DepartmentofAgriculturalEngineering AEN-15
R/GID-FRAME
GREENHOUSE
CONSTRUCT/ON
b y J . N . W a l k e ra n d G . A . D u n c a n
ExtensionService
Universityof Kentucky. Collegeof Agriculture. Cooperative
Agriculture. Home Economics. 4-H . Development
The developmentof plasticfilm and rigid sheetmaterial for the glazingof greenhouses
createda needfor a new
classof structuralframes.Such structuresideallyshould
have a minimum of shadingat a minimum of cost. The
surfacesof the framesshould be smooth,to permit easy
coveringwith either film or rigid coverings.
To permitefficient use of equipment for working the soil, interior
supportsshould be minimal. In addition to theserequirements,such factors as simpleconstruction,reducederection time, and a long structurallife are important. More
recently, the availabilityof fiberglasspanelsrequireda
structuresuitablefor thesecoveringmaterials.
A structurewhich incorporates
all thesedesirable
features to a high degreeis the rigid-frame.A rigid-frannis
essentially/an
arch with completelyrigid joints wherethe
loadsare transferredto the foundationin an efficientmanner. Consequently,
lessmaterialis requiredthan for nonrigid construction.This resultsin a minimum of cost per
unit of areacovered.Sinceno cross-bracing
or chordsare
required,there is only one framingmemberto casta shadow; henceshadingis at a minimum.The frarnesshown on
blueprintsfrom the Universityof Kentucky are of
woodenconstructionand haveonly threejoints
per frame.The framesare normallyfabricatedin a jib on a pavedsurfac€or
suitable framework and are
thereforesimpleand easyto
construct.
Th e lack of interior
b r a c i n g , c o l l a r b e a m s ,o r
chords simplifiesthe placing
of the plastic film and/or
f i b e r g l a s s .F i g u r e 1 s h o w s
some details of rigid-frame
construction.Figure 2 is an
exteriorview of a 28 foot by
48 foot rigid-frame greenhousecoveredwith fiberqlass.
This publicationprovidesstep-by-step
guidelinesfor
fabricationand erectionof rigid framesshownby University of Kentuckyblueprintsor other similarplans.
Rigid-Frame
DesignLoads
T h e K e n t u c k yp l a n sw e r e d e s i g n e d( 1, 2 , 3 ) o n t h e
basisof the main membersbeingof selectstructuralquality. The designloadsselectedwere ten poundsper square
foot live load or wind at 88 milesper hour. Thoughthe live
load usedis considerably
lessthan the designroof loadsfor
conventionalstructures,experiencewith both glassand
plasticcoveredgreenhouses
has shown suchdesignloadsto
be adequate.However,only high quality dried lumber
shouldbe selectedfor the main members.
Glue-Nailand All-NailedRigid Frames
The most efficientconstructionis achievedby usinga
v'nterproofglue to fabricatethe rigid-frames.With glue,less
plywood is requiredat the joints and fewer nailsneedto be
driven. Sufficient rrailsare used,though,to createa
pressurethat will hold the gussetstightly
againstthe main memberuntil the glue
sets.
The all-nailedframesare similar to the gluedframesexcept
larger plywood gussetsare
usedfor the joints to achieve
the required joint strength.
The same designloads were
used.The nailedframeshave
the advantagethat they can
be built outsidein cold
weather; whereasat temperatures lower than 600 to 70oF
glue will not cure properly
unlessused in a heatedarea.
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S I N G L EO R D O U B L EL A Y E RC O V E R I N G S
P L Y W O O DG U S S E T S
<--
OPEN INTERIOR
N EMBERSTpRESERVATIVE
G O O DQ U A L T T YT U O O D E M
T R E A T E DO R D E C A Y . R E S I S T A N TS P E C I E SR E C O M M E N D E D
S T E E L A N C H O RS T R A P
CONCRETE
Fig, 1.-General features of wooden rigid-frame construction,
masonryfoundationsmust be reinforcedto be adequate.In
commercial buildings, large rigid-framesare frequently
supportedby reinforcrd concrstefootings.Such largefootingsareexpensive
to build and requireskilledlabor.
