STEP U4 Handbook 2019 ENGLISH

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U4 – WRAPPING (EXTERIOR THERMAL INSULATION) 

INDEX 

U4 

TIME 

PAGE 

U4 Learning Outcome 5 

U4 Session 1 : Design and Planning ca. 6 hrs. 7 

Info: Thermal Insulation Composite Systems in Relation 8 

Info: Design and Planning: Details (Foundation/Windows) 1 2 

Tips: Planning-Checklist Wrapping 1 4 

001 -1 4 Hybrid Foundation, 002-1 5 Perimeter-Insulation, 003-1 6 Drainage, 

004-1 7 Roof Overhang, 005-1 8 Windows and Doors, 006-1 9 Scaffolding 

U4 S2: Constructions 2 days 21 

Info: Wrapping-Konstruktionssysteme 22 

Tipps: Konstruktionssysteme 24 

007-24 CUT centered, 008-25 CUT outside, 009-26 Binding Bales to the Wall, 

01 0-27 Spanning Bales down, 011 -28 Spanning Bales to the Wall, 01 2-29 Pallette- 

Hybrid-Constructions, 01 3-30 Cage for Bale Layers, 01 4-31 Drop Nose, 01 5-32 Direct 

Plaster, 01 6-34 Cladding, 01 7-35 Glass Facade 

U4 S3: Prefab-Constructions 1 day 37 

Info &Tipps: Wrapping-Prefab-Systems 38 

01 8-38 system/haus/bau / ASBN, 01 9-39 Jules Ferry Residence / Bet Gaujard, 

020-41 Complemedis / Werner Schmidt, 021 -42 Straw/Reed-Facade by Kengo Kuma 

Ass., 022-42 Waseda University Students: A-Recipe-To-Live-Straw-House, 

023-43 Enterprise Centre of University East Anglia: Prefab Straw-Reed-Facade, 

024-43 Schelfbauhütte: Montage System for Straw Bale-Wrapping, 

025-44 School Montreuil and Issy les Moulineux: Exterior Modular Straw Bale 

Facade, 027-45 Make your City Smart! / Paul Schulz, TU Vienna, 027-46 Calculation 

Building Costs 

U4 S4: Alternatives to Straw Bales ca. 2 hrs. 49 

Info &Tipps: Natural NAWARO-Alternatives 49 

023-47 Inject Straw Fibres, 024-48 Straw Mats, 025-49 Reed Mats 

Credits and Impress 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 organizing a wrapping 

straw bale building site and their solutions 

(weather protection, safety, logistics). 

• the symbols to be able to understand plans 

and construction drawings. 

• new and historical wall-constructions and 

their impact on wrapping (horizontal moisture 

barrier, position ofwindows, consistence of 

plaster, roofoverhang). 

• the different methods and techniques of 

wrapping, their requirements, advantages and 

disadvantages. 

• the necessity and the techniques to avoid and 

to close gaps (between bales and between 

bales and construction). 

• other bio-sourced insulation materials, that 

can be used additionally in straw bale 

building. 

• different fixings and their characteristic and 

the suitable methods of compressing. 

• different wrapping techniques and their 

requirements related to schedule, planning, 

budget and resources. 

• about techniques and construction details for 

the adjacent building elements (ceiling, walls, 

floor- and roofplates) avoiding cold bridges. 

• techniques to manufacture the additive base 

plate for straw isolation avoiding cold bridges. 

• 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 wrapping straw 

constructions. 

• handle the tools and machines which are used 

in wrapping construction. 

• apply different wrapping and retrofitting 

methods professionally. 

• resize and fix the bales and kompress them if 

needed. 

• fix the bales on an existing wall and fill gaps 

with straw or another suitable sustainable 

insulation material in order to produce a 

continuous layer of insulation avoiding cold 

bridges. 

• make a lasting connection between the 

wrapping and the existing construction. 

• read and understand the symbols of plans 

and construction drawings. 

• make supportive wooden structures and 

posts and lintels for the openings. 

• give advice to others, who make the plinth 

wall and other requested details. 

• prepare the substrate for following crafts 

(plaster, cladding, air- and wind tightness) or 

execute it in accordance with them (level and 

shave the straw surface, fix the plaster ground 

on wooden construction elements). 

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 wrapping (planning, preparation, execution, additional crafts). 

• coordinate and communicate the special needs of wrapping constructions with other professionals. 

• explain different methods ofwrapping with straw with reference to advantages and disadvantages. 

• select good quality bales for wrapping and supervise the whole wrapping process during the 

construction period. 

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SESSION PLAN S1 


Session Plan U4-S1 : Design and Planning 

Objectives: 

Trainer: 

Trainees ... 

… have the ability to read and understand architectural plans and 

construction drawings. 

