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I am a homeowner who likes to save money by performing DIY work. When possible, I prefer to serve as my own general contractor to reduce the cost of a project. However, when I talk with professionals about my plans and ask for advice, they often tell me that I need to consult with a professional engineer.

I want my home to be safe but hiring an engineer sounds like an expense I can't afford. How can I tell when it's really necessary to consult an engineer before performing work on my home? Why can't I just hire a licensed contractor instead?

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Here's a simple analogy1, 1a - if you're planning on modifying the skeleton of your house, then you ought to consult with a licensed Engineer before committing to any work.

And if your renovation is altering one of the house's systems, such as the plumbing, electrical, or heating, then you can most likely rely upon the contractor performing the work and you do not need to consult with a licensed Engineer.

So what's the skeleton of a house?
It's the framework of the foundation, walls, floors, and ceilings of the building. More accurately, it is the structural components that keep your dwelling standing as well as held together. Also keep in mind that significant amounts of nearby earthwork can affect the structure of the house.

House structure Foundation
Click on link for larger image

So what counts as a modification then? It's obviously more than drilling a hole into a wall in order to hang a picture, right?
A structural modification means moving or removing a piece that was originally part of the dwelling's skeleton. For example, there might be metal posts holding up beams running the length of your basement or garage. Those posts are helping transfer forces from one area of the house into a lower area. Moving those posts would affect the skeleton of the house. Another example would be the joists between the floors of the house. Those joists help distribute the load within each floor of the house. Significant modifications to them could impact the structural integrity of the house.

Load bearing wall
Click on link for larger image

Okay, so I can't touch anything associated with the foundation or framing of the house, right?
Well, probably not. But that's Murphy's Law speaking. In other words, the thing you want to change is likely to be a critical part of your house's structural integrity. But there are non-load-bearing walls within a house. Believe it or not, those walls can be knocked out with almost zero impact to the structural integrity of the house.

Wait, what? So I can rip out the wall I want?
Slow down again. Yes, there are some walls that can safely be ripped out. There are (many) other walls where you'd be foolish to do so. How do you tell the difference?2 Hire a structural Engineer and have a proper analysis done on your dwelling and the proposed change. Reasonably speaking, the original construction of the house wouldn't have put the majority of the walls in place unless they were necessary.

Blah, blah, blah. You're just trying to perpetuate a racket and drive up Engineering services revenue.
Please keep in mind that Professional Engineers have an ethical obligation to uphold individual and societal safety over any considerations for profit. The reality is that making changes to the structural elements of your house can result in catastrophic damage to your house if incorrectly performed.

Most good contractors will avoid any potentially catastrophic project from a healthy fear of the liability associated with the project. That's a key warning sign that you should heed. That apparently expensive consult with a licensed Engineer is nothing compared to the potential expenses you would be facing to fix an errant and ill advised change to the structure of your dwelling.

Ah, c'mon. It's just a simple, stupid post that's in my way. Moving it won't affect anything. Right?
Quite the contrary. Shifting where loads are transferred can increase the amount of applied force by an exponential rate. Said another way, "simple" shifts in things can create really big problems.

Okay, wait. Wow! this is apparently very complicated stuff. What should I do?
Structural analysis is complicated, and there are a number of factors involved that have to be considered. Generally speaking, the best thing you can do is to consult with a licensed Engineer and let them know what it is you want to try and accomplish. Also let them know what you're willing to compromise upon, so they can help balance between project expenses and requirements. Their job is to help you identify the right balancing point between your dream project and the cold, harsh reality of physics. As an added bonus, they have likely already helped many other clients address similar projects. And they will likely be able to point out additional considerations that you would not have considered.


Footnotes:

1: Please note, this answer is intentionally written in a conservative perspective. Why? Because it's the prudent approach to take when the consequences of a mistake could be catastrophic or just exceptionally expensive to repair.

1a: Also note, there are many variables at play and the range of considerations can be quite wide. There are modifications that should be answered with "Are you crazy?!" as well as modifications where the answer is "Sure, that shouldn't be an issue." This answer is meant to provide a starting point as a simple "rule of thumb."

2: Well scoped questions could potentially be asked here on Engineering or on DIY / Home Improvement. Asking about how to identify non-load-bearing walls, or asking about what building codes allow for modifications to joists ought to be on-topic for one or both of those sites.

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I can't answer for every home, but I do know California Board of Professional Engineer's regulations.

The board dictates for design, that anyone can design an improvement of a two story home with a basement. However, this comes with a two-fold liability for the design:

  1. The design must meet with pre-engineered building designs in California Building Code:

If any portion of the structures described above does not meet the conventional woodframe requirements described in Title 24 of the California Code of Regulations or in the building codes of the local jurisdiction, then the building official having jurisdiction shall require the plans, calculations, and specifications for that portion of the structure to be prepared and signed and sealed by a licensed engineer or a licensed architect.

