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8/2/2019 Vacuum Roofing System
http://slidepdf.com/reader/full/vacuum-roofing-system 1/4
...ventilated roofng which hugs tight-
ly to the substrate...
8/2/2019 Vacuum Roofing System
http://slidepdf.com/reader/full/vacuum-roofing-system 2/4
Dierences in pressure occur when a building is exposed to
wind. Negative pressure orms over the roo, whereas positive
pressure is exerted against the acades and can penetrate
into the building and up into the roo structure rom below. In a
strong wind and over large suraces, this results in high orces,which the roo structure and the roong membrane must be
dimensioned to withstand, and the loads are transerred to
the supporting structure. The ollowing methods are applied in
principle or anchoring the roong membrane and insulation to
the substrate:
BallastingThis method was once in very widespread use or fat roos,
although it is rarely specied on new buildings. Modern struc-
tures are oten optimized in respect o loads, and upgrading to
enable them to support gravel or some other orm o ballastis thus relatively costly. A ballast layer also makes the roong
membrane inaccessible or inspection and dicult to replace.
AdhesionThe dependence on the weather makes this an unreliable
method in a Nordic climate, although welding to the underlay is
carried out to some extent in conjunction with renovation with
an asphalt membrane. The method is used to a greater extent
in warmer parts o Europe. Compact, adhered constructions
depend upon the interaction between the materials in the build-
up layer, i delamination is to be prevented rom occurring.
Mechanical fxingThis is the predominant method used today, and it has been
in continuous development since the middle o the seventies.
Calculation models and dimensioning bases have been develo-
ped, which permit secure and eective installation regardless o
the weather and wind. The method is labour-intensive, however,
General
especially on a concrete substrate which requires
pre-drilling. This also causes puncturing o the vapour barrier,
which can be a disadvantage i the indoor climate is associated
with the risk o condensation in the insulating layer.
VacuumA roong membrane in contact with a completely airtight and
load-bearing underlay will, when subjected to a wind load,
transmit the orces involved to the underlay as suction and
without movement. Extensive experiences and documentationo the method are available rom the USA, and individual roos
have been on trial in Norway since 1985. In association with
the Norwegian «Statsbygg» and NBI, Protan has developed
and adapted the method to Nordic climatic conditions -re. NBI
Technical Approval No. 2281. In the case o substrates, which
are suitable or vacuum installation, the method orms the basis
or the most optimal roong membrane system in terms o both
technical and economic considerations.
PrincipleWhen the airfow causes negative pressure to orm over the
roo, the air volume between the roong membrane and the
airtight underlay expands, and it expands most where the nega-
tive pressure is greatest, i.e. in corner and edge zones. In order
to «drain» out this positive pressure and any losses rom leaks,
so-called vacuum vents are installed where the negative pressure
is expected to be greatest. We have acquired detailed knowledge
rom our experience o and studies into the aerodynamic fow
conditions around building structures. This knowledge provides the
basis or determining the requency and positioning o the vents.The vents have valves, which let the air out, but not in.
Wind comes over the roo in relation to rapid changes in its
intensity and the local direction. These sudden gusts o wind can
be seen as «rippling» in the roong membrane, similar to the eect
over a stretch o water. It takes a ew seconds or the pressure to
be equalized. However, large movements over time indicate a aulty
unction. A correctly designed and installed vacuum roo «sucks» itsel
rmly to the substrate.
A condition or establishing negative pressure in the intermediate
layer is that both the substrate and the attachment o the roong
membrane to it are airtight, or suciently airtight in relation to the vent
capacity. In practice 100% airtightness is sought, and the vent system
then acts as a orm o security in the case o any leaks.