… know different structural options. 

… know the advantages and disadvantages of every solution. 

Skills: 

Make a building schedule 

Organize and finish the work according to schedule 

Make a cutting list 

Calculate the building costs 

Methods: 

Theory 

Practice 

Lecture/talk 

Explanations 

Practice 

Organization: 

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 

Calculation of building costs (material, labour etc.) 

Study and develop a case-study comparing the results with 

other trainees. 

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. 

Place: 

Classroom 

Duration: 

3 days 

Equipment: 

Beamer 

Flip chart 

Documents: 

Info sheets: 

I1 Drawing basics 

I2 Characteristics of 

different options 

I3 Drawings of pros and 

cons 

Text sheets: 

X1 Drawing basics 

X2 Characteristics of the 

different options 

X3 Organization of building 

site and schedule 

Exercise sheets: 

E1 Make a building schedule 

E2 Cutting list 

E3 Calculating material and 

costs 

E4 Drawing construction 

details 

Evaluation: 

Multiple choice 

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U4 – WRAPPING (EXTERIOR THERMAL INSULATION) INFO 1 

U4-S1-I1 : Thermal Insulation Composite System 


U-Wert: 0,1 32 W/m 2 K 

PEI n.e.: >1 9 kWh/m² 

U-Wert: 0,1 28 W/m 2 K 

PEI n.e.: >23 kWh/m² 

U-Wert: 0,1 78 W/m 2 K 


U-Wert: 0,1 73 W/m 2 K 


U-Wert: 0,1 74 W/m 2 K 

PEI n.e.: >1 33 kWh/m² 

Straw Bales with Direct Limeplaster 

Bale density ca. 1 00 kg, complete 38,5 cm thick 

Surface: shaving, stuffing, plastering 

Wrapping-System: Material Price/m2 (AT) 

Straw Bales: around € 1 0,00 - 1 7,40/m2 (cert.) 

Constr. with/out window box: € 1 3,05 - 36,50/m2 

Lime plaster 2,5 cm, mesh, Rabolin: € 1 0,00/m2 

Material-Price complete: € 33,05 - 63,90/m2 

Straw Bales with ventilated Cladding 

Bale density ca. 90 kg, complete 45 cm thick 


Straw Bales: around € 1 0,00 - 1 7,40/m2 (cert.) 


diffusion open facadeboard (DWD): € 8,46/m2 

Batten, Counterbatten, Cladding: € 40,00/m2 


Naporo Hempmat + Capatect Facade 

20 cm Hemp Board/Mat, complete 21 cm 


Hempmat (Naporo): 24,91 - 41 ,52/m2 

Screw dowel, filler, plaster base, fibre glass 

mesh, CarboPorPlaster: € 24,80/m2 

+/-Windowbox with Insulation: € 23,45/m2 


Mini-StrawBales, Woodfibreb., Lime-Directplaster 

26 cm Straw, 4 cm SteicoProtect, compl. 32,5 cm 


Straw Bales: around € 8,00 - 11 ,20/m2 (cert.) 


diffusion open facadeboard: € 1 3,1 8/m2 

Lime plaster 2,5 cm, mesh: € 8,70/m2 


to compare: Baumit WDVS EPS-F 

1 8 cm EPS-F, complete ca. 20 cm 


EPS-F (Polystyrol-Insulation): 22,60/m2 

Adhesive filler, fibre glass mesh, primer, 

Silikat Top: € 1 7,09/m2 

+/-Windowbox with Insulation: € 23,45/m2 


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Prices: baustrohballen.at/sonnenklee.at/frischeis.at/haeuser-in-wolle.com/bauschilf.at/hagebau.at


U4-S1-I1 : Thermal Insulation Composite System 


Source: u-wert.net, infos without warranty 

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U4-S1-I1 : Thermal Insulation Composite Systems in Relation 


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U4-S1-I1 : Thermal Insulation Composite Systems in Relation 


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INFO 2 



1 2


INFO 2 



1 3


TIPS 


Session Plan U4-S1 : Design and Planning-Checklist 

Task: 

Calculate PEI 

of this foundation 

per m 

1 4 

001 

Insulated Hybrid Foundation: 

Concrete or not Concrete? 

In order not to have to build with organic, moisture-sensitive materials in the splash 

area, we have to somehow overcome the 30 cm - with a base or auxiliary 

foundation. In general, this is made of concrete, although we don't have much loads 

except a plastered straw ball wall. What actually speaks against concrete? Concrete 

is an artificial mixture of cement, sand or gravel and water. Usually. further additives 

are used. The required energy expenditure for the production of concrete depends 

essentially on the composition of the concrete. The component with the highest 

energy content is the cement. Furthermore, a distinction is made between reinforced 

and unreinforced concrete. The reinforcement degree has a significant influence on 

the production energy PEC (transport concrete C20 / 25: PEI: 31 5 kWh / m3, λ = 2.0 W 

/ mK, concrete blocks: PEI: 379 kWh / m3, λ = 1 ,35W / mK). 

