TELEBEAM LOFT CONVERSION SYSTEM
A presentation by Digby Rowsell, inventor of the TeleBeam system
This paper is to be read in conjunction with the presentation on the TeleBeam Loft Conversion system, a relatively new and unique way of converting existing roof trusses for loft conversions.
Roof structures fall generally into two distinct types;
· Traditional ‘hand cut’ roofs where the roof timbers are literally cut on site and most common in buildings up to the 1960’s. The main common rafters (often 100x 50mm) are often supported at mid-span with larger section timber purlins running horizontally. These purlins limit the rafter spans and transfer some of the roof loads down through props onto the internal loadbearing walls. These props in turn limit the span of the purlins.
The horizontal ceiling joists are usually fixed to the foot of the rafter to ‘triangulate’ the structure to prevent horizontal spread at the wall plate. Often ceiling joist supports (binders) are provided on top of the joists at right angles again to limit the span of the joists.
Older style roofs were often designed on empirical rules but since the 1960’s design span tables by TRADA and the Building regulations give guidance a to timber sizes.
· Prefabricated Roof trusses where the trusses are delivered to site ready fabricated by specialist manufacturers. These trusses are manufactured from small section, high grade timber, often spaced at 600mm centres through the roof and are designed to span from wall plate to wall plate with no support from any internal loadbearing walls. These are typically found in the majority of newer properties built since the later 1960’s
The most common type being the ‘fink’ pattern with the tell-tale internal ‘W’ bracing on every truss and can span often in excess of 8m without support
Ease of conversion/Design Loads
Generally, older style cut roofs are easier to convert than modern trussed roofs due to the fact that there are often internal loadbearing walls which will limit the design spans for the new support structure. Because of this older cut roofs can often be converted using larger section timbers provided alongside the ceiling joists that are designed to take the new floor loads and roof loads.
It is common however to under estimate the additional design loads that have to be considered in a loft conversion.
In a typical small detached three bedroom house, say 7m x 7m internally, the additional floor load that has to be supported by the structure amounts to around 6 tonnes !!! Imagine parking four Ford Mondeos in the roof space and you are somewhere handy to the actual mandatory loads that have to be considered.
From now on general reference will be made to modern trussed rafter roofs as these are more difficult to deal with.
Options for conversion of trussed roofs;
There are three main options;
1. Large steel beams running gable to gable with timber joists spanning between
2. Replacing the trusses with prefabricated Attic trusses alongside the existing
3. The TeleBeam system
Option 1 Steel Beams
The disadvantages of this approach are;
· Very heavy point loads at the bearing points in the gable walls
· The steel beams themselves are very heavy to handle and install (often in excess of 0.5 tonnes)
· Generally require a crane for lifting of larger steel beams
· For wider room widths the timber joists that span between the steel beams can be large (often 70 x 220 C24 grade timber)
· Difficult/time consuming to install with timber web infills and hangers
· Limited choice of stairwell location as the steel beams can often compromise headroom over the preferred staircase design/location.
· Difficult to incorporate dormers where the wall lines step out locally into the dormer zone.
· Bearing beams into party walls for attached properties (Party wall Act)
· Problems in drainage runs reaching svp locations with steel beams in the way
· Damage to property/rooms below ceiling level for provision of padstone supports
Option 2 Attic Trusses
· Can be difficult to deliver to site
· Still ideally require crane loading into place
· Difficult to make fit the existing roof profile
· Requires exposure of the building to the elements for fitting
· Often difficulty in trimming of staircase and dormer/rooflight openings
Option 3 The TeleBeam system
What is TeleBeam?
TeleBeams are lightweight telescopic aluminium beams that reinforce each truss to allow the bracing to be removed to open up the roof area. The triangulation of the truss is unaffected as the tie of the truss remains between the TeleBeams and the ceilings are unaffected by the installation of the beams.
Each TeleBeam comprises three components, a central rectangular box section floor beam (which usually equates to the new room width) and in each end an ‘I’ beam outrigger section which inserts inside the floor beam, usually overlapping by around 600mm. This allows shorter, lighter components to be manhandled into place.
Each truss is sandwiched and reinforced with a TeleBeam either side with the ends of the TeleBeams bearing on timber packers cut between the trusses to keep the beams clear of the ceiling. From the ends of the floor beams new vertical loadbearing studs are provided and are bolted to the trusses to transfer the roof loads down onto the TeleBeams. A high level ceiling collar is also provided to reinforce the rafters and reduce their design span.
Once all the supporting structure is in place the central bracing can be cut away to achieve a profile similar to an attic truss but constructed in-situ with minimal exposure to the elements as installation normally takes place from one side of the roof. In most cases three rows of roof tiles are removed on one side and the beams inserted from scaffolding in a single working day. Please refer to the installation guide annexed to the back of this document for a more detailed explanation of the process.
Main advantages of this method are;
· Ease and speed of installation
· Formation of working floor inside very quickly
· Beams are light to handle
· Extruded aluminium is very stable and does not warp or shrink like timber
· Can deal with wide spans (up to 8.4m clear span)
· Has LABC (Building Control) approval in England and Wales
· Can often provide a lower floor build up to maintain more headroom
· Provides eaves storage and easier access to drainage runs
· No steel beams in the way of staircase headroom
· Walls can step out locally into dormers
· Additional loads are spread over the whole building, no heavy point loads
· Improved health and safety on site
· Standard detailing/known beam sizes for a given span
· Can also be used in traditional roofs where timber is not sufficiently stron
There are five spans available, based upon a fink trussed roof with trusses at 600mm centres and standard tile loading (50kg/sqm). The span referred to as dimension ‘S’ is the clear span from inside wall plate to inside wall plate.
Beam section sizes, lengths and typical room widths are shown in the TeleBeam Cross Section table annexed at the back. Also included is the LABC approval reference number for Part A structural stability.
What about roof pitch and span?
TeleBeam works with any roof pitch and span within the limits specified in the LABC approval. Additional spans can be achieved and supporting calculations will be provided by TeleBeam where appropriate.
TeleBeam carry out a detailed roof survey for every project and provide a beam layout and cross section drawing showing the position of all new timber supports required and room width achievable.
Inherently on a trussed roof scenario there will be 12.5 or 15mm plasterboard and skim ceilings. If required additional fire protection can be provided by either under-tacking the existing ceilings or preferably provision of a fire resistant blanket laid on top of the ceiling e.g. Knauff Rocksilk 50 BS476 approved 30 min fire blanket. This is a much less invasive solution. It is however up to the Building Control Surveyor (BCS) to determine and agree the protection required (if any).
As in most conversion 22mm thick P5 tonged and Groove flooring is provided and can be laid directly onto the TeleBeams either by screwing or simply glueing as specified.
Stairwell openings are formed very much like timber joists stairwells with double or triple TeleBeam trimmers providing support for the trimmed TeleBeams off stainless steel hangers and bolts that TeleBeam supply as part of the system.