I want to replace the old carpet fittings with new Sisal Boucle. I am told I need a Firm step underlay (7mm), nothing thicker. Is that right? I'm worried about the noise insulation vs 11mm.

hi,its recomended that sisal is fitted on durafit underlay,this tends to be 7mm, you cannot use a conventional underaly as if fitting sisal the undelay needs to be stuck to the subfloor and then the sisal stuck to the underlay,also yes,due to the fact the underlay needs to be stuck to the subfloor you will need to ply over the top of boards

hi it is true that you need a firm underlay as sisal boucle differs from usual carpet floor coverings. Sisal is made from natural materials and requires a different installation technic. the underlay and installation charges are much greater than having ordinary carpet laid. The underlay must be firm, it does not matter how thick, just FIRM. Duralay is what I recommend, made by a company called Interfloor, who supply most of the flooring industry in the U.K. I would lay ply over floor boards, only if the floor boards are uneven, 12mm ply would make an excellent flat surface, however, you may need to get under your floor boards one day for existing pipes and wires, also, you will be raising the sub floor which means you will have to get your entrance door shaved and any other doors in the area of concern too. And this could also effect ajoining floors, like the landing. It will be slightly higher. About sound proofing, this should be done under the floor boards, just above the ceiling below. Technics of how to do this can be found online. best regards Robin