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An expert engineer, the most common framing mistakes

mark handler

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An expert engineer in wood structures identifies the most common framing mistakes and offers advice on how to avoid them.

http://www.housingzone.com/building-technology/top-10-framing-errors-and-how-prevent-them

The top 10 list of common framing errors includes:

1.Sheathing installed as a simple span. Sheathing should be installed over two or more spans, or three supports, at a minimum.

2.The strength axis is installed in the wrong direction. In general, panels should be installed with the long dimension or strength axis of the panel across supports.

3.Sheathing is ripped less than 24 inches and not properly supported. A narrow-width panel will deflect more than a panel 24 inches or greater in width. These panels are often installed on roof ridges, where workers are likely to walk during construction. The addition of blocking or edge-support clips will provide narrow-width panels with the support needed to handle heavy loads.

4.Glulam is installed upside down. When glulam beams are manufactured as unbalanced beams, there are different bending stresses assigned to the compression and tension zones, and the beams must be installed accordingly. When “Top” is stamped on the top lamination, that end of the beam should be up.

5.Panels are not spaced 1/8 inch at installation. Wood structural panels (plywood and OSB), like all wood products, will expand or shrink slightly with changes in moisture content. If expansion is prevented with tightly butted panel joints, buckling can occur. To prevent buckling and ensure optimum performance, the panel end and edge joints should be spaced 1/8 inch.

6.Overdriven fasteners. Improper fastening — including incorrect fastener location or size, or installation of fasteners through the panel and into the framing member — can result in structural and aesthetic problems that commonly lead to callbacks.

7.Inconsistent joist spacing. If the floor doesn’t “feel right” to the homeowner, you can expect a callback. A consistent deflection across the entire floor will keep the customer happy.

8.Inconsistent floor gluing. The number-one complaint about floors is squeaking. A properly glued-nailed floor system will work as a homogeneous unit, preventing most floor squeaks.

9.Improper water management. It’s important to prevent moisture intrusion in the building envelope and to allow for proper drying when moisture does get in.

10.Notching and hole cutting in the wrong places. Improperly made field notches or holes may reduce the structural capacity or the load-carrying capability of the structural framing member.
 

mark handler

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http://www.prosalesmagazine.com/engineered-wood/mind-the-gap.aspx





APA's presentations focus mostly on engineered products, which is not surprising since the association wants to make sure those products get installed correctly. Its list varies slightly, depending on which field rep is giving the presentation, but the most oft-cited items include the following:

No Gap.

Panels need a 1/8-inch space between them, or they can swell enough to buckle along the edges, causing waves to telegraph through roofing and flooring. APA inspectors see this more than any other mistake.

Poor Panel Supports.

A plywood or oriented strand board (OSB) panel needs to span at least three framing members. If it spans only two, it will lose strength and likely will buckle. Similarly, a panel less than 24 inches wide needs support along all four edges no matter how many supports it spans. APA says a lot of framers miss this.

Inattention to Grain.

Some framers assume a multi-ply panel performs equally well in all directions. Not so. Like solid lumber, it's strongest with the grain: that is, in the long direction of the top ply.

Overdriven Nails.

This is a big problem with shear panels. Nail heads are supposed to be flush with the panel surface, and will weaken the assembly if driven further. For instance, driving nails to 1/8 inch below the surface of a half-inch shear panel will reduce its shear resistance to that of a 3/8-inch panel.

Not Enough Glue.

Construction adhesive prevents annoying squeaks by keeping subflooring from rubbing against nails. If you're a builder who skimps on adhesive, every one of those squeaks will remind the customer of you.

Upside-Down Beams.

Some glu-lams come with a slight camber and will only perform to their span rating when properly oriented. When you see TOP at the bottom, it means "Turn over, please."

Inconsistent Joist Spacing.

This will cause an inconsistent feeling in the floor.

Improperly Notching and Cutting Framing Members.

This is one of the most common rough-frame code violations. While many of these cuts are made by careless framers, many others are made by plumbers or HVAC contractors.

Errors like inconsistent joist spacing or improper notching and hole cutting betray a misunderstanding of how structural frames handle loads. They're less prevalent than panel errors, according to Kositzky, but are common enough.

LACK OF DIRECTION:

APA-The Engineered Wood Association warns that failure to pay attention to the grain pattern in multi-ply panels can weaken the structure.

.
 

mark handler

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Inspection-ready checklist: 30 ways to pass your framing inspections - Dispatches from the field

http://findarticles.com/p/articles/mi_m0NTF/is_1_11/ai_97235112/

Failing your framing inspection can be expensive, especially if you have to stop work to fix mistakes--and then go backward and tear out work you thought was complete. Here are some of the most common framing mistakes that can cost you a red tag. Don't be surprised at how basic some of these are--framers are still messing up on some of the most obvious details.

Sill Plates on Concrete

* For houses on slabs, the bottom plates of all exterior walls and interior bearing walls must be pressure treated lumber secured to the foundation.

* Exterior walls must have concrete-embedded anchor bolts 6 feet on center with an anchor within 12 inches from each end--in each section of bottom plate.

