WHAT WEIGHT OF CSM FIBERGLASS MATTING DO I NEED FOR A FLAT ROOF

A very smart question, and one that i believe you'll not realize a good answer in anyplace. If you explore totally different fiberglass suppliers answers go from 450g to 600g and typically 900g chopped strand matting ( two layers of 450g ).  Why are the suppliers giving contradictory advice? Well for variety of reasons and that i shall attempt to explain. essentially they're attempting to grant you a 1 size fits all answer to a probably difficult question wherever there isn’t an easy answer, and everybody loves an easy answer don’t they. the matter is enlargement and contraction, movement of timber joists and decking.

CSM – fiberglass chopped strand mat, I actually have found 450g to be fine for many small to medium sized roofs of excellent solid construction, you will need to contemplate 600g for a bigger project or wherever frequent footstep is predicted. On an oversized roof two layers of 450g could also be advisable.

Of course it’s you who decide how thick to laminate your roof deck, you'll notice plenty of the fiberglass thickness stated by some suppliers are simply pure smart willed guesswork as they need not seen the task in question. Some can merely guess the higher the better, if one says 450g CSM and therefore the alternative 600g CSM it should not be supported any real scientific reasoning. ( or indeed any actual expertise within the case of plenty of suppliers )