The support of greenhousesizerigid-frameson concrete piers poured in holds dug by a tractor-mounted or
truck-mountedaugerhasbeeninvestigatedat the University
of Kentucky.Thesestudiesshowedthe pier sizeslistedin
Table 1 to be adequatefor greenhouse
rigid frames.Piersof
thesesizesarerelativelysimpleand easyto construct.
Table l. Pier Sizes and Depths for Greenhouse Rigid
Franr;sr
greenhouse
Fig.2.-Exteriorviewof 28 by 40 foot rigid-frarne
with
fiberglass
co\rering.
Regardlessof the method of fabricating joints, be
sureto follow the plansexactly!Strongjoints are extremejoint conly important in this type construction.Careless
struction can seriouslyweakenthe building.
Foundation Sy*em
On transferring load to the ground, the rigid-franc
developsa relativelylargehorizontalthrust. For the 4Gfoot
greenhouseframe, this thrust is approximately500 pounds
per frame for maximum roof loading. This means that
FrameLegSize(in.) PierDiameter(in.)
2x4
2xG
2x8
2x 10
2x 12
6
6
I
10
12
Pier Depth(in.)
24
30
30
30
36
lThese data are minimum values for typical soil conditions.
The diameters and depths rust be increased 30 to 50 percent for
loose, sandy, or wet soil,
Figure 3 shows the construction of a typical pier.
Sheet metal, wood, or heavy cardboardcontainerscan be
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used to form the pier above ground. The aboveground
portion can be squareor round. A steelstrap is placedin
the pier to reinforcethe pier, permit secureattachmentof
the frame to the pier, and transferthe horizontalthrust of
the frameto the footing. The positioningof the steelstrap
must be accurateif the framesare to be uniformlyspaced.
lf framesare to be seton a concreteor block foundation, the concretefootingshouldextendbelowthe frostline
the frame. Toe-nailingof frames to the sill plate is not
adequateby design standardsand therefore not recom
mended.Figure4 showsdetailsof properfoundationwall
construction.
GALV. METAL FRAMING AIICHOR
ON SILL OR STEEL STRAP
r Nc o N c .
BOLTS
{ r IO" ANChOR
4'-o'o.c. a 6" MAx.
F R O MS T U O
R I G I DF R A M E L E G
S T E E L A N C H O RS T R A P
s o L r Dc o N c .
W A L LO RB L K S .
W/ COFES FILLED
AT FRATES,
SILL SAME
W I D T HA S L E G
S T E E LR E I N F O R C I N C
TO FOOTINOIN CORES
RIGIO-FRAME
BELOYV
LEG
S O U A R EO R R O U N D
FORMINA
GB O V E
GROUND
8"r t2'CONC.
FOOTING
i+CIRCULARCONCRETE
r NH o L E
I p r e nP o u R E D
\
I
\-
- --/
Fig.3.-Details
of concretepier construction
for greenhouse
rigid
frames.
depth, usually eighteeninches deep for Kentucky (use
properdepth for other locations).A solid pouredconcrete
foundation or blocks should extend at least six inches
abovethe highestsoil level.
When masonry blocks are used with a footing to
support rigid frames,the cellsof the block directly under
the frameshouldbe completelyfilled with concrete.A steel
strap for anchoringthe frame and reinforcingthe foundation must be embeddedinto a concrete-filled
cell, as with
the piers describedabove.As an alternative,a sill plate
coufd be anchoredto the blocks with 1/2 inch by 10 inch
bolts four feet apart and the framesattachedto the sill with
galvanizedmetal framing anchorssuch as joist hangers,or
equivalenthardware.Use a framing anchor sized for the
framestudand usepropernailsrequiredby the anchor.The
foundation, however, must still be reinforcedby placinga
steel rod or strap in the core spaceof the foundation below
Fig.4.-Detailsof continuous
concrete
wall andanchoring
methods
for greenhouse
rigidframes.
Concreteblock walls 3-5 blocksaboveoutsidegrade
or wherethe wall is not backfilledrequirecompletefilling
to withstandthe horiof the coresor similarstrengthening
zontalthrust of the rigid frames.
