Dealing with thermal bridging in metal-framed extensions

Get frames with built-in thermal breaks first - that's your foundation and cuts the problem by half. After that, you're not overthinking it; layering external insulation over the frame perimeter and sealing around the edges properly makes the real difference, since aluminium conducts heat like crazy and no amount of interior stuffing fixes a poorly designed frame.

Thermal bridging's real, but it's not actually a nightmare if you design around it from the start rather than trying to patch it afterward. The thing everyone skips: insulate the *sill and threshold* obsessively - that's where most heat loss happens because people focus on the frame itself and leave the base connection to the main building uninsulated, which defeats half your effort. A thermal break in the frame helps, sure, but if cold is still conducting straight through where your orangery meets the house structure, you're losing the benefit.

The real win here is combining thermal breaks in the frames themselves with a continuous layer of rigid insulation on the outside - but the bit people actually miss is wrapping that insulation right around the entire frame junction, not just the wall cavity. Both thermal breaks and external insulation matter, so you're not overthinking it; the mistake is treating them as either/or when they work best together. I learned this the hard way with a conservatory addition at my place - we'd done decent thermal breaks in the frames, then realized we'd left a cold bridge running right along where the frame met the brickwork, and patching it afterward was a nightmare. The sill and threshold are definitely crucial, but equally important is making sure your external insulation actually overlaps the frame perimeter by a decent margin rather than stopping at the wall line.