACQ is to be in contact with any aluminum product. Aluminum is corroded in just days to a visible amount of corrosion.
Fasteners aren't always what they are cracked up to be....
In a recent on site removal of an exterior temporary ACQ wooden handicap ramp to a church that had been installed for only 18 months, I was able to examine hundreds of ceramic coated, "approved for use in all treated wood", star drive screws.
All, with a few exceptions, showed signs of corrosion, and most had significant amounts of damage. Corroded diameters were visually seen as readily smaller than a fresh out of box screw.
Go to GOOGLE and type in "Galvanic Reaction", or "Electromotive Series" , "Standard Electrode Potential".....or dig out an old high school chemistry book and go to the index. Check out the chart.
The book setting in front of me dates to 1963 and the chemistry was well known long before that in the early 1800's.
I hope this is clearer than mud !
............Iron Helix
Very interesting.... and well written.
So, I wonder how CCA lumber fits into this picture? It too has copper in it - right? But not nearly as much? After years of working with CCA lumber I can't say I noticed or heard of a particular problem with corrosion of, say HD fasteners.
One additional comment: you said >> Likewise inside a house with a conditioned environment of 30% humidity the rate of corrosion would be significantly reduced << But the lumber inside a house is not at 30%, even when the indoor relative humidity is - not sure I understand that, but am pretty sure that is a fact. Maybe it's something to do with the difference in the way moisture in the air is measured as opposed to the way moisture in lumber is measured?
I've had occassion to measure moisture content (MC) of exposed wood and furniture inside a conditioned house. 10% was the lowest and the highest was 14%.
HVAC/gas systems with gravity vent flues can actually lower interior relative humidties to below 10%, which would cause all wood to further dehydrate. Newer high efficency 90+ gas systems do not reduce interior moisture to the same extreme.
I have checked MC in areas that exhibit mold/mildew and those areas read above 18-20%.. I have not had access to bottom stud wall plates for a MC test in normal conditions. Most of the walls I have opened have an obvious water problem. Ditto for crawlspaces/mudsills/box sills.
The potential for leaks and condensate in wall systems and crawlspace area that the treater, fastener mfg.s, and "best practices" ask for all fasteners in ACQ lumber to be a minimum of hot dipped galvanized. Only Stainless is corrosion proof with ACQ.
I have razed exterior structures at several sites that were constructed using CCA and hot dipped galvanized nails. Initial appearances at nail heads indicated little corrosion, but upon disassembly the nail shanks in the space between the 2x deck boards and the joist were extremely corroded...even to the point of failure.
So as time passes on CCA for exposed installations we can expect to see failures. Likewise if we use the corrosion ratio as expressed above we could begin to see galvanized fasteners in ACQ to exhibits signs of failure in 3-6 years.
On a current job site this fall some painted steel soffit fascia was applied directly on on ACQ treated subfascia. The manufactured calls for a barrier between the sheet steel and ACQ lumber. The installed fascia cover had to be removed the following week to install the barrier and the metal was already exhibiting corrosion.
Each nail or galvanized nail through a deck board is just a small continuously running battery....much in the same way that grade school science allowed one to make a battery out of a lemon or potato and two dissimilar metal nails...wire nd a voltmeter to measure the electrode potential difference.
As to your question about CCA. CCA is has a chemical core of copper complexed to a hydrated aresenic. The arsenate gives the wood a high resistance to mold/rot as the arsenate is toxic to organisms.
The down side to complexed copper arsenate is that when the treated CCA wood is buried it will eventually rot and the resulting residues are high in arsenate. Secondly if CCA treated wood is burned the arsenates are converted to simple arsenic compounds which fall downwind from the burn site and leach into the soil.
The arsenate residues are toxic to humans on contact, upon inhalation and ingestion from edible vegatable crops that uptake the arsenate from the soil. This toxicity is the main reason for the removal of CCA from the market.
In order to make the new ACQ treated lumber as resistent to rot and decay the copper content had to be increased signicantly thus increasing it's corrosiveness.
I've read corrosion comparisons of ACQ to CCA ranging from 5X to 7X as corrosive. Either value is an indication of how powerful this product can be as an oxidizer of other metals.
Interior air moisture is usually measured in terms of relative humidity(RH). How much moisture is in the air at a relative to the temperature of the air and how much water vapor could it hold is saturated. I.E...If the living room is 70 degrees and a humidistat reads 30 then the 70 degree air in that room contains 30% of the total water vapor that it could potentially hold.
If the amount of water is measured at a weight per volume per temperature then you can quantify the actual amount of watter as absolute humidity (grams of water per cubic meter).
So air relative humidity is not the same quantative measurement as moisture content of wood and those two numbers numbers cannot be comparative values. Granted there is a relationship between drying of wood in a house and the relative humidity of the house. Lower winter indoor RH will slowly dry and reduce moisture content (MC) of wood. Reverse happen in warm months.
..............Iron Helix
Yours is the most concise and thorough report or explanation I have ever seen on this subject!
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BLUSH!
Thank you for the compliment!
.............Iron Helix
In the air, relative humidity is a measure of what is, relative to what is possible. The actual amt of moisture in the air and the measurement varies widely according to temperature since warm air can carry more moisture than cold air can. It take energy to keep those little molecules aloft.But in wood, the measurement is one of actual moisture in the wood, I think on a weight basis. It changes very slowly while RH in air changes hour to hour
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very nice information. Kudos
IronHelix, you have a abundant knowledge on this subject...THANKS very much for the info...it is much appreciated ........
What is your opinion on "MICRONIZED COPPER. QUATERNARY" that some manufacturers are using like osmose UFP ?.....
What are the drawbacks if any?.....will it replace ACQ?
I do not have any direct info on the specific brand of treatment that you have mentioned, but I will search it out when time permits.
.................Iron Helix
Edited 1/29/2007 7:36 am by IronHelix
Lots of information available...Google "micronized copper quaternary"!
If this product works as claimed by the treater then we have moved back to the corrossiveness of CCA, which means HOT-DIPPED GALVANIZED fasteners that would last 15-25 years in the open (Decks, etc). And for a long time in dry building conditions,
They claim that aluminum can be placed directly against the MCQ....but they hedge on being firm about this by indicating that there are environments where this will not work. In wet and other listed enviroments they still ask for a separation membrane, or ask to reference to manufactures' specifications for installation.
My climate area has 44 inches if rain a year....so I would not put aluminum products in contact with MCQ in exterior applications.
I welcome this product and hope it proves to be as touted, it will take away a lot of liability issues for our current use of treated materials in structures.
Currently the down side will be the limited distribution and availability of this new product in our slow to change local retail environment.
.................Iron Helix
There have been a dozen photos and reports here at BT of the ACQ causing advanced corrosion in as little as a couple of months
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Well, friday has come and gone, but there is no need for PT in the rafters and beam.
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I don't think what you want to know is actually in the book.
0n a building 20' wide, 2 2x8s can span 7'8"...it drops about a foot for every 8' added in span...so, working backwards, it still might not pass inspection...even though I agree it will work.
I have 2x10s on my 8' porch...but then, I probably read too much<G>
Abe says, "Man, you must be puttin' me on"
God say, "No." Abe say, "What?"
God say, "You can do what you want Abe, but
The next time you see me comin' you better run"
Well Abe says, "Where do you want this killin' done?"
God says, "Out on Highway 61."