Insulation Above Roof Deck

I m considering a roof design that would place all the insulation above the roof deck with no insulation below.

Insulation above roof deck.

Over roof insulation the gable overhang has been cut flush with the wall sheathing. Add insulation above the roof deck this approach fits current building science thinking in terms of putting the thermal control layer on the outside of the building structure. Foamular tapered roof insulation provides a thermally effi cient moisture resistant positive drainage slope for use under single ply or other types of roofi ng systems. Roof replacements shall comply with section c402 1 3 c402 1 4 c402 1 5 or c407 where the existing roof assembly is part of the building thermal envelope and contains insulation entirely above the roof deck.

I ve tried to follow the guidance across multiple articles and not counting the nominal r value of the non foam layers estimate the insulation above the roof deck to approach r 55 but in any event exceed the r 49 required. Also note that a new fully adhered membrane is installed on the original roof deck replacing the one installed 17 years ago is folded down to catch the top edge of the wall water control layer. In case the attachment doesn t open display correctly the assembly stack from top to bottom is. Minimum insulation r value requirements by state.

Placing a layer of fluffy insulation below the roof deck would needlessly complicate the. I would use polyiso with a top layer of eps as recommended in your blog post on the topic. The right thickness would need to be calculated to move the dew point above. For roofing replacements it is necessary to look at the ibc.

Insulation above the roof deck or air vapor impermeable insulation below the roof deck is needed for condensation control in an unvented roof. Roof insulation above deck prescriptive requirements april 2008 foamular extruded polystyrene insulation roof insulation above deck roof insulation is required by ashrae 90 1 the energy standard for all commercial buildings and for residential buildings greater than 3 stories in height. Non residential above roof deck this matrix provides the minimum insulation r values required by local and state municipalities. The ratio of insulation above the roof deck or air permeable insulation below the roof deck is a matter of climate and interior conditions.

The roof deck most underlayment most roof coverings membranes and air films cannot be considered insulation. The project is in climate zone 4 seattle area and i want to have an open beam look in the ceiling. Typically this would be achieved by adding polyiso insulation above the plywood deck. Recover roof insulation insulation low slope single ply above deck roof insulation system with cover board prma vegetative roof insulation vegetated waterproofi ng system.