STEP U3 Handbuch ENGLISH

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U3 – LOAD-BEARING STRAW BALE BUILDING 

CONTENTS 

U3 

TIME 

PAGE 

U3 Learning Outcome 5 

U3 Session 1 : Design & Planning 5 hrs 7 

Info presentation 1 : Design Basics 8 

Info presentation 2: Drawing Basics 1 0 

Tips: Load-Bearing SBB Pros 001 -1 2 and Cons 002-1 3 1 2 

Weather Protection I 003-1 4, Weather Protection II 004-1 5 

Organization of the Building Site – Planning 005-1 6, Preparatory Works 006-1 7, 

Building Schedule 007-1 8/1 9, Cutting List 20, Estimating Costs 21 

U3 Session 2: Construction & Statics 2 days 23 

Info 1 : Construction – Overview and Examples 24 

Tips: Bales and Walls Dressing Bales 008-26, Notching Bales 009-27, 26 

Compressing Walls with Trucker Straps 01 0-28, with Car Jacks 011 -29 

Info 2: Statics (Virko Kade) 38 

Info 3: Compression & Settlement 42 

Info 4: Legislation 44 

Info 5: Characteristics of the Planning Process 45 

Info 6: Remarks on Building Physics 46 

U3 Session 3: Tools & Practice 1 day 32 

Tips: Tools Splitting Bales with Bale Needles 01 2-32, Hedge Saws 01 3-33, 

Persuader 01 4-34, Gap Filler 01 5-35 

Info 2: Strings and Knots 36 

Appendix: Statics House Fliri (Peter Braun) 49 

Credits and Impressum 52 

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LEARNING OUTCOMES 


Level 3 (ECVET credit points: 1 5) / Level 4 (12) 

Knowledge 

Skills 

Trainees know … 

• about the existing national building 

regulations related to straw bale building. 

• the specific problems organising a load 

bearing straw bale building site and their 

solutions (weather protection, safety, logistics). 

• the symbols to be able to understand plans 

and construction drawings. 

• the necessity and the techniques to avoid and 

to close gaps (between bales and between 

bales and construction). 

• the reasons and the techniques to fill in straw 

in the required density and the specific 

methods of compressing and their application. 

• the techniques to fix the bales in the 

construction (corner detail). 

• the techniques to adapt the straw bales layers 

to the requirements of load bearing straw bale 

building. 

• the pros and cons of the load bearing 

technique and its requirements related to 

schedule, planning, budget, and resources. 

• the details for adjacent building elements 

(floor and roof plates, ring-beam and openings) 

according to load-bearing straw bale building. 

• the details for openings (windows, doors) and 

for intersections (chimneys, pipes, wires). 

• the reasons and the techniques to prepare the 

substrate with a plane and gap free surface. 

Trainees can … 

• control the quality ofexisting constructions in 

relation to its suitability for load bearing straw 

bale building. 

• handle the tools and machines which are used 

generally on straw bale building sites and for 

simple wood constructions. 

• choose appropriate bales for the load bearing 

techniques, resize, reknot and fix the bales 

together. 

• adjust the bales to the length of the 

construction elements in a suitable assembly. 

• do basic carpentry to make additional 

wooden construction aids in order to erect 

straight walls. 

• compress the assembled bales in different 

techniques in an adequate way. 

• fill gaps and holes with straw in a required 

compression. 

• fabricate base and top ring beam and fill it 

with insulation material and fix it adequately. 

• calculate building costs related to the straw 

bale constructions. 

• prepare all surfaces for the successive crafts 

people (plaster, cladding, wind- and air 

tightness) or execute these tasks in mutual 

agreement. 

• assemble the supporting wooden structures 

and the frames for openings. 

Competence 

Trainees can … 

• organize and attend the building site at all stages and adapt the working process, the use oftools and 

adequate techniques related to straw bale building (planing, preparation, execution, additional crafts). 

• co-ordinate and communicate the special needs of load-bearing construction with other professionals. 

• explain different methods ofload-bearing construction with reference to advantages and disadvantages. 

• inspect and select good quality bales for load-bearing construction during the whole building process. 

• control the general quality of the bales during the whole building process. 