Advantages Concrete: High compressive strength, good sound insulation, good fire 

protection, good moisture protection, high thermal mass, any shape 

Disadvantages Concrete: poor thermal insulation, aging process, "composite 

building material". 

Thermoblock-Bricks have an even higher primary energy content (perlite filled) 

Brick S, Poroton: PEI: 484 kWh / m3, λ = 0.09-0.11 W / m.K) 

One possibility is to reduce the proportion of concrete as much as possible and to 

use mineralic, insulating building materials instead. However, their properties are 

also very different: perlite (PEI: 1 87 kWh / m3, λ = 0.06 W / mK), foam glass (PEI: 224 

kWh / m3, λ = 0.07 W / mK), Leca (PEI: 850 kWh / m3, λ = 0.035 W / mK) as well as 

XPS have a higher primary energy content than concrete (PEI: 548 kWh / m3, λ = 0.1 6 

W / mK) ) Solution: 1 5 cm concrete blocks with perlite or foam glass. Thus, the 

primary energy content remains justifiable. 

Source ofallValues for PEC und λ:TU Munich


TIPS 



002 

Foamglass-gravel and Cork 

Perim.insulation instead of XPS 

Are there any ways to prevent concrete and XPS in the wrapping foundation and 

perimeter insulation? The starting price for comparison is: € 9.74 / m. 

If we take a single-storey building (3 m high), we have a static load of straw bales 

(1 00 kg / m3 = 1 08 kg / and lime plaster (1 400 kg / m3 = 1 05 kg), thus total of 227 kg / 

m foundation. This is comparatively little load. Furthermore, these wrapping loads 

are not carried completely by the foundation, but partly by the wall and the roof 

rafter (suspended construction). And the 6 cm foot threshold distributes the unequal 

loads. 

Now we know that foam glass e.g. is suitable as a capillary, heat-insulating and loadbearing 

layer under ground level. 30-40 cm foam glass gravel around the house are 

enough (price at 50 cm depth € 11 ,70 - 1 5,70 / m). In order to overcome the 30 cm 

above ground level, Mirapor proposes so-called wall bags. Foam glass could also be 

filled into gabions (30 x 30 x 30 cm: € 8.95) or as in the case of the Earthbags 

(Calearth), filled into PP sandbags (€ 0,83, 4 rows of á 40 x 60 cm = € 6.46 / mm). 

Another alternative is cork as perimeter insulation. Cork should not be placed 

directly on the damp ground, but it can bridge the 30 cm on top of foam-glass gravel 

(price at 1 0 cm thickness and 30 cm height: 1 2,53 / m). A lime-cement plaster with 

glass fiber mesh ensures that this auxiliary foundation does not settle. But: without 

guarantee! 

1 5


TIPS 



1 6 

003 

Advantages and Disadvantages 

of Drains in Restoration 

In the restoration and clearing of old building cellars no drainages are generally 

found. This has its good reason in building the floors of these basements. In many of 

the cellars, for example, only a loose brick is laid in the Wilhelminian era, which does 

not have any kind of sealing against the ground. If foundations are built, they are 

usually water-permeable and in no way waterproof concrete. On the outside, the 

floor materials were again installed in a slightly compressed manner, so that at the 

base of the walls only capillary moisture - ie soil moisture, which could not be 

removed by drainage - is present. If the soil situation remains the same, the 

installation of a drainage tube would be completely ineffective, since a drainage pipe 

only drains water in liquid form. 

The installation of a drainage system with leachable granules, drainage plates and 

drainage pipes on the exterior walls and foundations would considerably impair 

these cellar constructions. Water would permanently flew into the open-pore and 

leachable drainage package next to the basement, which would lead to continuous 

water input and damage on walls and foundations. In particular, the soil moisture 

present to date under the basement floor would convert to a moisture saturation of 

the soil, which could not be relieved by a functional drainage at the exterior side of 

the walls. 

Respecting this, drains in old buildings are not purposeful and usually senseless, 

especially since a drainage in water-bearing soil layers would only bring about a 

reduction in the water amount. (Source: trockenlegung-hannover.de/drainagen)


TIPS 



004 

Is there enough Roof-Overhang 

lateral and on gable-side? 

Roof overhang lateral: the distance from the façade to the respective eaves (drip 

edge); Roof overhang at the gable-side (Ortgang) beyond the façade. 

While the extension of the lateral roof overhang is relatively simple, static 

calculations are mandatory when the roof overhang on the gable-side is extended. 

