GUIDE FOR PROFESSIONALS

Transcription

1 Uniclass L68125:L52:P71 EPIC F821:E3:X71 CI/Sfb (47.9) Ln6 PERMA VENT B r e a t h e r M e m b r a n e s A Specifier s Guide to condensation in the roof space FOUR IN ONE Conventional Cold Vented Roof Cold Non-Vented Roof Warm Deck Habitable Roof Space

2 PERMA VENT B r e a t h e r M e m b r a n e A Product GUIDE FOR PROFESSIONALS to be used when installing Permavent, Permavent-MAX and Permavent-ECO. Content Permavent is a three-layered non-woven polypropylene breather membrane used as a roofing underlay or as a house wrap. Permavent s market leading specification is widely used throughout Europe. It is designed using the latest technology, incorporating all the requirements of the harsh northern environment. 1 What is Permavent 2 What are breathers 3 Ventilation/Vapour/Scottish 4 Design requirements 5 Installation guide 6 Cold-vented/traditional 7 Habitable roofspace/hybrid 8 Cold non-vented 9 Warm roof PERMAVENT BREATHER MEMBRANE Available in 1.5 x 50 mtr (75 m 2 ) and 1.0 x 50 mtr (50 m 2 ) PERMAVENT-DRY Vapour control barrier (VCB), cost effective, easily installed with the bright foil providing U value gain PERMAVENT-TRAY Black PVC eaves support tray (tilt fillet) to prevent membrane sag and provide gutter run-off PERMAVENT-TAPE Transparent reinforced double-sided tape is specially designed to stick Permavent to itself or any other substrate

3 Second generation breather will meet all your requirements Part E of the approved documents (conservation of fuel and power) is fast becoming the Government s political tool and pressure to save energy is becoming a main issue in modern building design. The energy efficient cold non-vented and warm roof style can only be undertaken using breather membrane technology. By eliminating the drafts that are part of a traditional roof space, the heat loss can be reduced by up to 25%. Recent conceptual modals and test rigs have shown that a vapour resistance of 0.16MNsg -1 (Permavent 0.15MNsg -1 ) is equivalent to 10mm continuous ventilation on small roofs and is the best performance level of breather membranes. Permavent is being proven as the right choice of roofing membrane. Why use Permavent? For non-vented roofs a good quality three-layered polypropylene (or polyethylene) permeable membranes with a vapour resistance of not less than 0.25MNsg -1 such as Permavent (0.15MNsg -1 ) is a requirement of the building regulations. For vented roofs, bitumous roofing felts are heavy, bulky, easily damaged during installation and become brittle through time as well as creating the plastic bag effect with vapour problems. Permavent is a very well suited product to the new build and refurbishment market. It is light and easy to use with a typical usage ratio of one roll of Permavent to five rolls of bitumous felt, it is surprisingly cost effective as a percentage of the new roof. Its tough design will virtually eliminate installation damage. It is UV stable for three months that enables a delayed covering of the roof tiles and will stay watertight and perform well for many years. Although roofs that require active ventilation work well, they must maintain this, and non-permeable membranes do not lend themselves to future changes to the home. Permavent is a highly adaptable product modern system that will help to create a healthy home whilst being cost effective. Permavent is versatile to use on each of the four main roof constructions. It offers good watertight properties, excellent vapour permeability, durability and strength. 1

