Design and Construction of Bioclimatic Wooden Greenhouses, Volume 2 E-Book

Gian Luca Brunetti

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 377

Veröffentlichungsjahr: 2022

Beschreibung

This book is the second of four dealing with bioclimatic design and construction by focusing on the most basic and polyvalent of modern environmental systems: the bioclimatic greenhouse, the "Swiss-army chainsaw" of architecture. More specifically, this second volume focuses on how the structure of bioclimatic wooden greenhouses may be designed and built. In more general terms, it helps us consider how to design and build the structure of bioclimatic, low-energy architecture, with low environmental impact. This multi-volume book covers both free-standing greenhouses that can naturally heat and cool themselves, and lean-to greenhouses that support the natural heating and cooling of buildings; this includes both agricultural greenhouses and greenhouses suited to host people. As a result, it is a trans-disciplinary work deriving its areas of concern from a broad range of study areas, spanning from environmental, to constructional, to structural, drawing the clarity of the approach from the fact that the topics are presented by a single author with a single voice and a designer's mindset. To achieve this, the book adopts a composite set of explanatory strategies and communication registers - including extensive support by 3D construction drawings and examples - and presents not only stateof-the-art solutions, but also experimental ones.

Leseprobe

Table of Contents

Cover

Title Page

Copyright Page

Introduction

1 Light Frames (Wooden Frames)

1.1. Commonest solution: platform-frame-like or balloon-frame-like curtain walls framed with studs/mullions

1.2. Types of connections in wooden construction

1.3. Types of connections between structural sub-systems

1.5. Alternative structural solution: trussed light-frame structures

1.6. Criteria for the construction of light-frame trusses and trussed portal frames

1.7. Intermixing parts of timber frames into light frames

1.8. Analogies with cold-rolled light frames

1.9. Arched and vaulted construction in light frames

2 Timber Frames

2.1. Intermixing light-frame parts into timber frames

2.2. Connections in timber-frame greenhouses

2.3. Structural solutions with the primary beams of the frames orthogonal to the front façade

2.4. Pole construction

2.5. Bracing strategies in timber frames

3 Foundations

3.1. Foundation walls and foundation sills

3.2. Construction strategies for foundation walls

3.3. Drainage around the foundation wall

3.4. Pavements

3.5. Platform frame floors raised above the ground

4 Heating and Cooling Systems; Watering Systems

4.1. Heating and cooling plants

4.2. Heat recovery via air-to-air heat exchangers

4.3. Passive and low-energy heating and cooling solutions based on the thermal exchange with the ground

4.4. Auxiliary heating systems

4.5. Auxiliary cooling systems

4.6. Integration of photovoltaic panels in greenhouses

4.7. Integration of passive solar heating panels in greenhouses

4.8. Watering systems

4.9. Solutions for water catchment and storage suitable for self-building

Conclusion

References

Index

Summary of Volume 1

Summary of Volume 3

Summary of Volume 4

Other titles from iSTE in Civil Engineering and Geomechanics

End User License Agreement

List of Illustrations

Chapter 1

Figure 1.1

The ordinary lean-to-greenhouse structure is built in a platform-

...

Figure 1.2

Example of the simplest possible relation between front façade an

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Figure 1.3

In this example, the rafters are anchored to the back wall (here

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Figure 1.4

In this solution, the plate on top of the studs/mullions has been

...

Figure 1.5

Combining the top plates with a header joist (fascia beam) adds r

...

Figure 1.6

Head-to-head butt joint side-nailed horizontally. A weak, shear-o

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Figure 1.7

Head-to-head butt joint double-side-nailed horizontally

Figure 1.8

Head-to-head butt joint nailed vertically. Another weak, shear-on

...

Figure 1.9

Head-to-head butt joint double-nailed vertically

Figure 1.10

Light-frame end-to-side butt-joint executed with screws or nails

...