Lumber
The lumber for the framingmembersshould be kilndried, good quality structurallumber (f = 1500 Fsi) or
better.This meansthe lumbermust be freeof seriousknots
or undesirablegrain direction. For maximum strength,
minor defectsshouldbe placedin the lower 1/2 of the leg
or the upper 112of the rafter.Thoughroughsawnlumber
can be used,it must be remembered
that high-qualityair or
kilndried materialis required.lf the lumber is not graded,
care must be taken to select good lumber for the rigid
frames.For high strengthgluejoints it is importantthat all
rough sawn lumber be dry (below 20 percent moisture
content,dry basis)and the joint endshaveidenticalthicknessfor plywood gussetapplication.This generallyrequires
planingto a commonthickness.
Preservative-treated
No. 2 Southern yellow pine or
standardgrade Douglasfir is most commonly usedfor rigid
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frames.lf redwood is usedfor the largerframes,one size
largerlumber may be neededto compensate
for the weaker
strengthand easiersplittingof redwood,
PreservativeTreatrnent
Glue
The only adhesive
recommended
at presentwhich has
the moistureresistance
capabilitiesdesiredand can be used
under normal conditions is ResorcinolResin (Figure6).
Due to the high degreeof moisturein greenhouses,
the use of decay resistantor preservativetreated lumber is
recommended.
Though lumbercan be treatedby brushing
or soakingwith preservative,
the poor performance
of such
treatment when compared to pressuretreated lumber
would make the use of the pressuretreated lumber the
most desirableand economical.ln exposuretestsuntreated
pine stakes in ground lasted 2-4 years, whereaspressuretreated stakeshad 20 to 30 yearsor more of serviceablelife
(e).
Only the water-borne salt-type preservativesare
recommendedfor greenhouses.
Thesetypes permit paintplants,
ing, are not toxic to
and do not causedamageto the
plastic or fiberglasscoveringmaterials(5). The oil-borne
types, like penta and creosote, are not recommended
becauseof their toxicity to plantsand coverings.
For more detailsof preservativetreatment for wood,
seereference(9).
Plywood Gusets
Becauseof the high moisture conditions cited above,
only exterior plywood gradeC-C or better should be used.
For glued frames, the face to be glued should be the
smooth uniform face. Pressuretreatment of plywood with
the salt-type preservativesor soak treatment of the cut
gussetedgesis recommended
so they havelife comparable
to that of the treatedlumber.
Plywood gussetsare usedon both sidesof the joint.
Usea jig to hold the lumberin positionand apply gussets
to
one side (Figure5). The framesmay be prefabficatedin
Fig.6.-Resorcinol
resinis a two-partglueusedfor strongglu+nail
joint construction.
This glue will "cure" at temperaturesof 600 to 70oF or
above.Do not use it if the temperatureis expectedto fall
much belowthis leyelwithin twenty-fourhoursafterapplying the glue. This adhesiveis a reasonablygood gap filler
Due to
and is tolerantof someminor surfaceirregularities.
its exceptional performance regardlessof the exposure
condition and it! easeof use,no other adhesiveshould be
substituted. Resorcinolresin glue is availablein most localities throughthe largerhardwareand lumbersuppliers.Tests
on the gluingof plywoodto treatedlumberat the University of Kentucky (7) indicatethat adequatejoint strength
can be obtainedwith the resorcinolresinglueand salt-type
preservative-treated
lumber if visible preservative
crystals
are removedby wire brushingor sandingprior to gluing
(Figure7). The moisturecontent of the lumber shouldbe
(
Fig. S.-Jig used in positioning and holding members for first gusset
application.
halvesthen latergluedtogetherat the erectionsite. (NOTE:
Apply a ridgegussetto one sideonly of a half-frameso the
halveswill fit together properly when assembledlater. See
F i g u r e1 2 . )
Fig, 7.-Brushing or sandingsurfacedepositsfrom treatedmembers
beforegluing.
