In this blog post, we will introduce you to the pitched roof construction and its components. The more in depth guidance you will find in the September 2018 edition of IBB Builder.
With regards to the maintenance and the use of the building, the thermal insulation plays the vital role. It is estimated that in pitched roofs approximately 30% of the heat energy generated by heating systems escapes easily. This significant amount comes from thermal bridging mainly due to the massive beams running through the roof structure via which the heat moves faster. Moreover, the moisture condensation in case of the poor ventilation might lead to the accumulation of moisture inside the roof and thus to the lowering of the thermal efficiency of the building.
Evaluation of the existing roof condition
Often roofs’ construction of the existing UK houses are already heavily worn-out with air or water leaks, smaller or larger damages due to age and exploitation. It is necessary to either completely replace the roof structure or roof covering or refurbish the damaged part. It is recommended to employ the surveyor to assess the condition of the roof. The specialist will check the roof covering, guttering, airtightness, ventilation and insulation efficiency. Moreover, he will be able to assess the condition of:
• POST PLATES – are laid parallel to the face of the wall and support rafters
• BATTENS – made of wood and nailed to the rafters to give support for the roof covering
• PURLINES – wooden or steel parts by truss or wall, used to support rafters
• STRUTS – give support to purlins to prevent detection and transmit roof loading to loadbearing structure below
• COLLAR – ties the roof at the purlin level
• CEILING BINDERS/HANGERS – support long span ceiling joists
We can distinguish between single roofs, double roofs, trussed roofs or trussed rafter roof. The position of the rafters make a huge difference in the roof construction. The standard fink roof truss is common for 35 percent degrees pitch or less, but does not allow for loft accommodation. In the case of attic truss roof the beam and struts make a wide opening easy to convert to living space.
Generally the spacing of rafters and ceiling joists should be not more than 600mm. The size and spacing of tile battens should be in accordance with the roof covering manufacturer’s recommendations. Battens and counter battens should be as specified in the engineer design. Nails for fixing battens should be 3.35mm (10 gauge) x 65mm long. For trussed rafter roofs not subject to uplift, the minimum fixing should be two 4.5mm x 100mm long galvanized round wire nails, skew nailed, one from each side of the trussed rafter. Alternatively, truss clips can be used. Metal straps might be required in some cases. Lateral restraint straps should have a minimum cross section of 30mm x 5mm and a minimum anchorage downturn of 100mm.
Pitched roof components include:
- RIDGE – the top of the roof constructed by the inclined surfaces at the top of the slope.
- VALLEY – place where two sloping surfaces intersects and the exterior angle is less than 180
- VERGE – the edge of the roof which run between ridges and eaves
- COMMON RAFTERS – run from ridge to the eaves at spacing of 30 to 45 cm
- TRUSS – it is the frame constructed of the triangles to support the roof top
- EAVES BOARD – ends of lower roof covering materials are rest on eaves boards, which is made of wood and placed at the bottom of rafters
- POST PLATES – are laid parallel to the face of the wall and support rafters
- BATTENS – made of wood and nailed to the rafters to give support for the roof covering
- PURLINES – wooden or steel parts by truss or wall, used to support rafters
- STRUTS – give support to purlins to prevent detection and transmit roof loading to load bearing structure below.
- COLLAR – ties the roof at the purlin level
- CEILING BINDERS/HANGERS – support long span ceiling joist