search.noResults

search.searching

dataCollection.invalidEmail
note.createNoteMessage

search.noResults

search.searching

orderForm.title

orderForm.productCode
orderForm.description
orderForm.quantity
orderForm.itemPrice
orderForm.price
orderForm.totalPrice
orderForm.deliveryDetails.billingAddress
orderForm.deliveryDetails.deliveryAddress
orderForm.noItems
EXTERNAL ENVELOPE Designing out condensation


Iain Fairnington of A. Proctor Group highlights some of the factors affecting pitched roof design, and how architects can design out condensation problems from the start


B


S5250 is the code of practice for condensation control, and includes the following reference in relation to design principles: Design for the control of condensation depends upon obtaining a satisfactory relationship between air conditions (internal and external air temperatures and humidity), and the properties of the external elements of construction (thermal and vapour resistance). The objectives should be as follows: prevention of harmful surface or interstitial condensation; prevention of mould growth; and economical reduction of nuisance condensation. Condensation control should be considered as part of the design process. Successful control will depend on factors such as prevailing winds, room layout, number of storeys and type of heating system as well as the more usually accepted aspects such as construction, heating, ventilation and moisture production. All these aspects, therefore, should be considered carefully and, as they are interdependent to a greater or lesser degree, they should be considered together.


The fundamental principle in designing to minimise condensation is to maintain a balance of the three factors – thermal and vapour properties of the structure, heat input, and ventilation – in order to achieve either low vapour pressure and/or high structural temperature. The building fabric, typical weather conditions and anticipated occupancy patterns and uses will all interact to define the moisture risks associated with the construction. These ‘ground rules’ form the basis of a good hygrothermal design strategy. Once an understanding of the building, weather and occupancy are achieved, the designer can focus on ensuring the heat, air and moisture movement within the structure is properly balanced. This critical balance of heat, air and moisture can be influenced by many factors depending on the precise nature of the project.


Refurbishment In refurbishment projects, there may be pre-existing condensation issues to resolve, particularly relating to convection tightness and cold bridging. The building may also have been modified or upgraded over its lifespan, and interventions such as double- glazing, blocking up chimneys and sealing draughts may have created condensation issues, which did not exist before. Modern materials may also have very different hygrothermal properties to those they replace. This might require special treatment in order to avoid problems, and necessitate sourcing unusual materials or skills.


New build On paper, new build presents far fewer problems, however, designers should bear the practicality of installation and site conditions in mind when detailing condensation control measures. The gap between ‘as designed’ and ‘as built’, can be significantly influenced by the level of skill and expertise of the contractors, and their awareness of the importance of vapour control. It’s also important to schedule work in order to minimise damage which following trades might cause to vapour control measures. Best practice will avoid plumbing and electrical services being run through membranes, which should provide a vapour or airtight seal. Providing service voids within the sealed envelope goes a long way to preventing these problems. Finally, construction moisture must be considered, and wet trades like screeding and plastering will introduce additional moisture loading that may not have been accounted for.


Timber frame Timber frame buildings are typically built under ‘drier’ off-site conditions, which not only reduces initial moisture loads but also means a wind and watertight envelope can be achieved in less time. Tighter tolerances and better quality


ADF OCTOBER 2018


69


This critical balance of heat, air and moisture can be influenced by many factors depending on the precise nature of the project


WWW.ARCHITECTSDATAFILE.CO.UK


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100