Extra time and care is needed to ensure that penetrations into the ceiling are properly sealed and that the loft space is protected from sources of water vapour, in accordance with the requirements of the Certificate.
If the ceiling is constructed without due attention to sealing joints and around penetrations, the opportunity for moisture ingress into the loft space and consequent risk of condensation occurring is increased. This is also true of conventionally ventilated constructions where the effect of wind movement over the roof can reduce the air pressure in the loft space and suck moisture laden warm air from the living space into the loft space. However it is recognized that the rate of moisture removal via the ventilated and unventilated approach is not the same. It is therefore important that the ceiling is sealed to an appropriate level. BBA computer modeling of the behavior of roofs has assumed effective ceiling defect areas of up to 10 square mm per square metre of ceiling. See also Q/A 6, 7 and 11.There are reports concerning flapping-noise in roofs incorporating some types of permeable roof tile underlay membranes in certain wind conditions. The BBA has, however, only received a very limited number of reports in this regard and therefore do not view it as a fundamental problem.
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山泉建筑材料特性及功能：
A、山泉防水材料具有良好的防水性能，有效阻隔风雨对室内的侵袭
B、提高居住舒适性
防水透汽膜被称为能呼吸的膜(membrane)，具有极佳的透汽性能，使水汽能够迅速排
出，降低室内潮湿度，有效避免霉菌和冷凝的形成，从而极大的改善了居
住环境的舒适性，并提高建筑物的耐久性。
C、山泉保温材料节能保温
通过有效阻档冷热空气的侵入，起到节能保温功能。与其它保温材料配套
使用，可以有效阻挡水汽渗入保温层，对保温层形成全面保护，同时由于
室内外温差造成的结露现象，也可以通过防水透气膜良好的透汽功能，使
水汽迅速排出，从而确保保温层的功效，达到持续节能的作用，
D、山泉墙体材料抗撕裂，耐磨，低温柔性好。
E、具有极好的抗紫外线、耐老化特点，夏季室外曝晒三个月，仍
保持良好的产品性能，产品经久耐用。
F、产品材料为改性聚烯烃膜和增强无纺布，符合国际环保要求。
G、产品柔软、轻薄，易于施工，不易留下施工死角。

  A2 Breather membranes have been used abroad in construction since the 1970’s. Membranes were first Certified by the BBA in 1982 as sheathing membrane for timber frame walls and as roof tile underlays in conventionally ventilated cold roofs. They were subsequently approved as roof tile underlays in warm roof constructions in 1982 and most recently in cold non ventilated roof constructions in 1999. At the time of writing this article, Certificates for roof tile underlays used as part of a cold unventilated pitched roof system in dwellings have been issued .

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Breathable membranes have been used in buildings for many years now and, more recently, in cold pitched roof constructions without traditional eaves ventilation. The benefit of reduced heat loss and not having to incorporate ventilators has seen their use grow but at the same time has attracted noticeable comment both from supporters of the application and from detractors who favour traditional ventilation solutions.

In light of this, the BBA has prepared this short article to clarify our view as independent assessors of ‘fitness for purpose’ of products and their application.

We have adopted a ‘Question and Answer’ approach to allow the easy identification of items of particular interest and/or concern to readers. The views expressed here are based only on the BBA’s experience in assessing breathable membranes in a number of applications over recent years. Products or applications which are outside the scope of published Agrement Certificates or national Codes of Practice have not been assessed by the BBA and are not addressed in this article.

Ningbo Shanquan Building Materials Co.,Ltd. was established in 2005. We occupy the area of 38.000 square meters, and own fixed assets of eight millions U.S. dollars. From the very beginning, we concentrate on the production of functional membranes products. The current production capacity is 35 million square meters per year, which will be enlarged greatly in the coming two years. At present, our main product is water proof water vapour permeable membrane,which is mainly used for roof construction and wall structure. Very soon, we will develop our production scope to other similar functional membrane materials, so that to satisfy the different requirements from the customers. Based on the horizontal integration with Zhejiang University, we have very strong R & D Ability, depend on which, we had designed and developed the full set of equipment and the production techniques to produce 3 layers breathable membranes with our own technical know-how. At the same time, we have the advanced test equipments and strict quality control system, which ensure the stable high quality goods and the high production efficiency. Stable high quality is always our persistent pursuit, high production efficiency enables us to provide the competitive prices so as to be the winner on the market. We hope to provide our customers the higher quality products with the competitive prices, hope all the customers will gain good effect from the co-operation with us. Our target is: hand in hand with customers achieve common development.