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…
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?
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.
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.
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? :p:p
The purlins seem undersupported, thanks E. But they are 2X8 on edge, span between purlin uprights, about 10 ft. :p???
I told the buyer it looked weak but he should get advice from a builder.
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.
That’s true for modern homes… and the braces must bear on top of a wall, not on top of ceiling joists, and the tops of the braces should be nailed to the sides of rafters. I see purlins installed just like these in the photos often.
The two 2x4’s running across are neither rafter ties (tie the bottoms of opposing rafters together)nor collar ties (installed in the upper third of the roof) and are a sign of someone not knowing what they were doing. Many, many older homes were built without collar ties and I would never call their missing as a defect in an older home unless I saw failure which I could relate to a lack of collar ties.
Here in Colorado, I often see 2x4 rafters in older homes that have significant spans. Very common in older homes, many of which also have no ridge, not a concewrn if rafters oppose. Sign of failure is key. Mention that it does not meet modern framing standards.
Whether or not it’s structurally adequate if there are no signs of failure would be a structural engineer’s call, but if it’s an older home and has successfully withstood the test of time, I call failures or defects, not failure to meet modern standards
