Suggested Changes to the IRC and Guidelines for Tiny Houses, updated

Suggested Changes to the IRC

by Thom Stanton, American Tiny House Association's Virginia State Chapter Leader

Thom defines a small house as being not more than 500 sq ft. and suggests these changes:

Section R327, Small Houses
  1. Access to the basements, underfloor areas and lofts shall be by means of alternating tread devices, ladders, or any means that complies with Section R311.
  2. The minimum floor areas of Section R304 shall not apply.
  3. The minimum ceiling height requirements of Section R305 shall not apply.
  4. Lofts used as sleeping areas shall not be required to comply with Section R310 provided that the loft opens to a floor containing an emergency escape and rescue opening.
  5. Basements and underfloor areas shall not be required to comply with Section R310 provided that the basement or underfloor area does not contain sleeping rooms.
  6. The minimum door sizes of Section R311.2 shall not apply.
  7. The hallway width requirements of Section R311.6 shall not apply.
  8. The guard requirements of Section R312 shall not apply to lofts.
  9. The automatic fire sprinkler requirements of Section R313 shall not apply.

Guidelines for Tiny Houses on Wheels, 2016 draft with comments

from the ANSI Standards Facebook discussion group

Table of Contents

  • 1. Definition
  • 2. Framing & Structural:
    • 2A. Trailers
    • 2B. Framing and fasterners
      • 2B1. Wood frames
      • 2B2. Metal frames
      • 2B3. SIPs
    • 2C. Tying the house to the trailer
    • 2D. Roofs
    • 2E. Windows
    • 2F. Lofts
    • 2G. Ladders/stairs
    • 2H. Slide-outs
  • 3. Heating: propane, electrical, wood stoves
  • 4. Cooling
  • 5. Ventilation systems
  • 6. Plumbing: including composting toilets
  • 7. Electrical & Solar systems
  • 8. Appliances
  • 9. Safety equipment and notices: fire extinguisher, smoke detector, CO detector, warning signs and manuals that pros should incorporate into builds for customers?

1. Definition

A tiny house on wheels (THOW), for the purposes of these Guidelines, is a structure which is intended suitable as a full time residence or year-round rental property and meets these five conditions:
  1. built on a trailer that was registered with the builder's local DMV.
  2. towable by a bumper hitch, frame-towing hitch, or fifth-wheel connection. Cannot move (and was not designed to be moved) under its own power.
  3. Is no larger than allowed by applicable state law. Comment: Some people do not want any size limitation. However, this makes it challenging for a buyer from out-of-state. It might be more useful to have specs here that would cover most states. (The typical THOW is no more than 8'6" wide, 30' long, and 13'6" high. Larger tiny houses may require special a commercial driver's license and/or special permits when being towed.) Please note:
    •  3.a.  Some states are more restrictive than others. Here's a handy but unofficial summary of size limitations. Please check with your local DMV for the laws in your state.
    •  3.b.  Roof height is from bottom of tires to the top of the highest exterior point on the house, including any protrusions. The roof height may be taller when stationary, as long as it is collapsible for towing of the THOW. Chimney piping may need to be removed for travel and then reinstalled to meet clearance requirements for use.
    •  3.c.  If slide-outs are included, the plans should be reviewed and approved by a structural engineer licensed in the state in which the THOW is built.

  4. has at least 70 square feet of first floor interior living space, and no more than 400 square feet (excludes any lofts).
    • Some people feel there should be no lower limit, but What about this - At 25 sq ft, and with a ceiling to low for the occupant to stand up, is this a house?
    • Should the maximum be 450 to allow for semi-trailers or should it stay at no more than 400 to be avoid overlapping with manufactured housing?
  5. includes basic functional areas that support normal daily routines (such as cooking, sleeping, and toiletry). Comment: Some people feel that neither a toilet nor a shower should be required. However, others are concerned that this would create a barrier to acceptance of tiny homes are permanent residences.

