Building with Hemp/Lime FAQ's
Q. I want to build my house with hemp/lime but the building department in my state have never heard of ”Hempcrete” and B&S are saying it must be state approved. What do I do next?
A. For all the hemp homes we have built in USA we have used the "Non-Conventional" codes or "Alternative Building Materials" codes which every state and B&S department have. Even in NZ where we are building many hemp homes presently we have used these same codes that every jurisdiction must have to allow people to build their own shelter under the constitution of the United States.
In some cases you may be required to sign an indemnity to the city before being granted a building permit.
Q. Can we build foundations with hemp or do we use concrete?
A. Hempcrete cannot be used below ground for foundations. You will see misinformation on the internet about using Hemp/Lime for foundations but that is not accurate. Cellulose exposed to below ground dampness for extended periods will deteriorate, like any plant material, even wrapped in lime.
Q. What happens to the hemp walls if it rains?
A. In Switzerland they have buildings made with Hemp/Lime that have been standing exposed to the weather for 10+ years without any stucco or plaster finish and they are still as good as the day they were built. We prefer to use a lime stucco finish to provide an inherently air-tight seal to the walls, as well as an aesthetically appealing look, similar to cement stucco except without Portland cement.
Q. What finishes can we apply over HempCrete?
A. Hempcrete provides its own substrate for application of lime plasters (stucco) directly without need for metal lathing. Or you may wish to use brick, wood or metal facing for aesthetics. Other than wood facings we install a breather baton so the Hempcrete can maintain air flow because metal is not permeable.
Q. Can we use Hempcrete for bathroom walls?
A. Yes, you can use Hempcrete in a bathroom and finish with lime or clay plasters that will breathe in and regulate moisture. In Europe people have been using lime materials for ages in bathrooms without the need for extraction fans.
Q. What finish can we give the flooring if done with hempCrete?
A. Hempcrete can be used to insulate floors, as shown on our website (click here) over which you can apply a sub-floor and then whatever flooring material you wish. We prefer to leave a 1" air gap between the floor joists and the subfloor to allow Hempcrete to breathe, thereby giving the best insulation value.
Q. Can the roof be done with hemp/lime?
A. Yes, the roof can be done with Hempcrete but remember, as above, there needs to be a 1" breathable air space between the top side of the Hempcrete and the underside of the roof sheeting material, presumably plywood, or Hemp Board, also available thru Hemp technologies.
Q. Does Hempcrete require expansion joints?
A. NO expansion joints are required using Hempcrete materials, unlike cement. Even when finishing Hempcrete with lime stuccos there is no need for expansion joints as lime is very flexible and will heal itself after only a couple of months. New buildings are prone to settling and cement finishes will crack as they are brittle whereas lime will crack but reshape itself because of its crystalline shape.
Q. Are there any special requirements when casting Hempcrete?
A. There are no special trades required to install Hempcrete walls, floors or roofs, making this material even more suited for non-skilled labor. Hemp Technologies provides initial training to anyone purchasing materials to get them started and learn a few technical issues associated with using these materials, such as forming, mixing, casting, tamping and finishing. Our charge for this certification fee is $1 per square foot of the project being built and is a one-time fee to cover our expenses.
Q. How big an area can we cast at once?
A. Casting into double sided temporary shutters, a 4-5 man crew can form and cast an average 200 cubic feet per day (7 cubic meters).
Casting into single-sided temporary shutters, a 3-4 man crew can cast an average 200 cubic feet per day (1 less man). This means a permanent interior wall liner using MgO is used instead of gypsum drywall.
Casting into double sided permanent shuttering, a 2-3 man crew can cast 400 cubic feet per day (6-800 square feet). Less men and more infill completed; definitely the best method.
Q. When mixing Hempcrete do you need to vibrate it like concrete?
A. NO. When mixing Hempcrete and casting you do not need to vibrate like concrete. There is no "slump" in Hempcrete as we limit the amount of water used to hydrate the lime binder. Typical mix is 4:1:1 being hemp, lime, water respectively, for a tamped mix.
Q. How much Lime Binder is used per cubic foot/cubic metre?
A. For 15kg (33lbs) of hemp hurd you will need 25kg (55lbs) of our lime binder. This will make 4.5 cubic feet. 1 cubic metre of Hempcrete will require 8 bags of hemp plus 8 bags of binder. Use our downloadable spreadsheet to calculate price of materials here (excludes freight and any applicable taxes).
