AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
MAT108:
Roof / Ceiling Framing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Now let’s talk about the code’s requirements for roof and ceiling framing.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
1
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
GENERAL
• Roofs < 3:12 – Members supporting joists
and rafters designed as beams
• Notches & holes controlled
• Joists & rafters supported laterally
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
A few general comments here about the IRC requirements:
For relatively flat roofs (slope less than 3:12) the joists and rafters have to be
designed as beams. Notches and holes are controlled as they are in floors.
And joists and rafters must be supported laterally.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
2
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Rafters
Ceiling joists
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
The governing concept in the roof/ceiling framing provisions is that loads on
the roof are going to attempt to push the walls out, and some resistance to
that push must be provided. Ideally that resistance would be provided by
connections between rafters and parallel ceiling joists.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
3
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Rafter
Metal strap
Nailed to
rafter
Lookout
Joists
Exterior wall
Ceiling Joists Perpendicular
2003 IRC To Rafters
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
However, there are situations in which joists aren’t parallel to the rafters and
the IRC makes provisions for that. Here’s one such solution. However, the
code doesn’t provide the details of how this is to be done.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
4
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Rafter
Subflooring
Nailed to
rafter
Lookout
Joists
Exterior Wall
Ceiling Joists Perpendicular
2003 IRC To Rafters
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
This is another solution, but again there are no details.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
5
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Rafter
Nailed to rafter
1x4 Rafter tie (no more than 4’ o.c.)
?
Lookout
Exterior Wall
Joists
Ceiling Joists
2003 IRC Perpendicular to Rafters
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
A third solution is listed, but again no details. In fact the whole subject of
rafter ties is muddled in the 2000 and 2003 editions of the IRC.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
6
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Rafter
Nailed to
rafter
Joists
Exterior wall
2006 IRC – R802.3.1
Ceiling Joists Parallel
To Rafters
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
In the 2006 edition of the IRC, the subject of rafter/joist connection has been
simplified. The general requirement is for all joist to be connected to rafters
at the top of the wall.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
7
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Nailed to
rafter
Rafter
Joist or rafter tie which must be:
- Min. 2x4
- Connected to each rafter
If no rafter tie, ridge to be
supported by engineered
wall or girder.
Exterior wall
2006 IRC – R802.3.1
Ceiling Joists Parallel
To Rafters
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Where joists are located above the top of the wall the joists have to be nailed
to each rafter or a rafter tie is required.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
8
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Nailed to
rafter
Rafter Tie
Rafter
Exterior wall
2006 IRC – R802.3.1
Ceiling Joists Perpendicular
To Rafters
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Where ceiling joists are perpendicular to rafters, a rafter tie is required.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
9
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Collar ties (or straps)
- Min. 1x4
- Upper 1/3 of attic
- Max. 4’ o.c.
2006 IRC – R802.3.1
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
The revised section in the 2006 IRC also requires collar ties (or straps over
the ridge board) as shown here. The intent is to reduce uplift of the upper
rafter ends in high wind loading similar to what’s seen in thunderstorms.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
10
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
At first glance, this appears to be the ideal situation – rafters and joists
parallel and meeting at the ends. However, if you’ll look closely you’ll see
that the rafters don’t actually meet the joists. For some reason there’s a
horizontal 2x4 separating them. Even though both are apparently connected
to that 2x4 the degree of continuity is questionable. And if you’ll look at the
ends of the rafters, some of them seem to have some sort of splice at the
very end, and since it’s a very small splice the very continuity of the rafter –
not to mention it’s connection to the joists – is likely to be compromised.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
11
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Rafter end flush against ridge
board to avoid horizontal shear
in rafter
Greater than the
cut end of the
rafter
Ridge board
min. 1” (nominal)
in thickness
Ridge Board
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Let’s talk some more about specific code requirements. The code requires
that the ends of rafters either be framed to each other, connected by gusset
plate, or bear against a ridge board. The intent is to provide both solid
bearing surface and a resistance to lateral movement. The caution here to
avoid horizontal shear isn’t found in the code but rather is a recommendation
from the wood industry.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
12
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
• RAFTER SPAN TABLES
• Pre-calculated
– 2000 edition: Error in 2x12 (10 psf DL)
– Corrected in 2003 edition
• Spans for 4 most common species
• Reference to AF&PA generic span tables
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Like joist spans, there are rafter span tables in the code.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
13
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Braced Rafters
Rafter span
Rafter span
Continuous purlin
(not less than size
of rafter)
Min. 45°
Alternate to purlin
(not mentioned in
code): Brace nailed
to each rafter
Max. 8’
Min. 2x4 brace
(max. 4’o.c.)
Joist
Bearing
walls
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
A provision that was carried over from the UBC and the old Dwelling Code is
the use of struts and purlins to brace rafters and increase their spans.
The struts must be supported on a bearing wall. While it’s conceivable that
the struts could be supported by a beam designed for that purpose, they
shouldn’t simply be supported by ceiling joists (even doubled ones).
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
14
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
WOOD I-JOISTS
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
We talked at some length about I-joists when we were talking about floor
framing. Let’s mention some other related matters.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
15
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Web
stiffener
Cut must not
overhang inside
of plate.