The administrative background has also to be added to the effort. When you renew 

the roof overhang at the gable side, you will have to obtain a building permit. In 

addition, building laws define a minimum distance to adjacent areas and also to the 

road. Finally, in many cases the neighbors will also have to confirm their agreement 

in writing. 

This also means that you need a structural engineer or architect who can design and 

sign the appropriate blueprints before submitting them to the building authorities 

for approval. 

Please check, before you cover an outer insulation, the roof overhang on all sides, 

for the wrapping with straw you need in the minimum case 36 to 40 cm on all sides. 

If this space is not available, it is advisable to think about thinner thermal insulation 

layers (for example with 26 cm minibales, flakes or other insulation) (see page 8 or 

tip 01 3). Or you extend the roof unconventionally: with a short extra roof under the 

main roof above the wrapped straw bale wall. This could be covered for example 

with a metal sheet (roofer / plumber, see picture on the upper right). 

17


TIPS 



005 

Solid Boxes carry the (new) 

Windows and Doors: 

If windows are left in the existing wall (e.g. because they still correspond to the 

thermal insulation standard), a thermal bridge is created because the straw bale 

wrapping insulation is completely open here. Windows are always the weak point in 

any house (8 - 1 2 cm wood or plastic frame has a significantly worse insulation 

value than 36 cm straw). In this case, the window frames must be massively 

insulated (outside), but this usually causes a problem (from the wall to the window 

wing it is usually not more than 5-6 cm). 

So windows are ideally removed and placed in the insulation area. Sturdy boxes (the 

larger the window or the (terrace) door, the more solid) are used for this purpose, 

which are pushed into the cavities after removal and are laterally fixed (and 

insulated). Concrete formwork panels meet these requirements better than OSB and 

are cheaper than natural three-layer panels. In addition, their impregnation provides 

a double rain protection (window sill). On the front, they are attached to our hybrid 

posts. The window sill is slightly sloped (2 °) and because the additional 40 cm 

insulation layer greatly reduces the amount of sunlight the box can also be beveled 

outwards (45 °). It is simpler, however, to extend the box only 1 8 cm to the center of 

the straw bale (where the windows are then installed at the front edge of the box) 

and the angle before is produced by cutting the bales (alligator / hedge trimmer). 

1 8


TIPS 



006 

Safety and Efficiency: 

Do we need a Scaffolding? 

Anyone who has lifted a 1 4 kg strawbale on a ladder standing in front of a wall and 

does not have the muscles of Arnold Schwarzenegger can sing a song of it: a 

scaffolding helps not only to save energy (and to not leave the motivation), it also 

helps to maintain the quality of the installation. Bales need to be compressed 

downwards with your weight (feet) or the persuader (wooden hammer) and with 

additional flakes to close the gaps to the adjacent bale, they must also be installed 

as flush as possible in a level with the neighboring bales ( so that we get a flat 

surface for the subsequent plaster). We are talking about quality work, which can 

only be done on a safe scaffolding. In single-storey houses, you may work perfectly 

with a few stable bucks and scaffolding boards. Or a smaller sliding aluminum 

scaffolding (which can be rented easily and cheaply, e.g. at geruestverleih.at: € 70, - / 

week). In two-storey buildings it is advisable to have a scaffolding erected by a 

scaffolding builder or master builder, as it can be used also by other craftsmen (e.g 

plasterers and roofers). Saving money here can ultimately become more expensive 

as not only the motivation of the straw bale builders or helpers is decreasing but 

also the workload during the post-processing of the wall increases massively. in a 

new building the bales can be infilled from inside, in wrapping also the plastering is 

carried out exclusively from the outside. So please do not save money on the wrong 

place. Additionally the construction site becomes much safer. 

1 9

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Session Plan U4-S2: Construction 

Objectives: 

Trainer: 

Trainees ... 

… know different structural options of wrapping and retrofitting 

and their characteristics and bale requirements. 

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

different techniques. 

… know the different options to compress the bales within the 

systems. 

… know the details of the connections: foundation, corners, 

windows, doors, roof etc. 

… know how to prepare the different surfaces for plastering. 

Skills: 

Execute wrapping and retrofitting construction methods 

Use of different compression and fixing techniques 

Organize and finish the work according to schedule 

Execute good connection details 

Knowledge of how to maintain integrity of the insulation 

Prepare different surfaces for plastering 

Methods: 

Theory 

Practice 

Practice on different wrapping and retroffiting systems 

Different structural options of wrapping and retrofitting and 

their characteristics and bale requirements 

Fixing the bales with different techniques 

Compressing bales within different systems 

Advantages and disadvantages of wrapping and retrofitting 

techniques 

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. 