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below20 peroent,dry basis.Preferably,
apply a coatof glue
to each surfaceto be joined (Figure8). lf a liberalcoat is
joints,applya coatof properlymixedresorcinFig.8.-For glue-nail
ol resinglueto eachsurface.
applied to one surfaoe,adequate bonds can be achieved
provided a slight bead of glue is squeezedout of the joint
aroundthe edgeswhen the gussetis applied.
Nails
For the glu*nail frames,6d common nails are used.
Thesenailsserveto hold the gussets
in placeand to maintain surface pressureand contact of the glued facesuntil
the gluesets(24 hours at 600 to 70oF or higher).Useone
nail every3-4 inchesaparton the gusset(Figureg).
Apply the eaveand ridgegussetto the one sidewhile
the membersarein the jig.
Handlethe framescarefullywhen removingfrom the
jig. Rotateand lay them asideto apply the remainingeave
gusset(Figure10). The secondridgegussetis not appliedso
the two halveswill mate together properly when later
assembled.
:
r,j',r "
,
'..1.,,:"
Fig. 10,-Applying the renniningeavegusset.
Stack the framesasideuntil the glue sets.Whenstacking, place wax papersor plastic film betweenconsecutive
framesif any glue is obaervedrunning from the joints. lf
this is not done, the stackedframesmay be gl.uedtogether.
ln the all-nailed frames, the nails are the fastening
agent and henceare vital. The nail sizespecifiedis 6d common or deformed shank (ring or screw shank types).
Though the nail patternfor the nailedframesis shown on
the blueprints,some staggering
of the nailsmay be necessary to preventsplitting. Use all the nails specified;any
fewerwill weakenthe joint proportionally.Figure1 I shoran
an all-nailedjoint beingconstructed.
joints,larger
Fig.11.-Forall-nailed
gussets
and6d common
or ring
shanknailsareused.
Fig, 9,-Nails (6d) are driven to hold the gusset snug against the
rnain members and permit handling until the glue sets. Notice the
beads of glue oozing from the joint, which indicates good glue-wood
contact within the joint.
ErectingRigid Frames
All concretework (piers,footing,and/or foundatio.n)
should be completed,kept damp, and allowedto cure at
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leastthree days beforeerectionof the frames.The exposed
steelanchorstrapsshouldbe paintedwith a rust-inhibiting
paint.
lf the rigid-frames
havebeenprefabricated
in halves,
then completeassemblyof the frames,usingproper gluen a i l o r a l l - n a i l e fda b r i c a t i o no f t h e r i d g ej o i n t ( F i g u r e1 2 ) .
Allow glue-nailjoints to cure 24 hours at approximately
70oF or warmer weatherand protect the freshjoint from
r a i nw h i l ec u r i n g .
(Figure
both on the sidesand along the roof is necessary
1 3 ) . F o u r s t r a n d so f n u m b e r 1 4 g a l v a n i z esdt e e lw i r e p e r
guy
bracecable is recommended;
however,plastic-covered
wire cable could be used (two or three strandsper cable).
Use 3/8 inch eye-bolts(with washerunder the nut) and
turn-bucklesfor attaching and tightening brace wires.
Bracingis specifiedat both ends. but shouldalso be provided about every50 to 60 feet alonga house100 feet long
or more.
Add 2 by 4 purlins.4 feet on center,cut-to-fit and
butted between the frames for attar:hment of covering
materials.(Caution: Do not notch the 2 bV 4's into the
rigid-frames
asseriousstructuralweakeningwill occur.)
FinishingDetails
Touch-,.rp
or final paintingof the framesand other
wooden structuralmembersshouldbe completed.A good
paintedsurfaceimprovesappearance
and light reflectionof
the structure.
A suitablecoveringmaterialcan be appliedaccording
to manufacturers'
recommendations,
Informationon types
greenhouse
and characteristics
of
coverings
can be obtained
from the sourceslistedbelow.
F i g . 1 2 . - A s s e m b l i n g f r a m e h a l v e sb e fo r e e r e c t i n gt h e f r a m e .
One or two coatsof exteriorwhite latex paint could
be appliedbeforethe framesareerected.