4 What are breather membranes? Breather membranes first emerged in northern Europe about fifteen years ago and tended to be spun-bonded polyethylene membranes adhered to a strengthening layer. Following research by the BRE and BSi it was established that a requirement of vapour resistance of below 0.25MNsg -1 would classify a true breather for use in warm deck and cold un-vented applications. These earlier membranes predominantly had a resistance of 0.23MNsg -1 and established themselves as market leaders. The researching agents always stressed the necessity for good building practice and detailing when using a cold non-vented roof system with the correct use of a vapour control layer being critical. Because the performance of these membranes was just inside this requirement, poor detailing would overload these membranes and incidents of condensation have occurred with aftermarket ventilation then being the only remedy. Second generation Permavent performs better Permavent is three-layered with non-woven polypropylene heat bonded either side of a hi-tech microporous functional film for use as a roofing underlay or as a house wrap. Permavent's structure is sufficiently fine to prevent liquid water penetration when in use, but not too fine to prevent transfer water vapour (molecules of water in air) out of the roof space. It is possible to adjust the performance of these functional films but at the cost of other performance requirements, too permeable and it might leak, chose a thicker, heavier product but at increased cost etc. Permavent has got the balance right and it is fast approaching market leader in Northern Europe. With more and more complex roof designs and good building practice not always being complied with it is so important to choose a top performing breather membrane that will not let you down. Requirements of use for a breather membrane Protection against the damaging affects of condensation in a roof space must be provided. By following modern building procedures you will eliminate drafts that have always cleared vapour. Therefore the vapour (steam and moisture in the air), which is generated in increasing quantities, has no means of dispersion. The roof space has become a buffer between the warm home and the cold outside. We know that vapour will travel through many materials (brick and plasterboard etc. But most commonly the loft hatch). This will form condensation as it cools on the coldest areas (usually the under-felt). The condensation can also contain bacteria, Leaving this unchecked will instigate mould growth that can manifest in many ways. This could seriously damage your home. Over the last few years reduced air movement through the home has resulted in increased vapour being present and poor building detailing has resulted in serious problems for some dwellings. Many traditional eaves vented roofs suffered from quilt insulation being pressed into the eaves and thus restricted the airflow causing condensation and fungal growth because the vapour was not dispersed. Modern design has also seen complex roof structures that create corners and pockets that are not cross ventilated and spot condensation can form. 2

5 VAPOUR. will travel through masonry, through plasterboard ceilings Vapour is present in all homes, more so in the months following construction. But our homes will never be rid of moisture vapour, through cooking, kettles, showers and bathing. The building regulations Part F make adequate provision for this through window ventilators and mechanical ventilation to bathrooms and kitchens. Vapour will travel through masonry, through plasterboard ceilings and especially through the loft hatches and lighting and pipe apertures. If moisture vapour is not removed from the building, complications can arise i.e: mould growth and also timber degradation. The use of Permavent-Dry vapour barrier is essential with the cold non-vented and habitable roofs and provides excellent protection against vapour when all peripheral edges and joins are sealed. It is then important that a sealed and insulated loft hatch is used and all lighting (recessed lights would cause many problems if not detailed properly) and pipe-work apertures are sealed well. Water tanks should be covered. The top of the brickwork cavity should be closed, this is because as the wall gets wet and is dried by the sun the resulting vapour will travel up the cavity and into the loft space. All the more reason to use Permavent. VENTILATION. these must create cross ventilation to eliminate un-vented voids Both the cold vented and hybrid roofs can be installed using most types of roofing membrane. Both types of roof must be ventilated at eaves level (10000mm/m 2 equiv 10mm continuous on smaller roofs or 25000mm/m 2 equiv 25mm continuous). These must create cross ventilation to eliminate un-vented voids. This sometimes requires connecting to ventilation at the ridge (5000mm/m 2 min equiv 5mm continuous). This may also be achieved with gable vents in the case of lean-to or tall roofs. Ridge ventilation is a requirement underneath the membrane in hybrid roofs and above the membrane on warm and non-vented cold roofs Eaves and ridge ventilators that are above the membrane are the subject of some debate, as they are known to reduce interstitial condensation to the underside of some slates. These do not allow for the fortuitous ventilation of some tiles (such as plane tiles). The affect of wind and atmospheric pressure can adversely affect the performance of breather membranes, when in addition to fortuitous ventilation. The Pros and Cons again raise much debate. The BSi advocates vents but the BRE stated that it is satisfied: if third party compliance is shown in the favour of no vents. In all cases long rafter lengths require special attention (such as larger counter battens) and advice from the tile or slate manufacturer should be sought. SCOTTISH PRACTICE. with the Permavent System Scottish practice of using sarking boards is compatible with the Permavent system providing the boards are of not more than 100mm wide and maintain at least a 2mm gap between them. Permavent can be manufactured at many levels of permeability but increasing its permeability would make it less durable and less waterproof like some other manufactured products. Permavent has been designed using all considerations to provide passive roof ventilation whilst still having excellent performance as a waterproof underlay with all the rigours of installation that are required. 3

