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Old 01-17-2008, 08:19 AM
Emilio Lizardo is offline
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Hey engineers -- how tall can you build with 2 x 4s?


Theres a new residential housing complex under construction near me; a series of buildings containing about 250 units. They are five storeys tall, and they're framed with freaking 2 x 4s! I can't get close enough to check with a tape measure, but they appear to be on 12" centers, with prefab trusses for joists, and trusses in place of traditional cripple studs over the larger window openings on the exterior walls. The stairwells and elevator housings are built with concrete and CMUs, but everything else is wood.

Is five storeys a realistic limit, or can buildings designed to carry these types of loads be built even taller using only 2 x 4s? What would be needed to make a wood sky scraper?
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Old 01-17-2008, 08:33 AM
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How do they deal with fire safety?
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Old 01-17-2008, 08:44 AM
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Are you sure they're 2X4's? Most jurisdictions have modified their code to require 2X6's, for increased insulation and strength. I doubt they would use 12" centers throughout construction, it's impractical for several reasons. As to a 5 story wood framed structure I'm not an expert, but it seems a bit much if all the elevations are independent, as you say.
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Old 01-17-2008, 09:01 AM
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I must say that I'm astonished that they would build a five-story building using wood frame construction, especially out of 2x4s. Also, putting the 2x4s at 12-inch O.C. seems pretty impractical. There would be hardly any room for utilities in the wall cavities.

Building codes for residential construction (up to three stories, IIRC) usually require 2x4s at 16-inch O.C., or 2x6s at 24-inch O.C. (I built my two-story house using 2x6s at 16-inch O.C. )

I'm particularly surprised because any multi-story building built to commercial standards (which generally includes apartment complexes) is usually built using steel columns (i.e. I-beams) along with non-load bearing light steel framing. The exterior sheathing is usually Dens-Glas instead of plywood, and the floors are usually concrete. Often you see concrete masonry units (CMUs) used for walls as well, especially on the first floor.

The general guideline that I've heard for wood-frame construction is a maximum of three stories, and again, this is generally only used for single-family houses and townhouses.

That being said, I don't know what the building code requirements are in your area. Presumably the builder received a building permit, and the local building inspector is conducting inspections?

P.S. While I am an engineer, I'm not a structural engineer, so take this all with a grain of salt.
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Old 01-17-2008, 09:07 AM
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On a semi-related hijack (I apologize), I live in a three-story apartment building built in the 20's... Is it still likely constructed/framed out of wood?
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Old 01-17-2008, 09:08 AM
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Is it possible the concrete walls are being prefabbed off site and the 2x4's are for aligning the walls when thay are later dropped into place? The 2x4s could also be part of the frame for molds used to pour concrete onsite.
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Old 01-17-2008, 09:12 AM
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Can you post a picture, so we all can have a squint?
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Old 01-17-2008, 09:25 AM
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118 meters


