I wanted to experiment with flat roof structures also, and it seemed like the best way to do that would be with the Quad Deck panels (we also used these to cover the basement). This is some explanation of how we did that.
First, the video.
The Video
The Basics
Quad deck is fancy formwork (Insulated Concrete Formwork, AKA ICFs) for pouring a concrete slab over an open space. To increase strength of the final concrete structure, Quad deck shapes the concrete into Ibeams. It also includes its own internal steel structure to help it resist deflection before the concrete cures. The EPS (expanded polystyrene) foam is the tough 25 PSI stuff.
When installing, there are a few key concepts to be aware of.
First, you need to support the weight of wet concrete until it cures. This means you will need secure shoring. The brochures show fancy specialized equipment, but scaffolding and cross beams works also. These need to be strong, so do a little math and make sure that your shoring can handle the load.
Second, the concrete is going to try and push the ICFs apart. If it can separate them, it will just spill thru between them and you will have a huge mess. Toe nailing screws thru the shoring cross beams and into the steel reinforcement in the ICFs can prevent them from moving apart. The “experts” who installed my basement used drywall screws. I had a much easier time using self tapping metal screws that could easily tap into the steel reinforcement in the Quad Deck.
Third, don’t forget you will need to remove the shoring later 😉 The guys who did my basement often put screws in at angles that were only possible if the Quad Deck wasn’t there. That gave me quite a hassle. Build your shoring from below so that it can be removed from below.
Fourth, keep in mind that the concrete needs to sit on the perimeter ledge. You will be removing that shoring, so the concrete needs to be firmly distributing its weight on the ledge around the perimeter. This means you need to remove all the insulation from the edge of the QuadDeck panels. It is tempting to leave some and let the ICF overlap the edge a little, but every bit of the ledge covered by the ICF is a bit of the ledge not supporting the load.
Fifth, you will need to mind the gap. After installing the quad deck. you can use spray foam insulation to close up any gaps between the wall and the quad deck. Remember from 4 that we don’t want any insulation on the ledge.
Sixth, following your rebar specs, and especially rebar for the bond beam around the perimeter, is critical for strength. Concrete is terrible in tension, you need the rebar for any sort of flat floor to carry a load because that load inevitably creates tension, especially in the bottom of the Ibeams.
Seventh, this is a pour, so close all the sides… Also, make sure that the perimeter wall is to the correct height for easy finishing, etc. Don’t just mark the wall where they should fill to, trim it off if you can.
Maybe I’ll come back and add more later.
The Gallery
A pic is worth a thousand words and here are a bunch of pics.
These beams will both support the load of the concrete and prevent it from separating the quad deck pieces (when screwed thru to the internal steel)
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First two pieces in place.
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I cut the quad deck on saw horses in the room below.
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From this edge, you can see how the quad deck fits together
The Pink insulation is to make it easy to knock out that opening later. It basically just prevents the concrete from filling that space.
THe underside after the quad deck is in. You can see the perpendicular beams that will keep the quad deck together.
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These pics should give you an idea of the building space… One wrong step and you are headed down.
Just the quad deck
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Just a pic.
This was where one of the edges of the quad deck broke off. It was too big to fix with spray foam.
The fix was to screw a board across the hole
We are ready to shoot, but still waiting on the gunite crew
In preparation for shooting the gunnite on the roof we needed to put up some forms that would keep the concrete from just falling thru. The radial vaults have simple curvature, so we could build the forms from boards pressed up against the steel arches. Making that happen took some compromises in the plan. As usual, challenges arose. Enjoy.
The Video
The Chimney
In the video I forgot to include any footage of the chimney going in. Basically, I built this form so the shotcrete would create a good base for my chimney on the vault. My one regret was that I didn’t think to close the top of the form in order to prevent the gunnite from going inside the chimney hole.
The Gallery
A picture is worth a thousand words and here a bunch of pictures
We started with full panels and planned to but joint them and attach batons over the ends. But it definitely didn’t work. So I just sat and thought about it for a while.
My first panel attempt.
The vault is radial, so simple curvature and a panel should have fit smooth. But I forgot that the outer edge is inset 2 inches from the bar, which means I needed to notch the panel so it would work out.
By the time we finished off the first vault, we had the plan mostly worked out.
Just a pic of progress
Sherri’s brother Steve showed up for a tour.
The second layer tucked in easily. The hardboard fit above the previous hardboard and the wood baton fit under the previous hardboard so it could be screwed into the steel arch. Then additional lath screws would be added from the outside to attach the hardboard to the batons.
Sherri working until past dark…
Here you can see that the playroom vaults don’t have the end caps on yet. I can’t add the panels until after the end caps go on.
Here you can see the insulated south wall. We plan to shoot the whole structure (roof and walls at once).
Sherri put the lath vaults together. Here she is still adding the the rebar chairs and screen. The rebar chairs keep the rebar fully embedded in the concrete. The screen keeps the wet gunite from blowing thru the lath. It isn’t strong enough to actually hold the concrete, the lath does that.
David at the end of the day…
Our friends (Ryan and Aaron) came over to help for a few hours. We needed to put the end caps on the arches, so we started with that.
A pigeon made a nest and we carefully worked around it.
