You need an expert when assessing the standard of care and identifying what a reasonable person would do during the investigation of an accident or failure in the built environment. (Refs 1) For example, an engineer who has investigated the cause of problems like the following:
- Personal injury accidents
- Component and catastrophic failure of structures
- Ground subsidence
- Potholes or tire-worn tracks in roads
But what do you do when the problem requires an expert with two or more areas of expertise? For example, engineering design expertise and tradesman carpenter experience – like in house construction.
I thought this recently when repairing my balcony that is made of timber planks. And another time when underpinning a deck supported on a waste fill. In both cases I would need an engineer with tradesman experience to assess if what I did was reasonable – a slightly unusual combo of expertise.
Repairing My Timber Deck
The tops of the outer ends of the inner two beams of four had rotted and no longer supported the deck planks properly. The beams had failed after 18 years. Why the inner beams and not the outer two? Also, why the tops of the outer ends of the beams and not the tops of the inner ends fastened to the house?
It was an easy call. It was a wetter environment at the tops of the outer ends of the beams beneath a lovely magnolia tree. The beams came to the end of their useful life for the environment they were in. All materials have a life in the built environment that engineers consider when designing.
Fixing the problem was an easy call too. Just replace the deteriorated beams with new ones. However, there is a difference in construction time and cost depending on how you do this.
The simplest, quickest, least expensive way involves installing new beams alongside the old ones. The old ones will rot away in time and the weight of the deck (dead load) and me and my family and friends walking around up there (live load) will slowly transfer to the new beams.
The more involved, slower, more expensive but possibly more conventional way involves temporarily underpinning the deck, removing the rotting beams and installing new ones.
Both repair methods will work but leaving the rotting beams in place is a tad unconventional. What would a reasonable person do, as required in a standard of care assessment? And where do I find such a person with lots of experience in both engineering and hands-on deck building?
I believe the bias in this situation would be to a person who has built a few decks but with some engineering experience.
Underpinning a Timber Deck
A friend’s deck had settled several inches over the years. The house and deck were built maybe 30 years ago. The wood deck and joists were supported on beams that in turn were supported by timber posts resting on concrete blocks. Typical residential deck construction.
Atypical was the concrete blocks resting on filled ground, not dense, natural ground typical of most of Nova Scotia. To make matters worse, the fill was a mixture of boulders, soil and tree stumps typical of waste material from a construction site. Fill, unlike natural ground settles over time; waste fill settles a lot.
But to give fill it’s due, the settlement decreases over time and becomes negligible in engineering terms. The time depends on a lot of factors including the type of fill and the natural ground below. I would expect a waste material like on my friend’s property to settle a lot and continue for a long time.
Measurements indicated the deck surface had settled about six (6″) inches midway between the corners at the rear. Examination of the bottom of the posts found a gap between the bottom and the top of the concrete blocks. The blocks had settled away from the bottom of posts as the waste fill settled. The gap was two (2″) at the midway post at the rear. Adding the size of the gap to the settlement of the deck indicated the surface of the waste fill had settled about eight (8″) inches in 30 years.
Fixing it was simple and easy, just install longer posts resting on the concrete blocks – a simple underpinning operation in engineering. But, what if the waste fill was still settling after 30 years and we come back a few months later and find gaps beneath the underpinning posts again?
Still an easy fix, install steel jack posts that can be adjusted in the future. The need for this adjustment would be apparent if the posts wobbled a little when examined later. Jack posts have a threaded section that can be screwed in or out like a big bolt – up or down in this situation – to remove any wobble.
But this requires periodic examination of the posts in the future. This could be avoided by excavating the waste fill at each post and supporting each concrete block on the natural ground below.
Another fix but a very expensive one, and a bit scary too because waste fills are unstable if you disturb them even after 30 years. Experienced engineers would leave the fill alone – let sleeping dogs lie – and experienced tradesmen certain to as well.
I believe the bias in this situation would be to a person with an engineering background who has built two or three decks.
Final thought on multi-expertise experts
The examples above are fairly simple but there are more complicated failures out there that require a team of expertise. What to do? For sure, be careful because there are those who claim more expertise than they’ve got.
The approach in engineering is to retain an engineer who would be the principal expert. S/he would identify the areas where additional expertise is needed and search for people in those areas and hire them. The principal engineer would then work with the sub-consultants/experts in determining cause. I did that when investigating the cause of a nail gun accident and also an old fuel oil spill.
- How the standard of care is determined when a failure or accident occurs in the built environment. Posted June 28, 2014 (The posted blog has been updated to October 30, 2020 as noted in the blog) A good read with lots of references.
(Posted by Eric E. Jorden, M.Sc., P.Eng. Consulting Professional Engineer, Forensic Engineer, Geotechnology Ltd., Halifax, Nova Scotia, Canada July 29, 2022 firstname.lastname@example.org)