Place: 

Workshop or building-site 

and classroom 

Duration: 

5 days 

Equipment: 

Beamer (projector) 

Bales 

Structure or model to work 

on with tools 

Documents: 

Info sheets: 

I1 Wrapping 

I2 Retroffiting 

I3 Details 

Text sheets: 

X1 Wrapping 

X2 Retroffiting (Best 

building practice) 

Power point: 

P1 Ex. Wrapping 

P2 Ex. Retrofitting 

Evaluation: 


Organization: 

Preparation of a structure to be wrapped or retrofitted, preparation of a structure to demonstrate 

different construction details. 

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

Order all the material needed for preparing the plastering. 

21


INFO S2 



22


INFO S2 



23


TIPS 



007 

CUT-Hybrid-Construction: 

centered - for direct plastering 

If the surface of the straw bale wall is directly plastered, the posts (usually planks 

2.5 x 1 5 cm are enough to hold the bales) are placed in the center. The back of our 

construction thus forms the wall of the old stock. The bale is simply pushed against 

the existing wall (on edge). If the wall is directly plastered, care must be taken when 

filling the bales to form a flat surface on the outer side (ie connect to the adjacent 

bales without gaps). In order to prevent the bales from slipping or falling out in 

hybrid constructions (where they are not clamped between the boards and the wall) 

they are fixed (nailed or screwed) after each row by battens (2.5 x 2.5 cm). Predrilling 

especially helps when the battens are nailed. This (5 m long) batten is entered in the 

bale (laid halm side) by cutting the straw on the surface with a bread knife or a wide, 

stable cutter. This additional 36 cm insulation (approx. 39 cm thickness incl. plaster) 

brings your house to low-energy standard. Alternatively, 26 cm miniballs can also be 

used (28.5 cm total thickness). 

24


TIPS 



008 

CUT-Hybrid-Construction: 

outside - for (Timber-)Cladding 

If the front of the bales is to be planked with diffusion-open boards (for example, for 

a ventilated wooden facade), we place the posts (2.5 x 1 5 cm or better 4 x 1 5 cm) 

flush with the front of the 6 cm thick wooden base. In this case, we do not need 

battens to fix the bales, since they are clamped between the wall and the boards 

(diffusion-open 1 6 mm DWD). If the wall is slightly sloped, our Wrapping wall should 

also be slightly sloped, just like in the assembly of a insulation composite system, 

which is usually not levelled. Otherwise, it must also be stuffed after each row, since 

crevices in the dewpoint area lead to convection and thus condensation. Please 

check the exact bale thickness before installing the hybrid posts, there are also bales 

which differ by the standard size 36 cm (about 34 cm thick). The bale density does 

not have to be as high (from 85 kg / m3) as with direct plasters (1 00 kg) and when 

stuffing, it is enough to fill the holes just in such a way that holes disappear, the 

straw doesn#t have to be well anchored. Contrary to the direct plaster, since the 

boards also hold loose straw. However, overhanging straw should be cut off, 

especially along the stands (hedge trimmer), so that the straw does not slide 

between the post and the board during assembly. Since here the individual rows are 

not fixed with battens (which also fix the distance of the stands), it is important to 

ensure that the posts / planks do not bend during the filling (especially at the 

corners). And it is advisable to fix the stands at least after each storey (2,5-3 m) on 

the wall. 

25


TIPS 



009 

Binding 

Straw Bales on the Wall 

Before the CUT hybrid construction was invented and adapted for wrapping, bales 

were attached to the walls with cords. New connecting cords were knotted on the 

two bale cords and these were then fixed to the wall (dowels and eyelets). This does 

not just sound like a lot of work, it is. In addition, there are other disadvantages of 

this (outdated) technique: the cords intersect the bales and deform them, fixing 

dowels in old walls can be a real challenge, the strings remain as in the load bearing 

straw bale technique on the bale, which makes shaving much harder (or impossible). 

The first layer of bales is attached to the base plate with small spikes (also as in loadbearing 

straw bale construction). Pointed 2.5 x 2.5 cm battens with a length of 

approx. 20 cm fit into a 3 cm drill hole in base wood, to prevent bales from slipping. 

The advantage of this technique (some argue with the continuous insulation area) is 

not clear on closer inspection, since hybrid posts (1 " planks) affect the total 

insulation value of the wall far less than e.g. remaining cavities, which are then filled 

with clay or COB or lime plaster. Of course, no "planking" for a wooden facade can 

be attached to this "construction", it can only be "plastered" directly. The technique is 

a mixture with or, rather, a relic of load bearing straw bale building, where bales 

have still been laid flat (47 - 50 cm bale thickness). Since we know that flat bales 

have a way worse insulation value than bales on edge, this technique is actually 

superfluous (unless wood is not available). 

