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Does Tyvek need an air gap?

Please note that Tyvek® Reflex requires an air space to provide thermal benefits.

dupont.co.uk - Frequently asked questions (FAQ) about DuPont™ Tyvek® and ...
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Frequently asked questions (FAQ) about DuPont™ Tyvek® and DuPont™ AirGuard® Membranes

Answers to some of the most frequently asked questions about DuPont™ Tyvek® and DuPont™ AirGuard® membranes for building professionals.

TYVEK® ROOF MEMBRANES Q&A

Topics:

Top Questions

Can Tyvek® breathable roof membranes be installed as a roofing underlay without ventilation?

Yes. Tyvek® breathable roof membranes are BBA certified for non-ventilated applications. No eaves or ridge ventilation is necessary.

Can Tyvek® roof membranes be used on new build and refurbishment work without ventilation?

Yes, but care must be taken to ensure that all internal linings are intact so that adequate vapour control is provided.

Are Tyvek® roof membranes suitable for installation into non-ventilated flat roof systems?

No. Tyvek® breathable roof membranes are suitable for non-ventilated pitched roof applications only. In flat roofing a Tyvek® roof membrane may only be used as a protection layer over insulation or as a separation layer between metal sheeting and a supporting deck.

What is the difference between a non-ventilated system and a sealed system?

Both systems are non-ventilated, but the sealed system includes adhesive tape at all laps in the Tyvek® membrane, penetrations and edge details. A counter batten over the roof membrane is included in the Tyvek® sealed roof specification.

Does the Tyvek® membrane need to be sealed?

No. Sealing the Tyvek® membrane is optional and is specified where maximum thermal efficiency is required.

Can Tyvek® roof membranes be left exposed temporarily, before the tiles/slates are installed?

Yes. The ultraviolet stability of Tyvek® roof membranes allows them to be left exposed for a period not exceeding 4 months. However, this will only apply when the membrane is adequately secured.

Can Tyvek® be used on a roof that has been constructed below the recommended minimum pitch of the tile or slate?

Yes, but the Tyvek® roof membrane should be installed in two layers (double felted) with staggered laps.

Can Tyvek® be dressed into the gutter as in traditional practice?

No. It is generally accepted as good practice for all roofing underlays to be stopped short of the gutter, overlapping a ‘proprietary eaves protection device’ (BS5534). This is a UV resistant eaves sheet such as Tyvek® Eaves Carrier that replaces the membrane as the ‘drip’ into the gutter. The roofing underlay should not be left permanently exposed to direct sunlight.

Using Tyvek® Roof Membranes With Counter Battens

Do counter battens need to be installed when the Tyvek® roof membrane is laid over rafters in an unsupported condition?

No, provided that the Tyvek® membrane can be draped sufficiently between the rafters. Tyvek® Supro should be used here.

When laying Tyvek® unsupported how much airspace beneath is required to allow the roof membrane to drape?

Approximately 10mm.

Do counter battens need to be installed when the Tyvek® membrane is laid directly over insulation in a fully supported condition?

Yes. As with all roof membranes a counter batten should be installed here.

Can Tyvek® roof membranes be installed using the draped method of application over counter battens?

Yes. Tyvek® Supro should be used for this method of application.

Can the Tyvek® roof membranes be installed beneath counter battens?

Yes. The membrane will then be laid in a taut condition which allows the laps to be sealed if required.

Can Tyvek® be laid directly over timber sarking without battens or counter battens as in traditional Scottish practice?

Yes. The slates may be secured through the roof membrane and into the boarding in the normal way. The sarking board will need to be timber boarding of 150mm width with 2mm gaps.

Is ventilation to the batten space required when using a Tyvek® roof membrane in a non-ventilated or sealed roof system ?

No. Natural air movement between tiles and slates will be sufficient to remove any water vapour from the batten space.

Can water permeate through the Tyvek® roof membrane when laid directly over insulation or timber boarding?

No. Tyvek® breather roof membranes are 100% water resistant yet vapour-open meaning water will not permeate the membrane, even when laid directly over insulation or timber boarding. However, care should be taken to ensure that counter battens installed over the membrane are tightly secured.

