Insulating a flat roof / hipped roof
Finnfoam boards can be used together with mineral wool insulation materials. In this scenario, Finnfoam boards must always be installed onto the warm side of the porous insulation layer. Support ledges for mineral wool are built out of Finnfoam boards inside the structure, simultaneously creating a vapour barrier and an unbroken insulation layer and eliminating cold bridges. Finnfoam cannot, however, be used to build a wind protection layer for the mineral wool as the wool materials must always be allowed to dry outwards.
Using a combination of Finnfoam and mineral wool is an excellent solution for flat and hipped roofs.
Finnfoam insulation reduces temperature differences in the mineral wool insulation, thereby helping to reduce air flow due to natural convection (warm air rising) within the mineral wool and improving its insulation properties. In this solution, the mineral wool layer does not extend much above the joists, making it easier to move in the crawl space. Cutting openings for ventilation and wiring ducts is easy and the through holes can be sealed afterwards using polyurethane foam to eliminate all leaks in the structure. The leak value is not, however, considered in the calculation of a structure's U-value. By eliminating all leaks in a single-family home, energy efficiency can be improved by 15% with no change to the U-value.
Finnfoam insulation boards are not favoured by mice for nesting purposes. Thanks to the insulating Finnfoam layer, the temperature of the mineral wool layer is reduced, making it less attractive for mice and other rodents.