Birdsmouth cut allowed
only at low end joist
bearing.
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
You can frame the roof out of I-joists, duplicating much of what’s done with
solid sawn lumber, but it’s important that the manufacturer’s
recommendations be followed just as was the case with floor framing.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
16
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Here’s another example of duplicating traditional construction using I-joists.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
17
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Keep in mind that the ridge in this application isn’t just a ridge board as
we’ve seen with solid sawn construction, but rather is a beam and should be
designed as such.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
18
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
This is a variation of supporting I-joists on the ridge beam. Note that lateral
support of the joists is still provided.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
19
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Notice in this example that the end of the I-joist is supported by a hanger
that supports the full joist assembly. A detail like you see on the right may
support the joist, but because it places all of the load on the web it may
cause failure.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
20
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
These are more examples of the flexibility of doing roof framing with I-joists.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
21
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
CONTINUOUS LOAD
PATH
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
As is always the case – but particularly in this type of framing where the
loads may be concentrated in manners not seen with solid sawn framing –
it’s important to provide a continuous load path to the foundation.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
22
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
METAL PLATE
CONNECTED
TRUSSES
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Now, let’s talk about metal plate connected roof trusses. They are so
common in construction today as to be almost invisible.
Be aware that the IRC provisions for trusses are much more extensive than
what’s been seen in the codes in the past. The code specifies specific
information to be provided on the truss drawings, requires that bracing be
provided in accordance with the drawings, and makes clear that alteration to
trusses shouldn’t be done without the approval of a design professional.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
23
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
GENERAL TRUSS REQUIREMENTS
• Truss drawings submitted to AHJ before
installation
–
–
–
–
–
–
–
Detailed slope/depth, span, spacing
Location of joints
Design loads
Joint connector type & description
Lumbers size, species, grade
Deflection
Permanent bracing
• Professional design where required by AHJ
• Bracing required in compliance with drawings
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
In contrast to what the older codes have required, the IRC increased the
requirements that apply to trusses. Drawing are required to be submitted to
the Building Official for approval before installation. The minimum contents
of those drawings are contained in Section R802.10. What you see here is
just a sampling.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
24
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
• Trusses made with traditional solid sawn
lumber
• Normally use dimensional lumber as chords
and webs
• Fastened with metal plate connectors
• National Design Standard for Metal Plate
Connected Wood Truss Connection,
ANSI/TPI 1-1995 (Truss Plate Institute)
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Typically trusses are made with solid sawn lumber chords and webs. The
IRC references the ANSI/TPI standard that you see here for the design of
metal plate connected wood trusses.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
25
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Truss Loads
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Trusses are designed to support loads in a plane parallel to the plane of the
truss. They aren’t intended to support lateral loads, which is why bracing is
required.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
26
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
• HB-91, Commentary &
Recommendations for
Handling, Installing &
Bracing Metal Plate
Connected Trusses
• DSB-89,
Recommended Design
Specifications for
Temporary Bracing of
Metal Plate Connected
Wood Trusses
• Wood Truss Council of
America (WTCA) job
site warning poster
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Temporary bracing, as well as permanent bracing that we’ll touch on in a
moment, should be provided. The truss industry provides job site warning
posters with bracing information.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
27
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
• Permanent bracing
– Transfer lateral loads from wind, seismic,
construction, or deadloads to the tops of the walls
and to the foundation
– Contribute to performance of individual trusses or
groups of trusses over their service life
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Temporary bracing insures that the trusses remain in place during
construction, but permanent bracing insures that the truss system will
perform properly during the life of the building.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
28
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Three Planes for Permanent Bracing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Permanent bracing is required in the 3 planes shown here. Often final
building elements – roof sheathing and ceiling finish in particular – may
provide a portion of that bracing. But bracing in the web plane has to be
added.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
29
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Racking of Trusses
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Even then lateral loading will still cause the trusses to bow. They just do so
in chorus.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
30
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Diagonal Bracing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
For t hat reason lateral bracing is needed.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
31
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
• Design of permanent bracing is responsibility
of building designer, not truss designer or
manufacturer
– Only building designer can know all anticipated
loads
– Design of permanent bracing must be on truss
drawings
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
The code is silent on who has responsibility to design what elements of roof
truss systems. What you see here is the philosophy of the truss industry.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
32
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
The truss designers provide a truss erection plan, and when in doubt about
some element of the roof framing, that plan should be consulted.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
33
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Even though truss design and erection can be tricky, it’s important to realize
that there are any number of serious problems that can be caught just by
paying attention to the basics. Here’s an example – improper spacing.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
34
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Here’s another example of a serious, but easily spotted, problem – missing
metal plate connectors.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
35
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
Roof/Ceiling Framing
New for the 2003 edition
• Connectors required for all
trusses
• Nailing still OK for rafters if
loads low enough
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
The 2003 edition of the IRC now requires the use of connectors of some sort
to tie trusses to the top of the wall. Unless needed for uplift resistance
greater than the capacity of the nails, nailed connections are still allowed for
solid sawn rafters.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
36
AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
American Forest & Paper Association
American Wood Council
QUESTIONS?
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Copyright © 2007 American Forest & Paper Association.
All rights reserved.
37