This one is personal. My girlfriend is selling this 1920’s house with a hip roof and is currently in escrow. The roofing contractor hired by the buyer is saying that the rafter spacing is inadequate and the roof feels “spongy” and, or course, recommending $19K in repairs to add rafters and replace the roof entirely. The roof was completely re-sheathed and shingled just 12 years ago…
Other factors: 1) this roof has stood for over 100 years, 2) we had 80 inches of rain this year with no leaks, and 3) there are only minimal snow load considerations in this part of CA.
I agree that the rafter spacing is inadequate by modern standards when there are only rafters and sheathing. But, in this instance there are also the strength of the purlins (the horizontal members, also known as skip sheathing) made of 1" nominal that add considerable strength to the roof, in addition to the overlaid OSB sheathing. I would like to see purlin braces, which is why the roof might feel spongy a bit, but I do not believe that is a critical flaw with no snow loads.
Does anyone have a reference to site that says the rafter spacing can be larger with purlins installed?
I’ve inspected a few hundred homes with that type of roof. Mine included except for mine is Gable. And most were a lot older than this home. Previously cedar/wood shakes. And I’m in an area of the country that gets plenty of rain and snow. Sometimes a foot or more of snow.
Few of them bounce. I know mine doesn’t and I’ve been on it many times. In fact I just had a new roof put on mine a few years ago. There were seven or eight guys on it. I think the roofer is giving you a line of crap.
I do not have any specific site for reference. But the test of time has proven this type of roof holds up.
Rafter lumber type and dimensions dictate spacing.
As well the skip sheathing is dressed with OSB.
There are collar ties and if everything is intact, what’s with the roofer’s referral? What type of roof covering is being put on the roof, Brain? Rafter Span Tables
That would not pass current building codes, but building codes don’t require updating all noncompliance items. For example if you’re required to get a permit to remodel the master bath you only have to upgrade the outlets with GFCIs in that bathroom. As long as the roof framing is not damaged and the roof is not leaking I would typically just comment the roof framing was typical for its age and once had cedar shingles/shakes. I would say rafter sagging is normal for its age and only flag excessive sagging or broken rafters as needing bracing or repair respectively.
From what I have observed, there is no damage to the framing or leaks. All the rafters are firmly attached to the hips (actually, really nice carpentry work). There is some minor rafter sagging, but I agree with you that that is normal for its age.
What this is coming down to is a roofer and general contractor (both with clear conflicts of interest, biding on the repair work), neither of whom are structural engineers, claiming that the roof structure on a 100-year-old roof is now suddenly inadequately designed, in their opinion.
I am a trained and experienced mechanical engineer, as well as home inspector. That said, I am still glad that two inspection guys with tons of experience, with absolutely no conflicts of interest, and “P.E.” in their title (I know what it takes to earn that), as well as all you “CMI” folks, pretty much agree with me. Thanks guys.
That’s the million dollar question. Splitting/cracking lumber, stress at critical intersections and fasteners and fastener patterns.
Sometimes optical illusion, the angle of position you are in can give the appearance of sagging. The collar ties are there to prevent that from occurring when installed properly.
If the framing is 100 years old and there are no issues to speak of then I suspect the weight of a an architectural shingle will be fine.
What roof covering material was on the roof frame in the first place? Skit sheathing to me is for roofing materials such as shakes and shingles. Architectural shingles weighs between 180-240 pounds whereas wood shingles weight 3.5 – 4.5 pounds per square foot or 350lb to 450lbs per square.
Seems to me some purlin bracing/strong backs would be a simple compromise and not incredibly expensive. Unfortunately, when you have people who benefit from their opinion you get bias. So an SE may be the only one able to settle the dispute.
Indeed. Strength and stiffness are two completely different qualities. Even though an aircraft wing can flex massively, it does not break - that is strength. I am positive that the strength is there in the roof structure. What they are really complaining about is the stiffness, which is not all that relevant, but I understand their ignorance.
