Rosin
A gummy substance produced from pine tree resin and used as a drying agent in paints and varnishes. 

Rot 
Breakdown of a material caused by bacterial action. Rot typically results from damp conditions. 

Rotate
To turn about upon an axis, such as the Earth. 

Rottenstone 
An abrasive material, typically limestone, used for smoothing surfaces. 

Rough Cut Joint
see Flush Joint. 

Rough File 
A coarse file used to remove large amounts of material. 

Rough Hardware 
Metal hardware such as bolts, nails and screws, which is used within the construction and is unseen. 

Rough Joint
Also called a flush joint, this mortar joint is troweled level and flush with the brick face. 

Rough-In 
The installation of portions of HVAC, plumbing, and mechanical systems that will be behind finished walls when the structure is completed. 

Rough Lumber 
Lumber with a coarse unfinished surface. 

Rough Opening 
The opening cut into a wall to accommodate a window, door, or similar structure. The rough opening is larger than the item, leaving sufficient room for proper installation. 

Round File 
A cylindrical file with teeth all around. 

Round Timber 
Timber, such as a pole, which is in its original form. 

Rout
To use a router. To remove excess material. 

Router 
A power tool used for shaping and carving wood. A high-speed cutting bit is maneuvered to remove material where desired. 

Router Bit 
The cutting bit used on a router. Bits come in various sizes and shapes for specific uses. 

Row House 
Single-family dwellings using the same roof and connected by common walls. 

Row Stores
Retail stores using the same roof and connected by common walls. 

Rowlock
A course of bricks laid on their edges with the ends exposed. 

Royalty
Money paid for the use of property to its owner, often for extraction of a valuable resource. Payment is usually based on a percentage of income generated by use of the property. 

Rubbed Finish 
A smooth finish used on concrete surfaces. Carborundum is used to rub the concrete until it is smooth. 

Rubber Flooring 
A type of flooring used most often in laboratories, manufacturing facilities, or locations where a non-conducting floor is required. 

Rubber Mallet 
A mallet with a rubber head, used to apply a blow without damaging a surface. 

Rubber Test Plug 
A rubber plug that is used to seal off sections of pipe to allow testing for leakage. 

Rubbing Stone 
Stone, also known as floatstone, which smoothes gauged brickwork. 

Rubble 
Pieces of brick or stone left over after the destruction of an old structure. 

Rubble Masonry 
Masonry structure constructed of irregularly shaped stones. 

Rubblework
Masonry, which consists of rough stones that are constructed irregularly. 

Rule
1. A regulation. 
2. A straight measuring device with distance markings. Also called a ruler. 

Rule of 72 and Rule of 69 
Rule of 72 is an approximation of the time it would take to double an investment when earning compound interest by dividing the percentage rate into 72 to derive the number of years required to double the principal. For example: an investment that yields an annual return of 20 % will double in less than three years.
Rule of 69 is similar to the Rule of 72, which is that a set amount of money invested at a certain percent per certain time period will double in approximately three years.

Rule of 78 
This approach used by banks to formulate a loan amortization schedule is often referred to as The Rule of the Sum of the Digits. This method of computing unearned interest is used on installment loans with add-on interest. The number 78 is based on the sum of the digits from 1 to 12. This causes a borrower to pay more interest at the beginning of the loan when there is more money owed and less interest as the obligation is reduced. 

Ruler
A straight measuring device with distance markings. 

Run
Horizontal distance covered by a rafter or staircase. Width of a step. Also refers to the horizontal distance of a roof from the top plate of the wall to the midpoint (see roof run). 

Run with the Land 
Expression that indicates a right or a restriction that will affect all current and future owners. 

Run of the Overhang 
The horizontal distance that a rafter overhangs the wall. 

Rung
Horizontal bars on a ladder. Also refers to horizontal supporting pieces between the legs of a stool or chair. 

Runner 
1. A long, narrow section of carpet or other floor covering.
2. A track installed on the floor or ceiling to accommodate a sliding door or similar device. 

Running Bond 
A method of laying brick where the bricks of each coarse are offset from the previous. Most brick veneer is installed in this way. 

Rural
Pertaining to the area outside the cities. Often characterized by farms, small towns and unpopulated regions. 

Rural Housing Service
U.S. Department of Agriculture program providing financing, when other funds are unavailable, to farmers and others to purchase rural property. 

Rural-Urban Fringe 
Area between an urban area and a rural area.

Rurban
Area, on the fringes of urban development, which is gradually being developed as an urban area. 

Rust
Reddish covering occurring on ferrous materials as a result of oxidation. Rust can be prevented by the use of special coatings that prevent oxygen from reaching the surface. 

Rustic
1. Country style. 
2. With a rough finish. 

Rusticate
To finish a wall in a rustic fashion. 

R-Value 
Measurement of a material's resistance to heat loss, most often referring to insulation products. The higher the R-Value, the slower the rate of loss.