Hybrid Flat roof - components missing from warm deck.

in regards to the osb deck and vapor control barrier you are definitely correct i would personally ask building control for the reasonings that there is no solid deck beneath the celotex

The correct build up for a flat warm roof construction is 18mm plywood. Then VCL layer , insulation fixed with thermal plugs, then the roofing product , if you put plywood on top of the insulation it will rot due condensation , plywood on top of insulation is NOT a warm roof , if insulating from underneath a timber deck a 50mm gap is needed and ventilated at both ends to stop the same issue

Warm deck 50mm celotex between joists then timber firings then 9mm plywood then vapour barrier then 100mm celotex then 18mm osb

Hi there, based on the description you've provided this method will cause issues within a couple of years! Causing the OSB to rot from within due to condensation build up! The best practice for a roof deck build up is, Joists, then firings, 12mm wbp plywood or osb, then peel and stick VCL, then 150mm TR26/27 insulation, then 18mm osb, then EPDM membrane. Given that the works on the roof are already done you now need to discuss with your architect and BC the best option to introduce a VCL under the insulation between the roof joists. VCL should not be installed under the roof joists if you're going to have spotlights on the ceiling! The idea of a VCL is to restrict the moisture passing through the insulation and condensing when it gets in contact with the cold temperature on the outside! I would suggest you explore the option of fitting 12mm wbp plywood between the joists and then apply either a liquid VCL or a peel and stick in between the joists and also wrapping the joists. Important to use a primer prior to the VCL. This may sound a bit much but it's a bit difficult to find a better way to get it done right. Unless they can remove the roof build up and start again with the right sequence. Wishing you the best of luck and hope you resolve this issue ASAP. DanEco Build Ltd

Based on the information you provided, it seems that there may be some issues with the construction of your flat roof. Here are a few points to consider: 1. Insulation Placement: You mentioned that the insulation is currently sitting directly on the firrings, which doesn't seem correct. Generally, in a warm deck construction, the insulation should be placed on top of the structural deck, not on the firrings. This helps to prevent thermal bridging and ensures that the insulation is continuous across the entire roof. 2. Vapor Control Barrier: It is advisable to include a vapor control barrier in a warm deck flat roof assembly. This barrier helps to prevent warm, moist air from inside the building from penetrating into the roof construction and condensing. Typically, the vapor control barrier is placed on the warm side of the insulation, which is the interior side. 3. Layering: A common approach in warm deck flat roof construction is to have a structural deck (such as OSB or plywood) followed by the vapor control barrier, insulation, and then another layer of decking. This second layer of decking provides additional structural support and acts as a protective layer for the insulation and vapor control barrier. Considering these points, it would be best to consult with a professional roofing contractor or structural engineer to assess the current construction and determine the best course of action. They can provide you with specific advice based on your situation and help ensure that the roof is properly constructed to minimize the risk of interstitial condensation and other potential issues.