  1. If there are any problems, the liability goes directly to the designer. Per California Professional Engineering Code 6737.3:

This section shall not prohibit a licensed contractor, while engaged in the business of contracting for the installation of electrical or mechanical systems or facilities, from designing those systems or facilities in accordance with applicable construction codes and standards for work to be performed and supervised by that contractor within the classification for which his or her license is issued, or from preparing electrical or mechanical shop or field drawings for work which he or she has contracted to perform. Nothing in this section is intended to imply that a licensed contractor may design work which is to be installed by another person.

As such, if you want someone else to design something new, and have the liability for designing it, they need to be a Professional Engineer. If you want to modify it yourself, you can - so long as you follow the pre-engineered plans. But the liability falls upon yourself. No contractor will design it for you to do it yourself - that's the law.

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To add to Mark's answer; most houses are built based on state building code, not designed by a Structural PE (structural is a defined specialization in many states). A Structural PE is expensive and usually only comes into play when you want to do something tricky that is outside of what the code allows. The code can only cover so many cases. For structural, material, and load exceptions, you need a Structural PE. And for spacing, layout, and use exceptions you need an Architect. Many firms will have both on staff. An experienced general contractor is good at staying within what the code supports because it is much cheaper.

If you are doing a major remodel it is often good to go to an engineer or architect, because they do this for a living and will catch the things you might not think of like toilet spacing or egress requirements. Its much cheaper to get those things correct upfront as opposed to when you go to install things or when your house is inspected before a sale. Also, if you are getting a loan for a remodel a bank will require a drawing of the proposed layout and sometimes require that drawing to be from an architect or engineer.

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Why can't I just hire a licensed contractor instead?

Basically, because a contractor does not have the education and is not required or expected by law to know what he is doing or telling you and/or to protect your best interests in doing so. A design professional (Professional Engineer or Registered Architect) does all of the above.

So when the stuff hits the fan and your DIY work collapses or starts to leak, a contractor is not responsible nor expected by law for the design of the work or for contract specs and you will not be able to recover your defective DIY work. Assuming your contractor does not disappear, the contractor's attorney will simply state that his proposal simply listed the work that you wanted him to do and he has no idea how a house works or what the design is all about (he doesn't have enough education remember?). And the contractor wins every time because that's the law. Don't let his tongue impress you.

And even if his proposal states that the work shall comply with all building codes, if the work doesn't pass inspection, a contractor is allowed to say I didn't know this code and I will have to charge you extra change order because by law a contractor is not expected to know the code (he doesn't have enough education remember?). Don't let his shiny red pick-up truck impress you (or his attorney's Mercedes).

And even if he gives you a labor and materials guarantee, if its defective design or a code violation, case law says a contractor is not expected to know the job is in violation or defective work if its simply something you asked or directed him to do as the owner and general contractor on the job. By the way, most roofing contractors for example have a statement that if the roof develops cracks more then 1/4 inch, the roofing guarantee is VOID my friend. Don't let the contractor's attorney's Mercedes impress you.

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  • $\begingroup$ But if I hire a contractor instead, they are on the hook for doing it right (and getting an engineer involved if required). At the point where an engineer is required, you still can't hold the engineer responsible if you built it wrong. You can hold a contractor responsible for building it wrong. $\endgroup$ – hazzey Dec 15 '15 at 18:24
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First you have to decide how far down the rabbit hole to go...

As with all things, the answer is going to be complicated and unique to every project. The easy way is to stop now and hire a Contractor. The Contractor is supposed to know what they are doing and know when an additional professional (i.e. Engineer) is needed.

This reduces your future liability for doing it wrong (i.e. places the liability on the Contractor) and allows you to get the project done without lots of research.

No turning back...

If you get to the point of your DIY project that you are asking yourself this question, you have likely already gone too far. Also, you likely don't want to ask anyone else (or pay for anyone else).

There are lots of rules-of-thumb or general guidelines that could be followed, but there are always exceptions (and ways to convince yourself that your project is special). The rules-of-thumb are all based on something. That something is usually...

Building Codes!

If you are in the US, get acquainted with the building codes that govern your structure. (Other countries should have similar codes.)

For a house, the two that you have to worry about are typically:

Both of these are available online as linked above. If your local jurisdiction requires a special year, check here: Resource.org

Note, all of these links are legal. Don't go searching the shady parts of the internet.

To the Books!

Read the section of the above codes that apply to your project. Try not to get distracted by the vast amount of other things in there though. You can lose hours of your life by finding interesting things that you never knew were specified by code.

If you have found the section that applies to your project and it all made sense, congratulations, you should have an answer. The answer may be specified by the code, in which case you now know how to proceed. If it isn't covered by the code (or you don't understand), then you need to hire someone.

It is that simple.

Oh wait, there is something more. You might not have a choice...

Permits!

You were going to get the permit that is required by your local city/county right? RIGHT?

The kind (and some are helpful, some are not) people in the permit office will definitely have opinions about what you will need to hire someone to do. Their opinions also come backed with fines if you don't comply.

California Guide

California has a guide that covers most of these issues: A Guide For Consumers

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