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Restoring a 200+ year old roof #30283 02/12/13 09:07 PM
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chrisr Offline OP
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I am an engineer currently working on repairing the roof of a house on a plantation in Louisiana built around 1800. They want to reuse as much original timber as possible, but some of the members will have to be replaced because of large cracks, splits, rot, etc. The house has relatively long overhangs that have gradually sagged at the corners over the years to the point that temporary braces were built under them to keep the roof from falling apart. I can size the roof members using cypress with today's grades, but I have little knowledge of what kind of stress grades to use on the existing 200+ year old members that still appear to be useable. I realize that this was built well before timber was regulated, but I still need to determine or assume some strength value for them. Any suggestions? Also, some of the existing sizes are overstressed using today's codes. Is there some kind of gray area code wise that applies to historic buildings like this that are only used as a sort of museum or do they have to meet the most recent code standards like any other building?

Re: Restoring a 200+ year old roof [Re: chrisr] #30284 02/12/13 09:46 PM
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Jay White Cloud Offline
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Hi Chris,

Historical variances are regional and site specific. Some states-municipalities are real supportive, other not so much. As a historical barn wright I see frames often that I'm told don't work or can't meet code, (bumblebees can't fly syndrome is what we call it in the trade.) Frame stood strong for two hundred year the way it was built, but now you can't build it that way because it isn't strong enough and will fall down? Consulting with one of the P.E. that are part of the TFG and have experience with historical timber frames could help. Give a call or email, should you need more info. Pictures would really help in understanding the frame better.

Regards,

jay

Last edited by Jay White Cloud; 02/12/13 09:47 PM.
Re: Restoring a 200+ year old roof [Re: Jay White Cloud] #30286 02/13/13 02:48 AM
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timberwrestler Offline
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I'd consult with a specialty timber frame engineer that's familiar with southern framing. You can look here for one:
http://timberframe.org/timber-frame-engineer.html

Re: Restoring a 200+ year old roof [Re: Jay White Cloud] #30287 02/13/13 04:35 PM
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chrisr Offline OP
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I think it's mostly a liability issue. It was built 200 years ago most likely using what we call here "the farm method" which is basically "eye balling" or guessing what sizes to make the members based on experience. Now that it is used as part of a historical landmark that is visited by the general public, I am guessing that it will need to meet at least some (if not all) of the current codes. The owners have hired us to advise in the repair and restoration which makes us liable should anything fail. The loads used from today's codes have built in safety factors and can be quite conservative at times which is why I am wondering if there any other factors involved for these kinds of situations. I will get in touch with a PE as suggested.

Pics below, thanks for your help!





Re: Restoring a 200+ year old roof [Re: chrisr] #30288 02/13/13 07:12 PM
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mo Offline
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What an interesting building!

Is that hat original? Those roof overhang supports appear to be near 15 deg. I am guessing they are bearing on the timber and then through to some sort of ceiling/ floor joist?

So those posts underneath the overhang were all added at some point afterwards original construction? I couldn't imagine that overhang working without some sort of plumb support. Maybe there is some evidence of previous posts set into the ground.

If so, you might have the case for an acceptable proposal to add more posts along the overhang and anchor them to a pier/footer.

What type of wind exposure are you dealing with?
Are the codes you are speaking of, the standardized building codes for standardized construction (that hence would not address this)?
In your area will a P.E. seal not trump structural code standards?

As for the case of adding more eave support through posts. Sometimes a good approach will be to make it obvious that the additions were not original so as there is no confusion that their was a later necessary addition.

It appears to me that if you can withstand the gravity loads at the corners (which appears to be working), you might have to deal with the wind loads. A couple more posts along the eave with proper anchoring might meet that.


By the way it looks like some strapping was added along the kingstuds adjacent to each door way.

I really like the introduced camber in the plates at the overhang.

Thanks for those pictures.

Re: Restoring a 200+ year old roof [Re: chrisr] #30289 02/13/13 09:45 PM
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Jay White Cloud Offline
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Hi Chris,

What a beautiful structure. This is classic Cajun/Creole Folk architecture, and by no means is this just "the farm method," it would not have lasted 200 years if that was the case. Those log walls and hipped roof are the skill of a master barn wright. They didn't guess at much of anything. They had very clear empirical knowledge and centuries of oral timber wrighting tradition behind them.

