Attic Construction Using Modern Engineered Timber Components
The wide growth within the use of attic construction to form the utmost use of the building envelope, as well as the dearth of consummate building labor, has resulted within the fast development of designed timber elements to be used not solely in floors, however additionally within the construction of the roof part itself.
This chapter addresses the developments, several of that, like bound rafters, area unit trade-named merchandise developed by specialist timber engineering firms. For that reason a number of the illustrations during this chapter, like those in Chapter half dozen that deal with bound rafter systems, area unit drawn from the assorted manufacturers’ technical and trade literature.
The Floor
Engineered timber within the varied forms illustrated in Fig. 3.13 has existed for a few sizeable times. However, the demand from the house building business normally for a product of higher quality than solid timber including the necessity for quicker installation and conjointly a stiffer floor while not creaks and squeaks, has resulted in AN explosion of built timber ‘joists’.
A recently rumored data point indicates that in 2005 some five hundred of all new homes currently use such merchandise in their floor construction, accounting for around sixty-five 000 homes within the UK alone. Bearing in mind that AN built timber beam clearly prices significantly over an easy softwood beam, it's price considering the benefits of the merchandise before staring at the assorted sorts out there and therefore the construction strategies used.
Better Quality Floor Construction
A stiffer floor giving higher ‘feel’ to the user, and a quieter construction avoiding the shrinkage thus typically related to typical timber. Most designed beam systems powerfully advocate that the ground deck is screwed and/or pasted to the surface to forestall floorboard joint movement.
Faster Construction
Claims of sixty-six reduction in time to put in the ground, i.e. usually 0.5 each day to put in associate designed floor compared to at least one and 0.5 days with ancient construction. With associate designed floor the ground beam system is delivered as a pack of premanufactured parts to express length, together with trimmers and blockings, etc., wherever like ancient construction, softwood joists to the closest normal out there length would be delivered that then ought to be cut, notched and cut as necessary before installation.
Reduced Cost
No wastage – every joist and trimmer is engineered to fit, and the better quality floor means no remedial costs in correcting shrinkage problems for the house builder.
Engineered timber, being a manufactured product, often carries a proprietary name such as Truss Joist, Parallam, Posi Joist, BCI Joist, Finn Joist, etc. but they fall into three main categories:
⇒ ‘I’ beams.
⇒ Laminated solid timber.
⇒ Fabricated timber using metal connector plates.
All of these fabrications seek to engineer the natural defects of solid soft wood out of the product, i.e. knots, splits, the variable slope of grain and density, to provide a stronger product of higher overall performance than that of its individual components, generally resulting in a better span to depth ratio than solid natural timber, without the associated shrinkage and distortion which occurs even with dry timbers. The following is a review of the different types listed above.
‘I’ Beams
These concentrate the forces imposed on the component when being used as a joist, beam, purlin, or rafter into the top and bottom flanges resulting in the ‘I’ shape so familiar with steel beams. A clear advantage is that they are lighter to handle compared to a solid timber beam of similar performance. The flange, i.e. the top and bottom member, can either be in solid conventional timber, or a further piece of engineered timber similar to the laminated timber described below.
The web is again constructed of a man-made timber product, which could be highly compressed timber fibers commonly known as hardboard, or OSB (oriented strand board) or plywood. The flanges and web are usually joined by high performance gluing in the factory. When being made to specific lengths, the ends will usually be solidly blocked to carry the stresses at the load-bearing point (see Fig: 1.1).
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| Fig: 1.1 Timber I beam |
Laminated Solid Timber
Glulam is after all laminated solid timber and might be seen in Fig. 3.13. However, most of the laminated timbers used as joists, beams, and purlins, etc. currently use abundant dilutant laminates and ar additional love plyboard construction within the thickness of the veneers (see Fig: one.2), then the normal thirty metric linear unit or forty metric linear unit thick laminates used with typical glulam.
However, in contrast to typical plyboard wherever different veneers have timber grain arranged at right angles to 1 another, most of the merchandise during this class have laminates parallel to 1 another secure by high-performance adhesives. The brand of 1 such beam, Parallam, describes its construction.
This specific product is after all solid, however in contrast to a bit of solid timber is very stable, and once more in contrast to a bit of solid timber, has all of the most important strength reducing options built out so facultative it to develop the strength of an associate nearly good piece of timber, giving a fair higher performance. Such timbers atypically used as trimmers and purlins and in alternative areas of high stress for that reason. usually, then, this kind of product may well be found as a trimmer supporting the ‘I’ beam delineated on top of.
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| Fig: 1.2 Micro laminated timber beam |
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| Fig: 1.3 Metal nail plate and timber beam |
Fabricated Timber Using Metal Nail Plate Connectors
This product, illustrated in Fig: one.3, is invariably the merchandise of the tied rafter manufacturer because of it uses constant engineering and producing technology wont to turn out the currently common tied rafter roof construction assemblies.
in contrast to the tied purlin illustrated in Fig. 3.13, the highest and bottom timber flanges for this way of designed beam or beam lie flat instead of vertically. This in fact offers an associate in Nursing improved bearing space for each the ground decking and therefore the ceiling and will increase the bearing space of the beam itself wherever it's designed into the wall or assault a hanger.
Posi beam by Mitek, Eco beam by Gang Nail, and Wolfs Easi-Joist all use similar construction to it shown in Fig: one.3. Each, of course, has its own style of ‘V’ formed metal strut connexion system, wherever as Alpines’ Twin–I Beam uses typical punched metal rectangular plates with vertical timber struts between the flanges as illustrated in Fig: one.4, however Alpine revert to timbers being employed vertically instead of horizontally with the systems mentioned on top of, though the timber is mostly abundant thicker than one would realize roof truss construction, once more to administer the higher support for floor and ceiling.
All of the punched metal plates connected varieties provide a copious open house for services between the joists, therefore avoiding the potential issues of incorrect notching and boring for services that are thus usually one in all the issues with the employment of even standard solid softwood floor joists.
Over notching with the installation of pipes on the side, and electrical installation on the lower surface will dramatically decrease the joist’s performance. Clearly, with the ‘I’ beam and also the solid laminated beams, the question of piercing for services needs to be self-addressed, and also the manufacturers’ literature ought to be fastidiously adhered to avoid weakening the ground diaphragm being created.
Warning!
When using any of the engineered components mentioned above do not cut, notch or boreholes in any element without checking with the designer or manufacturer. It should be noted that this applies to this particular manufacturer’s product, but similar information is available from all of the manufactured joist and beam companies. It should be carefully noted that no notching of top or bottom flange, i.e. the most highly stressed areas, is allowed.
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