PLEASE NOTE: Ruling 99-56-56-712 has been superceded by Ruling 07-24-1153. We include this page for your information and because it contains information which is useful to a discussion of how not to build a straw bale buidling.

My building official says I have to comply with BCC ruling 99-56-712. What do I do now?

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Despite what you may have read on the internet or been told by someone not familiar with the current straw bale construction situation in the province of Ontario building officials are not normally evil, power hungry villains. They are average people like you and me trying to do a difficult job. Your building official may not be familiar with straw bale construction and may need some help finding the information he needs to make an informed decision. It may also be that your building official knows about straw bale construction but has concerns about your plans.

If your building official asks questions answer them. If she asks for more information give it to her.

If your building official is insisting that you comply with BCC ruling 99-56-712 then he is probably not up to speed on straw bale construction.

Our response to the recommendations contained in BCC 99-56-712.

BCC Ruling 99-56-712 is one of the unfortunate products of the early revival of straw bale construction in Ontario. The ruling has been ignored by every building official who has approved a straw bale house since it was entered. In fact, we have been unable to have the ruling overturned because it has never been necessary to take another straw bale house to the Building Code Commission.

With respect to the 13 recommendations:

i. That the appointed independent consultant who is a recognized building science expert and a registered professional engineer in the Province of Ontario and that the architect of the project who is a registered professional architect in the Province of Ontario provide their professional stamps on the architectural drawings and details provided to the municipality;

Building departments normally require either an engineers stamp or an architects stamp. It is not normally necessary to have both. With the recent changes to the building code it is now necessary to have your plans stamped by a certified building designer.

ii. That the independent consultant ensure that the recommendations regarding straw bale construction contained in his report to the Commission are adhered to in the subject building;

iii. That the independent consultant review and approve the as constructed building and submit written confirmation of same with the municipality;

This is normal. The professional who stamps your drawings must visit the site to confirm that and must issue a compliance letter indicating that you did build the building according to the plans contained in the drawings.

iv. That the proposed straw bale wall assembly be used on the ground floor only of the subject dwelling;

There are a large number of multi-storey straw bale buildings in the province of Ontario. The Gallery of Straw Bale Homes and Buildings at the Ontario Straw Bale Building Coalition web site provides pictures and descriptions of many of them. These buildings include one and one half and two storey load bearing straw bale homes with bales stacked flat and on edge.

Some multi storey examples:

Gravenhurst 1500 square foot one and one half storey post and beam edge stacked infill.
Orillia 2100 square foot one and one half storey flat stacked load bearing.
Uxbridge 10,000 square foot two storey post and beam edge stacked infill.
Bolsover 1500 square foot two storey post and beam edge stacked infill.
Dorset 722 square foot one and one half storey light frame edge stacked infill.
Baysville 2200 square foot two storey light frame edge stacked infill.
Owen Sound 2500 square foot one and one half storey load bearing flat stacked.
Collingwood 1800 square foot one and one half storey post and beam edge stacked infill.
St. Thomas 2500 square foot two storey post and beam edge stacked infill.
Hillsburg 1600 square foot one and one half storey pre-fab load bearing edge stacked.
Guelph 2300 square foot two storey post and beam flat stacked infill.
Orangeville 2460 square foot two storey post and beam flat stacked infill.
Grand Valley 2800 square foot one and one half storey light frame flat stacked infill.
Moorefield 2900 square foot two storey post and beam infill.
Guelph 9000 square foot one and one half storey light frame edge stacked infill.
Buckhorn 2300 square foot two storey round load bearing flat stacked.
Peterborough 2000 square foot two storey load bearing/post and beam flat stacked infill.
Warkworth 1700 square foot one and one half storey light frame edge stacked infill.
Eldorado 2100 square foot two storey load bearing flat stacked.
Cooper 1500 square foot two storey post and beam flat stacked infill.
Madoc 1900 square foot two storey hexadecagonal post and beam flat staked infill.
Bancroft 2000 square foot one and one half storey post an beam flat stacked infill.
Bancroft 1400 square foot one and one half storey load bearing edge stacked.
Bancroft 1520 square foot two storey timber frame with edge stacked straw bale wrap.
Centerville 1500 square foot one and one half storey post and beam edge stacked infill.
Deseronto 2000 square foot two storey post and beam flat stacked infill.
Perth 300 square foot one and one half storey load bearing flat stacked.
Bishop Mills 1800 square foot one and one half storey load bearing flat stacked.
Ottawa 1890 square foot two strorey light frame edge stacked infill.
Ottawa 1800 square foot one and one half storey load bearing flat stacked.
Spencerville 4000 square foot two storey load bearing flat stacked.
Perth 1400 square foot two storey load bearing flat stacked.

v. That the proposed straw bale wall assembly be used in a non-structural situation only;

Research done at the University of Manitoba, Winnipeg (Report to the Ontario Building Code Commission) and at Queen's University, Kingston (Compressive Testing of Plastered Straw Bales, Compressive Testing and Analysis of Typical Straw Bale Plaster) are many times stronger than 2x6 walls in vertical (10 times) and lateral (4 times) loads. Straw bale walls far exceed the load bearing design requirements in the Ontario Building Code for load bearing capacity of structural walls.