Unfortunately today, we have a "bottle neck," in these "folk traditions." There just aren't many of us left around that know, and understanding these building styles, nor methodologies. Plenty are starting to learn again, but there is about a generations worth of maturing before many of them could come to a job like that, recognize what they are looking at, it's archetype forms, and restore it traditionally.

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Now that it is used as part of a historical landmark that is visited by the general public, I am guessing that it will need to meet at least some (if not all) of the current codes.
I'm not sure that is the case, Chris. If this is an historical landmark and used for historical interpretive work, it would not necessarily be true. It may, in its current condition, need to be cordoned off from direct public access, but there are local and national grants for historical sites that have clear mandates on mode and methodology for restoration. As I had mentioned before, each area is different. They may have to apply for a variance, and/or special consideration.

I also don't see much building that would not be considered "original work.” The bracing that is supporting the long eve is standard practice in that form of barn. It is representative of the vernacular, indigenous building methods of the Choctaw and Seminole "chickee," architecture, which did influence the Cajun and Creole Gulf Coast building modalities.

I do have some question about the hipped roof, does in have a flat section on top? I would love some pictures from that perspective and the inside of the frame as well, if that were manageable. Do you know if the building has ever been photo documented and architectural renditions done? This would be a great TTRAG project.

Quote:
The owners have hired us to advise in the repair and restoration which makes us liable should anything fail.
Are you a timber frame PE firm or historical restoration firm? Could you share what some of the project plans are for the structure. If this building is going to be altered, are there plans to have an historical report completed before the structure original designs are changed.

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The loads used from today's codes have built in safety factors and can be quite conservative at times which is why I am wondering if there any other factors involved for these kinds of situations.
That is very wise of you. This introspective pause by folks like you have saved many structures like this from being unduly harmed and changed forever, thus loosing one more piece of the puzzle, never to be found.

Thank you so much for taking the time to share this.

Regards,

jay

Re: Restoring a 200+ year old roof [Re: mo] #30291 02/13/13 10:19 PM
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Jay White Cloud Offline
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Hello Mo,

If you don't mind me sharing, I might be able to speak to some of your observations and Chris can correct me or add to them.

Quote:
Is that hat original? Those roof overhang supports appear to be near 15 deg. I am guessing they are bearing on the timber and then through to some sort of ceiling/ floor joist?
Hipped roofs are common in both folk styles of the Native American culture of the region and the French. The supports you noted are in compression only in this case, and do not pass through the log wall. In very rare forms there is a "corbels," or "stitch beam," configuration that could support them.

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So those posts underneath the overhang were all added at some point afterwards original construction? I couldn't imagine that overhang working without some sort of plumb support.
I would say the corner supports are added later. It is more often the case that there are never any posts and only perhaps the bracing as you see it. If the frame work is done correctly, this roof style becomes a "hung roof," very similar in function to the "tipping rafters," of a Dutch Barn. What does often occur during the life of the structure, is a major wind event will take place and the original compression braces dislodged and not restored properly, which intern can cause further failures.

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As for the case of adding more eave support through posts. Sometimes a good approach will be to make it obvious that the additions were not original so as there is no confusion that their was a later necessary addition.
That is very smart. In worse case scenarios, when you can't get the work done to historical standard, your suggested solution is the best. It preserves the original structure from further degradation.

Quote:
It appears to me that if you can withstand the gravity loads at the corners (which appears to be working), you might have to deal with the wind loads. A couple more posts along the eave with proper anchoring might meet that.
If done well and to original standards that is not necessary. There are cases where a museum will want to preserve even the original materials so you can install hidden cable of steel or Kevlar/Spectra that will take the loads but not be visible, or barely so.

I would note that the very hip/gabled roofs and light timber frame work of a "Chickee," is often the only thing left standing after a Hurricane. I have seen subdivisions built to Southern Florida where all the "new code," stick frames are flatted to the ground, and the only thing left standing are the "Chickee," pool pavilions in the back yard. It speaks volumes to the strength of traditional architecture and what modern man does't know, but thinks he does.

Quote:
By the way it looks like some strapping was added along the kingstuds adjacent to each door way.
I'm not sure of what you reference? I do see iron strapping, that could be original, that holds the sill beam to the brick foundation. Those are found on either side of the door.