2. Framing & Structural

2A Trailers

  • The trailer must be adequate for the weight of the tiny house, its furnishings and occupants.
  • The trailer must meet Department of Transportation (DOT) guidelines of the state in which the THOW is built or, if a custom build for a customer, the state in which the THOW will be registered.
  • If the trailer is built by the builder of the THOW, then the trailer should meet the following guidelines: TBD. Here are some notes from a trailer discussion:
    - Axles of 5,000 lbs are okay for smaller THOWs, though 7,500 or 9,000 is better.
    - Instead saying there must be x amount of axles, we should just specify that they should exceed the total weight. Others have just one axle appropriately rated.
    - Conforming outriggers or extensions for mounting bottom plates for walls should also be in the standard.
    - Consideration of moisture control from integrated "belly pans" should be added.
    - If someone frames their floor inside their trailer, then spray insulation with an underbody coating is sufficient instead of the belly pans or flashing.
  • The frame must be securely fastened to the trailer as specified below in the framing guidelines.

2B. Framing & Fasteners

  • New structural components (steel, lumber, plywood/OSB, ties, and fasteners) should meet the International Building Code, Residential Code. However, salvage materials may be used if they are of equivalent strength and durability as new materials that are specified in the code.
  • Fasteners must be corrosion resistant at structural tie-points and where the house attaches to the trailer frame. This is done so that a future water leak, or the actions of chemicals in treated lumber, do not damage structurally important fasteners. The two most common types of corrosion-resistant fasteners are 1) hot-dip galvanized nails and screws, and 2) coated exterior screws.
  • For engineered straps, hurricane clips, tension ties, joist hangers, and header hangers, use the fasteners recommended by the manufacturer. Only use the nails and screws designed for the engineered system. "Tico" nails (10d 1.5-inch) are the most common. SD series screws can be used for anchoring straps and tie-downs.
  • For the interior "envelope" (enclosed space) of the house, materials (plastics, glues, insulation, paints, and finishes) must be labeled by the manufacturer as safe for interior use or known to be chemically safe for interior use.
    • 2B1. Wood Frames
      • Wood frames must meet the guidelines for earthquake and high-wind loading in the International Residential Code for One- and Two-Family Dwellings, section R602. Proper bridging supports and frame supports are required.
      • Frame walls with graded 2x4 lumber and either 16d hot-galvanized ring shank nails or structural screws (extra strong, thin, sharp screws that meet stringent engineering standards. Made by GRK, Spax and FastenMaster), maximum 24" on center (recommended: 16" on center ).
      • Use appropriate headers and frames for windows, doors, and other openings. While building code allows as little as 16% of a wall to be braced (e.g., a 16 ft wall only needs 2' 7" of bracing), THOWs are subject to sustained wind loads and minor "seismic" loads. To add windows without increasing the need for bracing, you may use small windows that do not span more than one stud bay (a 14.5" rough opening for traditional framing). If open spaces make up more than 25% of a wall, crossbeams may be required for additional support. Consult a structural engineer. (Note: structural engineers may charge $100 or more per hour, and review of plans can take four or more hours. If you're low on funds, use a standard tiny house design).
    • 2B2. Metal frames
    • 2B3. SIPS: If Structured Insulated Panels (SIPs) are used, they must be installed according to the manufacturer's guidelines, and secured to the trailer in a similar manner as a wood frame.
    • 2C. Tying the house to the trailer
      Tie the walls to the trailer frame with one of these methods:
      • hurricane tie-down brackets and minimum 3/8" galvanized bolts.
      • a threaded rod and turnbuckles from trailer frame to top of wall plate, then hurricane roof ties to tie studs, plates, and roof trusses.
      • weld (for metal frames only)
      • another method that is detailed in the THOW plans and that has been reviewed and approved by a structural engineer.
      • We add a 2x6 pressure treated rim on the outside of our trailers This rim joist is gives us a 7'11" trailer width. The exterior plywood sheeting goes over this and is glued and screwed to the rim joist. This give a positive connection around the build. We also bolt the bottom plate to the trailer frame. We think this is a very strong house to trailer connection.
      • You need a wooden subfloor whether it is fully framed and dropped in the trailer or the plywood subfloor laying on the trailer,