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SESSION S1 


U3-S1 : Design and Planning 

Objectives: 

Trainees … 

… have the ability to read and understand architectural plans and 

construction drawings 

… know different structural options 

… know the dis-/advantages of every solution 

Knowledge and Skills: 

- Making a building schedule 

- Organization and execution of the work within schedule 

- Making a cutting list 

- Calculation of the building costs 

Methods: 

- Lecture/Talk 

- Explanations 

- Practice 

Trainer: 

Location: 

Classroom 

Duration: 

8 hours 

Equipment: 

Projector, Flipchart 

Theory 

Practice 

Basics of architectural plans and construction drawings 

Different structural options, characteristics and bale 

requirements 

Advantages and disadvantages of different techniques 

How to prepare a building schedule 

How to make a cutting list 

Calculate the building costs (material, labour, etc) 

Study and develop a case-study comparing the results with 

other trainees 

Unterlagen: 

Info Sheets: 

I1 Drawing basics 

Text Sheets: 

X1 Straw bale and 

legislation 

X2 Advantages and 

disadvantages of loadbearing 

X3 Characteristics of 

different options 

X4 Organisation of building 

site and schedule 

X5 Design basics 

Evaluation: 

Practical Test 

Organisation: 

Prepare a case study for every group of trainees (2–3 persons), study it in 

order to be able to compare it with the results of the participants. 

Final: 

Multiple Choice 

Oral Test 

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U3 – LOAD-BEARING STRAW BALE BUILDING SESSION S1 – DESIGN – INFO 1 

U3-S1-I1 : Design Basics 


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Understanding Architectural Plans 

Architectural drawings are a way of 

representing three dimensional shapes in two 

dimensions. When drawn accurately and to 

scale they can be used for a variety of 

purposes; from calculating quantities of 

materials needed to helping workers to 

construct the building to the right size and 

shape with doors and windows in the correct 

positions. 

Plan View: 

The plan view is the most basic drawing and is a “top-down” view of all or part of the building. Various 

information is shown in plans. A floor plan is typically used to show layouts of rooms, stairs, doors and 

windows and can be visualized as what you’d see if you looked down after cutting through the building at 

about eye level (1 500 mm above finished floor level), with everything above the cut removed. Typically a 

separate floor plan is included for each floor in the building. Other plans may show specific parts of the 

building, e.g. sole plate plan, bale plans, wall plate plan. 

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Elevations: 

Elevations are views of the front, back and sides of the building. Elevations are used to convey an impression 

of how the building will look from outside but are also used to show positions and dimensions of doors and 

windows, roof pitch and sometimes detail such as external finishes etc. 

Sections: 

Sections are used to show additional information. A section is, a bit like a plan view, a slice through the 

building. Sections are generally a vertical slice through the building and are typically used to show detail on 

the roof construction, room heights, foundations etc. A “cross-section” is a section through the shorter axis of 

a building, whereas a “long section” is a section along the longer axis. Sometimes several sections will be 

needed, especially where different parts of the building are different heights, have different roof 

construction/pitch etc. Large scale sections are often used to provide construction detail on specific parts of 

the building. 

Conventions and Good Practice: 

It is good practice to include scale bars on scaled drawings so 

that any distortions in scale (when printing, photocopying, 

converting between digital file types, etc) can be easily 

identified. The scale bars should be checked before measuring 

off drawings. 

Where sections are included they are normally marked on the plans 

and elevations with a line and arrows. The line shows where the 

building is “sliced”, the arrows point in the direction of view. Each 

section is typically allocated a letter, and this letter appears by the 

arrows at each end of the section line. 

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SESSION S1 – TIPPS 


001 

Advantages of the 

Load-Bearing Technique 

• Load-bearing construction uses less timber than other straw bale building 

methods, with straw carrying the structural loads. 

• Less timber means fewer thermal bridges compared to framed constructions. 

• Load-bearing is a very simple form of construction and for the most part uses 

only three basic skills: notching bales (around fixing posts for doors and windows), 

splitting bales and dressing bales. 

• The structural loading of the bales helps keeping the straw in place. 

Load-bearing technique with big bales: 

• High insulation value (U-value) of the walls (esp. with bales on edge) 

• Fast montage of the walls (with crane) 

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002 

Disadvantages of the 

Load-Bearing Technique 

• Unlike framed constructions (which can support a roof that works as weather 

protection), load-bearing is potentially more vulnerable to weather damage, 

unless some form of temporary roof or cover can be built. 

• Pre-fabrication off-site is not possible. 

• Because the straw is part of the buildings structure, repairs of any damage in it 

are more difficult compared with repairing damaged straw in timber frame constructions. 

•The lack of a frame means more care must be taken when building and compressing 

to ensure an even, level wall height. 

• Compressing the bales requires higher skill levels than placing them. 

• Load-bearing has no general building control approval in many countries. 