Michael hanging out with me while I was putting the forms up on the last standard sized vault.
Sherri working hard
Here is the pigeon after the vault forms are in place.
Sherri working on the second lath vault.
A standard end of the day pic.
Just a close up pic on a standard vault.
Pigeons make crappy nests. They are very sloppy and the eggs or chicks often fall out. This pigeon had 3 eggs initially. After the second one fell out, I decided to put some tape up to look after the last one.
I double sided the tape so it wouldn’t be sticky against the birds.
My father packing up the tools at the end of a long day.
We usually recycle bill board vinyls to help with waterproofing. They always have an image, this one made me laugh.
The smurf tube (ENT) electrical conduit will allow us to run wires up thru the vaults after the concrete is in place.
This smaller vault had too tight of a radius for the hard board, so we went with lath. I was able to put hardboard on the sides.
Inside of the dining room vaults.
Here is an electrical box mounted on a lath vault.
Why 4 tubes? Well, 2 are for the light and they go to 3 way switches on either side of the room.
The other two are to run power from another switch to another light. We go thru the box because building code limits the number of turns in the pipe between two boxes.
I wouldn’t have been able to add these boxes after vaults were on both sides, so I would add them between adding the vaults. So one vault, then the next electrical box, then the vault on the back side…
After the concrete is in place, I can drill thru the box so wires can access both sides.
Most vaults have one ceiling fixture with a 3 way switch on either side of the room.
We have had a lot of electrical inspections… And we passed this one too.
The hardboard would expand when wet and the stress would cause the screws to pop.
These screws are pretty thick (#14), but the boards were still popping the heads off.
I sited the wood stove template (according to code) on the floor and then setup my laser to pin point where the hole in the ceiling should be.
We built this form as a base for the chimney.
Once we started covering with plastic we would need to pull back the plastic everytime we worked on it.
We often worked past sunset.
A large bird tore this rabbit up and dropped the pieces in the house…
Covering the vaults with plastic was necessary for keeping the water off the vault.
In this segment, we formed the south wall for gunite. The video, details and pictures can be found below.
The Video
Details
Order of the layers
We had formed previous shotcrete walls with steel studs and lath and steel studs with XPS insulation. We liked the idea of combining the insulation in the form because it saved us the step of attaching it, however, the steel studs caused “void shadows” in the shotcrete and water could travel thru those voids, etc.
For this south wall, we decided to use the steel studs to form the XPS, but we would put the shotcrete outside the insulation, on the opposite side from the steel studs. We could then use just a single layer of XPS and then backfill between the Studs later to increase our R value.
If this were a load bearing wall that needed to incorporate rebar in the shotcrete, we may have come up with a different idea.
Curved Bucks
To make the curved bucks, I used CAD software to figure out the size and angles of the little wood blocks, making sure that the longest side was something easily measurable on a straight edge. In this case, I used a 5 inch length (4.999 is close enough to 5) and an angle. I setup the miter saw with a stop block so I wouldn’t have to measure each one. Then I would just need to flip the wood board for each cut so the blocks came out with the right trapezoid shape to assemble into the circle.
Gallery
A picture is often the best way to tell a story, so here are a bunch of them.
Here David is a little annoyed because he is digging out the footings while Michael (on the right side) is having fun welding in the rebar for the last vault.
Yes, I know a screen capture is a better way to get these sorts of images, but my work computer has all sorts of “security” features that make it easier if I just take a quick photo of my screen. In this case, it was just to have some reference in my pocket while I was out there.
The elevation view of the front of the house…
Since we would soon need to put in the door buck for the front door, we really had to nail down the choice of which size door we planned on installing. We decided to go with this cheap and standard front door instead of the larger entry with sidelites that we had originally planned.
I had bought a new compound miter saw, but I bought a cheap “performax” one from Menards. It was impossible to align. I couldn’t even get the two sides of the fence to align with eachother. I ended up taking it back and getting a Dewalt, which I was very happy with.
I welded on these little brackets to attach the steel studs to the steel Ibeams
I had told the boys not to touch the bucks if they could help it, so Michael usually ran thru jumping like this.
We took a mini vacation with friends during this part of the build…
For the blocks we were cutting, I would often get a screen shot like this to remind myself of the angles and dimensions.
In this case, I had made sure that the longest dimension was a nice and easy 5 inches.
Putting that ring together…
We used glue and then screwed the blocks together
I liked the look of the end grain…
David getting some extra screws into the circle window buck.
I thought this pic of the boys helping to lift the window buck into place was pretty cute…
Windows bucks in, but still lots of work to go
Setting up the last curved wood ledge…
Brody doing some final adjustments as he attached the steel studs to the underside of the curved wood ledge.
Michael likes doing this thumbs up pose for the timelapse when he walks by
The XPS formwork is pretty much done here
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There is always maintenance to do. In this case, the new Kubota I bought needed a hydraulic line replaced. I took this pic so I could remember what fittings I would need.
Part of life includes stopping to sharpen your blades. That lawn mower had a rough life on that construction site. The three blades on the left are the ones I took off it and the new blade is on the right… Ouch, I have never seen such wrecked blades, so I took a pic and then had a conversation with the boys about riding the mower over rocks.