Figure 1.11

Light-frame end-to-side butt-joint executed with screws or nails

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Figure 1.12

Light-frame end-to-side butt-joint executed with screws or nails

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Figure 1.13

Light-frame end-to-side butt-joint executed with screws or nails

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Figure 1.14

Lap joint between a post/stud/mullion and a beam/joist/rafter. T

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Figure 1.15

Lap joint between a post/stud/mullion and a beam/joist/rafter. T

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Figure 1.16

Some types of steel fasteners: a1. cramps; a2. staples; b. tensi

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Figure 1.17

Solutions for arranging the side edge rafters and the side edge

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Figure 1.18

This light frame of an attached greenhouse is complete with fram

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Figure 1.19

Here, the studs/mullions are discontinuous, and a double plate i

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Figure 1.20

To make a gable wall like that in the previous figure more rigid

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Figure 1.21

In this example, the rafters have been cantilevered out from the

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Figure 1.22

In this example, the greenhouse roof of the previous figure has

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Figure 1.23

In this example, the edge rafter is supported not only by the st

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Figure 1.24

Example of the joint between a glazed gable wall of an attached

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Figure 1.25

Collaboration of timber-frame (shown in red) and light-frame par

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Figure 1.26

Collaboration of timber-frame (in red) and light-frame parts in

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Figure 1.27

The back wall may be reinforced with steel bars coming from the

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Figure 1.28

To reduce the complication of enveloping the thermal storage wal

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Figure 1.29

The insulation, or the cladding of the insulation, may be positi

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Figure 1.30

The roof frame can be anchored to the vertical surface of the wa

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Figure 1.31

The sides of the greenhouse can be closed by the wall constituti

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Figure 1.32

As for the back wall, if the gable walls “wrap” the greenhouse f

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Figure 1.33

The greenhouse frame can be made higher than the back wall. In t

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Figure 1.34

Buttressing the storage wall towards the inside rather than towa

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Figure 1.35

In this scheme, the framed, top part of the back wall has been s

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Figure 1.36

Constructing a back frame independently from the massive wall si

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Figure 1.37

Design example of an attached greenhouse that is taller than the

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Figure 1.38

Types of wooden truss beams

Figure 1.39

Simple case of intermixing of lighter elements (light frame) and

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Figure 1.40

Vaulted greenhouse adopting a triangular curtain-wall-like confi

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Figure 1.41

Lamella roof in a barn interior at Gut Garkau Farm, Germany, 192

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Figure 1.42

Above: profile of a lamella seen from above and from one side (n

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Figure 1.43

Large-sized lamella vault in Berlin, by Elite Holzbau GmbH. The

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Figure 1.44(a)

Example of a geodesic dome constructed with timbers in El Pas

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Figure 1.44(b)

Example of a geodesign dome built with connections using cove

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Figure 1.44(c)

Example of a geodesic dome enclosed with opaque panels cut to

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Chapter 2

Figure 2.1

Combining a timber-frame structure with a light-frame envelope ma

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Figure 2.2

A greenhouse between two buildings in lower Bavaria, Germany. Exa

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Figure 2.3

How the light-frame components are arranged in relation to the ti

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Figure 2.4

In these arrangements, the light-frame structure of the roof is s

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Figure 2.5

In this variant, the upper edge of the light-frame wall is higher

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Figure 2.6

In this variant, the light frames of the roof and the wall are wi

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Figure 2.7

In this variant, the front wall is cantilevering out from the pos

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Figure 2.8

In this variant, (a) the height of the light frame of the front w

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Figure 2.9

In this variant, the section of the light-frame fascia beam (eave

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Figure 2.10

A hybrid solution is shown, in which the light-frame rafters sit

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Figure 2.11

Purlins are added onto this timber frame, both on the roof and o

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Figure 2.12

These half-frames are realized with double posts and double beam

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Figure 2.13

This timber-frame variant constitutes the completion of the prev

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Figure 2.14

In this timber-frame and light-frame combination, the primary el

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Figure 2.15

In this variant, a shorter (with respect to the previous image)