Regards,

jay

Last edited by Jay White Cloud; 02/13/13 10:27 PM.
Re: Restoring a 200+ year old roof [Re: Jay White Cloud] #30328 02/19/13 10:47 PM
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chrisr Offline OP
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Quote:
This is classic Cajun/Creole Folk architecture, and by no means is this just "the farm method," it would not have lasted 200 years if that was the case. Those log walls and hipped roof are the skill of a master barn wright. They didn't guess at much of anything. They had very clear empirical knowledge and centuries of oral timber wrighting tradition behind them.

Forgive me for underestimating the design. My knowledge of historical timber construction is limited, obviously.

Quote:
There just aren't many of us left around that know, and understanding these building styles, nor methodologies. Plenty are starting to learn again, but there is about a generations worth of maturing before many of them could come to a job like that, recognize what they are looking at, it's archetype forms, and restore it traditionally.

That is why I am here asking for help from experts such as you so that I can make educated decisions on how to go about this project. smile

Quote:
If this is an historical landmark and used for historical interpretive work, it would not necessarily be true. It may, in its current condition, need to be cordoned off from direct public access, but there are local and national grants for historical sites that have clear mandates on mode and methodology for restoration. As I had mentioned before, each area is different. They may have to apply for a variance, and/or special consideration.

The second floor has a series of murals and assorted artifacts that appear to be used for teaching so I don't see them cordoning it. It is my understanding that they only want to repair/restore the roof as close to original as possible and continue to use it as part of the interactive tour. That is why I am assuming that the structure will need to meet current codes.





Quote:
I do have some question about the hipped roof, does in have a flat section on top? I would love some pictures from that perspective and the inside of the frame as well, if that were manageable.

No, it has a ridge that hip out at both ends.



Here is a picture of the framing from the under side of the ridge.



Quote:
Do you know if the building has ever been photo documented and architectural renditions done? This would be a great TTRAG project.

That I have no idea.

Quote:
Are you a timber frame PE firm or historical restoration firm?

We do design timber structures, but we are not predominantly a timber frame firm nor are we a historical restoration firm. This is actually my first attempt at preservation or restoration of a historical structure which is why I have so many questions.

Quote:
If this building is going to be altered, are there plans to have an historical report completed before the structure original designs are changed.

To my knowledge there has been no discussion of a formal historical report being done.

Quote:
This introspective pause by folks like you have saved many structures like this from being unduly harmed and changed forever, thus loosing one more piece of the puzzle, never to be found.

Exactly. My intentions are to preserve the look and history of the structure by modifying it as little as possible.

Right now the main issue with the structure seems to be at the overhang corners. From a structural standpoint, what appears to be happening is that over the years the rafters have gradually settled or scissored out most likely due to heavy wind loads, general fatigue, and possibly the fact that the rafters are connected at the ridge with a wooden pin (seen in the attic pic above) which basically creates a hinge. This settling has led to the rafters being pulled away from their bearing points on the wall and the overhang perimeter beams being pulled away from each other at the hips and away from the supporting struts as shown in the pic below.



What would be ideal is to have a timber frame PE who is familiar with historical structures take a look at the building and sit down to discuss a game plan to restore it the right way. I am hoping it will not come down to a time constraint issue that leads to things being done only half way just so it will be done.

Re: Restoring a 200+ year old roof [Re: chrisr] #30334 02/20/13 03:49 AM
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Jay White Cloud Offline
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Chris,

I have contacted you offline, there is just too much to discuss and I have to many questions. I really would love to talk. Once I know more, posting additional information here will be assured.

Regards,

Jay

Re: Restoring a 200+ year old roof [Re: chrisr] #30335 02/21/13 12:59 AM
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Roger Nair Offline
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Hi Chris

The NCPTT has an article entitled "A Grading Protocol for Structural Lumber and Timber in Historic Structures" and a MS Access database at

http://ncptt.nps.gov/a-grading-protocol-...-2009-01/all/1/

The database is somewhat limited in the number of species covered but it may be useful in a site survey.

You may find a resource in the NCPTT since it is located in Louisiana.


National Center for Preservation Technology and Training
645 University Parkway
Natchitoches, LA 71457

Email: ncptt@nps.gov
Phone: (318) 356-7444

Re: Restoring a 200+ year old roof [Re: Roger Nair] #30338 02/21/13 02:37 PM
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chrisr Offline OP
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Thanks Roger. I did find and download the article and database but with time as an issue it would be much faster to enlist an expert rather than try to learn how to grade the timber on my own. I also contacted the NCPTT and oddly enough they pointed me here for help. After speaking with Jay White Cloud I believe that I am on track for creating a game plan to restore it the right way.

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