Dry papercrete is light, less than 20# per cubic foot with a light mix. And yes, mix does make a difference. This light mix would put a load of 20# per square foot on your rafters if you used 1' thick panels. If you ever develop a leak (it happens) and the papercrete absorbs water (papercrete loves water) then it will get heavy fast and that live load goes way up. You should design for that weight, with a safety factor. You wouldn't want the roof to come crashing down onto your bed during a nice soothing rain. I would design for live load of 100# per cubic foot of papercrete to cover the possible weight of the absorbed water.
I am speaking from experience. A decade ago I had a roof that was papercrete cast in place and exposed to the air while it dried. I left town for a couple of days and the monsoon season hit early. That roof went from 40# per square foot to a calculated over 200# per square foot in a few hours. The framing was not designed for that and the roof met the floor. Luckily there was nobody in between.
Already have another question, regarding WEIGHT.
We're good for 2".x 6" rafters according to the county span table, but how much does papercrete weigh? I suppose it depends somewhat on the mix and maybe we should try to add really light aggregate.
---In papercreters@yahoogroups.com, <christine@...> wrote:
I've been in this group for years and FINALLY get to build again. We finished the foundation for our living room / greenhouse addition on Monday and will hopefully be framing in a few weeks.
We're using primarily adobe for the outside walls, are only framing for corners, doors, windows and the roof. We're using 20 ft rafters for a conventional "flat" roof covered with OSB, crickets and parapets.
I'd like to use papercrete to insulate the roof, but don't know whether it should go on top of the OSB or inside between the rafters.
I'm thinking it would be easiest if we made papercrete panels and screwed them to the OSB and then put the elastomeric with the fabric to waterproof it. I'm afraid that if we pour the papercrete in place we'll end up with puddles and eventual leaks.
Also, eventually (when we have more cash), we'd like to add skylights or roof quality poly panels since we want to grow tomatoes and peppers etc. through winter in the addition. We're in NW AZ, lots of sunshine.
One problem is that I'd really like to waterproof the roof ASAP (before winter) and it would probably take months to make all the papercrete panels (it's a 32' x 20' addition)
So I suppose we could also make papercrete blocks to fit in between the rafters inside, like fiberglass insulation, but that makes it tough to add new water and electric lines and we always seem to change stuff. And of course you have to keep the papercrete in place (fight gravity) and it's tough to make them exactly the right size.
My partner would like to cover the rafters with wood for a ceiling, but I'm not sure where we'd get high quality lumber or panels that we can afford. Most of our materials like windows and doors are used.
We're buying a cement mixer from a neighbor and I'll start making some test blocks for over windows / doors where adobe is too heavy. Was hoping we'd get a tow mixer, but that's just not happening.
I haven't had a whole lot of time to think this through and having never worked with papercrete, I appreciate any and all suggestions!
Thanks,
ChristineNo virus found in this message.
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