Boolean operators are specific words used to combine keywords to improve the chances of finding relevant information. The most commonly used Boolean operators are AND, OR and NOT. Search results will contain both of the terms humour and therapy. Using AND decreases the number of results, because each time a keyword is added, the focus of the search is narrowed. Search results will contain one, or both, of the terms humour or laughter or comedy. Using OR increases the number of results, because a broader range of keywords is searched.
The actual cost of a flat roof depends on your location, the materials used, the complexity of the installation, and other factors. 1  Building a flat roof costs approximately $1.50 to $10.00 per square foot. 2  Assuming an average roof size of 1,500 square feet, that s a total cost of $2,250 to $15,000.
Flat roofs are simpler than pitched roofs, but still provide a variety of roofing options. The cost to install or replace a flat roof depends on size of the home and the material used, but the average cost for a modified bitumen roof for a 1200 square foot home is $4800. Materials: there are three main types of flat roofs: Built-up roof is the traditional flat roof made of layers of tar and gravel.