Many of the over 200 known straw bale buildings in the province of Ontario are load bearing (i.e. the straw bale walls are structural) including a full two storey flat stacked 4,000 square foot home which is the largest known two storey load bearing building in the world.

Powassan 2243 square foot one storey edge stacked load bearing.
Parry Sound 1750 square foot one storey flat stacked load bearing.
Alban 1550 square foot one storey flat stacked load bearing.
Kettleby 650 square foot one storey edge stacked load bearing.
Orillia 2100 square foot one and one half storey flat stacked load bearing.
Bracebridge 2000 square foot one storey flat stacked load bearing.
Owen Sound 2500 square foot one and one half storey load bearing flat stacked.
Orangeville 144 square foot one storey edge stacked load bearing.
Buckhorn 2300 square foot two storey round load bearing flat stacked.
Lakefield 1500 square foot one storey edge stacked load bearing.
Peterborough 2000 square foot two storey load bearing/post and beam flat stacked infill.
Norwood 2844 square foot one storey flat stacked load bearing.
Eldorado 2100 square foot two storey load bearing flat stacked.
Madoc 720 square foot one storey flat stacked load bearing.
Bancroft 1400 square foot one and one half storey load bearing edge stacked.
Plainfield 480 square foot one store edge stacked load bearing.
Carp 109 square foot one store edge stacked load bearing (x 2).
Perth 300 square foot one and one half storey load bearing flat stacked.
Bishop Mills 1800 square foot one and one half storey load bearing flat stacked.
Ottawa 1800 square foot one and one half storey load bearing flat stacked.
Spencerville 4000 square foot two storey load bearing flat stacked.
Spencerville 140 square foot one storey edge stacked load bearing.
Spencerville 140 square foot one storey edge stacked load bearing.
Merrickville 1600 square foot one storey flat stacked load bearing.

This being said load bearing construction in the province of Ontario does suffer from non-technical issues. The construction season in Ontario is also the rainy season and people building load bearing buildings find that they spend a great deal of money on tarps which provide at best marginal protection to their buildings and that they spend as much as half of their time putting on, tying down, adjusting, and taking off tarps. Most of the professional straw bale builders in the province of Ontario now prefer to use light frame construction instead.

vi. That the proposed straw bale wall assembly be constructed with a system of horizontal stabilizers consisting of a top ladder and bottom sill plate connected together with a series of pretension vertical tie down wires;

Tensioning wires are not necessary in non-structural (i.e. non-load bearing or "infill" straw bale walls.) They are normally specified in load bearing buildings to pre-compress the bales and to tie down the top plate to provide wind lift protection. Many builders are now using polypropylene pallet strapping and wire buckles for this purpose (3/4 polypropylene loops provide a minimum break strength of 2000 lbs.)

In straw bale construction the sill plate is called the "curb". The curb can be either 19" outside to outside or 14" outside to outside for flat stacked and edge stacked construction respectively. The outside edge of the exterior curb member should be placed 1" from the outside edge of the foundation system to allow a solid landing for the plaster skin. The space between the curb members is insulated with a non-wicking stiff insulation. Most builders in Ontario use 1" thick Roxul DrainBoard between flat curb members.

14 inch curb members on edge	14 inch curb members flat
19 inch curb members on edge	19 inch curb members flat

The common wisdom has held that the curb is intended to provide a path for liquid water that finds its way under the wall to pass without wetting the bales. In our northern climate we must provide excellent air penetration protection so we place a thick bead of acoustical sealant under the curb members. This would tend to trap any liquid water which somehow found its way into the curb. It is our opinion that the curb is far more important as a convenient place to attach the straw bale details such as mesh, flashing, and diamond lathe. As a nailing member the 1 5/8" edge of a flat curb member provides very little nailing surface and is often so filled with nail and staple holes as to provide little protection against water penetration. We prefer to use a curb on edge with blocking at convenient spacing insulated with 3.5" Roxul RXL80 commercial insulation. This provides a 3 5/8" nailing surface.

vii. That the proposed straw bale wall assembly be further constructed with angled re-bars laid flat on each course of bales at the dwelling's corners and that a series of spikes, having a length of more than twice the height of the bales used, be driven vertically downward into the bale courses;

The early understanding of the performance of straw bale wall assemblies relied on the mistaken assumption that the straw bears the load of the structure. This assumption has since been proven false by the work one by Dr. Kris Dick at the University of Manitoba, Winnipeg (among many others) who found that the straw bale wall assembly functioned as a structural insulated panel. The load flows through the top plate into the plaster then into the foundation.