* If the bolts don't land within a foot of the wall's end (they rarely do), you must install a powder-actuated fastener in place of the missing bolt.

* Interior bearing walls should be attached with powder-actuated fasteners at 32 inches on center.

Full Bearing

* A beam or girder bearing on a wall must have a column beneath it at least the same width as the beam. This adequately transfers the load through the wall and into the footing.

Shim Headers

* Shim gaps between the bottom of the header and the trimmer at window and door openings to achieve solid load transfer.

* Standard wood shims compress under load. You're required to use steel shim stock or steel washers.

* Hammer the shims/washers in tight.

Nailing Schedules

* The Universal Building Code specifies nailing patterns for structural wall sheathing of 12 inches on center in the field and 6 inches on center along the edges.

* Adjust your air pressure or your nailer's depth of drive to avoid penetrating the skin of the sheathing with nail heads.

Boring and Notching Studs and Plates

* Architects love to draw 3 1/2-inch stud walls in bathrooms that have to accommodate 3-inch-diameter vent pipes. Once the pipe is through your wall, there isn't much left of studs or plates. To pass inspection, you can add studs on either side of the piping or use specially designed metal plates to reinforce the bored-out studs.

Fire Blocking/Draft Stopping

* Install fire blocking in walls, floors, and ceilings to prevent creation of concealed space more than 10 feet long.

* If you frame a wall with 10-foot studs, you must fire block it to reduce the concealed space.

* If you have back-to-back walls with an air space in between, you need a full-height draft stop between the walls at 10 feet on center.

* When a drop ceiling intersects a wall, a row of fire blocks must be installed to block the drop.

Top Plates

* When joining two sections of plate end-to-end to create one long wall, the top piece of the double top plate must overlap the joint in the bottom piece at least 4 feet onto the next wall section.

* For walls intersecting at a 90-degree angle, there can't be a joint in either top plate within 4 feet of the intersection. If there is, you must add metal strapping to the top plate to tie the two walls together.

* Engineered floor and roof systems won't stand up without lateral bracing, as detailed in truss suppliers' drawings. The building inspector examines those drawings. If you don't brace the exact location called for, you'll fail inspection.

Damaged Trusses

* Engineers must design a specific fix for damaged truss webs and provide, an engineering stamp for each incident.

* A fix for broken truss "G3" on the last house doesn't necessarily apply to other similar damages. The inspector must see the manufacturer's paperwork on site.

Boring and Notching Beams

* Beams aren't supposed to have holes in them. If your plumber or electrician drills through your beams you'll need an engineer to re-calculate the decrease in the beam's efficiency.

* Keep the paperwork that shows the beam still supports the load it was designed for on site.

Correct Hardware

* If you're installing 2x12 joists, don't try to use those leftover 2x6 hangers; they won't pass.

* Nail off joist hangers completely--fill all of the holes with approved hanger nails. Hanger nails are designed with stronger heads than regular 8d and 10d nails, which won't pass inspection.

Stairs

* Check that your rise and run are correct and consistent, especially the first and last riser. Make sure they match your typical rise or at least don't vary by more than 3/8 inch.

* Check for adequate headroom.

* Fire block the wall running parallel with your stringers. And, if your stringers are 10 feet or longer, fire block between them so you don't create a diagonal fire chase.

Are You Really Ready?

* Have you received your plumbing, electrical, and mechanical inspections and are the tags on site?

* Is the building weather-tight?

* Are all of your approved drawings, building permits, copies of all prior inspection reports, and other relevant paperwork on site?

Build What the City Approved

If you change the approved plan, you must incorporate that change into your drawings and have the changes approved. If inspectors find you've deviated from plans, they won't approve the work.
 

fatboy

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Thanks Mark, I think I'll add those links to our webpage at work. Not like anyone will read them, but hey....... :banghd
 

ICE

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Thanks Mark. You should put that website link in the links forum.

Another serious flaw that I encounter too often is over-nailing. The schedule may call for edge spacing of 6" and 12" in the field yet it is nailed at 3" everywhere. I see where 4" edge spacing was called for and it was nailed at 2". Common sense would lead one to believe that more nails is better but it reaches a point where the framing splits and without beefing up the sill anchorage, you may not have gained much anyway. Add to that the fact that the structure was engineered and changing the values of shear walls is the duty of the engineer. He may not want a stiffer wall where they jumped up and put one.

 
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Mark K

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While the lists attempt to reflect good practice I will suggest that items 1, 3, 5, 7, and 8 in the original posting are not code requirements and thus unless the approved construction documents require them the inspector is not in a position to reject the work.

Wood compresses under load even if built snug without shims. There is no reason not to accept substantial wood shims. Where in the code does it say you must use steel shims?

Sheathing spanning one span can be code compliant. There are some situations where it is not possible to install sheathing spanning two continuous spans.
 

ICE

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Mark K said:
While the lists attempt to reflect good practice I will suggest that items 1, 3, 5, 7, and 8 in the original posting are not code requirements and thus unless the approved construction documents require them the inspector is not in a position to reject the work.Wood compresses under load even if built snug without shims. There is no reason not to accept substantial wood shims. Where in the code does it say you must use steel shims?

