Vacuum Roofing System

8/2/2019 Vacuum Roofing System

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...ventilated roofng which hugs tight-

ly to the substrate...



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-



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.



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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Vacuum Roofing System