This point has two parts: angled rebar laid flat in the corners and rebar pins vertical through the bales.

The requirement for angled rebar at the corners is unusual and the requirements in this ruling is unique in straw bale construction. The plaster applied to the straw bale wall assembly is much stronger than the straw. Any force which is sufficient to cause the plaster to fail will simply cause the bales to blow out along with the rebar.

The requirement for rebar pins is found in a number of building codes in the southern United States where the codes were written early in the straw bale revival and where the performance of the bale wall system was not well understood. Once again, any force which was sufficient to cause the plaster to fail would simply cause the rebar to tear out of the straw. Adding pins to a straw bale wall adds no more strength to the bale wall than adding nails to the foam would to a commercial cement and foam SIP.

viii. That the proposed straw bale wall assembly be further constructed with wire mesh installed on both the interior and exterior surface of the straw that spans from top to bottom of the wall and which are fastened to the top ladder and the bottom sill plate and that both wire meshes are tied together by a series of tie backs running horizontally through the straw;

The requirement for mesh is normal in the province of Ontario. Most professional builders are now using Tenax Cintoflex-D mesh. Many people believe that the mesh adds to the strength or crack resistance of the plaster. Since the mesh is bound tightly to the straw surface with the bulk of the plaster outside of the bale the mesh actually adds little to the strength or crack resistance of the plaster.

Adding stitched mesh to the straw bale walls does make them more stable before the plaster is installed and helps to hold loose straw stuffed into the gaps between bales in place. There are several examples of straw bale buildings without mesh in the OSBBC including a two storey full load bearing circular home.

2 x 4 welded wire mesh

Tenax Cintoflex-D

As you can see in the pictures above the mesh whether it is welded wire of plastic must be stitched to the bales. This prevents loose pieces of mesh from stripping the plaster off the trowel and from protruding through the finished plaster skin. Stitching is most often done with polypropylene binder twine on a bale needle. The bale needle is a 1/4" x 24" cold rolled steel rod with one end pounded into a flat spoon and drilled with a hold to accommodate the twine.

bale needle

ix. That the window and door units in the proposed straw bale wall assembly be supported with wooden framing members that are attached to the top ladder and bottom sill plate;

Window and door bucks are a good idea but are not absolutely necessary. It is possible to include a simple 2x6 and plywood box sitting on top of one or more courses of bales for the windows. The windows in these simple box bucks are unlikely to remain at a uniform height or to remain plumb before the plaster is applied. More often a 2x6 buck with a load bearing header is used. In some cases a 2x6 and plywood box is used with the window or door installed and all weather sealing and plaster preparations done before the box is installed.

Window and door bucks are a good idea and virtually everyone uses them. It is difficult to determine the eventual height of the top plate in a load bearing building so the bucks almost never extend from the curb to the top plate.

x. That the proposed straw intended for use in this dwelling consist of pre-stressed, two string bales with a minimum density of 113 kg/m3 and a minimum RSI value of 3.00 (for Zone 1);

This requirement is completely unnecessary. There is no research done in any jurisdiction which supports a minimum density or insulation value for the straw bales used in straw bale construction. Any bale which is tight enough not to fall apart under its own weight when it is lifted by its strings will work well for straw bale construction. For ease of handling, use, and plastering a bale with strings with equal tension (to prevent curving) which when picked up by its strings has a space between the strings and straw of four inches or less is idea.

xi. That the proposed straw be treated and dried prior to installation in the subject dwelling and that it be kept dry at all times during construction;

This requirement is completely unnecessary. There is no research in any jurisdiction which supports the need to treat the straw or two dry it in any way other than under the sun in the field where the cereal grain was grown. Several officials have attempted to set a maximum moisture content for the straw bales but these attempts have proven useless in practice. A good straw bale for straw bale construction should look good (be yellow and free from any obvious mould,) smell good (fresh not damp or moldy,) feel good (dry and firm to the touch,) and be light (25-35 pounds as heavier bales may indicate too much moisture in the center of the bale.)

The best testing instrument for a good bale is the human senses.

xii. That the proposed dwelling be constructed with a roof projecting 900 mm over the walls of the subject house; and

Most straw bale houses in the province are designed with wider than normal overhangs to protect the walls. Even with a 900 mm overhang driving summer rains in Ontario may wet as much as 3/4 of an 8 foot straw bale wall. CMHC research has indicated that even with direct wetting straw bale walls with cement containing plasters perform well.

xiii. That the proposed dwelling be constructed with a 710 mm high masonry splash skirt surrounding the ground floor perimeter of the house and attached to the subject straw and stucco wall assemblies.

Any barrier applied to the face of the straw bale before it is plastered seriously compromises the strength of the straw bale wall system by preventing the plaster skin from penetrating and adhering to the straw.

This has not been done on a single straw bale house since the house which was the subject of BCC ruling 99-56-712. If your municipality insists on compliance with this requirement we strongly suggest that you move or consider another method of building your house.