Flat Roof Insulation Strategies (For Architects and Contractors)

[@ASIRIDesigns]

*Get my climate specific guides to flat roof design available here:* asiri-designs.com/shop

[@JohnLee-db9zt]

Thank you. This is the most comprehensive easy to understand tutorial on flat roof construction I’ve seen.

[@eliinthewolverinestate6729]

I am doing warm roof on 6/12 pitch. Exposed rafters and roof board inside. I like mineral wool but it does cost. With post and beam timber frames we try to keep moisture going out of structure. I am used to seeing thick roof assemblies with purlin.

[@baysbill]

Can you help? Is there any way for me to increase the R-Value of the roof from inside, without removing the rubber and working from top down???? Details: I live in a 1000 sq. ft. ranch house built in 1960. The roof has about a 15 degree slope. When I pull down a piece of ceiling drywall in the open living room, I see a 2x8 rafter with 5 ½ inches of faced batt insulation. Then the roof deck, ½ insulation board and then a white rubber covering on top. Looks like it was all quality done at the time. ---- The 2-3 inch gap between the top of the insulation and the bottom of the deck allows it to breath, with vented soffit. Thank you if you have any ideas, as my web research has been unfruitful.

[@markstipulkoski1389]

"Polyiso: At a mean temperature of 75°F, the polyiso sample also exhibits a level of thermal conductivity which correlates to its published R-value of R6. 0/inch. However, as the mean temperature drops to 15°F, the R-value decreases to approximately R2. 0, representing a significant 66% loss in R-value." It also costs more than EPS or XPS. I would consider burying the the polyiso under a blanket of XPS so it will not be subjected to the most extreme cold, and thus, retain its marketed R-value. Note, Polyiso's R-value begins its plummet around 55F. So, IMO, Polyiso is a warm climate insulation.

[@ASIRIDesigns]

Yup! We discuss this very topic in the book and the ability to combine it with more thermally stable insulation types like you mentioned. Good stuff!

[@pranavpatel2968]

I'm assuming all 5 strategies listed would be for an unvented roof design, correct? Is there a reason why in Strategy 2 and 3 you cannot run ductwork in the rafters/trusses/roof framing area? As long as the insulation is touching the underside of the roof deck in an unvented design, this should be an acceptable practice, correct?

[@titagi]

Hi, thank you so much for this. I am looking for a product/strategy that can be applied on a flat roof terrace for thermal insulation. The waterproofing membrane has already been applied. I would like to install something without having to redo the whole roofing. Is there a material I can use to install before they install the decking of the terrace? If I install any thermal insulation, would I then have to redo another membrane on top? Do you know of an insulated decking system that can be applied on a finished flat roof? Any suggestion is welcome! Thanks

[@ASIRIDesigns]

Hey there! Great question - I'd have to take a closer look at the existing conditions that you're working with, as every project is different. It sounds like you could have the opportunity to create a great inverted/protected membrane roof, however, the addition of rigid insulation can throw off the heights of your existing exterior door thresholds. We do provide consulting services if this is something that would be helpful for you: asiri-designs.com/consulting

[@titagi]

@ thank you for your reply! I have been thinking about it and the best idea i could come up with yesterday was a raised insulated floor which could work provided the depth is ok. But i still haven’t found the right solution. The inverted system sounds cool and interesting too.

[@bigdougdog]

If I would like to have a decking surface on top of the flat roof it seems strategy 4 is the only real way I could do that. Would you agree or are there other options that could be used? What do you think the best way to insulate it would be? Thank you.

[@ASIRIDesigns]

Actually there are several ways to successfully accomplish a deck above a flat roof membrane, check out this video I released a few months ago: kzbin.info/www/bejne/oIfEgHpom8uGfNUfeature=shared