The manner in which load transmission takes place is or the
negative pressure to be transerred down into the airtight layer or
substrate, which in turn transmits the orces onwards into the suppor-ting structure. The underlay can be a reroong underlay or a surace
o bre board or concrete, or example. The procedure is based on
the act that this underlay is both suciently airtight and suci-
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All vacuum-installed Protan roong membranes must be desig-
ned by Protan’s AVT (Technical Applications) Department. Guid-
elines or the calculation principles and the associated basis or
NTG No. 2281 are regulated in a separate agreement between
NBI and Protan AS.Many actors have an infuenceon the vent positions:
• topography around the building, adjacent
building mass
• the orm and height o the building
• orm o the roo
• orm, height and projection by the perimeter
• inset storeys and installations inside the fat
area o the roo
On an «ordinary» fat roo, two vents are installed at each cor-
ner, both at the internal and external corners and at a distance
o every 15m along the ree perimeter.
Vent locationsNo vents are normally required along higher, adjacent buildings.
The loading is dierent on pitched roos and curved roos
and in these cases vents are also installed on either side o the
roo ridge. Exiting roos with dierent orms must be evaluated
in every individual case to establish whether they are suitableor vacuum installation.
New roofngIn the case o new buildings and roos where the Protan va-
pour barrier constitutes the vacuum-sealing layer, this must be
designed and mechanically xed as appropriate or an exposed
roong membrane. The vapour barrier can then also serve as a
temporary roong membrane during the construction period or
or a longer period i it is anchored against being blown o by
the wind. The rest o the insulation and the nal vacuum roong
membrane can be laid at a later stage.
ReroofngThe wind load capacity o a vacuum-installed roo can never
be greater than the capacity o the existing waterproong. In
reroong, it is important to examine the load-transer capacity
o the old roong membrane. This is in practice an equivalent
evaluation to that or the adhesion or welding o a new roong
membrane to the old roong membrane. The undamental
requirement is considered to be an intact bitumen membrane
o inorganic origin either mechanically xed or ully adhered to
the insulation and concrete underlay or lightweight concretesubstrate. The examination o an existing mechanically installed
roong membrane dating rom beore 1985 should also take
into account possible corrosion o the asteners.Provided that
the roong membrane and xings are still intact, a roo that has
been in place or 15 years or more will normally be suciently
securely attached. I upgrading o the xing is required in rela-
tion to today’s wind load standard, this can be done by increas-
ing the xing density and sealing the penetrations in the original
roong membrane. This question may arise or buildings in
areas that are particularly exposed to the wind.
ently strong to transmit the wind suction orces rom the roo.
It is also possible or positive pressure to occur in individual
buildings, which presses up against the roo rom inside. The
roo construction must be dimensioned to withstand these
loadings, and this is an important condition or vacuum roos.
Insulation between the roong membrane and the airtight
underlay has no signicance or the vacuum eect and
unction. Protan vacuum-roong systems can be used both or
new roong and or reroong. The system requires an airtight
layer in the substrate. This makes it particularly well suited
or reroong projects where the existing roong membrane
is still considered to be suciently intact and with sucient
anchoring to the supporting system.
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A vacuum installed roong system is based on
an airtight underlay, and negative pressure over
the fat area o the roo which will accordingly not
suck up warm and humid indoor air into the coldpart o the roo structure. The vacuum vents will
help any humidity trapped in or over the subjacent
airtight layer to dry out more rapidly and without
weakening the xing unction (corrosion).
This is an added benet compared to other
systems. Humidity trapped in roo structures can
Protan AS
P. O. Box 420 Brakerøya, N-3002 Drammen, Norway
Tel. +47 32 22 16 00 Fax +47 32 22 17 00
www.protan.com
be an «environmental bomb» i ungus and mould
growth occur. Especially in Nordic climates, it is
almost an impossibility to operate an all-year-round
roong business without trapping in some waterand humidity. The vacuum system, used in com-
bination with a roong membrane material that is
open to diusion, is a more secure way o avoiding
this problem, and this is justiably described as
«the most ventilated roong system».
Humidity
L a y o u t : D i g i t a l D e u s ,
T r y k k : L i e r G r a f s k e ,
A u g u s t 2 0 0 2 / 3 5 0 0
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