http://en.wikipedia.org/wiki/Gliwice_Radio_Tower

Quote:
Originally Posted by mks57
How do they deal with fire safety?
Quote:
* fire-resistance rated walls
* Firewalls not only have a rating, they are also designed to sub-divide buildings such that if collapse occurs on one side, this will not affect the other side. They can also be used to eliminate the need for sprinklers, as a trade-off.
* fire-resistance rated floors
* occupancy separations (barriers designated as occupancy separations are intended to segregate parts of buildings, where different uses are on each side; For instance, apartments on one side and stores on the other side of the occupancy separation.
* closures (fire dampers, fire-resistance rated windows and fire doors. Sometimes firestops are treated in building codes identically to closures. Canada de-rates closures, where, for instance a 2 h closure is acceptable for use in a 3 h fire separation, so long as the fire separation is not an occupancy separation or firewall. The lowered rating is then referred to as a fire protection rating, both for firestops, unless they contain plastic pipes and regular closures.)
* firestops
* grease ducts (These refer to ducts that lead from commercial cooking equipment such as ranges, deep fryers and double decker and conveyor equipped pizza ovens to grease duct fans. In North America, grease ducts are made of minimum 16 gauge sheet metal, all welded, and certified openings for cleaning, whereby the ducting is either inherently manufactured to have a specific fire-resistance rating, OR it is ordinary 16 gauge ductwork with an exterior layer of purpose-made and certified fireproofing. Either way, North American grease ducts must comply with NFPA96 requirements.)
* cable coating (application of fire-retardants, which are either endothermic or intumescent, to reduce flamespread and smoke development of combustible cable-jacketing)
* spray fireproofing (application of intumescent or endothermic paints, or fibrous or cementitious plasters to keep substrates such as structural steel, electrical or mechanical services, valves, liquified petroleum gas (LPG) vessels, vessel skirts, bulkheads or decks below either 140 C for electrical items or ca. 500 C for structural steel elements to maintain operability of the item to be protected)
* fireproofing cladding (boards used for the same purpose and in the same applications as spray fireproofing) Materials for such cladding include perlite, vermiculite, calcium silicate, gypsum, intumescent epoxy, DuraSteel (cellulose-fibre reinforced concrete and punched sheet-metal bonded composite panels), MicroTherm
* enclosures (boxes or wraps made of fireproofing materials, including fire-resistive wraps and tapes to protect speciality valves and other items deemed to require protection against fire and heat - an analogy for this would be a safe) or the provision of circuit integrity measures to keep electrical cables operational during an accidental fire.

[edit] Regulations
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Old 01-17-2008, 02:31 PM
Emilio Lizardo is offline
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OK, I went by again to take some pictures, and it may be framed with 2 x 6s, and not 2 x 4s as I had originally thought. But the spacing looks closer to 12" than 16" to my eye.

Here's an overview of the building under construction. Its one of several that ring a pre-fab concrete garage.

Here's a closer look at the framing -- you can see how dense the spacing is.

Here's a close-up of some of the detail around the window openings.

Here's one of the buildings that is largely complete. It was built the same way as the others, and you can see how tall it is.
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Old 01-17-2008, 02:47 PM
A.R. Cane is offline
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Looking at the closeup, window detail, pic, it looks like 2X6's on 16" centers. Still can't comment on the 5 story construction, but there must be some basic strutural tie in.
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Old 01-17-2008, 03:25 PM
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If that's the area that I think it is, it's right next to where a tornado traveled through the area in 2001.

http://www.weatherbook.com/collegeparkmain.html
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Old 01-17-2008, 04:52 PM
Emilio Lizardo is offline
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Quote:
Originally Posted by mks57
If that's the area that I think it is, it's right next to where a tornado traveled through the area in 2001.
Its about 5 miles from there. This is being built on land surrounding the PG Plaza Metro station.

Hyattsville is known for occasional microbursts though. During a storm a year or two back, the roughly one square mile around my neighborhood accounted for almost 1/2 of all of the power outages due to falling tree limbs and the like that PEPCO reported for the whole county.
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Old 01-17-2008, 06:16 PM
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From a purely load standpoint, I am not surprised; a stick-built structure is very light. The vertical stress on 2x6 framing for five storys doesn't seem high, assuming appropriate interior load-bearing walls and columns (even if the columns are made by built-up 2x6s).

There is some reason to be intuitively anxious, though: Stick-built framing is extremely dependent on the quality of all of the connections between the individual framing pieces. The whole thing at the end needs to end up as a single integral unit to be maximally strong. Every nailed joint counts; what is glued; how carefully the siding is applied; how accurately every piece is sawn so that all the load is not on one member; use of hurricane ties; and so on. In commercial construction where guys are using power nailers in cold weather, no inspection can really substitute for workmanship, and workmanship can be hard to come by when you are getting paid by the job.

It won't fall down but it wouldn't be my first choice in a stiff breeze. Specially a tall skinny sucker like the one in the picture.

Last edited by Chief Pedant; 01-17-2008 at 06:17 PM.
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Old 01-18-2008, 01:09 PM
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If you aren't worried about code, and it isn't strictly 2x4's, there is this 13 story, 144 foot tall house in Russia, billed as the world's tallest wooden house.
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