      • We use a 16 & 18 gauge cold formed steel for our frames. With a steel frame, we also use 16 gauge floor joists and weld rather than bolt them to the trailer. We do not tack weld, but solid weld all joints to create a stronger unit. We do not bolt because our insurance company was uncomfortable with that spec ad it implied that a frame could be removed from the trailer. And if it could be removed at delivery, that increased the possibility it could come off during transit.
      • A hybrid of welds with bolt together components has proven to work in the trailer industry at large (e.g. "home-built" trailers from Carry-On require one bolt for final assembly, and it's right at the tongue). In this way, it seems there could be an opening for a "hybrid" method of combined fabrication methods.
      • As one who's heavily involved with code change that could allow for legally building and living in tiny houses, however, the ability to separate the structural frame from the trailer (i.e. to convert from THOW RV to permissible residence) suggests employing an approach that maintains the ability to unbolt the structure -- in its entirety -- from the chassis, or at least the wheel assembly (e.g. Industrialized Building).
      • 1) Steel framing requires a thicker gauge than what is easily found at (most) big box stores. In order to be structurally sound.
      • Some of the framing systems such as the new Volstruck systems and more commercial types of metal framing can easily be adapted for a bolt on system, just as long as they utilize the same hurricane anchors and ties that are used in wood framing to secure a house to the trailer. Otherwise, the framing should be welded to the trailer and signed off on by a certified welder, metalurgist, or structural engineer. This allows for DIYers and pros to still frame in steel, allows for a couple popular designs that even allow the house to unbolt from the trailer on site, and still accounts for the safety requirements along the way.
      • Yes, you need a subfloor, but if you weld the frame to the trailer and integrate the subfloor framing into the cavity of the trailer, then the only purpose of the subfloor is to create a surface to attach the final decorative flooring to.
      • 16d ring-shank galvanized nails are extremely difficult to find/nearly nonexistent for nailers (16d ring-shank nails are readily available if you want to pound all your nails by hand.) I would specify 16d (3-1/2" or 3-1/4") galvanized smooth shank for the framing and 8d galvanized ring shank for securing the sheathing to the framing. The only company I know of that makes suitable screws for framing is GRK with their R4 screws. I believe they are 3-1/8". Also they are not particularly thin. As for the trailer bolts, I would think at least 1/2" diameter. 5/8" is the standard for full-size homes.
    • 2D. Roofs: Minimum roof slope (measured in rise over 12-inch run) must meet roofing material requirements. Vardo roofs are permitted.
    • 2E. Windows & other exterior glass must be tempered, laminated, or secured with shutters during tow.
      • Federal gov now days requires what they call safety glazing which generally is accepted as TEMPERED glass in any vehicle on the road which also includes TRAILERS with the exception of HOUSE TRAILERS (AKA MOBILE HOMES) which are moved once generally and considered permanent structures. Generally for all vehicles like autos, trucks, motor homes which have occupants, the front facing glass (AKA windshield) must also be LAMINATED safety glazing which means two layers of TEMPERED glass with a layer of plastic sandwiched in between the two pieces of TEMPERED glass (the plastic holds the windshield together when the glass breaks). Tempered glass is very important since it is much stronger and has higher impact capability along with the fact that it breaks into much smaller less lethal pieces. The importance of this is if your trailer is involved with an impact that breaks the windows you will not be launching lethal shards of glass towards anyone else. At one time PA Motor Vehicle Code did include the wording “tempered” but it has been removed and replaced with Fed Gov ANS Z26 Specs. ANS Z26 appears to include TEMPERED glass as one of the requirements to pass the spec. Tempered glass IS SAFETY GLASS but it is just one of many varieties of safety glass which can be a single layer of tempered glass to multiple layers of tempered glass with plastic laminated between layers to make bullet proof glass. In this case (of a travel trailer) safety glazing most likely will be interpreted as single layer TEMPERED glass (IE not standard plate glass or laminated multi layer tempered glass like windshield). Interestingly enough, some hard plastics may be substituted but I would think that they would not last as long due to scratching over time.
      • Tempered glass is required in vehicles, not trailers. A trailer is not to be occupied during transport. Nobody should be IN a house while it's being towed.
      • It's not about people being in the house while it's moving; it's about people living in the house.
      • Either tempered or used with an after market film to achieve the same goals. Shutters are an even extra level of protection.

      -- to be continued ---