2008 Oregon Residential Specialty Code: R703 Exterior Wall Covering; N1104.2 Insulation Materials; N1104.9 Moisture Control

This appeal is to recognize hempcrete as part of a non structural exterior wall insulation and finish wall system for a new detached bedroom constructed with timber framing as the structural framework.

Hempcrete is a lightweight infill material for use in exterior walls in conjunction with standard or advanced timber framing. Hempcrete is covered with a lime plaster that creates a weather resistant barrier that can meet the needs required by the following building codes.

Hempcrete is a combination of hemp hurd also known as shiv along with a lime binder and a water that is poured into form work around the structural timber framing. A weather resistant lime plaster is applied over the exterior surface to prevent water from entering into the wall system. Hempcrete is a breathable wall system and does not require the use of a vapor barrier and rain screen system that is required by code under R703 – Exterior Wall Covering.

R703 - Exterior Wall Covering

Hempcrete used for exterior walls is plastered with a lime plaster that is weather and water resistant. As a result of hempcrete's physical properties the requirement for and Exterior Wall Covering such as siding that functions as a rainscreen with a drainage wrap is not necessary to provide adequate protection from the physical elements. The hempcrete and plaster will also incorporate flashing in around windows, doors, and where the hempcrete meets the subfloor.

Hempcrete as a wall covering will meet the requirements of the code for R703.6 Exterior Plaster, but will use a Hydrated Lime plaster in replacement of a Portland Cement Plaster. The application of the lime plaster will follow the guidelines established by the hempcrete industry in Europe.

Hempcrete is a similar wall system to Light Straw Clay that has been approved by the City of Portland, but it also contains other beneficial properties that were of concern about the Light Straw Clay. Hempcrete cures through a reaction between the lime binder, air, and water eliminating any concern about moisture in the walls that may cause mold problems. Hempcrete along with lime plaster are much more resistant to water and mold the earthen plasters composed of clay as well as other natural wall systems such as Light Straw Clay, Cob, and Strawbale construction.

N1104.2 - Insulation Materials

Hempcrete meets the requirements as an insulation for exterior walls when used with the proper wall thickness of 12 inches. Hempcrete has an R Value of R2 / Inch so a 12 inch thick wall will have an R Value of R25 that surpasses the code requirement of R21. The appeal is asking for Hempcrete to be added to the code as an insulation material.

R Value @ 12 Inch thickness = R25
U Value @ 12 Inch thickness = 0.2 W/m2 K

N1104.9 – Moisture Control

Hempcrete meets the standards for moisture control due to its hygroscopic nature that allows the wall system to breathe. Hempcrete is a vapor-permeable material which absorbs moisture from the air when humidity is high (releasing it again when humidity levels drop). These properties are very important, both for the health of the building’s occupants and in order to keep the fabric of the building in good condition. In historic buildings hempcrete works in harmony with the original materials, allowing the building to “breathe”; meaning that water vapor can pass in and out of the wall rather than being retained within it to cause dampness or mold, and eventually damage to the building’s fabric.

The proposed design would use hempcrete as a non structural infill material with traditional timber framing constructed to the building code requirements. Hempcrete is a light weight infill material that also functions as an exterior and interior wall surface that is plastered with lime. The structural timber framing would exist at the center of the proposed 12” thick hempcrete wall. The timber framing can be constructed with 2x4 or 2x6 framing either 16 or 24 inches on center as code requires and additional framing or metal strapping can be used to provide the required shear strength. The timber framework is usually located within the center of the wall cavity at a thickness of 12 inches. The hempcrete is plastered on the exterior as well as the interior

Wall Thickness = 12 inches
U-value (K-m2/W) = .23
R-value (Ft2.oF-h/BTU) USA= 25
R-value (SI Units) = 4.35

The product that I would like to have reviewed by the committee is a blend of lime based binder and the woody core of the industrial hemp plant (hurd/shiv) to form a bio composite sustainable building material that is used in the creation of insulation walls, as well as insulation layers for floors and roofs. In a timber frame building, the material provides the wall form, the racking strength, and the insulation. In a steel frame, it provides the wall form and the insulation in one monolithic product.

