Assessment of old Residential Foundations 1

[CANeng11]

This is a general question about the assessment of old residential foundations. We regularly get asked to look at the structural health of 100 year old concrete foundations, usually for the purposes of potential renovations, or possible sales. Often times with these old foundations, there are clear issues with the foundations but any proper/complete fix is likely cost prohibitive. You often find there is settlement (often no footing under wall) and poor concrete condition (i.e. cracking, spalling, etc.). To properly address the issues, often may require a completely new foundation. But what is there now has been working for a long time, and we can usually assess that immanent failure is highly unlikely. So my question is, how do you approach a situation like this? Do you tell them that the condition of the foundation is poor and renovations are not recommended to the structure above, but structural failure does not appear to be immanent? And then list any recommendations you can (i.e. fix drainage on exterior). Any thoughts are appreciated.

 

[phamENG]

Sounds like you nailed it.

The "it's been working for a long time" argument irks me some. When you're dealing with a 100 year old structure, I agree it does mean something. Though it doesn't guarantee that it's seen what current code would require a new structure to be designed to. So I'm often leery of approving modifications based on that argument. And where I am, no building built in the last 65 years has ever seen the design wind loads required of a house. Even for the older ones, it's questionable unless they're right on certain parts of the coast line. It's been working for a long time, but lots of things work for a long time and then break. To prolong the life of it, it requires significant maintenance and repair as required. Sounds like this hasn't been happening on many of the foundations you're seeing.

So "it'll probably be ok if you don't add to the house but it's not compliant with current code" is probably a safe and reasonable line to take.

 

[r13]

Even with high confidence, I wouldn't put "imminent failure is unlikely" on the report, maybe verbally, because it is true only when we are present. Instead, list all defects and separate into two categories - immediate repair over visible defects that will lead to further damages; and deferred repairs, that are to be carried out when change of uses, and/or conduct renovations. Finally advise the owner to call for help immediately upon noticing structural changes, such as new defects, and/or escalated worsening of existing defects.

 

[WeezerMike1]

Yeah, I agree this is a tricky situation. A homeowner that's paying for an engineer will often expect some sort of definitive "safe" or "unsafe" conclusion. In reality, those terms aren't really meaningful, and it's all about levels of risk. An engineer that gives a definitive conclusion one way or another is at risk of being blamed for future failures, or blamed for the high cost of repairs.

If I was doing this type of work, I would try to establish reasonable client expectations before starting the work. What's their goal? Get that in the contract so it's clear what service you're providing. Are you giving recommendations to bring the foundations into compliance with the current code, or looking for severe/moderate/minor deficiencies? Are you giving a list of potential upgrades with priority rankings so they can fit the work into their budget, etc.

 

[NorthCivil]

In a past role (not particularly well paid, but very fulfilling and interesting)

I used to do timber frame residential alterations all day every day. This was in the pacific northwest, where i was fortunate to get up to my elbows in all sorts of 100+ year old timber frame houses, mostly functional, terribly framed, with beautiful timber. Often those old tudor houses, 3 levels or more tall, are sitting on foundation walls with 2-4" of frost depth. no reinforcement. concrete quality questionable. Not unusual to see a beautiful load bearing fir post placed over a 10" jagged rock, holding up half the house, successfully, for a century.

Our policy was, if we were going to alter or increase the loads over a foundation, the foundation required upgrades. underpinning, or placement of pads. if the loads were to remain the same, the foundation could remain unaltered.

if a client is spending hundreds of thousands of $'s to completely gut, re-structure, and refinish an old house, they can pony up 10K for upgraded foundations.

sure, it probably isnt needed in 95% of cases. the soil and existing foundations "probably" could manage with the re-arranged loadings.

but in the 5% of cases you get settlement, ruined finishes etc on your half a million dollar project, because new foundations were value engineered out, who is the bad guy? who pays to fix that?