Air & Vapour Control Layers (AVCLs)

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Is an air & vapour control layer (AVCL) required when using a Tyvek® breather membrane in a non-ventilated application?

An AVCL should always be installed over areas of high humidity regardless of whether the system is ventilated or not. This applies to bathrooms and kitchens, and to swimming pools and saunas in particular. Low humidity areas, such as offices, do not require an AVCL but can benefit from better airtightness and vapour control if one is installed. This can also help improve energy efficiency.

WALL MEMBRANES Q&A

Topics:

Top Questions Top Questions

Where does a Tyvek® breather membrane go?

In wall constructions, behind the external cladding / brickwork, etc.

What does a Tyvek® breather membrane do?

Tyvek® breather membranes help protect the structure and thermal insulation from external moisture and condensation. They also help to achieve airtightness and reduce convective heat loss from the building, providing the joints are sealed.

Do the joints in Tyvek® breather membranes have to be sealed?

No, sealing is optional.

Should there be a vented cavity/airspace on the outside of the Tyvek® wall membrane?

Yes, to allow vapour to escape to the outside atmosphere. The cavity/airspace may be vented naturally through cladding/tile joints, or ventilated with airbricks, vents etc.

Can a Tyvek® wall membrane be installed directly behind cladding or render and lathe?

Yes, but the breathability of the membrane will be less effective. Please note that Tyvek® Reflex requires an air space to provide thermal benefits.

Can a Tyvek® wall membrane be installed behind continuous metal sheeting, as the separation layer?

Yes. No, if Tyvek® Reflex is being used.

Can a Tyvek® breather membrane be left exposed prior to the external cladding being installed?

Yes, for 4 months, providing the membrane is secured sufficiently to prevent wind damage.

Tyvek® Reflex Tyvek® Reflex

Why use Tyvek® Reflex?

As well as providing protection against external moisture, condensation and air infiltration, Tyvek® Reflex considerably reduces the amount of heat that is lost by radiation.

Which way round should it be installed?

Tyvek® Reflex is installed so the shiny silver side faces a cavity.

Tyvek® Supro Tyvek® Supro

Can Tyvek® Supro be used as the breather membrane in a wall system?

Yes, Tyvek® Supro has all the attributes of a breathable membrane to BS4016 and EN13859. Its extra strength allows it to be surface applied or used in a ‘free spanning’ application.

What does Tyvek® Supro do in floor construction?

Tyvek® Supro provides a support for insulation, and helps to protect against external moisture, condensation and air infiltration.

DuPont™ AirGuard® Smart DuPont™ AirGuard® Smart

What is DuPont™ AirGuard® Smart for?

DuPont™ AirGuard® Smart is a strong and lightweight flexible air & vapour control layer (AVCL) with variable vapour resistance; this means its ability to resist the passage of water vapour varies according to the surrounding environment. If moisture is present, DuPont™ AirGuard® Smart reduces its vapour resistance to allow the moisture to migrate back into the building interior. While this is happening, the vapour resistance can be as low as 0.26 MNs/g (Sd 0.05m). If the structure is dry and building moisture levels are stable, DuPont™ AirGuard® Smart acts as a traditional AVCL.

DuPont™ AirGuard® Control DuPont™ AirGuard® Control

What is DuPont™ AirGuard® Control for?

DuPont™ AirGuard® Control is an internal membrane for installation behind plasterboard linings, etc. When all joints are taped, it forms a barrier against convective heat loss, and provides limited vapour control.

DuPont™ AirGuard® Reflective DuPont™ AirGuard® Reflective

What is DuPont™ AirGuard® Reflective for?

DuPont™ AirGuard® Reflective is a 100% airtight internal membrane for installation in roofs, below ceiling levels and in walls. When installed with a batten space, DuPont™ AirGuard® Reflective provides considerable thermal improvement to the roof or wall system. By using the product in conjunction with a Tyvek® Reflex breather membrane, significant energy savings are possible.

