Historic Roof Framing - Perennial Issues

[NewEnglandStruct]

These days I have been doing a lot of work on additions/modifications to older homes. Many of these roofs are framed in ways that are hard to model and review. Commonly there is a hip roof with no posting (presumably a tension ring is holding them up), or gables with no ridge and no effective rafter ties. The current project I am on involves very minor beam/wall modifications, however, I am at a loss for when to advocate for a major overhaul. If they are spending 200k to renovate a 1mil house, should I recommend that they install a ridge beam even though the roof is currently showing no signs of deflection. It's a can of worms.

I guess my question is: at what point do you reconfigure the whole structure of a 100+ year old house? And, are there any novel ways of analyzing such things (timber frame engineering tricks for instance)?

 

[jayrod12]

Often there's a chance that the roof sheathing is acting as a deep beam which allows for those houses without ridges or posts to stay standing.

And really, in old fashioned gable houses with proper ceiling joists, no ridge beam is required. The two rafters push against each other, and the ceiling joists deal with the outward thrust. I've rarely ever seen a tension ring except for vaulted ceilings. And even then, there's usually a different way they've skinned the cat.

 

[XR250]

I would give the customer the option to spend the money or not. Unless I am adding load or taking away structure or there is obvious deterioration, I am not inclined to mess with these old roofs as they usually defy analysis.

 

[NewEnglandStruct]

Yeah - that makes sense jayrod12, it's good to know I'm not the only one dealing with these issues, that's for sure. One annoying part of this particular house is that there are shed (essentially flat roof) dormers in the gable on one side, and the ceiling/floor joists are not acting to tie everything together for most of the length of the house (stairwells are also an issue here). I think I'll take XR250's recommendation and leave it to the owner to decide. My plan is to advocate for a supplemental ridge for general longevity, because it might prevent water intrusion in the future, and just piece of mind, but it's up to them.

 

[phamENG]

I deal with this from time to time as I work on quite a few historic structures. Generally I approach it like XR in terms of analysis - I only try if I'm changing it. This is mostly semantics, but I don't think these defy analysis - the fee deprives us of the time and information to do a full investigation and analysis. If I determined the quantity of nails in every connection and got all of the geometry figured out, and maybe have a sample or two tested I could apply a few assumptions and do a thorough analysis (understanding that "failure" in a new wood design is far from failure in the real world). But it would cost the homeowner the better part of $12k before I even start designing the new stuff, and who's going to pay for that?

So if I'm not messing with it, I don't mess with it unless I see an impending problem. If I'm altering it in any way, I do mess with it and make sure I'm comfortable with and can defend the end product. I don't give the owner the option because they won't spend the money on that either but I'll still be liable for it. And let's face it, the owner of a million dollar home can afford a better lawyer than me.

 

[ThorenO2]

I wouldn’t see the justification for installing a ridge beam unless there is measured deflection or deterioration. Best of luck, always tough decisions to be made in this profession.

 

[skeletron]

I think it's your responsibility to at least verbally let the Client know that other upgrades may need to be considered. As you start moving/removing walls the existing system changes and so you need to suss out (a) how much work has been done already without cueing other upgrades; and (b) how much work can you do before everything gets affected.

Recently I've also been told that it is wise to consider how long the Client will be living in that house. What are their plans? If they are flipping it or keeping it as a rental, I'd probably advocate a little harder to make sure the existing conditions were looked after. If they are making it their forever home, I'd advocate that some upgrades can provide better value in the future. And if they are making it their home on the budget they have, try to contain your work so you don't have too much funky analysis to reason out.

 

[le99]

I do struggle from time to time trying to figure out why a structure without the certain feature(s) has stood/functioned well over time. Often the inability to get to the bottom of the matter has refrained me from acting unilaterally, but to presenting my concerns to the owner for his/her consideration. The results were often positive if I can clearly point out the benefits of the addition.

 

[NewEnglandStruct]

Thanks for all the good advice. I am only making verbal comments about options at this time, and waiting for the framing to be more completely exposed. I think I was able to get a good understanding of what to do though, and how it affects the scope (where a new ridge would need to come down in the basement for instance), which is the best I can do at the moment anyway. Hopefully I can recoup the extra time as we move forward. It's a nice old house, and I hope we can improve it for a long time to come!