Idea

​​

Top home° hollow rafter

365

Description

The engineered rafter was a key component for the top home° prototype, a Passivhaus, that can be build without heavy equipment on site - so all elements need to be very lightweight. Depending on the climate, Passivhaus u-values require at least 400mm of roof insulation. Rafters become unnecessarily heavy and break the heavy insulation layer. A prefabricated hollow rafter element has the following advantages versus a solid wood rafter or a simple LVL beam: + elements can be broken down and transported easily, joined on site. This is especially useful for long spans, hard to reach building sites and other scenarios, where a crane is expensive or impossible, e.g. urban densification.+ increased stiffness and load rating for the same material use. + a single rafter appears solid, yet offers hidden internal space for cables, plumbing, HVAC services. All of these can be put in place while the rafter is still on the ground (safer work environment!). As one side is left open, all the services can be laid in, there is no need to pull cables and pipes (increased speed!). + the remaining hollow space is filled with insulation, e.g. blow-in cellulose fiber. Minimum width is 87mm (21mm panel+45mm T-Stud+21mm panel). T-Studs may be stacked, no maximum width. The elements for a rafter are fabricated with a CNC machine, preassembled in a jig and finished on site.

Key benefit

Less weight, better insulation, same load rating

Material list

+ Kerto LVL Q panel 21mm or similar wood sheet material.
+ Kerto LVL T-Stud 45mm
+ insulation, e.g. cellulose, mineral fiber

Example: A 21x900mm LVL panel may be cut in half, to produce rafters with a total height of 450mm spanning 5m.

Ecological values

+ elements can be broken down and transported easily, joined on site. This is especially useful for long spans, hard to reach building sites and other scenarios, where a crane is expensive or impossible, e.g. urban densification.+ increased stiffness and load rating for the same material use. No crane = even smaller CO2 footprint. + a single rafter appears solid, yet offers hidden internal space for cables, plumbing, HVAC services. All of these can be put in place while the rafter is still on the ground (safer work environment!). As one side is left open, all the services can be laid in, there is no need to pull cables and pipes (increased speed!). + the remaining hollow space is filled with insulation, e.g. blow-in cellulose fiber.

Links

Specification

  • Economical span (mm) 10000
  • Thickness (mm) 87
  • Airbourne sound reduction factor (dB)
  • Impact sound transmission (dB)
  • Resistance to fire class
  • Thermal properties 10.42 R 0.096 U

Documents

    Reviews

    • Idea to make a box-sections from wood uses less material and makes rafters lighter without the need to reduce span lengths. It’s also good idea to offer the possibility to utilize the cavity for HVAC installations. These kind beams are potentially good option for element production also.
    •  

    Comments

    Operation In Progress, Please Wait!!!