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Figure 2.16

In this variant, the transoms have been more clearly transformed

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Figure 2.17

An example of a timber-frame structure for self-standing solar g

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Figure 2.18

The back wall and the front wall of a solar greenhouse may be bu

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Figure 2.19

The construction at the ridge can be similar to that at the eave

Figure 2.20

Example of multiple dovetail connection

Figure 2.21

Open tenon-and-mortice joint between two beams

Figure 2.22

Open tenon-and-mortice joint between posts and beams

Figure 2.23

Pegged open tenon-and-mortice joints between two beams

Figure 2.24

Horizontal open tenon-and-mortice joint

Figure 2.25

Housed tenon-and-mortice joint. This connection is infrequent be

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Figure 2.26

Structure characterized by housed tenon-and-mortice connections

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Figure 2.27

Scheme of bolted (or screwed, or nailed) connection between colu

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Figure 2.28

Scheme of bolted (or screwed, or nailed) connection between colu

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Figure 2.29

Scheme of bolted (or screwed, or nailed) connection between colu

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Figure 2.30

Scheme of bolted (or screwed, or nailed) connection between colu

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Figure 2.31

Scheme of bolted (or screwed, or nailed) butt connection realize

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Figure 2.32

Scheme of bolted (or screwed, or nailed) butt connection realize

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Figure 2.33

Lap- and butt-joints obtained through tooth plate connectors in

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Figure 2.34

Bolted connection between column and beam obtained via an intern

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Figure 2.35

Heavy-duty bolted connection between column and beam obtained vi

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Figure 2.36

Bolted connection between a column and two beams obtained via an

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Figure 2.37

Screwed, nailed or bolted connection between a double column and

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Figure 2.38

Screwed or nailed connections between column and beam. To increa

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Figure 2.39

Bolted lap connection between continuous column and continuous b

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Figure 2.40

Bolted lap connection between continuous column and continuous b

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Figure 2.41

Types of ring connectors. From the TECO catalogue. Left: tooth p

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Figure 2.42

View of the lodgment of a split-ring ring connector in a damaged

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Figure 2.43

Bolted lap connection between a continuous double column and a c

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Figure 2.44

Bolted lap connection between a continuous column and a continuo

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Figure 2.45

Lap joint between double column and beam supported by an interna

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Figure 2.46

Lap joint between a single beam and a double beam

Figure 2.47

Composite beam obtained by bolting. As an extreme consequences,

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Figure 2.48

Left: exploded view of a crossed half-wood lap joint. Right: end

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Figure 2.49

Scheme of scarf joint with keylock. This traditional configurati

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Figure 2.50

Scarf joint above a foundation wall in a traditional solution. H

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Figure 2.51

The wooden plate at the foot of the posts is needed to anchor th

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Figure 2.52

The simplest footing for timber post: a “U” profile bolted to a

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Figure 2.53

In this case, the steel connector detaches the post foot from th

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Figure 2.54

Simple arrangement of U-shaped steel profiles that make it possi

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Figure 2.55

In this case, the foot of the posts is resting directly on the b

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Figure 2.56

In the solution on the left, the timber posts sit on one or more

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Figure 2.57

This kind of post-to-post-post-to-beam connection is suitable fo

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Figure 2.58

Example of the simplest possible attached timber-frame greenhous

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Figure 2.59

In this variant, the beam at the front is connected to the back

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Figure 2.60

In this variant, the knees between the posts and the sloped beam

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Figure 2.61

In this variant, the post-and-beam parallel frames are connected

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Figure 2.62

This post-to-sloping-beam connection is strong but more complex

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Figure 2.63

For this version to be advantageous, the post-to-edge-beam conne

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Figure 2.64

In this variant, the front beam is supported by a recess at the

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Figure 2.65

This timber frame (experimental) is entirely built with lap join

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Figure 2.66

In this solution, all of the connections are lapped, and the slo

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Figure 2.67

In this variant, wooden stops have been located above the edge b

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Figure 2.68

In this lap-joined variant (experimental), both the columns and

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Figure 2.69

In this fully lapped variant (experimental), the header beam has

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Figure 2.70

In this fully lapped double-post and double-sloped-beam variant

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Figure 2.71

Example of provisional bracing of a timber pole standing on a co

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Figure 2.72

When the uprights of the frames are braced against their beam, a

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Figure 2.73

This case is a follow-up of the previous one. The timber-frame e

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Figure 2.74

The light frame enclosing a timber-frame portal can be constitut

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Figure 2.75

In this case, the portal frames are connected through concentrat

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Figure 2.76

In this case, the portal frames are trussed

Figure 2.77

In the case of a trussed-portal frame greenhouse, if the chords

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Figure 2.78

A conventional light-frame roof and façade can be laid out on th

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Figure 2.79

These trussed portal frames (experimental) are built by asymmetr

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Figure 2.80

View of a trussed portal frame similar to that used in the previ

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Figure 2.81

The light-frame enclosure arrangement (experimental) may remain

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Figure 2.82

Example of bending-resistant bolted connection between an uprigh

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Figure 2.83

Example of “boxed” portal frames built with plywood panels outsi

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Figure 2.84

Example of trussed portal-frame structure with portal frames par

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Figure 2.85

Scheme of a Venlo-type greenhouse, characterized by ridge and fu

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Figure 2.86

Basic pole construction scheme. Legend: 1. rock, crushed rock or

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Figure 2.87

An interesting thing about the pole foundation is that it does n

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Figure 2.88

The pole construction is most commonly used in North-American ba

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Figure 2.89

A modern way to use the benefits of pole foundations escaping th

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Figure 2.90

The ground-embedded poles can be worked out to support a double

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Figure 2.91

The ground-embedded poles can also be composed of smaller planks

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Figure 2.92

The poles in a pole foundation do not necessarily have to be ful

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Figure 2.93

In this example, floor joists are laid out both onto the foundat

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Figure 2.94

In this example, the greenhouse frame is parallel to the façade.

...