26


TIPS 



010 

Down-spanning 

Straw Bales in the Wall 

The down-spanning of straw bales also comes from load-bearing construction 

technology. Admittedly, it compresses the bales quite good, thus closing up fairly 

reliably gaps between the bale rows. The packaging tapes, which are used for this 

purpose and are clamped with a packing tong, remain in the wall and - similar to the 

cords (tip 09) - are a hindrance when shaving the walls. Also the wood consumption 

does not really decrease compared to the CUT technique, because instead of the 

stands a massive, at least 6 cm thick and 36 cm wide, wooden top plate hinders the 

bales before constriction. As well the base plate has to be doubled so that the tape 

can be pulled through. And again, the wrapping tapes are guided through eyelets, 

which are fastened to the old stock wall every 50 - 1 00 cm. In the case of bad bales, 

this technique may have advantages due to the stronger compression with the 

packaging tong (and possibly precompression with truck straps). In case of good 

bales, the technique as well as the binding with cords to the wall (tip 009) is actually 

only one big disadvantage compared to hybrid CUT construction. 

27


TIPS 



011 

Straw Bales 

spanned to the Wall 

Jakub Wihan, the Czech strawball builder, who has worked with amazonnails for a 

long time, is the inventor of this optimized fixing technique, which is still used today 

in Slovakia (Boris Hoechel demonstrates the technique). Bbales are installed here 

again on edge, after the second row, a wrapping tape is placed on the straw bales 

and guided through two eyelets attached to the wall. On the front, 2 strips or round 

wood are threaded through the cords and formed into an "H" with an approx. 50 cm 

wide spacing board. As soon as further rows of bales have been piled up, the 

wrapping tapes are now pulled over the "H" connected to the eyelets of the back 

wall. This H auxiliary construction presses the bales towards the wall, with sufficient 

tension (and not too hard bales) the wood pulls into the straw bales and forms a 

straight surface at the front. The advantage of this technique is that the bales are 

attached to the wall with pressure (tension), exactly what we mean by fixing the 

bales to the existing wall. And the technique is relatively fast, you only need 2 

eyelets per "H" and can simultaneously clamp 6-9 bales on the wall. But once again, 

the disadvantages of this technique are: the durable fixation depends on the 2 

eyelets, if they are not well anchored, the entire bale wall falls, as well as if the 

wrapping band tears. Also here the strings remain on the bale and hinder shaving. 

Finally, at least the board must be provided with a plaster ground. 

28


TIPS 



01 2 

Straw Flakes for thinner Layers 

mounted with Pallettes 

Used pallets are a favorable construction material, usually cheaper than the wood in 

it. In addition, we do not need Euro pallets for this technology, but the more 

favorable pallets with a little more space between the boards at the top. These can 

be filled well with bale flakes while lying backwards on the ground. Afterwards, the 

filled and "insulated" pallets are simply screwed to the wall, thus compressing the 

protruding bales again compactly. From the front (visible) cavities can be re-stuffed 

(therefore also the slightly larger distance between the boards is ideal). In the spaces 

we fill clay with a lot of straw fibers (COB), which sucks the moisture from our 

dewpoint area, since clay is strongly hygroscopic (water-absorbing). As with a 

diagonal bracing, it must be covered with reed stucco or another plaster carrier. The 

advantage of this technique is that it can achieve lower insulation thicknesses up 

from 1 5 cm (pallet thickness). Depending on the distance between the wall and the 

pallet, the insulation thickness can be set individually. Pallets are solidly built, even if 

a nail is missing or riddled, it doen't fall apart. Who once tried to break a pallet, 

knows how stable they are. This technology is also extremely favorable at around € 

1 0, - / m2 of material requirements (wooden stands, pallet, straw). By the way, we do 

not fix the pallets directly on the wall, but on planks which are connected between 

base plate and the roof by a distance of the width of the pallets (for example 1 25 

cm), like our CUT posts. 

29


TIPS 



01 3 

Straw Flakes for thinner Layers: 

building a Cage 

As already mentioned for the pallet wrapping technique (tip 01 2), we need a kind of 

cage for thinner insulation thicknesses below 26 cm (mini bales) or 36 cm (standard 

bales) in order to fix the bale flakes. The thickness can thus be individually adjusted 

from about 6 cm (for example, if the roof overhang is not sufficient for whole bales). 

In order to fill the bales as efficiently as possible, post distances of 36 cm, 47 - 50 cm 

or 72 cm are ideal. 

Materials which are suitable for a cage: 1 ) diffusion-open boards (DWD), see also tip 

025 form a wind-tight outer plane, and are especially useful when a wooden facade 

is to be mounted (price for DWD around € 8, - / m2). See picture above. 

