PDA

View Full Version : Garage door header



Allen
05-18-2001, 11:22 AM
Looking for info on the dimensions typically used for a header and jack posts on an eight foot garage door. There will be a second story above the garage.

Thanks.

Davo
05-19-2001, 01:15 AM
For an 8 foot span,use two 2X12s with 1/2 inch plywood sandwiched between them. Use glue or construction adhesive and nail approx. 16 inch OC using 12d nails. Nail 3 per vertical row. Nail on both sides of beam. (This is for a normal 2X4 width wall construction. If your walls are made from 2X6s, use three 2X12s and sandwich 1/2 inch ply between each 2x so as to have a 5-1/2 inch width)

Normally, this beam will sit on top of a trimmer stud at each end, and a full size stud (king stud) runs behind the trimmer. Both the trimmer and king studs are nailed together with 12 d or 16d nails. I usually use 16d and clinch them, or drive them more on an angle so they don't protrude too far through.

Use 20d (preferred) nails, or 16d and drive through king stud into header. Use 12d and toenail header into trimmer stud.

Some people use two (2) trimmer studs along with the king stud on each end of a garage door header, to give header more bearing support. Won't hurt a thing. Just size your opening accordingly(header length will be longer by 3 inches total.....1-1/2 inch per end)

I believe a doubled 2X 10 beam with ply will work for an 8 foot span, but I would opt to go a little stronger whenever possible.

Of course, your cripple studs go on top of header and your top plate should be doubled.

George Roberts
05-19-2001, 07:39 PM
2 #2 2x10's will span 8' with a 10' tributary load, and a floor and roof above.

Your local code might require 2x12's for all headers (mine does).

Larry Craig
05-20-2001, 10:36 AM
Nothing worse than wondering if your header will sag a little over time, use the 2" x 12"s. Don't forget to put your bow up if they have one.

Glenn A. Davis, P.E.
05-20-2001, 03:55 PM
Dave,
Wouldn't it make a big difference whether or not the garage door was on the gable in or on the side and which way the floor load is carried.

I believe in conservative design, but outright waste is waste. Overdesign is taking shortcuts at the owners expense.

What are your thoughts on this?

JIM B.
05-20-2001, 09:26 PM
Lately we have been using 14 in. microlams for garage door headers, nailed every 12 in. with a row of four 12d nails.

When I frame for any header at six feet, up to eight feet, I will dbl. jack it, if the header is eight feet or over I will triple jack it,probably doesnt need that much, but thats the way that I like to do it.

Davo
05-20-2001, 11:24 PM
Glen,

To be honest, when Allen mentioned that a second story was to be above the garage door, I took this to mean the header was for a load bearing opening. You're right, depending upon which way the above floor is loaded does make a difference as to whether or not the header opening is to be considered "load bearing" or not.

BUT, let me pose this qestion to you.... Suppose the garage door opening is on the gable end and is not a load bearing wall. How WASTEFUL is it to still frame this opening as though it was loadbearing? (ie....2 2x12s with 1/2 inch ply resting on doubled jackstuds)

Won't a garge door be opened thousands of times? Won't the extra stiffness help out if the door is connected to an overhead electric door opener? (especially if the door opener happens to be the torsion bar variety, which is attached to the header)

The COST associated with such WASTE will amount to less than $20 total; assuming you can use a scrap piece of 7/16 or 1/2 inch plywood, which is usually used for sheathing a new home, and should be easy enough to find at that jobsite. And, even if you had to go out and purchase a new, full sheet of plywood just for this purpose only, the total cost (plywood, one extra 2X12, 2 extra 2X4 jackstuds) would still cost less than $35 overall.

$35 for a lifetime of no worries.....I'd gladly pay that extra amount.

Let's say that for sake of argument, an 8 foot door opening should not have a beefed up header if indeed the opening is not load bearing. OK.......well, what if this same wall was instead opened to a 16 foot span for a double car garage opening......how would you frame this non-load bearing wall? Due to such a large opening, I would still opt to frame it as though it were load bearing and to make this opening as stiff as possible; regardless.