Money, in a clear conflict of interest. I am pretty sure that the roofer never went into the attic. So, it was a roof covering inspection, not a roof inspection. His only complaint was the spongy feeling and said, paraphrasing “The roof is not safe. Need to deal with the structural issues before you pay me $10K to replace a 12 year-old roof that does not leak.” Then the general contractor guy, that is not a structural engineer or a roofer, comes out to do the structural assessment inside the attic and says the roof that has stood for 100 years is falling down, give me $9K to fix it. Neither have provided any specifics as to what the real problems are, if any, other than they think the rafter spacing at around 32" is not to modern standards.
Indeed, the rafters are actual 2" x 4" rough-cut, old growth (first cut) lumber. Might even be redwood. From what I can get from the internet, a rough cut 2" x 4" is around 30% stronger than a modern dimensional 2x4 that is actually 1.5" x 3.5". The fact that it is old growth lumber just adds even more to the strength.
IF…if the roof was spongy when I walked on it and yeah, yeah, “spongy” is subjective, but so is most of what we do, then I will recommend purlins and braces. Spongy for me is soft enough that an observer can easily see it giving under my 165lbs. Otherwise, if it is working, then it is working. I’ve had similar issues come up with the 20 or so houses that I’ve sold, and if the component in question is performing, whether conforming or not, then I say, “I don’t mind you asking, but the answer is No.”
Edit: Another thing to consider with these rafter homes is steepness. An 8/12 on the same span and spacing can support more weight than a 4/12 all other things being equal.
From recollections during my much younger youth, that lumber got stronger with age. Trying to cut or put a nail in it proved challenging at times. I remember sap bleeding out of the wood with age (which I’m sure many inspectors would find fault with). Sap turned to resin in the attic heat and make the wood even stronger.
No one mentioned the (Actual) 1 x 4’s between the 32" spacing.
Because you have never seen something, I guess it’s just wrong.
This roof frame was not designed for asphalt shingles, but something heavier. This is how they frame slate roofs. What’s the flaky OSB for? Nailing asphalt shingles.
What’s that 2 x 12" on end, crossing the attic floor?
And roof pitch is a concern?
I don’t see “subjective” in the definitions of the SOP. I do see;
(l) “Inspect” means the act of making a visual examination
If you want to measure roof deflection and put it in the report, go for it. It’s a fact, not a subjective opinion.
While I can provide a general response, I must emphasize that roofing and structural decisions should be made with the guidance of a licensed structural engineer or local building expert. They can provide the most accurate advice based on your specific circumstances, local building codes, and best practices.
That said, let’s address the points you’ve raised:
Historical Longevity: The fact that the roof has stood for over 100 years is a testament to its resilience and the quality of its original construction. However, it doesn’t necessarily mean it will continue to stand safely for another century, especially if there have been changes in the roofing materials, sheathing, or other components.
Recent Weather & Condition: The lack of leaks after receiving 80 inches of rain is promising, especially since leaks often indicate structural or material failures. Additionally, minimal snow loads in your part of California reduces the overall structural stress on the roof.
Role of Purlins: You’re correct that purlins (or skip sheathing) can add structural strength and distribute loads more evenly across the roof. They can help reduce the need for closely spaced rafters. The purlins essentially break up the span that a rafter has to support, acting as mini-beams. Thus, when purlins are installed correctly and are in good condition, they can allow for wider rafter spacing.
Feeling of Sponginess: The spongy feeling may be due to several factors – inadequate rafter spacing, deteriorating wood, issues with the OSB sheathing, absence or poor condition of purlin braces, etc. It’s essential to pinpoint the cause of this sensation. If the sponginess is due to the lack of purlin braces or inadequate bracing, adding those could be a much less expensive fix than completely reworking the roof.
In terms of references, you might consider:
Local Building Codes: While they tend to focus on modern construction methods, they might provide some guidance or historical context.
Historical Building Texts or Manuals: Older construction manuals or references may have more information on the accepted practices of the 1920s.
Consulting with a Historical Building Expert or Structural Engineer: Given that you’re dealing with a structure from the 1920s, experts who specialize in historic buildings might provide valuable insights.
Lastly, if there’s a disagreement between your perspective and the roofing contract assessment, consider getting a second or even third opinion. This can help ensure you’re making the best decision both for the safety of the structure and financially.