Guide on how to soundproof a roof from the inside

How to soundproof a wooden roof boarding
This guide is about soundproofing and insulating a wooden timber roof, if your roof has the same construction as shown in the images, the thermal insulation is a bonus. If you cannot fill the voids behind the boarding, because you have a PIR panel roof, you can still soundproof your roof, starting with step 4. The soundproofing of a roof can be necessary because of the lack of mass in the materials the roof is made of. This is the reason why outdoor noise is audible indoors. In the following guide, you can read on how to improve the soundproofing and insulation properties of your roof.

The roof boarding that is depicted in the first picture turned out to be entirely empty. As a result, it is cold during the winter, hot during the summer, and during all seasons you suffer from noise nuisance. The lack of mass and the absence of insulating filling cause these issues. The solution, however, is surprisingly simple. Lets start!

Roof boarding removed, showing the hollow uninsulated roof construction

Step 1: Sealing seams and cracks
Seal seams and cracks in the roofs construction, along the walls and floor, because they cause thermal and acoustic leaks. As for bigger cracks, we recommend using spray foam, for the smaller ones you can use a sealant.

Step 2: Filling the cavities (traditional roof)
The second, depicted in the picture below, is filling the cavities with a wool product. We offer two acoustic insulation wool products, in the image white Akotherm Basic is shown. We also provide a bit more dense Acoustic Cotton Wool product. While Akotherm has better thermal insulation properties, Cotton Wool provides a better acoustic soundproofing. We recommend to avoid empty voids by any means, because they allow sound and cold air to enter. If necessary, vapour penetrable foil can be applied to the roof boarding, making sure condensation problems won’t arise in the future.

When the spaces between the beams are at least for 80% filled with a wool product, Akotherm Basic or Cotton wool, it should look about the same as in the image. An extra wooden frame is added to the beams of the roof in order to facilitate mounting a double layer of plasterboard during a later step (step 4). Make sure the frame is sturdy enough to hold the weight of the plasterboard and 14 kg per square meter of Isomat, also in the next steps.

The roof boarding equipped with Akotherm Basic, polyester insulation wool.

Step 3: Mounting the first layer of plasterboard (traditional roof)
The third step consists of adding a first layer of plasterboard. This layer is meant to cover the insulation and closing up the roof. It also serves as a foundation for the soundproofing layer Isomat KE (step 4). Soundproofing mostly revolves around adding mass to a light construction. Plasterboard adds mass, regulates moisture, and is fireproof. Make sure that the plasterboard connects well to the walls and the building. Tip: pay extra attention to the connection in case of a rough wall, because a rough wall contains a lot of small cracks. Seal them with a sealant.

First layer of plasterboard mounted, the roof is now a closed construction.

Step 4: Mounting the soundproofing (traditional roof or PIR panel roof)
This step consists of applying the soundproofing product Isomat KE Fiber (type 14 kg/m², 5,7 mm thick). These soundproofing sheets are the most important step in soundproofing a roof. Isomat isolates vibrations in plasterboard, plywood or PIR panels which resulting a significantly increase of sound insulation due to its weight. One side of Isomat KE sheets contains a jute fibre inlay which provide for a better adhesion with glue. Use this side of the Isomat sheets to apply a thin layer of Stauf Extreme Tack. You will need approximately 0,3 kg per m² of Isomat. Let it dry for a short while. After 5 to 10 minutes you can mount the Isomat KE to the plasterboard or the PUR panel, depending on your roof. To this end, additionally use short nails with a flat head, since Isomat won’t stick by itself due to the high weight.

Isomat KE mounted to the first layer of plasterboard (or PIR panel).

Step 5: The finishing layer
As for the last step, we apply a finishing layer plasterboard, or plywood, on top of the Isomat KE in order to hide it from sight. This can be carried out in two ways: either by installing another layer plasterboard or by using another finishing material like plywood. This layer of material is to be screwed through the Isomat into the roofs construction, as shown in the image below. Make sure that no seams and cracks are left after applying the finishing layer, preventing sound leaks.

The soundproofed roof: Insulation wool, Plasterboard, Isomat KE, and again Plasterboard.

A successful project!
The pictures used in this guide probably won't win a award, we received them from a very happy customer, so we used them. In a short email, with these pictures, our customer stated: “Our sleeping room has successfully been insulated against Airplane noise”.

Questions?
Do you have questions about how to soundproof a proof? Please feel free to contact us, we will be happy to answer your question as soon as possible.