Figure 2.95

In this case, the posts are conformant to an ordinary light-fram

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Figure 2.96

This light-frame floor cantilevers out from the girder

Figure 2.97

In this example (experimental), the foundation posts are not com

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Figure 2.98

In this variant of the previous solution, the principal beams, o

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Figure 2.99

In this case (experimental), the double beams are symmetric with

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Figure 2.100

In this variant, because the joists do not sit on top of the do

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Figure 2.101

Example of arrangement combining the pole construction with pur

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Figure 2.102

Example of arrangement combining the pole construction with stu

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Figure 2.103

Arrangement combining a pole configuration with a wooden “skirt

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Figure 2.104

Main possible structural bracing schemes for a single-bay bi-di

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Figure 2.105

The bracing action here is obtained with cables laid out in “X”

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Figure 2.106

This solution is braced with timber diagonals arranged in a mar

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Figure 2.107

Moving the X-braced bays towards the greenhouse ends makes the

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Figure 2.108

In these cases, the bracing diagonals are positioned both at th

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Figure 2.109

This is image is a zoomed view on a structural bay of the braci

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Figure 2.110

This view constitutes the symmetric version of the one shown in

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Figure 2.111

In this case, the scheme of the bracing elements (highlighted i

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Figure 2.112

In this case, the bracing elements (shown in purple) follow an

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Chapter 3

Figure 3.1

The foundation most often runs along the perimeter of the greenho

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Figure 3.2

Relation between a timber-frame greenhouse structure and a contin

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Figure 3.3

The frames of the façades in this scheme of an attached greenhous

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Figure 3.4

In this greenhouse scheme for a lean-to greenhouse, thanks to the

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Figure 3.5

Mullions/studs can be laid onto the foundation with a waterproof

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Figure 3.6

The foundation trench may be filled with gravel to keep the zone

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Figure 3.7

The most complete solution entails positioning a filtering blanke

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Figure 3.8

Insulating the foundation wall as much as the greenhouse is econo

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Figure 3.9

The bottom transoms of the façade can be heightened with respect

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Figure 3.10

A frequent alternative to the previous solution is to place a pr

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Figure 3.11

Hollow concrete (sand-and-cement) block walls are the quickest a

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Figure 3.12

The concrete foundation and the hollow block masonry foundation

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Figure 3.13

The shallowest and most practical greenhouse foundation is const

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Figure 3.14

Scheme of a light-frame foundation based on ground joists anchor

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Figure 3.15

Scheme of a light-frame foundation based on stud/mullions anchor

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Figure 3.16

Scheme of a light-frame foundation based on edge joists anchored

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Figure 3.17

A dry, “quick” type of continuous foundation can be laid out on

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Figure 3.18

The first construction step after the trench is dug and the grav

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Figure 3.19

The next step is to drill holes into each foundation timber log

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Figure 3.20

Construction sequence for the gravel trench foundation

Figure 3.21

Several alternative arrangements can be given to the rods driven

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Chapter 4

Figure 4.1

Possible types of arrangements of the ground pipes. A. Two main c

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Figure 4.2

Joining technique between plastic corrugated ground pipes

Figure 4.3

A trench, possibly containing water, can be used as a summer grou

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Figure 4.4

Example of perforated fan-tube systems. Left: unit heater blowing

...

Figure 4.5

Construction scheme for a low-cost pool for water collection. Ste

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Figure 4.6

A low-cost water pond can be constructed even without digging int

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Figure 4.7

By creating waterproofed continuity between the roof of a greenho

...

Guide

Cover Page

Title Page

Copyright Page

Introduction

Table of Contents

Begin Reading

Conclusion

References

Index

Summary of Volume 1

Summary of Volume 3

Summary of Volume 4

Other titles from iSTE in Civil Engineering and Geomechanics

Wiley End User License Agreement

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Series EditorGilles Pijaudier-Cabot

Design and Construction of Bioclimatic Wooden Greenhouses 2

Design of Construction: Structure and Systems

Gian Luca Brunetti

First published 2022 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

ISTE Ltd27-37 St George’s RoadLondon SW19 4EUUK

John Wiley & Sons, Inc.111 River StreetHoboken, NJ 07030USA

www.iste.co.uk

www.wiley.com

© ISTE Ltd 2022

The rights of Gian Luca Brunetti to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s), contributor(s) or editor(s) and do not necessarily reflect the views of ISTE Group.

Library of Congress Control Number: 2022941486

British Library Cataloguing-in-Publication DataA CIP record for this book is available from the British LibraryISBN 978-1-78630-852-8

Introduction

The first volume of this work laid out the basis for bioclimatic greenhouse design; and the present one – the second in the series – deals with the construction design of greenhouse timber structures, covering a range of issues spanning from frame configurations, connections, the consequences of precision (or the lack of it), to auxiliary mechanical heating and cooling systems. The contents of this volume will add concreteness to the knowledge basis laid out in the first volume, and also widen operational opportunities. This is because usually design ideas can be addressed in more than one way, each of which can reverberate consequences back to primary design decisions. From this perspective, preliminary design ideas and detailed constructional ideas can be seen as the two sides of the same coin. These two sides will be examined separately in this work for the sake of the analysis, but their distinction tends to be very blurred in action.

