Insulating with Room in Attic Trusses

Hello All,

Looking to get some information on how to insulate a room using room in attic trusses. The house was previously a flat roof and a room in struck trusses were installed over the previous flat roof decking/sheathing. There is currently no insulation between the homes ceiling and the roof decking/sheathing. On top of the sheathing is currently the remaining 8” of styrofoam insulation that sat below the rubber roof.

How do I properly insulate on on top of the previous roof decking/sheathing for both the downstairs and the new room in attic.

Also, I do i insulate the rest of the room in attic which would be the walls and ceiling.

Thank you for any help you can share with me so that I can help my parents.

  • Lionso

It seems like you would use standard insulation & ventilation techniques.

Is there something different about this structure that leads you to believe that it requires something other than standard practices.

My apologies…I should have stated that I am not too knowledgeable when it comes to building/insulating. If this is the wrong forum I apologize as my parents were trying to save some money and make it a DIY project.

My uncertainties were what R value should sit on top of the old roof decking and what type of insulation would be best.

Also, is the attached picture accurate as far as what should be insulated?

That appears to be correct but the old roof should already be insulated.

You will get better ventilation if you use foam board & spacers as opposed to the easy to install premade baffles.

The best insulation would be spray foam and the insulation contractor that does the foam will be able to answer all your questions regarding insulation in detail.

The old roof did have insulation but my
opinion is that it wasn’t enough.

Above is a picture of the insulation that was on the old roof. When living there, winters were cold to the point where you could see your own breath. We also noticed that there is no insulation between the ceiling and roof decking. This is what got them thinking that they need more/better insulation before they close up the floors

Where your new room floor is, doesn’t need insulation. But leave what’s there, as a sound barrier.

There is no other insulation between the downstairs ceiling and the old roof decking.

Layers is currently down stairs ceiling, flat roof rafters with no insulation between, roof decking, old roofs foam insulation, room in attack trusses, then soon to be subfloor.