AIRGUARD® AVCL Q&A

Topics:

Top Questions Top Questions

What is DuPont™ AirGuard® Smart for?

DuPont™ AirGuard® Smart is a strong and lightweight flexible air and vapour control layer (AVCL) with variable vapour resistance; this means its ability to resist the passage of water vapour varies according to the surrounding environment. If moisture is present, DuPont™ AirGuard® Smart reduces its vapour resistance to allow the moisture to migrate back into the building interior. While this is happening, the vapour resistance can be as low as 0.26 MNs/g (Sd 0.05m). If the structure is dry and building moisture levels are stable, DuPont™ AirGuard® Smart acts as a traditional AVCL.

What is DuPont™ AirGuard® Reflective for?

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DuPont™ AirGuard® Reflective is a 100% airtight internal membrane for installation in roofs, below ceiling levels and in walls. When installed with a batten space, DuPont™ AirGuard® Reflective provides considerable thermal improvement to the roof or wall system. By using the product in conjunction with a Tyvek® Reflex breather membrane, significant energy savings are possible.

What is DuPont™ AirGuard® Control for?

DuPont™ AirGuard® Control is an internal membrane for installation behind plasterboard linings, etc. When all joints are taped, it forms a barrier against convective heat loss and provides limited vapour control. Using an Air & Vapour Control Layer (AVCL) Using an Air & Vapour Control Layer (AVCL)

Why do I need an air & vapour control layer (AVCL)?

Put simply, an air and vapour control layer (AVCL) helps to keep warm air inside the building and prevents condensation build-up with its airtight but vapour-open structure – keeping air in but allowing water vapour to pass through the membrane. When used in conjunction with Tyvek® breather membranes as part of a ‘sealed’ vapour-open roof, the benefits of using an AVCL like AirGuard® Control are considerable.

Must AirGuard® AVCLs always be used in conjunction with Tyvek® breather membranes?

AirGuard® AVCLs work best in conjunction with a Tyvek® breather membrane as part of a sealed ‘vapour-open’ roof structure. When used in this way, the AVCL makes sure the entire roof structure adheres to the principle of ‘vapour-open & airtight’, which is at the heart of the ‘sealed roof’ concept. However, both AirGuard® AVCLs and any of the Tyvek® family of breather membranes function perfectly well on their own. It is feasible to use an AirGuard® AVCL as an air and vapour control layer below a conventional felt lined roof. It will still provide certain advantages in terms of condensation control, although for maximum effect it really must be used as part of a fully breathable ‘vapour-open’ roof structure.

Is a vapour control layer absolutely essential in domestic roofs from a condensation control point of view?

In all cases where there is a conventionally ventilated ‘cold’ roof void, there is a need to limit the transmission of water vapour into the loft or roof structure. Similarly, with a conventional ‘warm’ roof construction, moist air must be prevented from entering the roof system. Unless a suitable breather membrane is installed, moisture will condense either inside the roof lining or on its underside, from where it will drip back into the insulation. In all conventional roof designs with impermeable bituminous or other underfelt it is essential that moisture movement into roof spaces is minimised with a ceiling-level vapour barrier, or by using taped and sealed duplex (foil backed) lining boards. That said, the use of a highly vapour-open Tyvek® breather membrane below the outer slates or tiles can, because of its very high vapour diffusion capacity, negate altogether the need for a vapour control layer in both ‘warm’ and ‘cold’ domestic roof designs.

What about industrial roofs? Do they still need a VCL?

Absolutely. Despite what some manufacturers will tell you, a vapour control layer is essential in the case of the vast majority of built-up metal roofing systems. While some designers may dispense with an outer breather membrane when using some naturally ventilated metal roofing systems, it is vital that a continuous air-barrier is always present on the warm side of the structure to contain the internal atmosphere and control diffusion and convection. DuPont does not recommend the dispensation of a vapour control layer in any industrial roofing situation since the insulation is still subject to some of the same ‘wind chill’ effects as a domestic roof, and its efficacy will be reduced by any absorption of condensed moisture.

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