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Roof structure, Buenos Aires (C) Daniel FriedmanRoof & Floor Trusses

Floor & Roof Trusses:

Photo Guide to Residential Roof & Floor Trusses. This article describes and illustrates the different types of roof and floor trusses used in residential construction. We describe common roof or floor truss defects that can be observed by visual inspection.

Page top photo: roof truss and purlin construction at a building used for tango milongas in Buenos Aires, photographed by the author.

This article series describes building framing materials used in different epochs of residential construction. Knowing when certain materials were first or last in common use can help determine the age of a building. Our page top photo shows modern floor framing details for a modular-constructed house.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Floor & Roof Trusses used in Building Construction

Wood Floor & Roof Truss Photos, types, defects

Truss example © Daniel Friedman at InspectApedia.com ...

Our photos show an attic view of modern roof trusses (above) and floor trusses (below). We continue with illustrations and definitions of the various types of trusses used in buildings, their materials, designs, and uses.

[Click to enlarge any image]

We add a discussion of truss damage such as by improper storage, improper installation, on-site modification, excessive point loading, and rot or mechanical damage.

Truss example © Daniel Friedman at InspectApedia.com

[Click to enlarge any image]

Above: open web wood floor trusses showing the addition of a strongback brace at the right side of the photo.

Below: modern ceiling trusses, illustrating that trusses are widely used to support all building levels: roofs, ceilings, and floors.

Ceiling trusses in a modern home (C) InspectApedia.com JWS

Illustration of Howe Trusses & Fink Trusses

Howe Truss example © Daniel Friedman at InspectApedia.com

These illustrations illustrate two common wood roof truss designs: the Howe Truss - above, and the Fink Truss - below.

Fink Truss example © Daniel Friedman at InspectApedia.com

Below: our photo illustrates that in some buildings trusses may have been constructed on-site (and may lack engineering analysis or reliability).

[Click to enlarge any image]

These photos are of a 120-year old cabin roof supported by site-built trusses, courtesy of an InspectApedia reader.

Truss roof in a  120 year old cabin (C) InspectApedia.com

Common Truss Defects & Damage in Residential Buildings

Roof truss plate © D Friedman at InspectApedia.com

Summary of Common Truss Defects

Some examples of truss defects and damage include wood truss connector plates loose, separated, not properly repaired.

Watch out: truss plates or "gusset plates" that are damaged or disconnected can cause complete truss failure and even a building collapse as we document later on this page.

You may need to look closely at the steel connector plates on wood trusses for signs of separation, or on occasion, an amateur or improper "repair" of loose truss plates using roofing nails.

Some common defects we find when inspecting wood truss construction in residential buildings are illustrated below.

Trusses Cut or Modified at the Jobsite

Truss strongback reinforcement cut to install HVAC duct (C) Daniel Friedman at InspectApedia.com

Wood trusses that have been cut or modified, such as the removal of the bottom chord of a truss to install an attic stair are improper and unsafe and violate building codes unless the changes have been specified and inspected by a licensed design professional such as a civil or structural engineer.

Especially in the case of failure of trusses, almost all failures are caused by insufficient or absent bracing and poor principles during erection. (Hansson 2011)

In our photo above, the green tags stapled to every roof truss state that horizontal bracing is required for the truss to perform properly. The green tags read:

Permanent horizontal bracing required.

Trusses Damaged by Leaks & Corrosion

Truss connector plate damaged by roof leak and corrosion (C) Daniel Friedman at InspectApedia.com

Truss plates may be damaged by roof leaks or high moisture that causes rusting and corrosion and ultimately weakening of or separation of the connector.

Truss Plates Separated From Truss Chords or Members

Truss plate separated, probably by mis-handling of trusses at the jobsite (C) InspectApedia.com B ... Truss plate separation means structural failre is at risk (C) InspectApedia.com B ...

Some of these truss connector failure photos were contributed courtesy of an InspectApedia reader who found these conditions during the construction of a new home in Washington state.

Vertical or Horizontal Separation of Truss Members: Plate or Connector Failure

Below: Vertical separation of truss components due to truss plate separation, probably due to truss mishandling at the jobsite.

Vertical separation of truss components due to truss plate damage (C)  InspectApedia.com B ... Truss vertical separation and failure due to plate damage (C) InspectApedia.com B

Improper Truss Plate Repairs

Below: an improper truss plate repair effort: hammering nails through the truss plate

Improper repair of separated russ plate by adding nails (C) InspectApedia.com CB

Watch out: simply pounding the truss connector plate back into position is not likely to work: replacing the plate into the exact-same holes where its prongs were originally pressed will not secure the plate to the wood.

Attempts to re-locate the truss plate to one side so that you can hammer it into a new position on the wood will result in dislocated, weakened truss members.

Furthermore, hammering onto a truss plate that was originally installed by special equipment is going to deform and bend it so that many of its connecting points simply won't bind to the receiving wood at all.