Sheathing spanning one span can be code compliant. There are some situations where it is not possible to install sheathing spanning two continuous spans.
I don't think most of what Mark posted was meant to be taken as code. The one place where I saw a code body mentioned it was the "Universal Building Code". Martian winds can reach what, 600...800 MPH.
 
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mark handler

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ICE said:
I don't think most of what Mark posted was meant to be taken as code. The one place where I saw a code body mentioned it was the "Universal Building Code". Martian winds can reach what, 600...800 MPH.
I agree :)
 

brudgers

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ICE said:
I don't think most of what Mark posted was meant to be taken as code. The one place where I saw a code body mentioned it was the "Universal Building Code". Martian winds can reach what, 600...800 MPH.
The Moon is a harsh mistress...but some people are into that sort of thing.
 

Alias

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#2 has been the one that I've caught here the most. I have seen the stamp facing horizontal instead of perpendicular (as in ICE's post) more times than I care to think about. Then there was the time that I saw panels that were stamped for horizontal installation.
 

ICE

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JMORRISON said:
Question to ask when item #4 is spotted on bottom of beam; "What does TOP spell backwards."
I have caught this mistake. I have found the word stamped and I have found where the word was removed with sand paper. The contractor that sanded the beam gets special treatment, even all these years later.
 

ICE

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Alias said:
#2 has been the one that I've caught here the most. I have seen the stamp facing horizontal instead of perpendicular (as in ICE's post) more times than I care to think about. Then there was the time that I saw panels that were stamped for horizontal installation.
#2 applies to roof and floor sheathing but not shear walls. With shear walls, as long as all edges are nailed, the panel long dimension can be parallel or perpendicular to framing members.
 
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Alias

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ICE said:
#2 applies to roof and floor sheathing but not shear walls. With shear walls, as long as all edges are nailed, the panel long dimension can be parallel or perpendicular to framing members.
Sorry, mistyped. I have a designer here who calls it out on brace wall panels. Most of the local contractors install with the arrow pointing skyward.
 

zigmark

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Since the jabbing has already started, how exactly do you obtain "expert engineer" status, it sounds so much more advanced than P.E.

Great post Mr. Handler, I too am considering borrowing the information for use if for nothing else but a good information to hand out as a method of getting others to start thinking about the types of construction practices to avoid. The "What Not to Do" in the conventional light framing realm.

Thanks

ZIG
 

ICE

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Alias said:
Sorry, mistyped. I have a designer here who calls it out on brace wall panels. Most of the local contractors install with the arrow pointing skyward.
Sue,

Here is an example of what not to do. They didn't block and nail the horizontal edges. I just don't take pictures of correct work.

 

mark handler

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ICE said:
They didn't block and nail the horizontal edges.
Blocking of horizontal joints is not ALWAYS required.

http://www.cbs.state.or.us/bcd/programs/residential/interps_rescinded/94-27.pdf

R602.10.8 Panel joints. All vertical joints of panel sheathing shall occur over and be fastened to common studs. Horizontal joints in braced wall panels shall occur over and be fastened to common blocking of a minimum 1-1/2 inch thickness.

So, seemingly, the IRC requires blocking everywhere. But wait, there are exceptions!

Exceptions:

1. Blocking at horizontal joints shall not be required in wall segments that are not counted as braced wall panels.

2. Where bracing length provided is at least twice the minimum length required by Tables R602.10.1.2(1) and R602.10.1.2(2) blocking at horizontal joints shall not be required in braced wall panels constructed using Methods WSP, SFB, BG, PBS or HPS.

3. When Method GB (Gypsum Board) panels are installed horizontally, blocking of horizontal joints is not required.

Under the IRC, you must block all plywood- or OSB-sheathed walls that are counted as shear walls. Except, if you double the length required, those long sections don’t have to be blocked.
 
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ICE

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mark handler said:
Blocking of horizontal joints is not ALWAYS required.http://www.cbs.state.or.us/bcd/programs/residential/interps_rescinded/94-27.pdf

R602.10.8 Panel joints. All vertical joints of panel sheathing shall occur over and be fastened to common studs. Horizontal joints in braced wall panels shall occur over and be fastened to common blocking of a minimum 1-1/2 inch thickness.

So, seemingly, the IRC requires blocking everywhere. But wait, there are exceptions!

Exceptions:

1. Blocking at horizontal joints shall not be required in wall segments that are not counted as braced wall panels.

2. Where bracing length provided is at least twice the minimum length required by Tables R602.10.1.2(1) and R602.10.1.2(2) blocking at horizontal joints shall not be required in braced wall panels constructed using Methods WSP, SFB, BG, PBS or HPS.

3. When Method GB (Gypsum Board) panels are installed horizontally, blocking of horizontal joints is not required.

Under the IRC, you must block all plywood- or OSB-sheathed walls that are counted as shear walls. Except, if you double the length required, those long sections don’t have to be blocked.
A strange thing happened here. When I click on the link, nothing happens. When I click on the "reply with quote" button, all of this came up.
 
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