Residential: concrete roof or conventional?

[ABHW]

What would be more cost effective: a conventional roof or concrete, over 48ft. x 20ft. ICF foundation walls? Anyone know of good systems out there that will span 20ft.?

 

[Ron]

Hollow core slabs with topping will span 20 feet. Good approach if you want a flat roof. If you want sloped roof, consider light gage trusses.

 

[sdz]

A concrete roof would weigh a lot more than a trussed roof (timber or steel) and would require additional substructure to support it. Also you might get leaks through a slab.

A concrete roof might be the choice if you want a trafficable roof.

 

[concretemasonry]

The question of extra support obviously should be examined, but it is unlikely anything additional would be required because of the relatively short spans if the soil has any reasonable capacity.

The roof dead load is greater, but the use of concrete allows the use of the thermal mass roof to be similar to the walls. Thermal mass or whatever term is used is another way of saving money on mechanical equipment and energy, despite this is a relatively small home.

A trussed roof would be less costly, but the wood walls could have been chosen if it was simply get low initial cost. Not everyone is led around by the pink pather that neglects many other factors.

Dick

 

[apsix]

But thermal mass is only really useful when the insulation is outside of the mass.
The insulation will require cladding over.

 

[concretemasonry]

In an ICF structure, the insulation is on both sides of a wall. Ideally, no insulation on the interior will provide the maximum benefit of the concrete mass. Since the mass benefits are long term and not hourly (short term) there is still a benefit despite some insulation inside the mass. Any way you cut it, an ICF wall is still a heavy wall that qualifies to get the mass benefits with the conservative benefits dependent on the annual climate cycle.

For the roof you get far more mass benefits if the insulation is above the mass.

In either case, the concrete structure with rigid insulation is far superior to frame or truss construction with and equivalent amount of insulation. - The worst is steel stud with fiberglass where an R19 fiberglass batt will give you as little an an R11 wall, depending on the stud spacing (not even including the infiltration losses).

Dick

 

[chicopee]

In places such as Okinawa,Japan, which I visited on two separate occassions, residential construction (including rooofs) were of concrete material. I suspect the weather dictates such construction.

 

[csd72]

a 300 deep timber I beam would span 20' (JJI or similar).

 

[ABHW]

Thank you everyone. Some useful tips and information. The reason I was thinking of going with a concrete roof over this 48ft.x28ft. section of the house is to save on costs associated with labour plus sheeting, shingling, insulating, drywall on ceiling, etc. I was going to look into some type of coating (for asthetic purposes) to put over the concrete ceiling on the inside to avoid material and labour costs associated with using drywall. Essentially the goal is to weigh the cost of building a conventional roof or a concrete one based on materials and labour required in each case.
I was thinking 4x8 sheets styro insulation on exterior over roof. I was going to go with a 30 mil. pvc barrier for waterproofing, but there are better materials such as rubber roofing that I could use over the insulation.

 

[ABHW]

***oops... I meant 48ft. x 20ft. area of the house.