Another characteristic of this volume is that it devotes special attention to self-buildable solutions. This is done with two aims. The first is to address not only the professional reader, but also the non-professional reader; and the second aim is to demystify construction techniques. This has been done considering that, due to the pragmatic nature of constructional knowledge, constructional knowledge tends most often to be passed on to others through narrations that only very loosely relate causes and effects (constructional prescriptions). By emphasizing the aspects of self-buildability of greenhouse frames, this volume looks for the causal relations of things and attempts to demystify the stiffness and unavoidability of construction “rules” and rules-of-thumb – modern as well as traditional.

The most important thing to consider about the constructability of greenhouse structures is that the connections between wooden elements constituting the frames (beams, columns, studs, rafters, purlins) – at least, the connections which are not arranged in trusses – are not resistant to bending: that is, they can only – or mainly – transmit shear1. To transmit bending forces, timber components should usually be made rigid by arranging diagonal elements in triangular shapes. This may seem to be a strong limitation, but it is not; indeed, this does not prevent the possibility of deriving many constructional solutions from the primary considerations, and potentially evolving them beyond recognition.

One final note: as with all the other volumes composing this work, this volume will also deliver, together with a basis for sedimented knowledge, some experimental, innovative contents. The reader will be made aware in due places of the experimentality of the contents, so as to make them aware of the necessity of taking extra care in handling them. In this second volume, key examples of such experimentality are constituted by the trussed configurations presented in Chapter 2, and by the timber log and gravel trench foundation presented in section 3.2.8.1.

On references

The book by Alward and Shapiro (1980), despite being more than 40 years old and mostly featuring single-sheet enclosures, due to the level of interest and variety of the solutions it proposes and the constructional “taste” involved, is still a great reference as regards the constructional design of timber solar greenhouses of the lean-to type. The book by Shapiro (1984) is closely related to that by Alward and Shapiro (1980), but is wider in scope, because it not only covers the domain of construction, but also involves a multidisciplinary approach to design. The book by Neal (1975) is an antecedent of these works.

Other essential references for the present work are the book by Marshall (2006), which is a thorough guide to platform-frame style greenhouses; the book by Fischer and Yanda (1977), which focuses on low-cost solutions for platform-frame attached wooden greenhouses, experimented diffusely at the beginning of the 1970s; the book by Herzog and Natterer (1984 – in French and German), which develops a highly cultured architectural analysis on the integration of attached wooden greenhouses and buildings. The volume of proceedings edited by Hayes and Gillet (1977) conveys the breadth and depth of the debate about solar greenhouses in the second part of the 1970s.

Other references that influenced the writing of this book are as follows.

The structural and functional characteristics of European climate greenhouses were investigated in review articles by von Elsner et al. (2000a, 2000b). Lagier and Dastot (2008) is a lean reference of techno-scientific advice.

The book by Haupt and Wiktorin (1996 – in German) analyzes the constructional side of greenhouse design, making reference primarily to steel structures, and also touching upon wooden structures. Haupt (2001 – in German) keeps a similar line of analysis, but with a briefer theoretical treatment and extended range of examples based on built case studies. Zappone (2009 – in Italian) focuses especially on the thermal design of lean-to greenhouses, also including construction considerations.

The book by Schwolsky and Williams (1982) explores the construction side of passive building design, mostly featuring timber and wooden frames, while the book by Temple and Adams (1981) focuses more specifically on solar collection systems.

The books by Lorenz-Ladener (2013) and Schiller and Plincke (2016) are comprehensive guides to the design of solar greenhouses, also taking into account constructional aspects. The books by Drexel (1999 – in German), Fisch (2001), Stempel (2008 – in German) and Price and Greer (2009) are references delivering pure constructional advice.

The books by Jones (1978), National Research Council of Canada (1981), Mauldin (1987), Kolb (1990 – in German), Lees and Heyn (1991), Schmidt (2011) and Toht (2013) are technical references bringing novelties and inventiveness about construction solutions into the general scenery.

The books by Kurth and Kurth (1982), Freeman (1994, 1997) and Nengelken (1996 – in German) touch upon construction considerations, but are focused on the matter of greenhouse gardening and growing.

The books by Williams (1980), Wolpert (1989 – in German), Bastian (2000 – in German) and AAVV (2002) keep a middle ground between greenhouse gardening and architectural construction, while Jeni (2005 – in German) and Timm (2000 – in German) lean completely towards architecture.