• Potential moisture issue with dew point between straw and external render. 

Load-bearing technique with big bales: 

• Relatively large floor areas necessary for walls 

• Montage only with crane 

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003 

Weather Protection in 

Load-Bearing Building Technique 

In a wet climate like that of the U.K, protection against adverse weather needs to be 

factored into the build. On a small build it may simply be a case of covering over the 

works on a daily basis with temporary protection until the roof has been built and 

waterproofed. However, normally this approach is far from ideal and can lead to a 

stressful and vulnerable build process. 

Alternative solutions include: 

• Scaffolding with protective sheeting, (including a sheeted roof on “flyover” 

scaffold trusses). 

• The permanent roof structure can be built temporarily propped to provide protection. 

This can be done either by building the roof at height on a temporarily 

propped wall plate … 

• … or by building the roof on the floor below, craning it to height and propping 

in place. 

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004 

Alternative Solutions 

for Weather Protection 

In either case, the propped roof should be approximately 1 50mm above its intended 

final position to allow the insertion of the uncompressed bales. Provision should be 

made for lowering the propped roof to allow for bale compression (e.g. by using 

Acrow props). 

Below: Temporary propping detail with prop screwed into side of wall plate. Note the 

chock screwed into the side of the prop to help support the wall plate. 

Whichever approach is taken, secondary bale protection should also be used (e.g. 

covering the tops of unroofed bale walls with secured tarpaulins, roofing felt etc). 

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005 

Organization of the Building Site: 

Planning Process 

Some processes may take unexpectedly long periods of time and some materials 

need to be ordered well in advance of when they’re actually required on site. By 

working out a schedule in advance and identifying any potential “bottlenecks”, work 

on site is much more likely to run smoothly, minimising unexpected delays. The 

schedule should include the following items: 

Design work: This is very open-ended – time will depend on the approach. Designs 

can be arrived at very quickly or can be the result of years of careful consideration 

and gradual evolution of ideas. It is worth spending time at the design stage to get 

the concepts right – it’s much easier to work out ideas on paper (or the digital equivalent) 

rather than doing and redoing work on site. 

Planning permission: In some countries it will take at least eight weeks for a decision 

to be made even in the most straight-forward planning applications. Controversial 

ones may take much, much longer. Bear in mind that there is no guarantee an application 

will be approved. Some types of work do not require planning permission 

(e.g. Permitted Development), although in some cases a notification procedure must 

still be followed. Check with the Local Planning Authority (LPA) for clarification. In 

some cases, additional approvals may also be required (Conservation Area or Listed 

Building consents, ...). 

Building Regulations Approval: is usually required in addition to planning permission. 

Approval may take from 5–8 weeks, although sometimes site work is permitted 

before formal approval is issued.




006 


Preparatory Works 

Time should be allowed for works that need to take place before straw work can 

begin. This could involve: 

• site clearance 

• excavation to level 

• excavation and construction of foundations 

• ground floor structure, including any services beneath (waste pipes, new gas, 

water and electricity connections) 

• sole plate and upright fixing posts 

• temporary weather protection (propped roof or similar) 

• security fencing 

• secure storage on site (tools & equipment, straw bales etc) 

• access, parking, delivery, covered working area etc. 

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007 


Building Schedule 

Many natural materials are seasonal and sourcing may need to be done a long time 

in advance or at a particular time of year. Straw is baled in August so to have bales 

made a certain way and available in May, it may be necessary to talk to a local farmer 

the summer before. Coppicing of hazel for stubs and pins stops at the end of 

March, so sourcing them can be difficult if left until the summer. 

Even for more “mainstream” materials, there can often be a considerable delay between 

ordering and arrival on site. Whilst many components are often available “offthe-shelf” 

or at short notice (e.g. regular softwood timber sizes like 1 00x50mm for 

sole plates or OSB sheets), it is good practice to source more unusual components, 

especially those required to seal the building from the elements (to make it “wind 

and watertight”) and check how long they will take to arrive so they can be ordered 

in plenty of time. Such materials would include doors and windows, materials for 

the roof structure (trusses or cut roof materials), the roof covering and external 

render or cladding. 

If a lime render is to be used externally, the build should ideally be scheduled so the 

lime is applied early enough in the year that it has time to carbonate well before the 

first frosts. 