The hemp lime material is well suited for the innovation and repair of old timber framed buildings as a viable and sympathetic replacement for the original wall in fill. The hempcrete is not a load bearing material. The material can be used with any structural framing system to provide the support for the insulating wall form in new build and extension applications

The hemp lime material is rodent, mold, insect, and fungus resistant and has excellent fire resistance to conform to current building regulations.

The high thermal performance and air tightness of the hemp lime material means that single skin structures are sufficient and do not require insulation layers. The ability of the walls to breathe and store heat allows for a passive self-regulation of the temperature and humidity within the building, often reducing the need for air conditioning.
?The vapor permeability also delivers a protective environment against corrosion from deterioration mechanisms and extending its longevity.

APPLICATION OF TECHNOLOGY

Construction Method:

Timber Frame

The timber frame should be designed to support the snow load and load from the upper floors and roof. This would normally require the services of an engineer or timber framing specialist. A typical domestic timber frame would use 2 x 4 or 2 x 6 studs at 16 inches or 24 inches on center. Traditional and advanced framing techniques can both be used as the structural framework for hempcrete. Attention must be paid to the junction between wood-hemp in the case of visible external frame. Other types of frame may be used, but require an adapted design.

Mixing

• The hemp lime material can be manufactured on site with a concrete mixer or pan mixing machine. Mixing is best done in a pan mixer. A slow speed of rotation is recommended.
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• The hemcrete mixture is composed of the hemp shiv and a lime based binder with water. Depending on the source of the lime binder, adjustments may be needed by recommendation of the manufacturer for the mixing.

RATIO = 1 Bale of Hemp Hurd (37 Lbs) / 1 Bag of Lime Binder (55Lbs) / 10 Gallons of Water

• Add approximately 40 -60 liters or 10-15 Gallons of water to the mixer depending on the desired consistency.
• Add the lime binder and allow the material to mix for about 2 to 5 minutes until thoroughly into a lime slurry. The water ratio will vary depending on the mix that one is trying to achieve for the fluidity, density, and level of moisture needed for the project.
• Add the hemp hurd to the lime binder and water mixture allowing for the ingredients to fully mix for 2 to 5 minutes.
• Using a dustbin lid to seal the drum mixer can help reduce the dust during the dry mixing stage. Alternatively adding most of the water to the lime based binder first, before adding the hemp shiv can help to reduce the dust.
• Vary the water to suit the conditions, weather, and time delay before the placing of the hempcrete. The hemp is absorbent so the mix will dry out if it is left to stand.
• In all cases, the aim is to obtain a homogeneous mixture in order to produce an aerated concrete in which the particles of hemp are well covered by the binder, avoiding the formulation of pellets, balls, or lumps.
• Do not use material that has been let to stand for longer than the recommendations by the lime binder manufacturer as the lime binder will start to set up.

Shuttering

• Plywood is often used as shuttering. The plywood can be oiled with vegetable oil or other concrete forms work that have a layer of melamine to help release the forms from the hempcrete. This shuttering should be constructed accurately and where spaced away from the timber frame, hollow tubular spacers (water pipe or similar pvc tube) will allow the shutter to be screwed to the frame at an exact distance. The hemp lime material is lightweight so the shuttering can be less robust than conventional concrete form work. In some instances permanent shuttering may be used such as Magnesium Board to form the final finish to the wall. If using permanent shuttering, the panels used must be clean and must allow the external wall to meet the statutory requirements for flatness for applying the render.

