Engineering and Construction
Assignment Tasks A Housing Association is developing a typical small housing estate of 20 houses for social use, semi-detached ar
First Floors and Roofs
1A) Should be (400 words)
2B) Should be(250 words)
3B) Should be (500 words)
3C) Should be(500 words)
22 Nov 2020 13:24
Assignment Tasks: A Housing Association is developing a typical small housing estate of 20 houses for social use, semi-detached arrangement on a brown field site in Liverpool. The houses are 2 storey with garages and front and rear small gardens. The project is planned for 10 months from February to November.
1a – Site Investigation, Groundworks:
Describe the process of a site investigation considering site conditions, the proposed development and environmental considerations.
2a – Foundations, External Walls and Ground Floors
Detail a cross section of the substructure to just above DPC level including external cavity wall and ground floor construction, displaying specification of fabric materiality to meet the recommended new build U values required. This can be a ‘Scaled’ construction detail e.g. scale 1:10 or a proportion drawing, including all annotations and specifications.
2b – Foundations, External Walls and Ground Floors
Justify the selection of the main components for your detail. Note – there is often not one ‘right’ answer – every site and situation is different
3a – First Floors and Roofs
Explain and compare traditional timber joists (softwood joists) with timber I-joists (factory-made joists) for the first floor of the proposed new houses. In your answer, you need to consider the following perspectives – fire and the Building Regulations, design and form, load, buildability, clients, occupiers, cost and durability. The answer should be in a table form not written essay style
3b – First Floors and Roofs
Explain, with illustrations where appropriate, the typical recognised construction types/design options of a flat roof for the garage. You must consider the following in your explanation: I. Current construction types for the designs, considering the material/technology selection. II. Building regulations, thermal design which includes position of insulation and prevention of condensation. III. Provision for falls and drainage.
3c – First Floors and Roofs
Explain, with illustrations, the typical recognised construction types/design options for pitched roofs for the proposed new houses. The answer should discuss rafter and purlin cut roofs and prefabricated trussed rafters.
First Floors and Roofs
Pitched roof is the type of roof that slopes downwards, whereby is two parts of an angle come from a central ridge, with other involving one part from lone edge to another. In the construction of new houses, three options for pitched roofs are considered. They include the rafter and purlin cut roofs and prefabricated trussed rafters.
Rafter Cut Roofs
The cut roof is a types of pitched roof construction that involve a traditional method of cutting the timber on site and constructing the roof using rafters , ridge boards, joists and purlins. When using the rafter cut roof method, three concepts are considered including support at wall plates, support at purlins, and support of purlins. The support at wall plates in rafter cut roofs is obtained by rafters being birdsmouthed over and skew-nailed to the wall plate (Woodspec, n.d). In the constriction, rafters should be triangulated with a ceiling tie to support any horizontal loads. In support at purlins, the rafter is fixed to a cant top allow the installation of a purlin vertically and the rafter birdsmouthed over and skew-nailed to the purlin. In support of purlins, is achieved by load bearing walls or structural beans and horizontal thrust from the purlin. The illustrations of the three detail concepts of rafter cut roofs are provided in the figures below.
Purlin Cut Roofs
Purlin cut roofs involves two major detail concepts. The first is the purlin support and arrangement. As illustrated in the two figures below, section A indicates the arrangement at junction of rafter, purlin, hanger, and collar tie. Section B illustrates the arrangement at junction of hanger, binder and ceiling joists. The sizes of binder and hanger are normally 100×36 mm, whereby the hanger and binder are used to provide the ceiling joists with support. Section C illustrates the arrangement of struts at ceiling level where there is an overlap of the ceiling joints at a surrounding wall (Woodspec, n.d). At section D, strutting of purlin on to a load-bearing wall is conducted, where the straining pieces for horizontal cater for the horizontal thrust from the strut. However, in the process that the purlin cannot be propped onto a load-balancing wall, section D (alternative) illustrates an alternative where the purlin can be propped on specially designed joists. The concept of purlin slices is illustrated in section E, where halving joints that are of a minimum of 150mm long with support offered directly below them are used to connect purlins.
Typical Purlin Support Arrangement
Typical Purlin Support Arrangement
Prefabricated Trussed Rafters
Truss roofs are made up of factory made trusses that are just erected as they are delivered well already completed. The prefabricated trussed rafters are made specifically for the new homes, with each truss delivered to the site being attached to the wallplate and placed at around 400mm centers (Colm Flynn, 2013). The trusses are then secured to the wall plate by the use of galvanized steel truss clips. Ro ensure the trusses stay in an upright position, they are supported by the bracing, which is placed length ways and also diagonally across the trusses. The figure below illustrates a detailed prefabricated truss roof.
Woodspec, n.d. A Guide to Designing, Detailing and Specifying Timber in Ireland. Available at
Colm Flynn, 2013. Prefabricated Truss Roof. Available at < http://constructionstudiesq1.weebly.com/prefabricated-truss-roof.html>. [Accessed 23 Nov. 2020].