About Us

GRM Windows have been at the forefront of window and door innovation for nearly five decades. Fabricating Rehau uPVC windows and doors throughout the years in our state of the art factory in Pontyclun, South Wales. Our customers range from Contractors with projects of new build developments of over thousands of homes in Scotland to Devon, to small independent traders, many of which have been with us since the start and every type of window business in between.

GRM Windows have the values that you would expect from a well-established family business; those of commitment, trust, honesty and respect. These foundations drive our vision as we continue to grow and innovate for the future.  A small but perfectly formed team – the best version of us yet! We have over 90 years experience in the UPVC window and doors between us, and that’s just in the office.  Easy to get hold of, easy to get answers out of, we’re as honest and truthful as we can be with the information we provide, from lead times to delivery.

Family run, MD Richard Gambling has pursued his passion in the UK Passivhaus sector, assisting profile partners REHAU with the development of cutting edge thermally efficient windows and doors becoming one of the first UK fabricators to fabricate Rehau Artevo and previously Geneo – click here for more info on that.

Established in 1979, by Richard’s father Gareth, the business has gone from strength to strength. Innovating and improving with the years. Being the pioneers with REHAU profile, from one of the first to fabricate REHAU PVC Bifolds to now fabricating REHAU’s Artevo Passivhaus standard windows and doors.

The factory has also grown with the business, with machinery being invested in when needed to be ahead of the curve with our technology, welcoming the new STUGA 4 autoflow into the fold in spring 2025.

Richards background in architecture drives his passion in the Passivhaus and Commercial sectors, advocating for REHAUs artevo to be specified in projects all over the country. He is skilled in communicating with everyone involved in these projects, from the architects to the installers.

REHAU is a global leader in polymer-based solutions, renowned for its high-performance window and door systems. As a trusted partner of GRM Windows for nearly three decades, REHAU provides innovative products like the Artevo window system, which combines sleek design with exceptional thermal efficiency and sustainability. GRM Windows manufactures and supplies REHAU systems, and are incredibly excited to further develop this partnership with GRM’s innovative new door system: The Circuit Collection.