Rolf In MA
Structural
- Mar 18, 2024
- 5
Wondering about necessary layers on a rooftop deck:
Underlying structure is composite concrete-on-corrugated-steel (Vulcraft 3.5" dovetail galvy decking w/ 5.5" total slab).
- On top of that goes 12" EPS. (Crazy regs here in MA - they require R60 on roofs now!)
- On top of EPS goes tapered rigid foam for drainage.
- On top of rigid foam (stay with me here) goes ferrocement topping. (I have experience with these systems and find them bulletproof, maintenance-free, and utterly static over multiple decades. Although it's not a common solution in the US, I find it vastly superior to any other flat roof topping, including direct EPDM over foam).
Here's where we have options:
Option #1: Pour reverse-taper thin reinforced concrete 'pavers' on top of ferrocement to bring roof deck to level, with channels in between for drainage, leading to roof-edge gutter system. Channels could be coated with waterproofing for extra insurance, and filled with stone to give totally flat roof deck appearance.
Option #2: EPDM membrane over ferrocement surface, similar detail with concrete pavers/ channels. (Note: pavers could be rigid foam-core to reduce weight, also wrapped in ferrocement, and 'glued to the membrane with EPDM-appropriate adhesive. Same peastone-in-channel detail.)
Option #3: Install 'floating' deck, entirely independent of EPDM membrane, hovering over roof surface, suspended on steel framing bolted to vertical deck railings. Note: this roof deck *could* conceivably have a lot of people on it.
(Option #3 was proposed by another member of the team. I understand the impulse to protect the membrane. However, I wonder about heavy stresses being placed on mechanical fasteners and deck rails, as well as the additional expense. In my experience, distributing loads the way to go, and we've got ample structure here between the concrete slab and the ferrocement topping, with additional load distribution from the 'pavers.' I don't see the need to do more than that. EPDM membrane is probably a good idea, though, and fully compatible with cement chemistry.)
Thoughts? Thanks!
Underlying structure is composite concrete-on-corrugated-steel (Vulcraft 3.5" dovetail galvy decking w/ 5.5" total slab).
- On top of that goes 12" EPS. (Crazy regs here in MA - they require R60 on roofs now!)
- On top of EPS goes tapered rigid foam for drainage.
- On top of rigid foam (stay with me here) goes ferrocement topping. (I have experience with these systems and find them bulletproof, maintenance-free, and utterly static over multiple decades. Although it's not a common solution in the US, I find it vastly superior to any other flat roof topping, including direct EPDM over foam).
Here's where we have options:
Option #1: Pour reverse-taper thin reinforced concrete 'pavers' on top of ferrocement to bring roof deck to level, with channels in between for drainage, leading to roof-edge gutter system. Channels could be coated with waterproofing for extra insurance, and filled with stone to give totally flat roof deck appearance.
Option #2: EPDM membrane over ferrocement surface, similar detail with concrete pavers/ channels. (Note: pavers could be rigid foam-core to reduce weight, also wrapped in ferrocement, and 'glued to the membrane with EPDM-appropriate adhesive. Same peastone-in-channel detail.)
Option #3: Install 'floating' deck, entirely independent of EPDM membrane, hovering over roof surface, suspended on steel framing bolted to vertical deck railings. Note: this roof deck *could* conceivably have a lot of people on it.
(Option #3 was proposed by another member of the team. I understand the impulse to protect the membrane. However, I wonder about heavy stresses being placed on mechanical fasteners and deck rails, as well as the additional expense. In my experience, distributing loads the way to go, and we've got ample structure here between the concrete slab and the ferrocement topping, with additional load distribution from the 'pavers.' I don't see the need to do more than that. EPDM membrane is probably a good idea, though, and fully compatible with cement chemistry.)
Thoughts? Thanks!