Truss Arching or "Uplift"

Truss uplift, a cosmetic not a structural defect, caused by truss arching due to differences in moisture level among horizontal bottom truss chords is discussed separately

at TRUSS UPLIFT, ROOF

and at ROOFING NOISES - due to truss arching.

Broken Truss Chord, Inspector Falls into Toilet

Watch out: the bottom chord of the roof truss is often used to support the ceiling below.

But the bottom truss chords, especially with pressed-on gusset-plate wood roof trusses, may not support the weight of an inspector who walks on them. Worse, the bottom chord of the truss is often hidden from clear view, buried in attic floor insulation.

Hybrid roof and floor trust combination © Daniel Friedman at InspectApedia.com

Our wood roof truss photo at above left shows a design that would have been less likely to collapse when walked-on. The bottom chord of the roof truss is formed by a wood floor truss. The two trusses are bolted together at the truss ends using plywood gusset plates.

The author [DF] standing on a truss chord while installing an attic fan, suddenly found himself one floor down, in the bathroom of an unsuspecting condominium owner who had no idea that a contractor was working in the attic over her head while she was using the toilet.

As the dust settled from this painful and embarrassing incident we investigated the broken roof truss bottom chord.

A large knot through the bottom 2x4 truss chord had not interfered with the truss function while the chord was in tension - it's usual load. But when walked-on and when the contractor stepped on to the chord right over the knot, it simply broke in two, leading to an accident.

Below our photos show details of finger-jointed wood truss web connections.

Truss example © Daniel Friedman at InspectApedia.com ... Truss example © Daniel Friedman at InspectApedia.com

Truss & Roof Collapse from Point Loads or Snow Loads

Truss roof collapse, apparently from excessive loading during re-roofing (C) InspectApedia.com GR

This photo was contributed by an InspectApedia.com reader. It appeared to investigators that the truss-supported roof collapse shown above occurred as a result of excessive loading or point-loading during re-roofing, perhaps by having piled heavy materials at a single, poorly-chosen location. .

Watch out: while it is common to use a lift or crane to deliver roofing materials to the roof during a re-roof job, do not leave heavy re-roofing supplies such as pallets of shingles or roofing membrane concentrated in a single spot.

Good practice is to spread the materials over the roof surface, or out along stronger roof sections such as over supporting walls, rather than leaving the materials piled in a single central location.

Below: evidence suggesting roof truss member separation and breakage under a roof suspected of snow load damage or other weight from above.

Roof truss damage apparently from snow loading (C) InspectApedia.com Robertson R ... Truss loading failure (C) Inspectapedia.com GR

Metal Floor & Roof Truss Photos

Truss example © Daniel Friedman at InspectApedia.com

Our photos illustrate the use of steel roof trusses below a flat poured concrete roof.

Below you can see that steel roof trusses are not completely immune to damage from water, leaks, and rust.

Truss example © Daniel Friedman at InspectApedia.com

We don't consider surface rust to be of structural significance on these trusses, but if the rust has advanced to flaking exfoliating steel rust then the integrity of the truss and thus the structure is questionable.

Below our photograph illustrates a steel I-joist also used in roof and floor construction.

Also see  I-JOISTS, FLOOR & ROOF.

Steel web Truss example © Daniel Friedman at InspectApedia.com

Reader Question: when did building codes change on roof truss spacing?

Old log cabin © Daniel Friedman at InspectApedia.com

Photo above: OSB-webbed I-Truss floor joists resting on a steel beam in a modular-built home.

(Dec 11, 2014) SHYANNA said:

Hi, do you happen to know when the building code for roof trusses changed from 24in to 16in. What year?

Reply:

Let's get this roof truss spacing information a bit more accurate:

Roof truss support systems are designed by engineers and architects and generally comply with AS 1720.1 that includes various loads and forces such as wind loading, nailing schedules, etc.

Trusses are typically spaced on intervals of 600mm (23.6" or 24"), 900mm (35.4" or 36"), or 1200mm (47.2 or 48") apart or "on center" depending on the live and dead loads of the roof.

Roof truss spacing may be on a variety of spacing intervals depending on truss design, size, type, loading and span, and for roofs, roof pitch may also be a factor.

Some common spacings using floor trusses as an example, include 12" on center (o.c.), 16" o.c., 19.2" o.c., and 24" o.c. - Excerpt from Span Tables for Joists and Rafters, (C) 1993, American Forest & Paper Association, Washington D.C.

History & dates of the design and use of site-built and factory-made roof trusses, king trusses, A-trusses, and web truss contributions invited, CONTACT us.

Truss Installation Instructions & Failure Research

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2022-12-04 by InspectApedia (Editor) - house has tree trunks for rafters

@carol white,

Please post some photos (one per comment, as many comments and thus photos, as you like)

and tell us the basics: country and city of location

In particular, anybody who built their own house might use a tree trunk for a beam or rafter even today - so from that fact alone I can't guess the age of your home .

BUT do take a look at FRAMING AGE, SIZE, SPACING, TYPES

where we list many clues that you CAN see to guess at building age, such as types of saw or tool marks, nails and other hardware, and more.

