extending roof overhang

[therigwelder]

I built a room unto my home.I sheathed the roof with plywood and then it dawned on me that i didnt have enough roof overhang.so my idea is {a horizontal ladder} nail a 2x4 across the end of the rafter tails,nail some 12" blocking 16" oc then nail a 1x6 fascia finally i will lay a strip of plywood extending the roof sheathing before i cover the roof with felt.is this acceptable

[JMHdesigns]

therigwelder,

I am a truss designer with over 20 years of experience.

You should attach a 2x? scab along side of the existing truss or rafter. The scab should be 2/3 longer than the overhang. For example, if the yielding overhang you desire is 12", then you should scab a 36" 2x? along side of the existing rafter or truss. The scab lumber should be the same size and species of the existing rafter or truss top chord.

You should use 2 rows of 12d nails in a staggered pattern to connect the scabs.

Depending on the horizontal overhang distance, the plywood sheathing (1/2" APA CDX or 15/32" APA OSB) should also cover 2/3 of the existing roof.

If the horizontal overhang distance is more than 24" with a 30# PSF LL then you should consult with a licensed engineer for upload and shear considerations.

If your roof pitch is lower than 3/12 or greater than 12/12, you should also consult with a licensed PE for lateral loads and other considerations.

Attaching a 2x ladder frame to an overhang eave is not calculated the same as using a 2x outlooker ladder on a gable end, which is what I believe you are attempting to do.

Jeff

[therigwelder]

thanks
thats what i did i built a outlook on the downslope eave.i will tear it back off tommorrow and do it the way you suggested.do i also have to cut my sheating back 36" right now my rafter and sheathing are flush on the end?if i dont cut it back i will end up with a 12" strip of plywood covering the scabs.not much support eh?i live in the deep south so my roof is only sloped 4 or 5 degrees,its a small room though 8x12 so how much lateral consideration should i give to it.being a welder fabricator i wish wood worked like steel.thanks for your help
therigwelder

[JMHdesigns]

therigwelder

Several questions will need answers to solve your situation concerning the roof sheathing and scabs since the roof pitch is less than 3:12.

1. You say the structure is built in the deep south, would this be the Florida Building Code?
2. If not in Florida, what building code? (BOCA, IRC, IBC, SBCC, etc.)
3. Are you in a high wind area of 100mph or more?
4. What is the roof live load in your area?
5. What is the actual roof structure, rafters or trusses?
6. If rafters, what lumber size, species and on center spacing?
7. If trusses, what is the top chord lumber size and on center spacing?
8. Is the soffit raked or sloped?
9. What is the actual roof sheathing material size? (1/2”, 15/32”, etc)
10. Is the run of the soffit 8’-0” or 12’-0”?

Since the roof slope is 4 or 5 degrees ( 4 degrees is 13/16:12 and 5 degrees is 1 1/16:12 ) the load calculations are normally doubled for the overhang. Also, roof shingles are not normally warranted for slopes less than 2:12. Are there shingles or other roof materials like rubber, metal, gravel on tar that would need to be taken into consideration?

Although the structure is small (8x12), the load calculations would be the same as if it were a structure that was 30’-0” x 40’-0”. You should not sell yourself short just because the structure is not “big”. Furthermore, the local building inspector (if you pulled a permit) would not care if the structure were only 8’x12’.

Jeff

[therigwelder]

let me see if i can answer any of these questions,the room i built is a lean to type.it has 2x4 rafters 24"oc with 2 rows of block bracing on 4' oc.the overhang is on the 8'10 side.therafters are yellow pine.this room connects to the eave of the house so i could not continue the roof slope of the house i needed all the ceiling room i could get.i plan to use rolled roofing or corrugated steel the roof sheathing is 1/2 pt plywood.i extended the rafters today to gain the overhang i need as far as live loads i dont really know what that is.i live in rural south mississippi.there is no building inspectors or building permits

[JMHdesigns]

Here's the deal..

The 2x4 SYP #2 rafters are overstressed by 402% with a deflection of over 4"! (Based on 1999 Standard Building Code, 30# LL, L/240 LL Defl. Limit, 12' rafter @ 24" o.c. with 12" O.H.)

You will need to increase the rafters to a minimum of 2x6 SYP #2 @ 16" on center. Based on the same load and code criteria, the 2x6's are adequate by 16%. The rafters must be fully braced on the bottom with 1/2" drywall or eqiuv.

Here are the calc's:

FAILED 2X4 http://www.jmhdesigns.org/Project_fail.pdf

PASSED 2X6 http://www.jmhdesigns.org/Project_pass.pdf

Once you have corrected the rafters, the 1/2" sheathing should not be a problem. Just remember to start the roof sheathing at the end of the overhang.

Hope this has helped you.

Happy New Year..Jeff

[therigwelder]

the rafters are only 8' 6" overall [including the 12"overhang].the framing and sheathing is complete for the room,so starting over on the roof is not desirable.what if i scabbed another 2x along side each rafter making the rafters 3.5x3.5? another idea would be to insert another 2x between the 24"centers making the layout 12" centers.i can acess the rafters inside the room .I nailed the sheathing on 4" making it difficult to remove

[JMHdesigns]

therigwelder,

Since the span is 7'-6" with a 12" overhang, they will work at 12" on center as you suggested.

Here are the calc's:
2x4 12" o.c. passed: http://www.jmhdesigns.org/passed12oc.pdf

I still have concerns with the 12" strip of 1/2" roof sheathing. However, this is probably okay since you are using the metal roofing.

Jeff

[JWmHarmon]

If your rafters are to small (2X4) in relation to the span, you can decrease the span by installing a beam perpendicular to the 2X4 rafters. This beam would have to extend to the side walls and have additional studs or posts installed to support it. This beam would shorten the unsupproted span of the rafters.

This beam could be steel or wood.

It could be decorative as well. You could use your imagination to create a work of art that also functions as a structural beam.

[therigwelder]

hello jeff
i did away with the 12" strip of sheathing on the overhang. i pulled the sheathing up and relayed it starting from the overhang,however i ended up with a 10"strip against the house.i figured it woul be better to have it there than on the overhang.i am rather dissapointed in this roof ,i have a belly in the roof ,now its guaranteed to hold water.
lets see if you all can help me design a better roof. I went with 2x4 rafters to keep below the home roof if i use 2x6 rafters they will be higher than the existing roof and thats building a flat roof.if i put a slope on them[ lets say the height of the 2x6]i figure to be above the home roof 3-6"how would i tie this into the home roof and make it weather proof?should i use 16"oc or will 24oc suffice using 2x6?
now for the next thought,is epdm a good roofing choose?it seems simple to use ,cheaper and carries up to 50yrs of dependable service,also i think the bonded would be better than the mechaniclly fastened type
therigwelder

[therigwelder]

well i got a new roof framed out,1x6 on 16"centers.i was only able to get a 1/2 on 12 pitch,i guess that pitch will shed water i hope not to have any ponding problems.the ridge of the new roof is a 1/2' above the eave of the existing roof what is the best method of sealing this seam?

[lolitad]