One of the first considerations when it comes to interior house paint is the base. There are two schools of thought, each with their pros and cons. Some brands commonly sold to contractors for commercial projects are oil-based, meaning the chosen pigment is mixed with an oil derivative called alkyd. Oil-based paint provides thorough coverage, and the finished coat resists moisture well. However, oil-based paint releases a high level of volatile organic compounds (VOCs) as it dries, and it can only be removed from floors, brushes, and clothing with strong chemical paint thinners. In fact, many states have actually banned the use of oil-based paints because of their VOC levels and hazardous ingredients.
An example of the wall measurement would be: 40 linear feet of bedroom space, x 8 wall height, =  320, x 2 = 640. Minus 1 door (60) and 2 windows (80) = 500 sq feet being painted. Then divide the 500 by 400 (sq feet per gallon), and you get 1.25 gallons (4.73 L) needed for that room. For this, you'd need 1 gallon (3.8 L) and 1 US-quart (950 ml). If the amount it comes out to is over 1.3, we recommend just getting 2 gallons (7.6 L) so that you have leftovers if needed, since 2 US quarts (2,000 ml) costs essentially the same as a gallon in most stores.

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While you may choose to paint a door, ground-level window trim and other parts of your house’s exterior, it’s really a job best left to the professionals. One of the main reasons is experience. An experienced painter knows how to handle the prep work, spot problems and identify sources of future trouble, all while getting the job done more efficiently. They are also experienced with spending long hours on tall ladders. If you want high-quality work, it’s best to hire a professional painter near you. 
If you have kids, pets, or occupants who will damage the walls, it is recommended to go with washable matte, eggshell, or satin, because these paints can be easily cleaned and are more durable. However, flat paint can be touched up more easily and hides imperfections better, so if you are selling the home, it is highly recommended to go with flat. Bathrooms with showers/tubs should go in semigloss- unless you are selling or want a specific design look, then use satin. 
When determining the total cost of a home’s exterior project, you’ll want to include things like the trim, a garage, foundation, windows and doors. All work is calculated by square footage and sometimes by the linear foot, such as in the case of trim. Your contractor will give you a price for the entire project unless you specifically ask for each item separately.