2) 2.5 x 2.5 cm strips/battens at intervals of max. 1 0 cm have the advantage that they 

can be directly plastered with appropriate plaster thicknesses (2-3 cm) without 

plaster grounds (but with mesh). The advantage here is, as with the pallets, the 

filling of the interspaces with clay (when plastered with 

lime directly on top, we use 5-6 parts of clay and 1 part 

of lime) thus keeping our straw insulation layer dry as 

with Fachwerk-houses. See picture on the left. 

3) It is also possible to use bamboo, (reed) mats or 

similar solid materials, depending on the regional 

availability. 

30


TIPS 



01 4 

Break between Perimeter- and Wall 

Plaster: Dripping Nose 

To prevent moisture transport from the cement plaster in the splash water area (30 

cm above ground level) up to the lime plaster facade, these two plasters must be 

separated by a horizontal barrier. This droplet is essentially an extension of the 

horizontal barrier between the strip foundation and the base plate of the 

construction to the outside, in such a way that water can drip off (picture above left). 

The dripping nose is at the same time the stiffening of this metal strip. Ideally, better 

use zinc, aluminum or stainless steel instead of galvanized sheet, which is a few euro 

cheaper but not permanently rustproof, if it is not painted. The drip can be fixed on 

the outside of the base plate (with roofing nails) or under the foot threshold. It then 

stands horizontally to the outside (plaster thickness + 5 mm overhang) and then 

bends obliquely downwards to the dripped nose. Each tinsmith will bend such a 

sheet in short time in the desired length. A 5 cm strip of Steico Underfloor can be 

clamped above the metal (picture on the upper right). A further possibility is to cover 

the entire base in the splash area with metal, the drip nose is then just above ground 

level (Center). 

31


TIPS 



01 5 

Direct plaster on Straw Bales: 

rainproof and windproof 

Straw surfaces - properly prepared - are excellent plaster carriers. For this purpose, 

straw bales must be well baled (or compressed) to a minimum density of 1 00 kg / 

m3. The surfaces must be shaved ad levelled with the hedge trimmer and hollow 

spaces should be filled with as long straw as possible. It is not advisable to store the 

straw bales for month or years (so that the smooth but protective wax layer 

disappears). The surface - after shaving - is so rough that the clay and lime plasters 

hold on to this plaster carrier (the straw is shaved / cut off with the hedge trimmer 

with strong pressure). Excessed wood parts wider than 2 cm must be covered with 

plaster grounds (such as reed stucco, Steico Unerfloor, soft fiber board, Heraklith BM 

or cork) or heavily roughened (every 3 cm). Connections to window frames, doors, 

roundwood stands, etc. must be air- and wind-tight (tapes, apu strips, multiple 

plastering). Because earth- and lime plasters leadeasily to rust in metals, metals in 

touch with plasters must remain permanently rust-free (stainless steel, zinc, 

aluminum). 

32


TIPS 



01 6 

Timber Cladding on Straw Bales: 

Boards and Ventilation Areas 

The safest method of protecting straw from rain and moisture is a wooden facade. 

Since wood with a μ-value of > 20 (spruce dry 50, damp 20) has a moisture-braking 

effect, a back-ventilation is to be provided, which allows the moisture from the room 

air diffuse outwards. In the case of vertical ventilation areas, 3-5 cm are sufficient, 

horizontal ventilation areas (flat roof) should be 8-1 0 cm. They are usually built with 

battens and counter battens, so that the air can sweep from all sides through the 

ventilation area. The first lattice is always installed in the direction of the boards / 

planks of the wooden facade, the second is then 90 ° to it. In order for air to circulate 

(which practically always works by the solar radiation on the façade when the air is 

heated), an air inlet of at least 3 cm in width at the lower end of the wooden façade 

and an equally wide air outlet at the upper end has to be installed. This openings are 

covered with a bird protection mesh (picture on the upper right), so that no animals 

(eg wasps) can enter here, this perforated mesh should be relatively fine (2-3 mm). 

The second layer of rain protection underneath the façade then usually forms a 

diffusion-free, but also water-repellent, wind-proof layer: this is usually achieved 

with diffusion-open panels (DWD) or with a two-layered clay plaster: the second (fine 

plaster) layer closes the cracks of the base plaster. In order to be windproof even 

under the battens, it is advisable to plaster the clay over the entire area and to install 

the battens afterwards. 

33


TIPS 



017 

ventilated Glass Facades in front of 

Straw Bales: visible Straw 

Building physics says that a (not wind-tight) insulation layer, which is not enclosed 

(ie aerated), loses its thermal properties. The estimates range from half to 1 00%. 

Therefore an unplastered or unplanked straw bale house should not insulate at all 

(which is easy to check, anyone who has once built such a house knows how fast it 

can be warm, but it can cool down quickly when the insulation area is ventilated). 