Q. What is the density of Hempcrete?
A. 93.6 to 136.4 Kg/M3 (206 - 300 lbs/M3) or 2.6 to 3.9 kg/cubic foot (6 - 9 lbs) depending on tamping and whether you install MgO as permanent interior lining board (do not use drywall/jib-board). Compressive strength = 116 - 145 pounds per square inch (52.7 - 66 kg).
Q14. What is the best working temperature for casting Hempcrete?
A. We have installed hemp/lime below 6 degrees Celsius (21.2 F) with no adverse effects but definitely not recommended; too bloody cold! Try to work with Hempcrete above 5 Celsius (40 F).
Q. How long does Hempcrete take to cure before rendering with lime?
A. Allow 6-8 weeks typically (depending on climate/season) to let the Hempcrete dry to around 12-15% moisture content. If you try to apply lime renders prior to proper drying you will see brown leaching stains on the lime render from lignens leaching thru the Hempcrete. Building code for lime render cladding is 20-22mm (3/8", 3/8", 1/8"). This same condition applies to plastering the interior of a Hemp/Lime wall.
Q. Can we spray Hempcrete (like Shotcrete)?
A. Yes you could but you would need special equipment that costs around 50,000 Euros and training specific to spraying Hempcrete. Casting is still the preferred cost-effective method.
Q. How soon after casting can you remove the form work?
A. You can remove the form work immediately after casting or the next morning, to allow the drying process to begin with air circulating around the material. Don’t worry - it will hold its shape.
Q. Can you use Hemp/Lime for retrofitting existing homes?
A. Yes, in most cases you can remove the drywall and exterior cladding and then form up around the studs to cast Hempcrete, then either re-clad with metal or siding or brick (as long as you use adequate breathing spaces) or render with lime. You can also use MgO to replace the drywall on the interior or plaster straight onto the Hempcrete with lime plaster.
Q. How about framing: any special conditions?
A. Hempcrete is regarded as a non-structural, monolithic infill material, cast around the structural timber or steel frame of the structure. Typical framing standards in North America require 2x4's at 16" on center however with support from structural engineers, we have reduced the amount of timber framing by 30% by framing at 24" on center using 2x4's, both on single and double story structures. This is because Hempcrete will harden and in fact help to brace the structural members.
Q. What is the mixing time of 1 cubic meter?
A. Most people use a regular mortar mixer (horizontal) in which you can mix 100 liters (25 lbs or 11.5 kg) of hemp with the required ratios of Lime binder and water. The water goes in first, then the binder, mixed for 2 minutes, then hemp is added and mixed for another 1-2 minutes until all the shiv (hurds) are covered with the lime binder. By running 2 mixers you will double your output without need for special equipment. For options on mixers available, please reach out to us and we can advise on type of mixer depending on size of project.
Q. What is the cost difference between a 6" wall to the 12" wall?
A. Depending on climate zone you are wishing to build in will determine the thickness of wall required to achieve adequate insulation. The most common thickness is 12" (300 mm) based on temporary forms being used both sides of the cast wall. However, if using permanent forms tamping is eliminated from the equation and a thinner wall will achieve the same R-Value.
Q. Do you have a cost per square foot of wall?
A. There is a typical 12" wall costing download available on our website (click here).
Q. Does that cost include labor?
A. Labor costs ~US$12/square foot installation ($420/m3). Please check your local area for relevant material/labour rates as these can vary greatly by country, State and Region.
Q. How did the idea of using hemp for building come about?
A. Building materials have been morphing for some years but many companies simply ”green wash” existing materials to make them look more agreeable to consumers. Industrial Hemp has been on our planet for thousands of years and used in many ancient structures together with limes long before we had conventional cement. We have adopted a carbohydrate approach to building healthy homes without the need for petrochemical where possible.
Q. What was the process while starting Hemp Technologies?
A. We traveled extensively throughout Europe visiting with people who had been building with Hemp/Lime for many years to gain the knowledge necessary to bring these materials to other countries, including USA, where construction waste accounts for almost 50% of land fills and job site waste 19%.
Q. How is hemp more beneficial in building compared to other materials?
A. Carbohydrate based building materials are healthier and less damaging to humans. Toxic petrochemical materials are responsible for many illnesses and increased medical bills. Hempcrete is breathable and is completely non-toxic due to all natural materials. Plus, Hemp/Lime protects the structural integrity of a home and therefore will last considerably longer than conventional construction.