Placing

• After mixing the hemp lime material, it is then tipped into the shuttering and leveled to form a 300mm / 12 inch thick layer. It is then lightly tamped before the next layer is tipped in. Simple pieces of wood are ideal for tamping. We recommend making a small trial section to establish the level of tamping required. 1 bale of hurd/shiv mixed with 1 bag of binder should fill 200 liters at a target density. A plywood box of 0.5m x 0.5m x 0.8m will be ideal as a 200 liter test box.
?Striking Shuttering

• The shuttering can be removed the following day and the spacer holes filled with the hemp lime material. The shutter panels are removed by sliding them sideways. In order to encourage drying, they must be removed as soon as possible.
Service Penetrations

• Service penetrations in buildings area a source of air leakage and heat loss. We recommend that the hemp lime material is cast around any service penetrations to avoid air leakage.
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Curing, Protection and Aftercare

• After removal of the shuttering the hemp lime material should be protected against the extremes of the weather (frost, rain, snow, and drying winds). In moderate weather no protection will be required. Building with the hemp lime material should not take place at temperatures below 41 degrees.
?Alterations

• The hemp lime material is very easy to alter if changes are necessary. Within the first 6 hours, it can be simply dug out, shuttering altered and then recast. If the hemp lime material has set )(even years later) it can simply be cut out with a simple hand or powered tools.
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Suitable Finishes

• The hemp lime material is normally finished with a lime render on the outside and a lime plaster on the inside. However as long as the finishes are vapor permeable, a number of options can be considered to suit the style and development. In all cases, external walls in the hemp lime material must have a protective covering on the external face, these include :

• Timber cladding, with a breathable membrane and/or ventilated air gap separating the two.
• Tile, slate, or shingle hanging with a breathable membrane and/or ventilated air gap separating the two.
• Brick or stone facing, laid in lime mortar.
• Mathematical Tiles
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Hempcrete is an alternative building material that provides healthy and sustainable housing as well as being environmentally friendly. Hempcrete is a breathable wall system that can be used with traditional timber framing. One reason for using hempcrete is that it is resistant to mold, fire, and insects. Hempcrete also absorbs CO2 from the air into the wall where it continues to harden the lime over time while acting as a CO2 sink. Hempcrete has a R value of R2/Inch so a 12 inch thick wall will be at a minimum of R24. Hempcrete also has a low U value of 0.23 helping to increase the overall energy efficiency of a building.

The combination of patented air-lime based binder and the woody core of the industrial hemp plant results in the capture of significant amounts of carbon from the atmosphere. Calculations show that approximately 110kg of CO2 per m^3 of the hemp lime walling material is sequestered. The carbon is then locked into the fabric of the buildings constructed.

The hemp lime material is a low energy building product. Construction costs can be lower than for current traditional building materials and their associated labor for installation.
Cleaner, greener alternative to standard home building supplies. Plus it has the ability to reduce the carbon dioxide from the atmosphere.

It is a breathable walling system, promoting healthy indoor air quality and reducing issues relating to the development of mold. Along with other great benefits as being mold, fire, pest resistant, no waste, inherently airtight and the reduction of carbon dioxide in the atmosphere.

The hemp lime material has a high thermal insulation that means they are comfortable to touch and radiate a warmth in the room. The high vapor permeability that facilitates the through transfer of humidity avoids the development of condensation and trapped moisture within the building. This has combined effects of improving the air quality and controlling the humidity as well as reducing the potential for growth or irritant molds and fungi that may affect the occupant's health.

Fire testing carried out by the CSTB in France on a 300 mm / 12 inch thick walls of hemp lime blocks laid in lime mortar with no plaster or render showed that the wall remained intact for 1 hour and 40 minutes. The blocks did not fail at this time but the mortar joints did.

On a personal note, after a long disabling illness, I was diagnosed with CIRS (chronic inflammatory response syndrome) due to exposure to toxic molds (stachybotrys, aspergillus, penicillium, cladosporium) My body lacks the ability to detox toxins from molds, chemicals, and metals. This means, I must live in a home that is as free from such things as possible. After extensive research, hempcrete was the only viable option for the stability of my long term health. The way we currently
build is ripe for growing mold and filled with products that produce toxic levels of indoor VOCs. After all, the most toxic of molds, stachybotrys, after one hidden leak only takes 72 hours to grow. For me that is unacceptable, and quite frankly, for all of us it is unacceptable. Toxic mold is not just toxic to those like me, it is damaging to all people, especially women and children. My hope is by building with hempcrete, I can educate others to this affordable and accessible option that exists for a healthy non-toxic home.