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BULDING SCHEDULE 


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CUTTING LIST 


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ESTIMATING COSTS 


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SESSION S2 


LOAD-BEARING CONSTRUCTION 

Objectives: 

Trainees know… 

… different structural options for load-bearing construction and 

their characteristics and bale requirements 

… how to fix the bales, to stabilize the system and all the different 

techniques 

… different options for compressing the bales 

… details for how to connect with other building elements; 

foundations, corners, windows, doors, roof, etc. 

… how to prepare different surfaces for plastering 

Competences and Skills: 

- Building with load-bearing straw bales 

- Using different compression and fixing techniques 

- Organization and execution of the work within the schedule 

- Executing good connection details 

- Maintaining integrity of the insulation 

- Preparing different surfaces for plastering 

Methods: 

Theory 

Practice 

- Theory and practice of load-bearing construction 

Different structural options for load-bearing, their 

characteristics and bale requirements. 

Fixing the bales, and different techniques 

Compressing bales within different systems 

Details of connections: foundation, corners, windows and 

doors, roof, etc. 

Preparing different surfaces for plastering 

Study and develop a case-study comparing the results with 

other trainees. 

Fixing the bales, and different techniques 

Compressing bales within different systems 

Preparing different surfaces for plastering 

Trainer: 

Location: 

Workshop or building-site 

and classroom 

Duration: 

1 8 hours 

Equipment: 

Projector 

Straw Bales 

Structure of model 

to work on 

Tools 

Documents: 

Info Sheets: 

I1 Dressing bales 

I2 Details 

Text sheets: 

X1 Load-bearing 

(Best building practice) 

Presentation: 

Examples Load-bearing 

Evaluation: 


Final: 


Oral Test 

Organisation: 

Prepare load-bearing build, prepare structure to demonstrate different construction details. 

Order bales, prepare tools for measuring, cutting, adjusting bales, fixing, compressing. 

Order all the material needed for preparing for plastering. 

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U3 – LOAD-BEARING STRAW BALE BUILDING SESSION S2 – INFO 1 



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U3 – LOAD-BEARING STRAW BALE BUILDING SESSION S2 – INFO 1 



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TIPPS S2 


008 

Preparing and 

Dressing Bales 

Left; bale to be dressed and joint between undressed bales 

Right; “dressed” bale and joint between dressed bales 

It is good practice to inspect and dress bales before use; checking the bale has been 

kept dry and is free from seed heads etc. Bales tend to bulge up in the middle of the 

end face and drop away towards the corners. 

“Dressing” the bale involves flattening off the ends to allow bales to meet more 

snugly. Straw can be slid under the strings, moving straw from the high points in the 

centre to the lower parts at the sides and corners. 

Dressing bales gives a much better junction between bales, improving thermal performance 

and minimizing work later (reduces need to stuff gaps etc). Dressing bales 

can be most easily done by a pair of people working together as shown below. 

The bale can be held in place by the two people pushing against it from opposite sides 

with one lower leg each. 

Both hands should be made like garden claws; palms held flat, fingers splayed 

slightly apart and angled down and back towards them. 

Both ends of the bale should be dressed before the bales are laid or worked further 

(e.g. split, notched etc). 

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TIPPS S2 


009 

Notching Bales 

Where a straw bale wall meets a post (for example at window and door openings, at 

junctions with other materials etc) bales will need to be notched. This improves airtightness 

and minimizes draughts and also helps make the wall rigid. 

There are two sizes of notch that may be required. Where two bales will meet at the 

post, one on each side, each bale should be “half-notched”: the depth of the notch in 

each bale should be equivalent to half the diameter of the post (for a 1 00mm / 4” post 

this would mean a 50mm deep notch). This typically occurs beneath a window. 

Beside windows and doors, the post will be entirely recessed into the straw with a 

“full notch” – 1 00mm deep notch for a 1 00mm / 4” post. 

The process is very simple. For a 50mm notch a piece of 1 00×50mm / 4×2” timber is 

laid across the centre of the bale where the notch is to go. An old saw is used to cut 

the straw using the timber as a guide. After the first few strokes to mark the cut, the 

timber should be removed and the saw angled slightly outwards as it will naturally 

tend angle inwards, resulting in a “V”-shaped cut if unchecked. Once one side of the 

cut is done, the wood should be replaced before removing the saw blade so the 

timber can again be used as a guide for a cut the other side. The depth and size of the 

cut should be checked using the guide timber. When the notch is the right depth and 

shape, the timber should sit snugly inside it with the top of the timber flush with the 

surface of the bale. 

For a full notch, the process is identical but using a 1 00×1 00m / 4×4” guide timber. 

