Professional doubling of the rafters

In particular, with the tightening of energy laws and the rise in energy prices, the roof insulation has massively in the focus of home improvement. For older houses but usually very thin rafters, which are not sufficient for the prescribed insulation thickness. Then the rafters have to be doubled up. There are not only several methods, also with the mostly accompanying insulation certain aspects have to be considered.

Reasons for the doubling of rafters

Until the 1980s, relatively thin rafters were used for the roof. The load-bearing capacity simply had to be sufficient for the intended roofing and the expected snow load. But many trends can be observed today where a rafter doubling makes sense.

  • roof insulation
  • roof extension
  • Increase roof load for other roof tiles, photovoltaic or solar thermal

How you double up also depends on the insulation measures

Already due to the tightened energy saving laws, the roof renovation or modernization is usually accompanied by an insulation.

  • rafter
  • Insulation between the rafters
  • Under rafters

Rafter doubling outside

From this, however, it can also be concluded that you can double rafters inside as well as outside. The outer doubling of the rafters is usually accompanied by a comprehensive modernization. These are usually so-called cold roofs, ie roofs that have no insulation whatsoever. In this case, anyway, an external insulation must be installed.

Doubling and inner dams: the conditions

There are many special features to consider, the insulation material must be impermeable. Otherwise condensation and condensation will collect on your interior insulation, mold and sponges will follow soon. The doubling of the rafters in the interior is therefore required for Dämmmaßnahmen and interior work. Consequently, it must be an insulated, warm roof.

With which you can double the rafters

Once these fundamental questions have been clarified, different materials and duplication techniques are available to you. Classic working material for doubling is and remains wood in the form of battens. There are also XPS (polystyrene foam insulation strips), which, however, enjoy no great popularity.


When doubling, you can do the following.

  • You double up the rafters, attaching the new slats to the rafters
  • They double the battens across the rafters

Double rafters lengthwise

Double the rafters in the direction of travel, you get a deeper gap, so you can use very strong insulating mats. However, this also results in a disadvantage that becomes apparent in the description of the transverse doubling. Finally (after doubling and dams), a vapor barrier, a foil, is laid airtight on the insulated rafters.

Double rafters across the direction of travel

First, fill the spaces between the rafters with suitable insulating materials. This can be mineral wool, but also a Klemmfilzmatte. Now, as with the longitudinal doubling of the rafters, the vapor barrier is mounted and sealed airtight everywhere.

Now screw the battens across the rafters. Preferably at the same distance as the rafters have him to each other. Now you can also fill these gaps with insulation material. The previously indicated advantage arises because so no cold or thermal bridges on the rafters arise, after all, they are also covered with insulation.

Further tasks of the rafter doubling

In a doubling mounted transversely to the rafters, you can also better carry out the electrical installation with a planned interior fitting. In addition, the rafters additionally help to support the later interior fittings, which are usually made of plasterboard.

Tips & Tricks

Make sure you choose really dry wood when choosing the roof battens. Otherwise, the battens may of course be rough-cut.

If your roof has no insulation, which makes it a warm roof, you must first make the diffusion-open external roof insulation. This is true even if it was "insulated" with bituminous membranes. Bituminous membranes are not permeable to diffusion, if a rafter doubling with intermediate rafter insulation were used, there would be condensation that collects on the bitumen and penetrates into the insulation.

Roofing is often recommended by roofers when heavy roof tiles are to be used or a solar system is installed. Often it is only a cost-saving compromise to a new roof or roof.

Of course you will find in the house journal also detailed instructions for [insulation of rafters] and trusses.

Video Board: Using Walls Instead of Purlin Braces to Support Roof Rafters – Attic Remodeling Tips