The Tiny House Builder calculator includes many of the basic equations for building a tiny house (small framed building) from bottom to top including the footers, foundation, slab, floors, walls/rooms and roof. Tiny Houses are increasing in popularity and the good news is that nearly all of the materials needed are available at the local Lowe's or Home Depot. With this calculator you can take your plans and make reasonable estimations on the supplies you'll need to get your tiny house under roof.
The basic building
The Tiny House Builder calculator includes formulas grouped in three TABS (Roof - Frame - Foundation) that roughly correspond to three distinct components and phases in the development of a building. Click on the TABs (right) to see the functions.
The ROOF tab has equations associated with roofing, including the count and cost of rafters, roofing plywood, and shingles. The shingle equations includes price estimates based on shingle price point observations from national providers like Lowes and Home Depot. The unit prices used here are based on a vCalc data repository of pricing ().
The FRAME tab has the most equations. These equations include those related to the count and cost of floor joists, sub-floor boards, wall studs, and drywall. For anything above a simple one room structure, you will have to develop your estimates room-by-room. The cost data comes from vCalc's tables (see list below) which come from the nationally advertised prices and are updated approximately every two months.
Starting from the bottom and going up, the Foundation equations include calculations for the amount of concrete needed for a footer, and then the amount of materials (concrete or block) needed for the foundation walls. And then finally, the amount of concrete needed to pour a slab in the basement to complete the rough construction. These formulas are are all based on the dimensions of the building. However, the block count estimator is based on standard block sizes in the U.S.
The basic construction of a building is the same for many structures. With few exceptions, a building requires a foundation or piers, a frame and a roof. Many buildings have basements that are below grade or partially below grade and these are typically made of block, poured concrete in forms or stone in order to stand up to exposure to the earth. Foundations are often coated with moisture blocking substances (e.g. tar), and perforated piping is often laid in a gravel bed, outside of the base of the foundation and covered by a silt barrier (paper) to drain water away from the base of the foundation in a french drain. The frame of the house is built on this foundation, and in the modern era, the frame is physically attached (bolted) to the foundation. This last step is widely performed to keep a house on its foundation during earth quakes. The boards that are bolted to the foundation are generally referred to a foundation sill plates and are used to affix (nail, screw or bolt) the deck and joists for the first level of the building frame, to the foundation.
The first part of the wood frame is the deck of the first floor. The deck typically has side boards (skirts) that are vertically placed around the foundation with joists running across the span and nailed into the skirts at the ends or affixed to the skirts via joist hangers. The end of the joists rest on the plate and have a direct conveyance of their load (weight) through the solid plate to the foundation. In some cases, when the span of the basement is too great, a beam is erected mid-span for the joists to convey their load in a third place (both ends and on the beam). The architectural design should account for this. Beams must rest on part of the foundation and/or on post (molly columns) that rest on concrete piers comparable to the footers of the foundation.
The frame of a building can have several floors, multiple rooms and each room can have doorways and windows, not to mention many built-in features (e.g. closets). Between rooms are passages and hallways and between floors are stairs. But the basic framing of walls and floor is consistent in most structures. Between floors you will find decks that are made of joists that are roughly surfaced with sub-flooring. Joists are either strong pieces of lumber like 2x12's or I-joist made of composite materials or even steel. The span of the joists and their separation are greatly dependent on the structural load that they will have to bear, but there are some industry standards (e.g. 16" separation). When the spans of joists over rooms are too great, beams are required. Nonetheless, the framing of the building is primarily composed of the walls (interior and exterior). These walls separate the rooms and carry the load (weight) of the floors and roof above. Walls come in many categories including:
It is common that load-bearing walls have a double top board (plate). However, some non-load bearing wall can have a single plate on the top. Interior walls are typically covered with drywall or paneling to enclose things like wiring and plumbing and to provide a surface for fine finishes.
Exterior walls are typically strengthened with structural panels such as plywood, have wind braces (diagonal steel) and are covered by a vapor barrier to keep the difference in moister (outside to inside) from leaching into the housing materials. Exterior walls are also used to attach the outermost surface of the house (brick fascia or siding) to the frame. The exterior surface may be siding or even masonry (brick or stone). In the latter case, attachments are connected to the exterior wall and integrated into the masonry seams (mortar joints) as the exterior facing is laid.
All exterior walls are load bearing, which means they carry more weight than that which is directly above them. The weight they bear includes the load of floors that span open spaces and then rest on the load bearing walls. These walls typically have standard spacing of vertical members (16" centered studs) and doubled top plates to provide strength between the studs. It is important for the architect of the building to methodically transfer the weight of every component of a building through every load bearing component down to the foundation and ensure adequate strength is built into the design and materials to carry the load for the life of the building. This all sounds complicated, but some wonderfully simple buildings exist and are still strong after centuries.
Above the frame of a building is the roof. The attic which is formed by the roof frame on top of the house is typically the location of the greatest layer of thermal insulation such as fiberglass. The roof serves the primary purpose of shielding the frame of the house from the water of rain and snow above and of carrying the load of snow (in some climates) until it melts. Roofs have load bearing structures, either rafters or trusses that convey the weight of the roof to load bearing walls (e.g. outer walls). Plywood or purlins are attached to the surface of the roof frame as a base for the final roofing material. The most common roofing material is the shingle which is nailed in layers on plywood. However, there are numerous other roofing materials from thatch, to tile to standing-seam metal.
Once a building is "under roof", conventional wisdom suggests that the job is half done. For help completing the construction job, consider the following vCalc calculators:
The equations in this calculator are a subset of the equations in the vCalc's construction library and are meant for estimation purposes only.
As always, we are looking for ways to improve vCalc's libraries of equations and encourage the public to provide updates and comments to this wiki to make this a better tool for the general public. The pricing information is gleaned from nationally advertised prices on web sites for lumber providers (e.g. Lowes or Home Depot). Please check your local stores for more accurate pricing and point them to vCalc. vCalc would welcome the national advertisers to publishing their materials pricing directly to our free pricing repositories.