What's your thoughts on this? Do you think opening size should dictate how headers should be framed, irregardless of whether wall is load bearing or not? Or, in your opinion, does size of openings make no difference as to framing techniques?

Davo.

Davo
05-20-2001, 11:30 PM
Gl;en,

Please note, In my above post to you, I said "gable end" when referring to a non-load bearing wall. What I meant and should have said was the "sidewall end". I tried to correct the original post, but damn if I can figure out how to re-edit once I have already posted. Sorry.

Davo.

Glenn A. Davis, P.E.
05-21-2001, 11:20 PM
Davo,
You raise some good points. The question that comes in my mind is where do you stop adding strength to a wall?

I've been asking myself this question for over 30 years. When I first got out of school, the senior structural engineer in our firm would design fairly significant structures rather quickly by rounding up everything usually to make the math simple as this was precalculator days and ofcourse no computers. If he were designing reinforced concrete for example, He would round his demensions to the conservative side, conservatively round the numbers in the equations so he could do the math in his head, go to a rebar chart and round up to the rebar size. If the spacing needed came out to be 8 1/2", he'd put them on 6". Then after all that he go up another size just to be conservative.

Someone later pointed out the pitfalls of overdesigning rebar and he curtailed the practice.

But the point I'd like to make is that there are professionals who know what they are doing that establish certains standards for live load, dead load, fiber stress limits etc. The safety factors are already there in the protocol and that is the standard. To just keep beefing it up arbitrarily becomes a waste at some point.

I once saw a bay window assembly that had so many studs in it there was no room for insulation. That is not good. And worse, in tropical climates the interior walls will mildew where the studs and headers are.

People who build ultra conservatively because they don't know how to figure it or won't hire an engineer who can, and engineers who overdesign just so they can do it quick and know their ass is covered may not be providing what customers expect to pay for. At leat, that is what I am throwing out for discussion.

A good engineer can provide completely adequate strength without over doing it. A monkey can overbuild enough that he doesn't need to know anything about structures to know that it will be strong enough, but is that better?

Also I have seen hip roofs constructed so poorly that the framer put 4 or 5 braces under the ridge joints to make sure it won't fall and believes he is building a better structure. The owner has to walk around all those braces in the attic storage and will never be able to convert the space to living area with braces running diagonally to every nearby load bearing wall. I would prefer to design and build a good joint, make sure my loads travel well to the foundation and leave out all of those braces and still have a stronger structure.

As for the garage door header questions, technically everything is carrying some load whether it is considered a load bearing wall or not. I am suggesting that a designer/builder should adopt a standard and design to it. If he is uncomfortable with the standard, adopt a more conservative standard and design to it -- as opposed to beefing stuff up willy nilly. It doesn't do any good, for example to beef up a joist that is supported by a flimsy girder. Better use of the money would be to plan the design and make each component as strong is it needs to be.

Yes, the size and number of the jacks depends on the load and the span. Now that we have computers, it doesn't take long to size the members according to the minimum standard or whatever standard you choose. But I don't think it serves the industry well to just make things stronger for the sake of making them stronger.

As for the impact of garage door openers. I haven't seen a specific protocol on this. Some designer/engineer might decide the header size and then double the safety factor because of the impact loadings. That's OK but don't triple it arbitrarily just because its easy to do. That's my point I was raising.

On simple spans you come across in residential construction, I ussually design about 25% over minimum building code and try to be consistant. If a client was building a spec house and wanted it to be the absolute minimum, that is what I do.

It is painful for me to wallk in a new house and see fortyleban dozen studs under a steel beam because the thing is heavy as hell and probably carrying a lot of load. It makes me think that the designer/builder doesn't have a clue what his loads are. I would much rather know that because the load is 6000 pounds there are 3 studs under it, instead of putting 6 because I don't know what the load is and I'm willing to spend another $15 to be safe.

I don't believe it is good practice to make any wall "as stiff as possible" except in a case where there is no way to make the wall as strong as I know it needs to be. Then I would make it as stiff as possible if it would still meet a minimum standard.

glenn

Davo
05-23-2001, 02:18 AM
Hi Glen,

I was a carpenter in a steel mill for 10-1/2 years. about 70% of all our work was concrete related. Formed many a pour, both with common lumber and with panels; placed and tied off thousands of feet of rebar, and have placed many types of anchoring devices (ranging from the simple anchor bolt, to special all thread bolts up to 2-1/4 inch dia. and 5 feet long).