Care should be taken to avoid the strings either being accidentally cut or slipping into 

the notch. Notching can be carried out much quicker and more accurately using 

machines such as alligator or shark saws. 

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TIPPS S2 


010 

Straw Bale Walls: 

Compressing with Trucker Straps 

Currently the most widely used method is to squeeze the straw using trucker straps 

with a ratchet fixing. 

These are typically passed under the sole plate, around the straw and over the wall 

plate, as shown in the picture. The straw can then be compressed between the two 

plates by tightening the straps. Straps are placed on each side of each door and 

window opening, at each corner and at regular intervals elsewhere. Straps are 

positioned so that alternate straps have their ratchets on opposite sides 

of the wall (the straps tend to compress more on the ratchet side of the wall so 

alternating helps to even out the compressive pressures). 

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TIPPS S2 


011 

Straw Bale Walls: 

Compressing with Car Jacks 

This method can only be used where there is a suitably braced, robust 

surface to set the jacks against. The most common use is to compress bales under or 

above a window. A temporary 1 00x1 00mm beam can be securely fixed between the 

upright fixing posts as a jacking point. A permanent 1 00x1 00mm beam can be 

rebated into the top of the highest bale below the window (or the soffit of the lowest 

bale above) and pushed using the jacks to compress the straw. When fully 

compressed the permanent beam is fixed into place and the temporary one 

removed. 

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SESSION S3 


TOOLS FOR LOAD-BEARING STRAW BALE BUILDING 

Objectives: 

Trainees know … 

… the tools and machines used on the straw bale building site 

… specific problems of straw bale building site organization 

… how to solve any technical problem conveniently 

Competences and Skills: 

- To handle tools and machines which are used in load bearing 

straw bale construction 

Methods: 

Demonstration 

explanation 

practice 

Trainer: 

Location: 

Workshop or building-site 

Duration: 

4 hours 

Equipment: 

Tools 

Theory 

Specific problems of straw bale building site organization 

Unterlagen: 

Info Sheet: 

I1 Tools 

Text Sheet: 

X1 Building Site 

Evaluation: 


Practice 

Handling the tools, visiting building site 

Final: 


Oral Test 

Organisation: 

Looking for an appropriate building-site in the surroundings or preparing different tools and material for 

the demonstration 

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TIPPS S3 



01 2 

Splitting Straw Bales 

with Bale Needles 

Bale needles may be useful or even indispensable for load-bearing straw bale walls 

(in this case each new row of bales needs half-bales). In the infill-technique, the bales 

are compressed more easily with adding flakes between two plates. Bales can 

also be compressed to a certain density by simply rebinding it with strings, 

depending on the strength you tear, or with screw clamps. But as bale needles are 

connected to straw bale building like the halms to the bale, let's look at these tools. 

Actually a pointed wooden stick with two holes at the top is enough for their 

function (since there are two new cords needed –- one for the right, one for the left 

bale part). There are also combined bale needles (which are connected to a 

bar/handle, which pull all four cords through the bale at the same time (two upper 

and two lower – instead of the two existing cords). After you pulled your strings 

through the bale, the cords are knotted to each half-bale. There are special knots, as 

they are known from sailing. After you rebound your halfs, the original two cords are 

removed, thereby maintaining the density of the bale. If you took the right strings on 

the right half bale you can divide your bale (otherwise, if strings are crossed, you 

have two connected half-bales). So you can definitely say that some straw balers 

make a science out of a simple thing. 

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TIPPS S3 



01 3 

Straw Bale Tools: Shaving 

Surfaces with Hedge Saws 

We do not only want to squeeze a few protruding stalks with hedge saws, in most 

cases we want a plane surface to save plaster and to avoid different drying times, 

even if bales are slightly differently thick or bulged or not exactly installed plane. 

Even if there are customers who prefer a more organic-hunched surface, in most 

cases they mean slight bumps in the (hand-)plaster and not simply covering uneven 

bales with the plaster. The cutting of the hunches of straw bales is a long-term work, 

but it really becomes hard work with not really sharp hedge saws. Unfortunately 

sharpening is often as expensive as a new one. A tip to save energy is to pick hedge 

saws with a rather shorter sword (about 50–60 cm). The longer the sword, the more 

pressure we need to push to the bale surface, and the harder it is to shave a round 

wall or vault inside. In terms of strength: from 450 W, hedge trimmers are robust and 

strong enough. The sharpness of the knives is much more important. Hedge saws 

are among the very safe machines (since they cut only between the knives). 