The booklet by Matana (1999 – in French) regards attached greenhouses, and is closely related to the aspects of the French market. The booklet by Ibbotson (1964) is a constructional reference (today, historical) featuring the first outcomes of experimentation with polyethylene films.

The books by IEA (1999, 2000) lay out scientifically referenced criteria and examples for designing and constructing passive solar collector systems of all types, including greenhouses. The books by Kornher and Zaugg (2006) and Smith (2011) are useful guides to the design and construction of passive solar collectors. The publication by the New York State Energy Research and Development Authority (1982) features three highly detailed projects for the construction of solar air collectors to be hung on walls.

Carter (1981) provides design and construction advice for solar building renovation, with an emphasis on problems regarding residential wooden buildings. Wing (1990) takes a similar approach, with an emphasis on extension and remodeling, but without specific passive solar implications.

Kern (1975) is a seminal book about alternative construction technologies, and Twitchell (1985) collects interesting cases of solar architecture from the solar “golden age” of the 1970s.

Pracht (1984 – in German, and translated into French) is a sophisticated, technically complete and tasteful book on wooden construction. Herzog et al. (2004 – in German, and translated into English) is a book on wood construction complete with examples. Kolb (2008 – in German, also translated into French) is a complete reference on the technical evolution that occurred after the turn of the millennium. Moro (2009 – in German) is filled with precious information about timber construction and façade design. Wagner and DeKorne (2002) and Miller (2004) are sources of guidance for self-construction filled with practical advice. Along the same line, Carrol (2005) focuses on techniques and tips for solo building.

The books by Oesterle et al. (2001) and Bonham (2019) provide design and construction advice on double skins in high-rise buildings, and Compagno (2002) provides design and construction advice about the automated management of high-tech building façades.

Note

1

Because of this, in Volume 4, section 2.4, when calculating the wooden structures, we will assume that the bending moments at the connections are null or 0.

1Light Frames (Wooden Frames)

A light frame is a frame constituted by diffusely distributed elements held together by many connections, usually simple to execute and subject only to small forces. Some building norms for greenhouses (like the current ones in use in the European Union)1 distinguish structures subject to small displacements from structures subject to large ones, and greenhouse frames in general (both light frames and timber frames – i.e. heavier frames) fall into the first category – that of the structures subject to small displacements. Post-and-cable structures, hoop-and-cable structures, tent structures and any case of structures involving cables as primary components can, instead, fall into both categories, being often allowed to have considerable displacements under wind loads.

Light-frame greenhouses are greenhouses in which the vertical elements that bear the transparent enclosures (glass panels, or plastic panels, of plastic films) also support the greenhouse structure. Vertical supports in light frames are indeed directly constituted by studs or mullions rather than by columns. Light frames are therefore the simplest of construction solutions for a greenhouse. This simplicity, however, comes at the price of requiring the designer to strike a compromise between aims related to different functions: in particular, the load-bearing function performed at the greenhouse level, the function of holding in place the elements of the transparent enclosures, and other functions like assuring air-tightness, water-tightness, and durability. As regards the terms “stud” and “mullion” as they are used in this book: the two types of construction elements can be similar and even identical, and which of the two terms is most appropriate depends on the context. The term “stud” is commonly used for lean vertical supports that are enclosed between opaque panels, while “mullion” commonly designates the lean vertical supports to which the transparent enclosures are anchored, and that remain in plain sight. Dimensions of typical sections of stud and mullions vary, but timber sections of 5x10, 6x10, 6x12, 5x15, 6x15 or 6x18 cm are fairly common for small greenhouses.

Under many viewpoints, the light-frame construction of a greenhouse resembles that of a balloon-frame house (a light-frame house in which the studs extend from the top of the foundation wall to the roof, even in multi-story configurations). However, the light frames of greenhouses are commonly enclosed with transparent panels one structural bay wide, rather than opaque plywood panels or planks two or more bays wide.

In this context, horizontal wooden plates are positioned at the foot of the studs/mullions (as mediation elements between the studs/mullions and the foundation walls/sill plates), and at the top of them (as “ties” holding them together), and each roof rafter (or roof joist) is supported directly by the studs/mullions beneath it, with the horizontal plate in the intermediate position (see Figure 1.1). However, the alternative also exists of directing the load of the rafters onto the header joist (or fascia beam), or, in any case, onto a header edge beam, rather than directing it onto the plate on top of each stud/mullion. The described solution constitutes an equivalent to the one commonly adopted in platform frame structures, which is also the simplest and cheapest one that is available.