I know where you're coming from when it comes to concrete. Most, if not all our pours required more rebar, with closer spacing than was really needed.

Our Foreman would always ask us to figure out how many yards of concrete we would need for each pour. (He was too lazy to come down to the jobsite and figure it out himself.) Well, we all knew how to compute this; it's really not hard to do. We would report back to him with our figures and he would always add 2 to 3 yards extra to our number. He then would forward this number to our Asst. Supertendent for review, and he in turn would normally pad the amount needed by another 1 to 2 yards. This number was then forwarded to our Superintendent who actually called in the order, and (you guessed it) he too would pad it some. The trend of thought was that it was better to order too much, than be caught short, and risk a "cold joint" before another truck could arrive . On average, we always had at least 6 yards ( one time we had in excess of 20 yards!) that we did'nt need and it wound up being dumped on the ground. Talk about waste.

As for consulting with Engineers, it was next to impossible to get one to come down to our jobsite. The best we ever got from them, was a bench mark that they shot on an existing wall somewhere, and a set of prints that had been subbed out to some firm in Canada, and most figures were all listed in metric!

Although it was the duties of field engineers to work the transit and be at the site to field questions and interpret the spec drawings, those duties invariably fell into our laps instead. Field engineers were always scarce until the day of the pour; which by then was too late for changes anyway.

I am now in the residential contracting business and am looking at finding me a P.E. that I can use from time to time. Hopefully I will have better luck than what we had in the steel mill variety.

Since I am not a P.E. and do not yet have the good fortune to retain one in a business relationship,I rely on printed material made available to carpenters to help with my framing problems. Most, if not all of these tables dealing with span ratings for beams, girders, joists, rafters, and headers, were compiled by P.E.s like yourself. These tables are presented to us for the express purpose of being used.

Likewise, there are many other tables dealing with live loads, dead loads, wind shear loads, fiber stress, footing depths, frost depths, exposure ratings, etc. all being made to the carpenter/builder. All of these ratings were computed and checked by P.E.s

My point is this.....for most average situations, one can simply rely on the tables to figure out what is needed. Case in point.....You said you like to buid to the minimum allowed design factor and then add in 25% safety margin. OK, according to my header span tables, two 2X8s with 1/2 inch ply can safely span 8 feet maximum IF SUPPORTING ONLY a ceiling and roof above it. Add a 25% margin to this formula and you wind up using 2 2x10s with the ply. For a header to safely span 8 feet and support one floor, ceiling, and roof load above it, the recommended header size is two 2X10s with the plywood sandwich. (This second example is the example I assumed that Allen was referring to; although I agree assuming is dangerous.)Based on the 25% margin, this header would be adjusted to two 2X12s sandwiched; which was my original recommendation to Allen.

Allen did'nt give enough info, but if he had, ultimately your own criteria that you would use, and the listed table spans that I would use would come out to be one and the same. Is this by accident? I don't think so.

The building industry has relied on P.E.s and their special knowledge for over a century. Most of this expertise provided by P.E.s like yourself have been passed on in the form of tables. These tables are made available to builders all the time. When new materials are introduced to the builder (microlams; gluelams, hardi plank, etc.) almost always this material is accompanied by engineering specs that describe how and where this new product should be used.

I personally think it would be a waste of time and money to consult with a P.E. on every residential, run-of-the mill project. I believe P.E.s are best to be used when the builder cannot find any info regarding a specific problem. If there are no tables available, and no past experience can come into play on a unique situation, then by all means the builder should mnost certainly consult with a qualified P.E. to obtain the answers needed in order to build correctly.

