Originally Posted By: mpatton This post was automatically imported from our archived forum.
I inspected a home built in the 40’s that has had major renovations done in the past 10 years. I understood many of the issues/remodels but had a concern when I saw the “new” roof from within the attic. When I viewed the roof from with in the attic (hip roof) I discovered that the original roof had been a flat roof with rubber membrane. The rafters were stick built spanning approximately 28’ from front to back of the house on a pitch of approximately 4/12.
The wall structure of the home is block with stucco finish and the perimeter walls are approximately 12" above the membrane roof.
What concerned me was that the rafters do not have any collar ties and that the rafters sit on the top plate with a birds mouth notched in them. The top plate appears to be secured to the top of the walls. Also space approximately every 10' or so is a vertical support with a short piece of lumber under them resting on the original roof as a support.
My concern is the lack of collars and in a heavy snow for example that the rafters pushing downward would also push the walls outward causing failure of the block wall/roof.
Originally Posted By: rfarruggia This post was automatically imported from our archived forum.
I’ve come across this quite a few times where the collar ties have been stupidly removed. Most often it will take a while for the effects to show (outward bowing of the side walls, flattening of the roof almost like a pagoda, etc.). Leeds to a lot of other problems too, like gutters seperating from the fascias, seperation of ceiling and floor joists, window and door frames losing square. Nasty stuff. Leave those collar ties alone. Luckily, if the roof dosen’t collapse when the are removed, the problems arise gradually and can be corrected if caught quickly enough. Could certanily lead to catastrophic failure if let go.
That said, I see these problems mostly were the roof pitch is greater than that in the photo. Also gable roofs are a lot more fragile in this regard than hip roofs. I would notate the lack of collars or kneewalls in your report, but if you are not seeing any noticable deflection or sagging after 10 years, it probably is unwise to call it a defect.
Originally Posted By: mpatton This post was automatically imported from our archived forum.
Thanks for the input.
For clarity this is a hip roof but the front to back is much narrower than the length of the house, basically the house is 28' X 80' Plus. With that said it will act very much like a gable roof.
-- Michael Patton
AA Home Inspection
Serving Northern KY & Greater Cincinnati OH
Originally Posted By: roconnor This post was automatically imported from our archived forum.
… Great post and explanation of the difference between rafter ties and collar ties … … I saw that Fine Homebuilding article you linked, and it has an excellent discussion of common framing problems.
Note that ya can go higher than 1/3 above the walls with the rafter ties, but it has to be an engineered design to work ... with larger rafters and heavier bolted connections ... ... Also, for new construction IRC R802.3.1 would require an engineered (alternate) design for anything other that rafter ties at the wall top plate or ridge girders. The connections are usually an issue.
Mike ... for a roof structure like that there needs to be either a tie across the building (low rafter ties, ceiling joists, or strap ties) or the ridge can act as a beam with adequate strength and supports. Either option will keep the ridge line from sagging and also keep the walls from bowing outward.
I would suspect there isn't a heavy connection where the rafters connect to the old wall (e.g. rafter framing angles and grouted sill anchor bolts), along with possibly an inadequate lateral connection of the old roof structure to the walls, in order to use the old roof framing as the lateral tie. So It looks like they went with the ridge support option on that one.
But it looks like it was hack posted, and the ridge "girder" may be undersized to span between the posts. I would also be very concerned with what was below those posts, and look for any sagging of the old roof/ceiling and along the ridge line between supports.
Just my opinion and 2 nickels
-- Robert O'Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee
I am absolutely amazed sometimes by how much thought goes into doing things wrong
Originally Posted By: rray This post was automatically imported from our archived forum.
Someone needs to sit Erby down and just record all his links and all his web sites. He always has some of the most awesome links and articles to share.
Originally Posted By: mpatton This post was automatically imported from our archived forum.
Erby,
Nice post and a great link.
Yes I incorrectly described the rafter tie as a collar tie.
Quote:
Rafter ties or cross ties need to be in the lower third of the distance between the ceiling joists and the ridge beam. This gives them the leverage they need to prevent wall spread. In a lot of buildings, the celing joist actually also function as rafter ties by being connected (in some fashion) to the rafter.
Robert,
Well explained, thanks for the information, and confirming what I was thinking in several areas.
In the report I took the smart road "Picture #2, Recommend having a qualified contractor or engineer inspect and assess the adequacy/method of the roof framing."
Truth be told everything about the roof structure looked questionable from within the attic.  Another reason when able to access the attic to enter as well as walking the roof. I am a believer if accessible go for it. As always there are exceptions to this statement.
Thanks for the input.
-- Michael Patton
AA Home Inspection
Serving Northern KY & Greater Cincinnati OH
… I saw that Fine Homebuilding article you linked, and it has an excellent discussion of common framing problems.