Hardboard: a manufactured wood fiber panel, ranges in density from 50 to 80 lb. per cu. ft.
Header: a structural member that is horizontal supporting the load over an opening, for example over a door or window. Also known as a lintel.
Half Lap: joinery method in which material is removed from each of the members so that the resulting joint is the thickness of the thickest member. Most commonly in half lap joints, the members are of the same thickness and half the thickness of each is removed. They are quick and easy to make and provide reasonable strength through good long grain to long grain gluing surface. The shoulders provide some resistance to racking.
Hanging Stile: the stile in a doorway to which the hinges are attached.
Hardness: a wood’s resistance to scratching, denting, cutting, pressure or wear.
Hardwood: wood from non-monocot angiosperm trees. Hardwood is of higher density and hardness than softwood, although there is large variations in actual wood hardness in both groups, with the range in density in hardwoods completely including that of softwoods; some hardwoods (e.g. balsa) are softer than most softwoods, while yew is an example of a hard softwood.
Head Jamb: the horizontal member at the top of a door frame or window frame.
Headroom: the clear space between the cieling and the floor line; often used to describe clearance in a stairway.
Heartwood: wood that has become more resistant to decay as a result of deposition of chemical substances. Once heartwood formation is complete, the heartwood is dead. It appears in a cross-section as a usually colored circle, usually following the growth rings in shape.
Heat Gun: electrical device that emits a stream of hot air, used to dry and strip paint, apply heat shrink tubing, apply shrink film, dry out damp wood, bend and weld plastic, soften adhesives, heat shrink wrap on packaging, and thaw frozen pipes. Similar in shape and construction to a hair dryer, though they run at much higher temperatures.
Heat Transmission Coefficient: describes the hourly rate of heat transfer for one sq. ft. of surface when there is a temperature difference of one degree F. of air on either side of a surface.
Hip Roof: a type of roof where all sides slope downwards to the walls, usually with a fairly gentle slope. Thus it is a house with no gables or other vertical sides to the roof. A square hip roof is shaped like a pyramid.
Hemlock: a genus of medium-sized to large evergreen trees, ranging from 10–60 m tall, with a conical to irregular crown. Wood obtained from hemlocks is important in the timber industry.
Hollow-back: removing part of the wood on a member’s unexposed surface to allow for irregularities in a mating member’s surface.
Hollow Core Door: a flush door having a core assembly of strips or studs that support the outer faces.
Horn: the extension of a sill, jamb or stile.
Hydrophilic: a substance which absorbs or mixes well with water.
Hydrophobic: a substance that repels or does not absorb water.