Nevertheless, you can tweak neatly with hedge saws (a small cut with painful 

bruising is the result). It can happen when you sit on the scaffolding shaving the 

walls. More often, if you don't take care, you will cut the cable and cause a short 

circuit. Therefore, it is best to carry the cable over the shoulder. Or choose a model 

with battery. 

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TIPPS S3 



01 4 

Straw Bale Tools: the Straw Bale 

Hammer or Persuader 

This wooden hammer "persuades" each bale (at least as long as it is not fixed with 

battens). It is a must on each straw building site and also easy to manufacture with 

leftover construction wood. Only the handle should be sturdy (typically hardwood). 

Do not screw the handle to the wooden plates too often (twice should be enough), 

otherwise it will break more easily at this point. The persuader should be heavy, but 

it is used with a swing to move the bales back into the row, or to connect the upper 

bale with the underlying ones well. 

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TIPPS S3 



01 5 

Straw Bale Tools: 

Gap Filler in Two Sizes 

No one can fill straw bales between posts/rafters (or stack them over one another in 

the load-bearing straw bale building) without leaving any holes at all. This is due to 

the fact that bales are often rounded at the edges rather than square; on the other 

hand, cavities can also develop when filling (densifying) with layers. And finally it 

happens again and again that, for structural reasons, there is a (diagonal) squared or 

round wood in the insulation area, such as the planks of an intermediate ceiling. In 

order to fill these cavities with (loose) straw and prevent convection in the 

insulation layer as well as thermal bridges, we use selfmade, simple stuffing tools. 

Of course, you can also stuff with your hands (fingers), but I wouldn’t recommend 

that for larger areas. After some days you cannot move your fingers any more. 

Especially if the wall is to be plastered, it is important to stuff the straw in the same 

density as the bales nearby, so that the weight of the plaster does not pull it out 

again. 

For these purpose we need two gap fillers or "stuff sticks", made of strips of 25×25 

mm (1 ×1 ") for the small and 25×50 mm for the large one. So we are building a "T", 

which we screw together once or twice (6–8 cm screw, 5–6 mm hole pre-drill). The 

smaller handle has a length of 1 5 cm, the larger handle has a length of 25–30 cm, 

which we bevel at the top like a screwdriver (with a jigsaw or crosscut saw). Finally, 

we put a small notch in the middle of the "cutting edge", so that the straw to be 

stuffed is bundled together more effectively. Finally we take sandpaper (or a rasp) 

and round off all edges a little bit. 

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U3 – LOAD-BEARING STRAW BALE BUILDING INFO 2 

Cords and Knots 


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STRUCTURAL BEHAVIOUR 


Virko Kade: 

Structural Behaviour 

Like any other building material, straw bales react in a very specific way to forces 

working in on single bales or on the whole building. Settlement is as much an issue 

as is known from traditional wood construction. The ductility of the straw bale 

results in (besides good thermal and acoustic insulation) an extremely good 

performance withstanding earth quakes. Tests conducted in the USA showed no 

failure even exposed to earth quakes of the highest level! 

Performing our own tests, we put a weight of 35 KN (3.5 metric tons) on a small 

bale, which did not destroy it. Only seconds after it was almost back to it’s original 

size, and after five minutes it was exactly like before the test. 

What loads can a straw bale wall bear without collapsing? 

The structural engineer Bruce King, who was part of the development of the straw 

bale building regulations in the USA, recommends not more than 500 kg per meter 

of straw bale wall as upper limit and calculation base. According to the building laws 

in the States however, the walls are supposed to bear the loads without being 

plastered. We put several tons per meter on a plastered sample straw bale wall 

without facing structural failure. Only the wall plate was forced between the two 

plastered surfaces. Massive snow loads on some of “my” buildings amounted to an 

actual load of 1.000 kg per meter wall and more without causing any cracks in the 

plaster. We can learn from this, that a heavy roof truss with roof tiles doesn’t work, at 

least with small bales. It makes sense to construct a roof as light as possible and 

reinforce it with a structural partition wall as “snow insurance”. Furthermore using 

small bales one-storey buildings are advisable, at least with the usual Alpine snow 

loads in mind. The Swiss architect Werner Schmidt proved that with big bales even 

3.5 storeys and substantially higher snow loads can work (see appendix Statics 

House Fliri p. 80). 

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What height of a straw bale wall is legally possible? 