Q. Are hemp building materials cost effective?
A. Hemp/Lime materials are comparable in cost to traditional brick and block construction.
Q. Are hemp building materials safe/healthy?
A. There is documented evidence that Hemp/Lime has contributed to more than 50% reduction in sick leave and absenteeism in Europe where they have been building with Hempcrete for +/- 30 years now.
Q. How does hemp help cut down on energy use?
A. Because Hempcrete is super insulating the need for additional mechanical heating/cooling is reduced. For example a typical home will have 1 ton HVAC per 500 square feet. Using Hemp/Lime for insulation will reduce that requirement to 1 ton per 1500 square feet (60%) That equates to another cost saving when building with Hemp/Lime.
Q. How did your team/company come together?
A. Hemp advocates with special skill sets have gravitated to Hemp Technologies thru the education we provide online for hemp. Over time certain people have naturally evolved into working with us to promote hemp building, as well as other hemp related products.
Q. What are the legal issues that come into play? Are there any?
A. We have no legal issues around building anywhere in USA/Canada, or any other country for that matter. The issue in USA is not being able to grow Hemp. As one CNN reporter put it. ”its like we can buy the bread but we can’t grow the wheat”. Until the Federal Government relaxes their stance on Industrial Hemp and allows farmers to grow this wonderful life giving plant in USA costs will remain high in comparison to other petrochemical based building materials.
There are a number of states that have passed legislation to allow farmers to grow iHemp but we still cannot import the seed to grow it. That’s the real issue.
Q. Animal bedding: how does hemp assist in this area?
A. Hemp is a premium animal bedding and 85% of all hurd production in Europe goes into pet bedding currently. Hemp absorbs 4 x more waste than other bedding materials yet decomposes 2x faster after use. This makes hemp very good for use as a fertiliser after being used for bedding. Yes, it is more expensive than other bedding materials but reduced labor costs over time make Hemp more affordable over all, and better for your pets health and wellbeing.
Q. What are Hemp Technologies' future plans? Can we hope to see hemp building mainstream in the United States?
A. We are building one house at a time and helping to educate others on the use of these natural, highly sustainable building materials. Like any new materials introduced into the market, more demand will reduce costs, making it more and more affordable to build with these materials as time goes on. Also, localising the source for binder materials will help more people afford to build with Hemp/Lime.
Hemp Technologies is ever evolving - watch this space for "pre-fab" modular build panels, saving 19% on-site waste !!
Q. What would it take to have hemp building in more states?
A. We provide training to builders, home owners, architects, engineers, DIY’s and other professionals to use Hemp-Lime for building. Its only a matter of time before Hempcrete is mainstream.
Q. Are the materials similar to concrete ?
A. Hemp-Lime is 1/3rd the weight of cement thus requires lighter foundations - see Structural Engineer.
Q. How popular is hemp mulch for gardening and compost?
A. Hemp is a fabulous mulch, absorbing 4 x it weight in moisture and retaining it longer than other mulching materials. Your plants will love it.
Q. How does one study or get into careers/businesses involving hemp?
A. Start by reading thru all the information available free on our website. From farming to processing to uses of Hemp you can get a solid understanding of Industrial Hemp and its uses from us and other websites dedicated to promoting the value of Hemp, the miracle plant. We also provide a global map of hemp builders so it’s not hard to find someone close to you to help build your hemp home. We help by supplying the materials at wholesale pricing that you will not find anywhere else.
Q. How long will it take until hemp homes/buildings are affordable for everyone?
A. Hemp homes are affordable NOW, from US$150/square foot, plus your land and ground works costs. Banks are recognising more and more that building with hemp/lime is very, very energy efficient and have given mortgages to people based on the reduced energy costs. PLUS, insurance companies give us up to 60% discount on fire insurance because Hempcrete is non-combustable!!!
Get started today by contacting us here. We have certified Hemp-Lime building associates all over the globe who will assist in making your space a healthy place.
NOTE: Hemp Technologies assumes no liability from any person, company or entity who decides to mix and use ”Hempcrete”. Customers are advised to consult and/or use a licensed general contractor (GC), architect/designer and Structural Engineer (SE) before undertaking any hemp-lime building projects.