6 Design requirements The BSi documents 5250:2002 Code of Practice for Control of Condensation in Buildings and BSi 5534 Code of Practice for Slating and Tiling are widely recognised by controlling and professional bodies as an authoritive work with direct references to breather membranes and their use. Although these documents are open for interpretation we have used some of the main points along with our own findings below; The type of roof covering and subsequent design should always be well thought out if the roof is to remain healthy. People don t open their windows as much as they should (for security reasons, heat loss etc) and yet modern homes have more en-suite and showers. It is important to remember that lifestyles change and in twenty years time the house will not be used as it is now. Permavent will cope with all these changes. To reduce the Vapour (moisture) that will affect the loft space this moisture must be extracted at source (extractor fans, window vents). Even with a fully ventilated roof, complex design will create ventilation voids around valleys, dormers etc. Permavent will cope with all types of roof design. Good detailing of the vapour control layer is essential to reduce the amount of vapour entering the loft space; loft hatches and pipes entering the loft should be positioned away from the bathroom or well detailed and sealed to reduce vapour. Ensure that the top of the brickwork cavities are closed to avoid vapour from the brickwork etc, from entering the loft. Correct use of the cold non-vented roof style will reduce the heat loss in the roof space by up to 25% by eliminating the movement of cold air. Traditionally ventilated roofs should ensure that any ridge ventilation is smaller than the eaves ventilation to avoid the reverse affect. The use of Permavent will avoid the wind noise (flapping) that the first generation of polyethylene breathers suffered from because of their stiffness. It is possible for a membrane with too low vapour resistance to suffer from the reverse affect. This is where the moisture or dew that forms under the slates from the night before can return through the breather when the morning sun heats the slates and vapour occurs. Tried and tested Permavent has the balance right. BSi 5250; d states a preference toward the use of vapour permeable roofing underlay. 4

7 1 2 Ensure that your ventilation requirements have been met. Install the Permavent-Tray eaves protection by simply nailing to the the rafters Apply the Permavent-Tape to the eaves guard 3 4 Unroll Pemavent across the rafter and apply the Permavent- Tape to the top Lift the Permavent and remove the protective film from the tape and stick the Permavent back down 5 6 Apply the battens and work up the roof in the usual way Lift the laps or Permavent and remove the protective film to stick the joins of Permavent 7 8 Finish the roof in the usual way Permavent allows daylight working in the loft space without the need for additional lighting 5