In countries with specific straw bale building regulations the condition is being 

upheld, that the ratio of height and width of the wall should be < 6:1. This means a 

maximum of eight small bales on top of each other. The actual height of the room 

can be varied to some extent by adjusting the height of the wooden construction at 

the base and of the ring beam. This very regulations recommend for small bale 

constructions, to keep the length of a straight wall without bracing (e.g. with 

partitions) below six metres. A realistic limit according to my personal experiences!




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COMPRESSING & SETTLEMENT 


Virko Kade: 

Compressing and Settlement 

In load-bearing straw bale building, the bales are usually installed “lying flat”. 

Because the orientation of the straw is more or less uniform thanks to the pressing 

process, the stems are lying on the floor or parallel to it, respectively. 

In principle, thus the settlement can be bigger compared to an upright installment of 

the bales (which is common in certain timber frame constructions), but “standing” 

bales are running the risk of snapping under pressure, which would lead to the wall 

collapsing. If the bale/stem orientation is lying flat, the stalks are pressed into one 

another and wedged tight. The higher the pressure, the better the stability. Soon a 

single bale as part of a wall construction can no longer be moved or put into a better 

position. Corrections should therefore be done before the compression with straps. 

Generally speaking, straw bales should already be compressed as much as possible 

during the “brick”-laying; e.g. you could chose the heaviest person at site and let 

him walk on the wall crest every two or three layers. 

Nevertheless: Be careful when fitting bales in openings that are actually too small! A 

bale that is too long and is nonetheless forced into place with all strength moves 

other bales to the side, the corners are bulging outwards, the point load on window 

frames can get very high and so forth. 

When using small bales, the wall height is already below the theoretical measure of 

36 cm × 8 bales only by compressing it with a persons weight. Ideally the compression 

should be done mostly with straps and ratchets rather than by the weight of the 

roof truss. Therefore the strap-compressing should be exhausted before mounting 

the roof truss. The amount of settlement is the result of so many variables, that it 

can hardly be calculated. 

With small bales, the difference between the actual and the theoretical measurements 

can be between 5 and 7 %, with jumbo bales it’s 0 to 0.5 %. The compressing 

of big bales yields almost no measurable results, it’s importance lies in the enabling 

of an even settlement. Furthermore the resistance of the bales towards roof loads is 

increased. And: The straps which remain below the plaster are the only statically 

effective bracing against wind load. 

42


COMPRESSING & SETTLEMENT 


43


BUILDING LAW (IN AUSTRIA) 


Virko Kade: 

Building Law: Legislation 

in Austria 

44 

The straw bale building regulations differ very much from country to country. Many 

countries don’t have any specific regulation at all, others only recommendations. 

The most precise laws are to be found in the USA, which comes with advantages 

and disadvantages. E.g. the so-called chicken wire has to be used flat-spread, which 

can cause problems in wet climates, not to speak of electromagnetic radiation etc. 

On the plus side the regulations provide some sort of planning security, especially 

with regard to load-bearing constructions. Consequently the majority of straw bale 

buildings in the USA are load-bearing in the making, like in several other countries, 

btw. 

In Austria there is no general building control approval including a structural 

calculation. The certified bales are only approved with regard to insulation 

properties, fire resistance and humidity. When using them for insulation purposes 

only, it is usually no problem to get a building approval, even insurance companies 

nowadays have listed straw bales as building material. 

If you’d like to build with structurally loaded straw bales, however, an individual 

authorization is required. That means, that the building control can simply give its 

approval “one house at a time”, ideally without the need of any further proof. It helps 

the cause to refer to existing buildings as well as to the ecological advantages and 

the high level of innovation of this building technique. Written documentation 

(books, brochures), that shows how far the professionalization of straw bale building 

has come in Europe, can also help the authorities to rethink. But it is still possible 

that one has to provide a structural report. In this case it’s usually of little help to 

quote the building laws and structural surveys of other countries; you’ll have to 

deliver. Which can be quite time- and money-consuming, if you find a structural 

engineer at all. 

In the past it was often enough to convince the construction site management 

(master builder, carpenter) to incur liability for this construction method to satisfy 

the building control as well. Extensive structural tests aiming for a general building 

control approval according to the Austrian norms would unfortunately be very 

expensive and require a huge effort – too big a price considering the public and 

trade interest, which is not overwhelmingly high.



DESIGN 

Characteristics of Planning SBBs 

Each planning should take into account the specifics of the wall constructions (with 

regard to materials used and special features). This is particularly true in straw bale 

building, since the building material is not familiar to many planners and yet it 

requires a different way of thinking. First, of course, we should consider the bale 

dimensions – which are not precise and not following any industrial standard. A small 

bale has a fairly exact width (between 45 and 50 cm, according to the baler); the 

height may also vary according to the baler, but the most regular size is 36 cm. 

