Information My Roof Truss Manufacturer May Require When Designing My Roo

Sooner or later both as contractor or residence proprietor, chances are you’ll have to order roof trusses. Whether or not the roof is for a easy picket shed or a posh hipped attic extension, it’s useful to know what info the truss designer might have.

It’s most definitely your construct could have proceeded from an architect’s drawings and far of the element you require can be specified there. In additional complicated circumstances there possibly engineers specs as nicely, giving particulars resembling wind bracing and specifying loadings.

Dialogue of the varied sorts of roof Gutters construction is past the scope of this text and can hopefully be coated in additional publications. Nevertheless, as a part of the design course of and thru discussions along with your architect, you’ll have resolved points resembling:


  • Hipped or gabled roof design
  • Vaulted or flat ceilings
  • Using the loft area as residing lodging (room-in-the-roof)


While certainly not exhaustive, this text explains a few of the terminology chances are you’ll encounter. It outlines a few of the concepts chances are you’ll want to consider prematurely of your assembly along with your truss designer.

1. Transient anatomy of a roof truss

You’ll be able to consider a easy frequent roof truss as a triangle; with two high chords (rafters) of the identical pitch assembly at an apex and related at their base by a backside chord (ceiling tie). This ‘shut couple system’ is the fundamental form from which most roof truss designs develop.

Throughout the truss, connecting the rafters and ceiling tie collectively, are numerous webs. These webs kind triangular patterns which assist distribute the forces throughout the truss (triangulation of forces). The most typical type of roof truss used for dwellings is the fink roof truss, recognizable by the distinctive w-shape fashioned by its webs.

2. What’s the general span of the roof truss?

Measured in millimetres, the general span of a roof truss is taken into account to be the span over the wallplates. It’s outlined as the gap between the surface edges of the 2 supporting wallplates. These normally coincide with the setting out level of the truss, the place the undersides of the rafter and ceiling tie meet. Most often subsequently, the general span can also be the size of the ceiling tie.

3. What’s the top/pitch of the truss?

The pitch of a roof truss is the angle fashioned by the rafters to the horizontal and is measured in levels. Mono pitch trusses have only one rafter and subsequently one pitch to think about (consider a proper angle triangle). Widespread trusses such because the fink roof truss are twin pitch, normally having the identical pitch on both aspect.

There are circumstances the place you may want a twin pitch truss with completely different angles, both as a nuance of design or the place you might be matching in to an present roofline.

In case you are unable to offer a roof pitch, the truss designer can use the truss top. The peak of a roof truss is outlined because the vertical measurement from the apex (higher most level of the truss) to the underside of the ceiling tie.

In the event you keep in mind your highschool math, you may see the connection between the pitch and the vertical top.

4. What’s the roof truss spacing?

In the UK roof trusses are historically spaced at 400 or 600 millimetre centres. These measurements work properly with these of in style wall end boards and panels, being 2400 by 1200 millimetres.

600 millimetre has develop into a well-liked roof truss spacing for timber body buildings. This does imply much less roof trusses are required and symbolize a big saving. Nevertheless, the trusses can require barely bigger timber sections and greater nail plates. There may be additionally a possible for deflection in battens supporting heavier roof coverings resembling pure slates, which can develop into evident.

When utilizing a roof end resembling box-profile or light-weight sheeting, rafter spacing could also be elevated following the manufactures specs.

5. What are the overhang, eaves and fascia element?

The overhang is the extension of a rafter (or ceiling tie) past its help or bearing (wallplate). The eave is space after the purpose at which the overhanging rafter passes the exterior face of constructing. In lots of circumstances this can be an exterior pores and skin and never the identical because the truss bearing wall.

The overhang and eave line present the width for the soffit; the board fastened beneath the eaves to hide the timbers.

The fascia board is a horizontal board fitted alongside the size of the constructing and glued to the tip of the truss overhangs. The fascia itself is normally constituted of a plastic spinoff, fastened in opposition to deteriorating within the solar.

6. What’s the operate of the roof?

The plain reply is that the roof gives the framework supporting the roof end, defending for the constructing. Nevertheless, roof trusses do way more than this and supply numerous different features chances are you’ll want to think about, together with:


  • Architectural aesthetic
  • Integral features (help for the interior ceiling finishes and many others)
  • Assist for companies (water tanks and many others)
  • Assist for insulation, different power
  • Entry for upkeep
  • Storage
  • Room-in-the-roof


All of those symbolize separate articles in their very own proper. Nevertheless, it’s price briefly mentioning the notion of storage in loft area or attic rooms. You will need to contemplate fastidiously the quantity of fabric you might be accumulating in your roof area. In case you are more likely to have any particular storage wants you need to point out these to your truss designer.

7. What’s the loading on the roof truss?

In addition to potential storage throughout the loft area, the truss designer additionally has to think about numerous different loading elements. These embrace:


  • tile or slate hundreds
  • The constructing location
  • Wind load
  • Snow load
  • Ceiling hundreds
  • Ceiling finishes
  • Water tank hundreds
  • Storage
  • Attic trusses
  • Flooring hundreds
  • Inside finishes
  • Storage
  • Inside or exterior openings


Most of those hundreds are factored in by the truss design software program throughout the design course of. Once you present your location the wind and snow hundreds may be routinely attributed. You should still want to offer some info, an excellent instance being the kind of roof tile sort you’re going to use.

8. Are there any inner load bearing partitions?

The design of the constructing or the inspiration footprint, will outline the placement of the exterior load bearing partitions and thus the bearing factors for the roof trusses. For sure truss sorts, notably attic trusses and hip ends, the place of any inner load bearing partitions may be influential. Fairly often this additional help can scale back rafter and ceiling tie sizes and make tough openings or spans doable.

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