8 All roofs fall into one of only four categories for ventilation and insulation, each category has many permutations COLD-VENTED ROOF SPACE. has the most problems and is most inefficient This is most common roof type in use even though it has the most problems and is the most inefficient. You must provide adequate ventilation to this roof space (building regulations F2) as well as a high degree of insulation (building regulations L1) to the separation between habitable room space and roof space, usually at ceiling level. In order for condensation not to be a problem it is critical that the roof space is ventilated thus dispersing any vapour that is present. Old roofs that have no underfelt are draughty thus giving good ventilation, but the loss of a tile meant the roof would leak and they also had a very high heat loss ratio. Recent history has seen the introduction of a bitumous membrane (1F) to combat heat and tile loss problems but the introduction of loft insulation at ceiling level together with inadequate ventilation has, in essence, created this condensation problem. Even if the roof has eaves ventilation the wool insulation is often jammed into the eaves thus restricting the ventilation or conversely the insulation is left short creating a thermal bridge in the corner of the ceiling in the room below, resulting in mildew. Both of these problems are a breach of the building regulations and are difficult to correct remedially when faced with local enforcement. Cold-vented roofs will continue to be widely used throughout this country through existing properties that need re-roofing because practical problems would make the job not cost effective. INSTALLATION GUIDE Permavent must be installed the correct way up, this is, darker blue side with the lap indicators and Permavent writing outward. Permavent should be unrolled along and parallel with the fascia (or eaves line) and held in place using the battens whilst working up the roof in the usual way. Laps should be a minimum of 100mm but we recommend 150mm and even 200mm on shallow pitch roofs of less than 20 degrees. Hips should be overlapped by 300mm and valleys should be under lapped by 300mm following the line of the valley. Permavent-Tape is a super strength double sided tape and can be used to fix Permavent to sarking or insulation boards such as in Scottish practice. In all cases, although Permavent is a breather membrane containing U.V. additives which enables a delayed finishing of the roof covering (up to three months), an eaves carrier tray (or tilting fillet) should always be installed to where the felt runs over the fascia and into the gutter. Because of the high tech, lightweight design of Permavent the laps should be taped and sealed using Permavent-Tape. When Permavent is used on a cold non-vented roof, taping and sealing of the roof laps and joins is essential to prevent moist or cold air and wind from entering the roof space. As with all breather and lightweight membranes, if used with wide batten spacing or counter battens, there is a risk of flapping that could be noisy or even leak if the roof is not yet tiled in, especially if the pitch is shallow. Taping of the laps with Permavent-Tape as well as correct detailing will eliminate this risk. Vent pipes, roof lights and apertures on the roof should be sealed with Permavent-Tape and any nail tears or damage must be repaired. 6

9 HABITABLE ROOF SPACE (hybrid roof). the resulting condensation would then run would leak through This type of construction is most common in loft conversions. Many types of membranes have been used before, on some occasions it has been known that non-permeable or no membrane has been observed. In accordance to independent authorities, this system should incorporate the effective use of a vapour control barrier such as Permavent-Dry installed directly underneath the insulation. The ventilation at eaves level must be connected to the ventilation at the ridge via a minimum 25mm gap (BS5250) between the membrane and the insulation although good building practice has established a 50mm gap as the norm. Non-permeable membranes can be prone to problems because any problems with the vapour barrier could result in interstitial condensation especially on long rafters. The resulting condensation would then run down the insulation boards to the join and leak through to damage the finished ceiling. Some specifies have, in recent years, designed a warm roof on new build with a 25mm vented space (in essence a hybrid) between the insulation and the breather but there have been reports of interstitial moisture forming and leaking through the joins in the insulation, the BSi now recommends Permanent sealing of all insulation joins in this system. This means that the use of a warm roof with Permavent laid directly on, and then ventilated, is now more preferable. Permavent used in conjunction with the Permavent-Dry vapour control would be a permanent and effective use of the hybrid system. COLD-VENTED AND HYBRID Place your Permavent-Tray Eaves Protector carrier over your facia ensuring that each carrier laps the next one by at least 75mm and is sealed together using Permavent-Tape. Ensure the ventilation is correctly installed. Unroll the Permavent-Tape along the length of the eaves carrier about mm up from the back of the fascia and leave the protective tape in place. A strip of Permavent at least 600m wide should now be installed up any valley section if, for example, preformed G.R.P Valleys are being used. Unroll Permavent along the line of the eaves with the bottom of Permavent covering the eaves carrier and Permavent-Tape but not hanging over the fascia. Permavent should not be pulled tight but allowed to slightly dip (about 5mm) between the rafters. Staple or nail the very top of Permavent (this will be covered by the lap of the next run) and fix the battens at your required spacing. Lift up the lower section to reveal the Permavent-Tape on the eaves carrier, peal off the protective tape, and stick Permavent to the eaves carrier. Apply the Permavent-Tape to the top of the newly laid Permavent within the lap in the same way that it was applied to the eaves carrier. Repeat the previous actions and carry on up the roof battening and sticking the laps as you go. When you reach the ridge you should consider the other side of the roof and ensure that Permavent is lapped over the ridge by the final roll and laps the other side fully. Ventilated ridge will have its own installation instructions that should be followed. Where rafters/wall plates abut masonry that rises above the roof line, Permavent should be extended up the abutment (wall/chimney etc) by at least 75mm. Provision should be made to guard against sagging. 7