The construction sequence can follow two paths: (a) the studs/mullions can be put in place vertically on the wooden bottom plates, keeping them vertical with bracing elements, then joining them with a top plate; or (b) the stud/mullions can be used for building the wall frames horizontally (on-site or off-site), and then the frames can be tilted up vertically in their definitive position. The latter solution, which is typical of platform frames, is the most common. In both cases, the bottom plates are composed of a lower plate (usually constituted by pressure-treated lumber) anchored with anchor bolts to the foundation wall, and of a top plate (constituted by ordinary construction lumber, and belonging to the wall’s frame) nailed or screwed to the studs/mullions. Similarly, the top plates can be composed of a bottom plate (tie beam) belonging to the wall frame, anchored to the studs/mullions, and by a top plate (header plate) holding together the plates below (being lap-joined with it, overlapped with the joints non-coincident), as well as the whole framed wall panels (Figure 1.1), or they may be constituted by a single component.

Figure 1.1The ordinary lean-to-greenhouse structure is built in a platform-frame-like manner under all aspects. In gray, the wall shared with the building. The structure of the gable wall is not shown. Legend: 1. Strip foundation; 2. Bottom plates (below: treated lumber; above: construction lumber); 3. Mullion; 4. Top plates (two, one on top of the other, with the joints not coincident – the plate below is also known as the “tie beam”); 5. Header plate (or fascia beam); 6. Rafter; 7. Ledger (continuous); when anchored to a masonry wall or a concrete wall, the anchorage can be obtained through expansion dowels; 8. Stop between rafters (non-continuous)

It is interesting to note that a thorough knowledge of the criteria for the construction of light-frame greenhouses is important not only because light-framed greenhouses are common (especially in the context of small-size greenhouses), but also because light frames are used in timber-frame greenhouses as well (see Chapter 2). Indeed, timber-frame greenhouses often combine timber-frame solutions and light-frame ones. Indeed, as it will be seen in the next chapter, in timber frames, the relation between the structure and the transparent enclosures is usually solved with the aid of secondary structures of the light-frame type – utilizing mullion, transoms, purlins and/or rafters.

The construction of light-frame greenhouses is simpler than that of timber-frame ones, because it requires applying only one construction method; but the sizing of light frames can sometimes be a rather delicate operation, deceptively simple, except when it involves short spans and short heights – in which case, the oversizing of the frame related to the fact that the frame is performing in the same time as a load-bearing structure and as a skeleton of the envelope is unnoticeable. This happens because the framing elements used in light frames have to satisfy both the general sizing requirements derived from the fact that they are greenhouse-scale structures, and the specific, localized sizing and joining requirements regarding the transparent enclosures and their connections, related to their nature of envelope systems.

Figure 1.2Example of the simplest possible relation between front façade and roof in a light-frame structure of an attached greenhouse. Each rafter rests on a mullion/stud, via a top plate anchored to the foundation (or on ring beams, in arrangements above ground level). How the roof rafters are connected to the back wall (here not shown) differs from the way shown in the previous example: indeed, they are anchored to a ledger at the back of the roof, which is, in turn, anchored to the façade

Figure 1.3In this example, the rafters are anchored to the back wall (here not shown) via a ledger positioned below them, like in the example in Figure 1.1; but here the stops between the heads of the rafters are not used

Figure 1.4In this solution, the plate on top of the studs/mullions has been doubled but, unless the two plates in question are connected so as to collaborate in bending (which is not usual, but may be obtained by diffuse nailing or screwing), each rafter still has to rest on the mullion/stud below

Figure 1.5Combining the top plates with a header joist (fascia beam) adds rigidity to the structure at the eave and reduces the need to make each rafter rest on the mullion/stud below

On references

The book by Allen (2014) is very strong on platform frame techniques and has been a useful reference in writing this book. Burrows (1967–2013), Haun (1998), Wagner (2005), Benoit (2014 – in French) and Thallon (2016) are high-quality books specifically focusing on the platform-frame construction technique. Feirer et al. (1997), Canadian Wood Council (1991), Spence (1999) and Engel (2011) are thorough references about wooden carpentry and joinery, covering both platform-frame and timber-frame construction.

1.1. Commonest solution: platform-frame-like or balloon-frame-like curtain walls framed with studs/mullions

Generally, the spacing of the studs/mullion is defined on the basis of the following criteria: (a) in the case in which glass panels are used as transparent enclosures, the space between mullions should be slightly smaller (at least approximately 1–1.5 cm per side, depending on the quantity of movement that the structure is allowed to undergo) than the size of the glass panels, in order to allow for a sufficient overlap of the glass panels themselves to the frames (Figure 1.9, Volume 3). (b) In the case in which synthetic transparent panels (polycarbonate, acrylic, fiberglass) are used, the space between mullions may vary from slightly less than the width of the transparent panels (about 1–1.5 cm, similarly to what is required in the case of glass panels) to a fraction of it (minus a space of again at least about 1–1.5 cm per side for the overlap of the panels at the side), when the panels are wider than one bay. This is because synthetic panels, unlike glass ones, can also be traversed by screws, nails or bolts in intermediate positions along their width. This allows their width to span multiple bays (Figure 2.11, Volume 3).