On 2022-12-04 by carol white

My house has tree trunks for rafters how old could it be records only go back to when it passed into private ownership in 1920

On 2022-10-25 by InspectApedia (Editor)

@Anonymous by private email,

IMO the added weight of solar panels ought to be within the range of dead + live load weight the roof has to be designed to handle in any event - such as from snow.

BUT

Inspect the trusses completely before the work begins - look especially for connectors that are loose or damaged
or of course for other truss snafus like broken or cut trusses.

Other readers: Hinged roof trusses such as those used in some modular construction are described at

MODULAR HOME CONSTRUCTION

On 2022-10-25 by InspectApedia (Editor) - will hinged style roof rafters handle the extra weight of solar panels?

@Anonymous by private email,

IMO the added weight of solar panels ought to be within the range of dead + live load weight the roof has to be designed to handle in any event - such as from snow.

BUT

Inspect the trusses completely before the work begins - look especially for connectors that are loose or damaged
or of course for other truss snafus like broken or cut trusses.

On 2022-10-25 by Anonymous by private email

I have a 2 story modular home built in 1988. From your site I seen the hinged style roof rafters that I have. My question is will those handle the extra weight of solar panels?

They would cover the front & back of the second story roof and the back of the lower roof. They just look so poorly made with 7/16 OSB.

You definitely can see the line as you mentioned 2' up from the gutter.

At least they're on 16" centers. Though I have to say that the house had no house wrap which is specified in every siding installation manual, was surprising.

And using all four screws on a receptacle instead of a pigtail, to me means they aren't inspected.

I could go on.

I can't seem to find anyone that has a set of drawings for this home in Pine Hill Lakes subdivision Antioch, Illinois to see any of the specifications. Any thoughts on that. - Anon

On 2022-04-13 by Inspectapedia Com Moderator

@Dann,

The manufacturer of trusses will certainly have some requirements for storage on site between the time of delivery and the time of installation.

If you can identify the truss brand or manufacturer you can find those and compare those instructions with your observations.

Perhaps you could try again to post a photo by using the add image button.

On 2022-04-13 by Dann

Hello, the picture attached shows the truss that was installed in a newly constructed home located in central FL. Is the wood damaged or rotted? It was sitting outside for 4 weeks in the rain and it certainly did not look that way when materials came in.

On 2021-01-07 by danjoefriedman (mod) - does truss needs any mid point support

David

Roof truses are normally designed to support their roof over the truss span without a mid point support, and more to the point, the bottom chord of a properly designed, installed, and un-damaged truss is in tension and ought never be sagging nor need such support.

On 2021-01-07 by david

Have an older home with howe style roof trusses spanning 26 feet. 2 x 4 construction throughout the truss. Want to know if this truss needs any mid point support

On 2020-02-01 by danjoefriedman (mod) - cracked web truss kingpost needs repair

Leif

If that were my kingpost I would sister another vertical 2x alongside it, toe-nailing at an angle, with 10d common nails from both sides at say 8" intervals, after first clamping the old and new 2xs together so that nailing will be between snug members; better still apply construction adhesive before clamping and gluing.

You could of course hire a qualified structural engineer but I suspect that if there is on other building damage the cost of the engineer will be many times the cost of even an over-compensated repair like reinforcing the split original vertical support on both sides.

Pay attention to the bearing surfaces at the top and bottom of the enlarged, strengthened post and to the connections between the post top and the roof and attic floor (or truss bottom - as I can't see the bottom) to which it is attached.

On 2020-01-31 by Leif

@danjoefriedman,

Fortunately the home is located in central Texas, so snow or loading of that nature is not a concern.

I do not know the origin or when the damage occurred. It is possible that when I purchased the ~5 years ago, it was damaged by the roofers dropping squares of shingles onto the deck, but that is only a guess. It may have occurred before I purchased the home.

Cracked web truss in Texas home (C) InspectApedia.com Leif

On 2020-01-30 by danjoefriedman (mod)

Leif

While vertical cracks in vertic wood posts are not normally a structural concern, this one i. A web truss at a load point is different. It seems to me that reinforcement repair is necessary

If you live in a country subject to heavy snow loads you should do that repair before the roof is loaded again. It may be that all that is needed is some sistering of 2x material.

On 2020-01-30 by Leif

Cracked web truss in Texas home (C) InspectApedia.com LeifWhile working in my attic to install some lighting, I noticed that at least one of the trusses had a web member(?) with some cracking that looks to be clear through. (I can see 'daylight'.)

This particular truss supports a portion of the roof where multiple ridges meet. I have not noticed sagging on the roof, when observed from the ground, but I realize that inspecting up on the roof will be able to give me a better idea if there is some issue.

How urgent is it that this be inspected by a structural engineer? What might be the solution or fix for this?

I suspect one could try to injected glue or a construction adhesive into the crack, clamp the crack shut and sister some plywood or 2x4s to try and stabilize the truss-member. But I realize that none of the load will be transferred to these sistered pieces.

I have attached a photo, and I have additional photos from other angles that I could also provide.

 



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