10 COLD UN-VENTED ROOF. have made it the most cost efficient against performance This most modern type of roof has only become possible through the recent introduction of breather roofing membranes. Although cold un-vented is not the best performing type of roof, the recent changes to part L1 of the building regulations, requiring increased levels of insulation, have made it the most cost efficient against performance. By eliminating active ventilation, the roof space is therefore 25% more thermally co-efficient requiring less insulation. The only problem with this type of roof is that it will only work effectively when installed as a complete system using good working codes of practice. A cold vent roof requires that the roof space is isolated from all but residual amounts of vapour by means of a vapour control barrier of non-permeable sheeting such as Permavent-Dry. The use of this control barrier, fixed to the joists for example behind the plasterboard, will prevent the ingress of vapour through the ceiling. Permavent should be laid on the roof in conjunction with a counter-batten to allow eaves to ridge ventilation over the top. The laps and peripheral edges of Permavent must be stuck and sealed using Permavent-Tape. The type and style of insulation may vary quite considerably and all manufacturers will supply relevant information in accordance with the latest building regulations. COLD UN-VENTED ROOFS This type of roof is laid in much the same way as a traditional roof but care must be taken to ensure the system is installed with good working practice. This roof has no active ventilation of the roof space (no soffit, eaves or ridge vents) but relies on the Permavent System of vapour control. It uses vapour barriers between the habitable rooms and the roof space (usually at ceiling level) with Permavent keeping the roof dry and healthy. Because of the vapour escaping the roof space, advice should be sought as to counter battens or ventilation over the top of Permavent** 8

11 WARM ROOF. the best performing of the roofs This is the best performing of the roofs. It is suited to most applications although it is in part the most expensive. It does not lend its self so well to remedial applications. It often requires a re-roof or the original roof level needs to be raised. Because the insulation is on the outside of the building (like an overcoat) this illuminates the main roof design problem of interstitial condensation, for there are no voids for the vapour to condensate in. The main use of this form of roof is when the roof space is habited as an original design (Dormer, mansard style) or when the ceilings are vaulted or of course when design necessitates a flat roof. Only vapour permeable membranes with a vapour resistance of not more than 0.25MNsg -1 such as Permavent (0.15MNsg -1 ) should be laid directly onto the insulation (usually phenolic boards). Wet or damp rafters should not be closed in and, of course, there should be no voids in the insulation. Building regulations (L1) state such a requirement for insulation, that the rafters can now cause a thermal bridge, thus requiring insulation to span the exposed edge. Permavent breather membrane should be laid onto the insulation with a counter batten to allow the moisture to run off and not get trapped by the battens. WARM DECK ROOFS Fit an eaves carrier as before and lay on the first roll of Permavent directly onto the insulation or rafters. Because Permavent cannot dip between the rafters a counter batten of at least 10mm must be laid up and on top of the rafters. This counter batten will allow any rain or moisture to run under the normal roofing battens and off the roof. If the counter batten space is to be used for ventilation then advice should be sought**. Carry on up the roof as before using Permavent-Tape and counter battening and battening as you go. COLD UN-VENTED AND WARM DECK ROOFS **Information concerning whether or not you should ventilate the gap between Breather membranes and your roof covering (tiles etc) has not been fully defined by the controlling bodies. Permavent works so well at releasing vapour from the roof space that interstitial condensation can form on the underside of the roof covering (slates etc). However, some coverings such as plain tiles allow sufficient air to pass through them as to clear any vapour that has escaped the roof and passed through Permavent. Tightly fitting coverings such as manmade slates or steel sheet may trap this vapour causing interstitial condensation that can adversely affect them. Ventilation should therefore be used over the fascia and at the ridge to clear it. You should check the advice of the tile, slate or roof covering manufacturer before you proceed without ventilation. 9