Carefullyrotatethe first frame into verticalposition
on the piers or foundationand temporarilybrace it with
boardsto groundstakes.Anchorthe legsto the foundation.
Erectremainingframes,anchortheseto the first framewith
the eaveand ridge boardsin the gussetnotchessnown on
the blueprints,and anchoreachframeto the foundation,
PerrnanentBracing
Sincethe greenhouses
haveno structuralsheathing
to
p r o v i d ep e r m a n e nbt r a c i n gw, i r e b r a c i n gr u n n i n gd i a g o n a l l y
Plansand LiteratrrreAvailable
P l a n sf o r r i g i d - f r a m eg r e e n h o u s e isn c o r p o r a t i n gt h e
featuresdiscussedaboveare listed in KentuckyBuilding
and EquipmentPlanscatalog,availablefor reviewat your
C o u n t y E x t e n s i o nO f f i c e , o r P l a n S e r v i c e ,A g r i c u l t u r a l
E n g i n e e r i n gD e p a r t m e n tU, n i v e r s i t yo f K e n t u c k y L, e x i n g t o n , K e n t u c k y4 0 5 4 6 - 0 0 7 5B. l u e p r i n t sa r e a v a i l a b l ea t a
s m a l lc o s t .O t h e rl i t e r a t u r eo n g r e e n h o u s eh e a t i n g v, e n t i lation, covering and related phases of structures and
e n v i r o n m e n ti s a l s o a v a i l a b l ef r e e o n r e q u e s tf r o m t h e
aboveoffices.
List of References
( 1 ) C u r t i s ,J . O . a n d H a n s e nE, . L . ," L u m b e r R i g i dF r a m e s
r
-
-""t''
*
I
I
,"'
Fig. 13.-Diagonal bracing with galvanized or plastic-covered steel
wire.
f o r F a r m B u i l d i n g s ,U
" n i v e r s i t oy f l l l i n o i s ,E x t e n s i o n
Service
C i r c u l a8r 1 2 , D e c e m b e1r 9 5 9 .
t2l C u r t i s ,J . O . . " D e s i g no f N a i l e da n d G l u e d P l y w o o d
Gussetsfor Lumber Rigid Frames," University of
l l l i n o i s E x p e r i m e n tS t a t i o n , B u l l e t i n 6 5 4 , M a r c h
1960.
( 3 ) Douglas Fir Plywood Association,"Plywood Rigid
FrameDesignManual,"DouglasFir PlywoodAssociaForm 62-170A.
tion, Tacoma2, Washington,
(4) Forest Products Laboratory, "Wood Handbook,"
United States Departmentof Agriculture,Agricultural HandbookNo. 72, 1955.,
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(5) Kaufert, F.H. and Loerch,D.A., "Treated Lumberfor
(6)
(71
GreenhouseUse,t' 1il;nn"rotaForestryNotes,No. 36,
Universityof Minnesota,1955.
Walker,J.N. and Cox, E.H.,"Designof Pier Foundations for Lateral Loads," Transactionof ASAE, Vol.
9, No. 3, pp 41742O, 427, 1966.
Walker,J.N. and Walton, L.R., "Gluing of Plywood
to Treated Lumbe4" Transactionsof ASAE, Vol. 9,
No.5, pp 669-670,and
674,1966.
(8)
(e)
Walker,J.N. and Slack, D.C., "Propertiesof Greenhouse CoveringMaterials,"Transactionsof ASAE, In
Press,1971.
TreatDuncan,G.A. and Walker,J.N., "Preservative
ment of GreenhouseWood," AEN-6, University of
Kentucky, Cooperative Extension Service, July,
1973.
Ofiice, College ol Agticulturc,
UniveBity ol Kentucky, Room S-105, Agriculturcl
Science Building-North,
Lexington, Kentucky 40516.
lssued in turtherance of Cooperative Extension work, Acts ot May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Charles E. Barnhart, Director ol
Cooperative Extension Service, University ol Kentucky College of Agriculture, Lexington, and Kentucky State University, Frankfort.
lssued6-73,9M to 11-73;2M-2-87