Both bring the shop-floor temperature down. The choice usually comes down to whether the roof is being touched anyway, and whether production can stop.
Underdeck: work from inside
Foil-faced glass wool or rockwool is fixed against the underside of the roof sheet, held with GI mesh and clips. The roof stays watertight throughout, the work happens from inside on scaffolding or a boom, and it can usually run alongside production with area-by-area handover.
It is the right answer for an existing shed where the roof is sound and the problem is radiant heat on the shop floor.
Overdeck: work from above
Rigid board — XPS, PUF or PIR, or rockwool lamella where fire class governs — is laid above the deck, under the waterproofing or the sheet. It keeps the structural deck out of the daily thermal cycle, which also extends the life of the membrane.
It is the right answer when the roof is being built or re-covered anyway, because the insulation adds little to a job already being done.
How we decide
If the roof is coming off, do overdeck. If it is staying on and production cannot stop, do underdeck. If neither is obvious, we measure the roof surface temperature and the internal radiant load and quote both, with the payback shown for each.
If you would like this applied to your own plant rather than discussed in general terms, send us the details and we will put a specification in writing.
03 Comments
Rajesh Patel
20 Aug 2026We had exactly this argument on our steam line last year. Wish we had read this before we re-did it twice.
Sneha Desai
20 Aug 2026Clear and practical. The point about specifying against maximum temperature, not running temperature, is the one people always miss.
Imran Shaikh
20 Aug 2026Good read. Would like to see a follow-up on cladding detailing for coastal sites.