I'm sure the person who wrote the article in your post had the best of intentions, but I question this statement:
If you are doing electrical work and a fire occurs at a later date you better have the certified documents for the work or the insurance company will refuse the claim. The same holds true with plumbing work as well.
In the first few years that I started operating my apartment block I was told that ALL plumbing and electrical work in commercial buildings had to be done by licenced plumbers or electricians, or the insurance company would deny the claim.
So, I contacted my insurance agent with The Co-operators, and she said that wasn't the case at all. Every insurance company recognizes that most landlords of small apartment blocks do many of the repairs needed themselves. She even reminded me that most small apartment blocks have caretakers with no formal training in any trade that are often called upon to do small plumbing and electrical repairs, any one of which could cause water damage or a fire.
Similarily, an insurance company would have to be inexcusably naive to believe that all homeowners hire professionals to do all the repairs needed and renovations wanted in their homes as well. That would presume that insurance companies simply haven't noticed all the home centers popping up in every city in the country to sell homeowners the materials needed to do that work themselves.
This web site recognizes that many home owners do their own home repairs and renovations and suggests that insurance claims may be denied if the work done doesn't meet local building codes:
http://content.members.fidelity.com/Inside_Fidelity/fullStory/1,,1278,00.html
MOST homeowners are astute enough to be aware of what they are and aren't knowledgeable about, and will familiarize themselves with local building codes pertinant to their project before starting the work.
The article also suggests that homeowners should recognize that renovations will increase their home's value, and that renovations or additions to their homes may result in the value of their homes exceeding their insurance coverage. In that case, any claim would be limited to their coverage, not the actual value of their homes.
But, this is not at all the same thing as saying that the work has to be done by a professional or the claim will be denied, which is precisely what that article claims.
Besides, if you were the judge in a case where an insurance company was refusing to pay for water damaged caused by a dead water heater in an attic, and the insurance company's defence was that the water heater was installed by the homeowner 18 years ago, and not by a licenced plumber, what would you think? Most likely you'd think that the insurance company was just using this as an excuse not to pay up. The water heater was obviously installed well enough to last as long as it should. Why then, would you presume that the judge in such a case wouldn't think the same as you and accordingly rule in favour of the home owner?
Finally, it's blindingly obvious that if an insurnace company requires homeowners to hire professionals do ALL the repairs and renovations in their homes or any claim will be denied, they have an obligation to make homeowners fully aware of that fact. If they're not making you fully aware of that, then if they deny your claim because the work wasn't done by a pro, the courts are going to see that as a scam perped by the insurance company on you, and will make the insurance company pay up regardless of what the fine print says.