How do we insulate the attic?

Open and closed?

Open cell foam insulation

Open-cell polyurethane foam insulation is a lighter material, its cells are partially open, which allows air to flow. It was developed in the 1980s and became popular in Canada in the 90s, where it was often used as an alternative to mineral wool. It is an ideal choice for insulating floors, ceilings and wall surfaces, especially in places where complex, hard-to-access cavities need to be filled. When the material is applied, it effectively fills gaps and voids, enveloping all elements in the space.

The advantage of open-cell foam is that it can be applied in large thicknesses without being damaged. At the same time, it does not form a vapor barrier by itself. It can be applied up to a thickness of 50 cm, and then cut smooth to create a vapor barrier layer before covering it with plasterboard. Due to its air sealing ability, it performs well, especially for complex shaped surfaces and floor structures. Its sound insulation capability is excellent, which is a big advantage for rooms above garages, for example. One of the cheapest solutions.

Closed cell foam insulation

Closed-cell foam insulation can be used in smaller thicknesses, but has a much higher density. In our climate, where a vapor barrier is needed, most people choose closed-cell foam because it provides stronger insulation. Closed-cell foam is used almost everywhere to minimize steam problems. Closed-cell foam is also the better solution in situations where little space is available, as it provides high thermal insulation performance even with a small thickness. 

Waterproofing

 The use of open-cell foam on a wooden roof or even metal sheet roofs can be risky, especially if it gets wet. The open-cell foam lets water through and collects it almost like a sponge, which becomes visible late. When the water starts to drip, the roof may have already been significantly damaged, and it may be difficult to determine the exact location of the water.

In contrast, closed-cell foam offers a significant advantage in terms of waterproofing. Although not the primary waterproofing (which is provided by tiles or shingles), it forms a secondary line of defense that prevents water ingress in 99%. If the roofing material is damaged, the closed-cell foam allows only a minimal amount of water to pass through, which minimizes the damage.

Vapor barrier

The need for a vapor barrier layer depends on the type of foam used. In the case of open cell foam, a vapor barrier is required to prevent the penetration of vapor. In the case of closed-cell foam, however, the foam itself provides the vapor barrier function, since the vapor permeability of the material is extremely low (125 ng/Pa.s.m² for a thickness of 2.5 cm), which can practically be considered a vapor barrier.

Which is the right solution?

 Both insulation methods have their advantages and disadvantages. Open-cell foam should be used where hard-to-reach cavities need to be filled and where sound insulation is important. However, closed-cell foam is recommended to be used where higher thermal insulation performance is required, there is little space available, or water and vapor sealing is a priority.

The final decision is always made taking into account the specific building and the client's needs.