One last thing, a lot of span rating tables were composed years ago and were for "old growth" lumber; which was quite a bit stronger than the common grades that are being milled out today. New growth lumber is not nearly as strong, nor as stable, which is why the gluelam, microlam, and other engineered wood beams are making such a popular entrance into today's market. However, not everyone can afford these new products; and, with all the formaldehyde glues and resins in some of these products, a lot of health conscious people don't want them. Hence, we must revert back to common lumber. Because the new lumber is not quite as strong as yesteryear, builders opt to go up a size or two over the recommended tables. Is this bad? I think when new tables start coming out reflecting only new growth type lumber qualities, you'll find the builders were "right on the money" by going a tad bigger.

As for "willy nilly," not all states require their builders to pass competency tests. This is a shame! Everyone who walks thinks they can "swing a hammer." Unfortunately, this is not so.It's these type of guys who give the industry a bad name. It's these type of guys who don't know that charts and tables exist; they just build the way they saw their Uncle do something one time! Because the almighty dollar takes precedence over quality, these type of guys have been able to survive, and good builders who won't take shortcuts, wind up on the losing side.

What we need are for all builders to be required to pass actual competency tests, and be properly licensed. When this finally happens, you won't see all the "shoe maker" jobs that you earlier described.

Have a nice day.

Davo.

Dick
05-23-2001, 08:44 AM
Davo & Glen:
Nice exchange on the problem from two differnet perspectives. There is a lot of truth in what both of you say.

Davo:
On the subject of competency tests: Licensing tests should be composed, at least in part, of essay questions and not just multiple choice. Here in California, many incompetent individuals get licenses by paying $200 to a "school" that provides them with questions from past tests. The state is tightening up by investigating experience, but a contractor is a business person and there should be a way of judging their ability to think and analyze problems. There should also be much more emphasis on the building code in use. Fortunately, California has gone to a state building code as opposed to every jurisdiction having their own version of a model code, so that is now possible.

Glenn A. Davis, P.E.
05-23-2001, 11:45 AM
Davo,
I enjoyed your story about the concrete- each person adding a little to be safe, and ended up wasting a lot.

I agree with everthing else you said. NOthing wrong with using tables (as long as you use the right table and/or the table is applicable to the actual condition.

glenn

George Roberts
05-23-2001, 07:07 PM

George Roberts
05-23-2001, 07:09 PM
I made the post about 2x10's being sufficient given 10' tributory load and 2nd floor. (I should add my name to the end of my posts).

The 1&2 Family building codes provide a reasonable level of safety and durability not a minimum level when properly used.

One could pick the worst lumber from a graded pile, position all of it in the worse possible manner, and use all of it at its code allowable limits and still build a house that meets minimum safety and durability standards.

But, in general, most building materials exceded the codified engineering requirements by a good margin, are used in a reasonable manner, alligned reasonably, and are not used near their allowable limits. Therefore we get reasonable houses without beefing up portions like this garage door header.

George Robert

Warren
05-23-2001, 08:16 PM
I too liked the exchange & perspectives of Glen & Davo. There is one subject not addressed though. How does a person go about choosing a "GOOD" engineer? Or architect? There seems to be a problem with large ego's from time to time. Case in point, we were opening up the back of a 2 story house for a 1 floor addition. We were to remove 18 Feet of bearing wall & install a solid beam to support the 2nd floor & the new roof. All designed by a so called good architect with an in house engineer. As we let the weight down on the wood beam we got better than 2 inches of deflection. As this was holding up the job, we went out & got a steel beam sized by the salesman at the supply house. NO DEFLECTION was seen. Just some very irate professionals at the architectural firm. We fireproofed the I beam then wraped it in wood. What this taught me (I was about 22 years old at the time) is that experience is sometimes of more value to our customers than a so called professional who is reluctant to get alittle mud on his or her boots & go out & see how things get done in the field. LEAD ON DAVO !!!

Richard
05-27-2001, 10:23 PM
Too much over thinking going on hear. For time and strengh just use a 4x12 with a single trimmer. Double trimmers are for openings over 8'. You waste too much time building a little header.

Greg Gibson
05-29-2001, 03:37 AM
I agree totally with Richard,and if you're still worried about the thing sagging go with a 4x14.

My God, It's only a 8' garage door opening.

Next thing I'll see is people trying to bill $400,000.00 for a damn single car garage.