But if the wind is hindered by a glass or Plexiglass layer (of course glass must also 

be ventilated, so cold air flows into the ventilation area), and according to 

calculations of the house of the future project "Biohof Achleitner" (20 m-long straw 

bale wall behind glass), the heat gain in this "glass house" is greater than the loss 

due to the lack of wind resistance: U-value: 0.11 4 W / m2K (plastered: 0.11 6 W / m2K). 

Maybe this is right for the south 

side ... Nevertheless, such 

techniques (similar to bottle 

walls) are at least to be 

questioned: for sure they serve 

more aesthetics than building 

physics. 

34


TIPS 



Sarah Wigglesworth´architectural office in London / Guest House in Chile, AATA Arch. 

35

36




Session Plan U4-S3: Prefab Wrapping Constructions 

Objectives: 

Trainer: 

Trainees ... 

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

site. 

… know specific problems of straw bale building site organization. 

… know how to solve any technical problem conveniently. 

… know accident prevention regulations, how to recognize 

dangers and save working practices. 

Skills: 

Handling tools and machines which are used in straw bale 

construction 

Methods: 

Demonstration 

Explanations 

Practice 

Place: 

Workshop or building site 

Duration: 

4 hours 

Equipment: 

Tools 

Theory 

Practice 

Specific problems of straw bale building site organization 

Trying the tools, visiting building site 

Documents: 

Info sheets: 

I1 Tools 

I2 Building site 

Text sheets: 

X1 Tools 

X2 Building site 

Power point: 

P1 Tools 

Evaluation: 


Organization: 

Looking for an appropiate building-site in the surroundings; prepare different tools and materials 

for the demonstration 

37


INFO & TIPS S3 



01 8 

system/haus/bau-Module, entwickelt von C. Kastner, H. Gruber, W. Schmelz 

38





01 9 

Jules Ferry Residence in St. Die des Vosges (FR) von Bet Gaujard Arch.: 7stöckiger Bau 

39





Jules Ferry Residence in St. Die des Vosges (FR) by Bet Gaujard Arch.: 7storey-building 

40





020 

Complemedis AG, CH: Wrapping with prefabricated modules by Werner Schmidt 

41





021 

022 

Straw/Reed-Facade by Kengo Kuma, Japan; below: Waseda University Students have 

developed this prototype: Straw cools through evaporation in summer and heats 

through fermentation in winter 

42





023 

024 

Enterprise Centre/University East Anglia, UK; Schelfbauhütte in the Alte Brauerei, DE 

43





025 

School in Issy les Moulineux and Montreuil, FR: external mounted straw bale modules 

44





026 

Make Your City Smart Project by Paul Adrian Schulz: conccrete slab building with DIYstraw 

bale walls: social living in Vienna (Partner: ASBN); 

ASBN-Project InsulateGreece with a similar idea against Fuel Poverty, GR 

45





46





Make Your City Smart Projekt-Calculation for the project by Paul Adrian 

Schulz: Materials and Work in Straw Bale Walls +/- Self-Building (DIY) 

47

48


INFO S4 


Session Plan U4-S4: Alternatives: Straw Injection-Systems 

027 

49


INFO S4 


Session Plan U4-S4: Alternatives: Straw Mats 

028 

50


INFO S4 


Session Plan U4-S4: Alternatives: Reed-Mats 

029 

A) 25 cm Reed (5 Layers) 

U-Value: 0,208 W/m 2 K 

PEI n.r.: >1 7 kWh/m² 

€ 52,50 - 75,80/m2 

B) Straw, Reed-Insulation-Board, Lime-Direct Pl. 

26 cm Straw, 5 cm Reed Mat, complete 33,5 cm 


Straw Bales: around € 8,00 - 11 ,20/m2 (cert.) 


Reed insulation board (bauschilf.at): 8,47/m2 

Lime Plaster 2,5 cm, Mesh: € 8,70/m2 

Material - complete price: € 38,22 - 56,17/m2 

51

STEP – Straw Bale Training for European Professionals 

UNIT 4 – Wrapping (201 7) 

©/Editor/Texts/Tipps: Herbert Gruber (ASBN) 

Co-Workers: Helmuth Santler, BuildStrawPro-Team (Erasmus+ 

Projekt) 

Design & Photos: Herbert Gruber; more Photos: Naporo (8) 

Hagebau (8), u-wert.net (9), Geocell (1 5, 1 6), Misapor, 

Kurkfabriek (1 5), Horst Danner, GrAT (22), Virko Kade (23), 

Kengo Kuma (36), Icons: Michael Howlett (SBUK) 

This Handbook bases on 

the Handbook by the Leonardo- 

Group STEP (201 5) 

52

STEP U4 Handbook 2019 ENGLISH

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