But: The bales become smaller by compression, so this height vanishes after the 

second or third layer. How much settlement you actually have in the end is not exactly 

calculable, so always calculate a bigger settlement to prevent the top beam from 

touching or resting on the window sill and endangering the entire statics. Stiff 

components such as intermediate walls or additional supports should be installed at a 

fixed height when the setting has been completed. Before that, work with scaffolding, 

e.g. threaded rods. Window sockets are designed ideally 20–30cm below the top beam 

and infilled later. For smaller windows that are walled in, calculate the total height of 

the window frame a few centimeters smaller than the theoretical bale dimension. 

The length has the greatest variance in straw bales. It can be set as desired in the 

baler, but still depends on the swath (width and stroke length of the tracks in the 

field) and the driving method. Even well-made small balls can have a variance on 

average of up to 1 0 cm or more. For a load-bearing building I calculate with a length 

of 1 00cm (which is regular for proper-density-bale dealers). That said: the length of 

small bales is not that big an issue, many of them have to be resized anyway, which 

can easily be done. In the case of big bales, however, it can take 20–30 min per piece 

(assuming crane/forklift is available). 

Theoretically, the length of most jumbo bales is 240cm. Although big bales are far 

more precise than small ones, some are still longer than others, gaps between bales 

occur … suddenly the wall is 20cm longer! Therefore I calculate in the planning with 

245cm length. Filling a gap later is definitely the least effort. Every second row, 

however, we still need half-bales to build properly bonded. At best you order the 

half-bales from the straw merchant before harvesting (some more than you need). I 

order with my desired length minus 5–1 0cm. 

In order to be able to work exactly and to facilitate window installation and plaster 

connections, all wooden components of the wall should be planned level with the 

straw surface, so both can be plastered in one layer. 

We should definitely focus on the following points regarding the statics: 

• no point loads on the top beam 

• avoid thrust forces on the wall crown (ring beam / top beam) 

• do not put loads on a blunt end wall, always arrange wooden posts here 

• use only the same bales for a building, preferably from the same harvest 

• enough additional bracing by intermediate walls (snow loads) 

• bearing walls (usually two): as few and as small windows as possible 

• max. wall length without bracing (for small bales with 50cm width): 6 metres 

• roof loads should be as small as possible (small bales) 

45


BUILDING PHYSICS 


Virko Kade: 

Remarks on Building Physics 

In central and northern Europe we should take into account a number of points that 

are less important in other parts of the world: 

• avoid metal parts in the straw, especially in the outer third (threaded rods, etc.) 

• avoid thermal bridges to ensure good insulation; furthermore, thermal bridges 

increase the effect of weak points 

• never place bales directly on concrete, always use a thermal separation 

• place the first row of bales always on wooden base plates (at least 5cm) in order 

to avoid water damage 

• do not use plasters which contain cement on the outside, only pure lime 

plasters; use clay plaster inside 

• interior constructive changeovers with straw walls such as partition walls, 

ceilings, etc. should always be sealed well, for example with plaster or clay fleece 

or similar 

• first bale layer should be above the splash water area (> 30cm) 

46


QUESTIONS ABOUT DETAILS 


Virko Kade: 

Questions about Details 

Wall bushings (pipes, cables, etc.) 

• Electricity and water (interior) 

• Chimney 

• Plaster preparations 

• Weather 

• Scheduling 

• Costs 

47

48


STRUCTURAL CALCULATION 


Peter Braun / House by Arch. Werner Schmidt 

Load Bearing Straw Bale Building: 

About the Static Properties of Straw Bales 

Load Distribution 

The central bearer concentrates the load. 

49





Model: Office building of the city of Lausanne, architects collective carpe 

50





Deformation 

51

STEP – Straw Bale Training for European Professionals 

UNIT 3 – Load-bearing Straw Bale Construction (201 7) 

Editors/Tips: Herbert Gruber, Helmuth Santler (ASBN) 

Virko Kade, Michael Howlett; Coworks: BuildStrawPro- 

Team (Erasmus+ Projekt) 

Design & Photos: Herbert Gruber; Virko Kade, Werner 

Schmidt; more Photos: Werner Schmidt, provided by 

Architects. Illustrations/Icons: Michael Howlett (SBUK) 

This Handbook is based on 

the Handbook by Leonardo- 

Group STEP (201 5) 

52

STEP U3 Handbuch ENGLISH

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