In this context, the transparent panels (of whatever material) are usually anchored to the frames by pressing them against the frames themselves, as seen, by means of pressure caps (that may be constituted, for example, by wooden plates, C-shaped steel profiles or extruded aluminum profiles), with the mediation of gaskets on both faces of the transparent panels (Figures 1.2 and 1.3, Volume 3).

In the most ordinary solutions, the connections between the frame elements are performed by means of nails or screws positioned orthogonally to the elements, when possible (Figures 1.10 and 1.14), and otherwise are nailed or screwed diagonally (Figures 1.6, 1.7, 1.8, 1.9, 1.11 and 1.4). Statically speaking, single-nailed or single-screwed connections work like hinges, and multiple ones may not, but in any case, a light-frame connection lacks the rigidity which is necessary to obtain rigid connections unless the configuration of the connections is trussed (i.e. it contains triangles). And constructing frames without rigid connections requires bracing them for stability against horizontal forces. To this, it has to be added that, when trussed configurations are used, because light frames are composed of small-section, low-resistance elements, for bracing them, usually it is not a good idea to rely on short and strong, “concentrated” bracing members spanning only near the zone of the connection (of the kind of schemes in the right-hand half of Figure 2.104). In those situations, the opposite is usually appropriate: diffuse, distributed diagonals involving the whole span of a structural bay, or even spanning several bays (as in the schemes in the left-hand half of Figure 2.104), should be more appropriately used.

1.2. Types of connections in wooden construction

Connections in light frames are conceived to make the construction operations as simple as possible. This is what modern carpentry is often about. They are therefore executed by simple nailing or screwing. Nailing and screwing, however, are also used in timber-frame connections. This shows that the distinction between light-frame connections and a timber-frame one is not precise. Indeed, it is less precise than that between light-frame structures and timber-frame ones. There is a great deal of middle ground between the two types of technique.

The most common light-frame connections (which are also the most common in timber frames) are the butt joint and the lap joint. The butt joint can be of the head-to-head type (Figures 1.6 and 1.8) or of the head-to-side type (Figure 1.10). Both butt joints and lap joints produce non-bending-resistant connections which, statically speaking, can be interpreted as pinned connections. This is not due to the fact that the nails or screws could not be positioned so as to obtain a lever arm large enough to make the connections rigid, bending resistant, but to the fact that the individual connections of which a composite connection is made are usually not strong enough to make the derived connection bending resistant and at the same time simple.

1.2.1. Head-to-head butt joint

Head-to-head butt joints are usually not suitable for execution by means of simple nailing or screwing (Figures 1.6–1.9), but rather by means of cover plates: which, in the simplest (and weakest) configurations, are asymmetrical (i.e. placed on one side of the connection only), and in the strongest configurations are symmetrical (i.e. placed on both sides) (Figure 2.28). The cover plates add a certain rigidity to the connections in such a way that the longer and more overlapped they are, the more bending resistant and rigid the connections are (Figure 2.32).

For executing a butt joint without plates, there is no choice other than placing the nails or screws diagonally in the components, so as to position them in directions as mutually divergent as possible, so as to make them offer resistance against extraction (Figures 1.6–1.9). At a statical level, what is obtained is, in any case, again a pinned joint, of a kind, though of course more resistant in compression than in tension.

The cover plates can be made of steel (Figure 2.28) or wood (Figure 2.31).

Figure 1.6Head-to-head butt joint side-nailed horizontally. A weak, shear-only-resistant connection

Figure 1.7Head-to-head butt joint double-side-nailed horizontally

Figure 1.8Head-to-head butt joint nailed vertically. Another weak, shear-only-resistant connection

Figure 1.9Head-to-head butt joint double-nailed vertically

1.2.2. Head-to-side butt joint

In the case of the head-to-side butt joint, one end of one element is positioned at the side of the other. This connection can be performed again (a) by means of two cover plates (Figure 2.28); (b) by means of one or two angles (single and asymmetrical, in the case of the weakest connection type; double and symmetrical, in the case of the strongest – Figure 2.27); angles which, in the case of light frames, are nailed or screwed, while in the case of timber frames, are bolted or screwed; and (c) by means of only screws or nails. In this case too, the nails/screws should be placed so as to be as divergent as possible from each other and prevent extraction, when tension is possible, and should be straight otherwise (Figure 1.10).

Figure 1.10Light-frame end-to-side butt-joint executed with screws or nails orthogonal to the frame components. Splitting of the wood at the head of the joist is a serious risk in this case. For this reason, this connection is not suitable for heavy loads