Let's start by differentiating between a home improvement and a home repair. A home improvement, as the name implies, means improving something. It is usually a renovation to create more space, change the layout of the house, improve energy efficiency, or to make aesthetic changes. This report will deal with the simpler topic of home repair--basically replacing things that are worn out or fixing things that are broken. Here are some very basic rules to follow.
If you know what you want done, you can compare apples to apples when reviewing quotations. Otherwise it would be very hard to compare various quotes if every contractor has a different repair strategy.
Be prepared to stick to your guns. Many contractors will tell you that the job is much bigger, much harder, or it must be done his way (because if you don't, it will be dangerous, or much more expensive the next time).
As home inspectors, we are often faced with contractor opinions that differ drastically from the recommendations in our reports. In most of these cases, the contractor is proposing unnecessary work.
While you are at it, ensure that the contractor has appropriate licences and insurance.
The contract should have a start date and a completion date. (On larger contracts, sometimes a penalty clause is included for each day the job extends beyond the completion date.)
The contract must also contain a payment schedule. The schedule should not demand very much money up front and the payment should be based on stages of completion as opposed to pre-determined dates.
Remember to hold back 10% of each payment for 45 days after the completion of the job to determine whether any liens have been placed on the property (as a result of the contractor not paying his sub-contractors).
Also, don't expect much in the way of a guarantee if you are simply asking a contractor to undertake band-aid repairs. Many contractors will not simply patch a damaged valley flashing, for example, even if they are 95% sure that the repair will work. This is because there is still a 5% chance that they will get complaints to fix a subsequent leak. In fairness, the leakage is not their fault. They just do not want the hassles. Consequently, many contractors will suggest repairs which are overkill (replacing the entire side of the roof, for example) to reduce the potential for complaints. A significantly lower price can be obtained, if you explain to the contractor that you expect him to do his best, but you aren't going to make him responsible for the future of the entire roof based on a $300 repair.
We trust that the above information will help people in their dealings with contractors, realign expectations, and perhaps avoid pitfalls. And by the way, Carson, Dunlop & Associates Ltd. does not make recommendations for contractors.

