How many cross-ties, if any?

[jkogel]

This is a wing added to the original house, simple gable roof. The quality of workmanship is generally good and there are no visible issues. The 2X4 rafters have a span of about 10 feet each, on 16" centers, plywood sheathing. There is a 2X6 ridgeboard installed supported at the ends only, (by the gable end and the old roof). I did not see a butt joint in this ridge, but there likely is one. The rafters are supported at mid-span by I think they're called purlins, 2X8's on edge with a few supports down to the ceiling joists. I did not report any concerns here but My Question -
Are the two 2x4 crossties adequate for this 20 foot roof section? They are simply nailed into the rafters. I commonly see shorter shiplap cross-ties, often on every pair of rafters, or some additional ridge support. We get occasional dumps of wet snow here, I seem to remember that happening...

John Kogel
www.allsafehome.ca

[dbucknavich]

Originally Posted by jkogel

This is a wing added to the original house, simple gable roof. The quality of workmanship is generally good and there are no visible issues. The 2X4 rafters have a span of about 10 feet each, on 16" centers, plywood sheathing. There is a 2X6 ridgeboard installed supported at the ends only, (by the gable end and the old roof). I did not see a butt joint in this ridge, but there likely is one. The rafters are supported at mid-span by I think they're called purlins, 2X8's on edge with a few supports down to the ceiling joists. I did not report any concerns here but My Question -
Are the two 2x4 crossties adequate for this 20 foot roof section? They are simply nailed into the rafters. I commonly see shorter shiplap cross-ties, often on every pair of rafters, or some additional ridge support. We get occasional dumps of wet snow here, I seem to remember that happening...

John Kogel
www.allsafehome.ca

If those aren't engineered trusses, then I don't know how they figured 2x4 rafters with no collar ties. Being an addition, I would assume this is an Uncle Bob job, without approved designs. How old is the house, and how old is this area?

[Bruce A. King]

The only way 2x4's could be used is if they are part of engineered trusses.

With the snow load there, that is real bad construction.

Its even incorrect for non-snow load areas.

Proper 2x4 trusses for that application would have so many webs present it would be kinda hard to see through the attic.


It now needs 2x6's scabbed on with a lot of braces and ties.

[dbucknavich]

Originally Posted by bking

It now needs 2x6's scabbed on with a lot of braces and ties.

Very likely Bruce, but I think its important to note all we should say is that it now needs an approved architectual design. I would not prescribe the remedy here, other than noting the unprofessional framing methods and referring.

[Dale Duffy]

Originally Posted by bking

The only way 2x4's could be used is if they are part of engineered trusses.

With the snow load there, that is real bad construction.

Its even incorrect for non-snow load areas.

Proper 2x4 trusses for that application would have so many webs present it would be kinda hard to see through the attic.


It now needs 2x6's scabbed on with a lot of braces and ties.

I agree with Bruce, I would certainly think that 2x4's are undersized not being engineered trusses.

A set of blue prints from an architect stamped from a city official as approved would be the only thing which would change my mind.

[dbucknavich]

Originally Posted by dduffy

I agree with Bruce, I would certainly think that 2x4's are undersized not being engineered trusses.

A set of blue prints from an architect stamped from a city official as approved would be the only thing which would change my mind.

Thanks Dale. You would agree with Bruce......you would. Me? I'm just chopped liver over here. Nothing to see here. Please disperse.

[Larry D. Kage]

Yes, even with the purlins, they appear over spanned. Here is a span calculator for rafters and joists.

[David P. Valley]

Originally Posted by jkogel

This is a wing added to the original house, simple gable roof. The quality of workmanship is generally good and there are no visible issues. The 2X4 rafters have a span of about 10 feet each, on 16" centers, plywood sheathing. There is a 2X6 ridgeboard installed supported at the ends only, (by the gable end and the old roof). I did not see a butt joint in this ridge, but there likely is one. The rafters are supported at mid-span by I think they're called purlins, 2X8's on edge with a few supports down to the ceiling joists. I did not report any concerns here but My Question -
Are the two 2x4 crossties adequate for this 20 foot roof section? They are simply nailed into the rafters. I commonly see shorter shiplap cross-ties, often on every pair of rafters, or some additional ridge support. We get occasional dumps of wet snow here, I seem to remember that happening...

John Kogel
www.allsafehome.ca

2 x 4 Rafters?????

I'm willing to bet that a building permit wasn't issued for this build.

I'd like to see the flex on this roof field on a good snow load....

[dbucknavich]

Originally Posted by dvalley

2 x 4 Rafters?????

I'm willing to bet that a building permit wasn't issued for this build.

I'd like to see the flex on this roof field on a good snow load....

David, you'll be able to see the flex from the living room when all the snow comes barreling into the house.

[Emmanuel J. Scanlan]

The struts (braces) for the purlins are not adequately placed. The struts should be every 4' - 6' apart. It's obvious these are not.

[jkogel]

Thanks all, including Dylan.
This addition was built we are told with a permit and has stood as we see it here for more than 15 years, asphalt shingles are worn out. Maybe it's been that long since the last big snow!
BTW, truss designs do not rely on ridge support, while this design uses the ridge and purlins to support the rafters.
Anyway I agree, it looks weak, 2X6 rafters would be better, will now check that span table.

John Kogel
www.allsafehome.ca

[jkogel]

Originally Posted by lkage

Yes, even with the purlins, they appear over spanned. Here is a span calculator for rafters and joists.

Larry, as you probably saw, max Horizontal span for a Fir 2X4 is 4'8". The addition width by the realtor's tape is 18'9", divided by 4 for the spacing between the purlins = 4.76 or 4' 81/2". The rafters span a bit more than this but not horizontally.
Are we splitting hairs here?
The purlins seem undersupported, thanks E. But they are 2X8 on edge, span between purlin uprights, about 10 ft. ???
I told the buyer it looked weak but he should get advice from a builder.

John Kogel
www.allsafehome.ca

[pdickerson]

I don't know why everyone is so down on 2x4 rafters. According to the calculator, A DF(N) #2 2x4 24" oc can span 5'-10" horizontally at a deflection limit of L/240. My beam/joist design software says 6'-0". The rafters in the photo are well within these limits and so do not present an issue in terms of their size.

The issues I see in the photos are lack of collar ties (if there is strapping connecting opposite rafters over the ridge board, collar ties are not needed), and improper support for the 2x8 strongback. In addition I would want to confirm that the strongback supports are fastened adequately and that they land on interior load bearing walls and are not simply supported by a ceiling joist in mid-span.

[David P. Valley]

Originally Posted by pdickerson

I don't know why everyone is so down on 2x4 rafters. According to the calculator, A DF(N) #2 2x4 24" oc can span 5'-10" horizontally at a deflection limit of L/240. My beam/joist design software says 6'-0". The rafters in the photo are well within these limits and so do not present an issue in terms of their size.

The issues I see in the photos are lack of collar ties (if there is strapping connecting opposite rafters over the ridge board, collar ties are not needed), and improper support for the 2x8 strongback. In addition I would want to confirm that the strongback supports are fastened adequately and that they land on interior load bearing walls and are not simply supported by a ceiling joist in mid-span.

I don't know what software you are using, but 2 X 4's absolutely are not allowed in my state, I don't care how short of a span it is. we've got snow loads that'll crush a roof and the structure below it, if it's not built properly.

[Bruce M. Graham, III]

Now that picture brings back some memories, live in Sault St. Marie Michigan for a while, lots of snow.